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TT31 Mode S Transponder
Installation Manual
00455-00-AP
18 June 2014
Trig Avionics Limited
Heriot Watt Research Park
Riccarton, Currie
EH14 4AP
Scotland, UK
Copyright Trig Avionics Limited 2006 - 2014
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TT31 Transponder Installation Manual
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CONTENTS
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ENVIRONMENTAL QUALIFICATION FORM................................................................. 29
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1. Preface
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1.1 Purpose
This manual describes the physical and electrical characteristics and the installation requirements for a
TT31 Mode S Transponder. It also describes the TT31 ADS-B functionality for a compliant ADS-B
Out installation using 1090ES.
1.2 Scope
This document applies to the installation of the TT31 Mode S Transponder.
At the publication date of this manual the software version identifier for the TT31 is 3.13 and the
FPGA version identifier is 020714a. The software and FPGA versions are subject to change without notice.
1.3 Changes from Previous Issue
In addition to minor editorial changes, the following are the changes between issue AO and issue AP:
2.1 TT31 Description Added text about ADS-B.
3.3.2 ADS-B Installation Approval Added text about STC program.
5.7.11 GPS Position Input
6.1.9 ADS-B Configuration
9.2 ADS-B Installations
12 ADS-B Compliance
14. Connection Diagrams
Added Garmin ADS-B Plus protocol.
Added example GPS position source data.
Added section.
Added data for Garmin 4x0W and 5x0W GPS units. Added additional compliance data.
Added new drawings showing typical ADS-B connections.
1.4 Document Cross-References
00454-00 TT31 Mode S Transponder Operating Manual AE
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2. Introduction
2.1 TT31 Description
The TT31 Mode S panel mount transponder is an ED-73B Class 1 compliant Mode S level 2es datalink transponder, with support for extended squitter, elementary surveillance and SI codes. The TT31 is also a DO-260B Class B1S compliant ADS-B out participant. The TT31 meets the relevant environmental requirements of ED-14D, and is certified to ETSO 2C112b, ETSO C166a, TSO C112 and TSO C166b.
The TT31 transmitter power output is nominally 240 watts, and the transponder runs from either 14 volt nominal or 28 volt nominal DC power supply with no configuration changes required.
The TT31 transponder responds to both legacy Mode A/C interrogations and to Mode S interrogations from both ground radar and airborne collision avoidance systems. In all cases, the interrogations are received by the transponder on 1030MHz, and replies are transmitted on 1090MHz.
In the Mode S environment, S stands for Select, and a Mode S interrogator can selectively address a single transponder. This allows accurate position plotting with lower reply rates, which in turn reduces frequency congestion and interference. As a side benefit, power consumption by the transponder may be reduced, and simple datalink services can be supported, such as ADS-B. It is however crucial to the reliable operation of the system that each aircraft has a distinct Mode S address. The Mode S address is allocated by the registration authority for the aircraft, and must be set when the TT31 is installed.
The TT31 can be configured to transmit version 2 ADS-B using the 1090ES datalink.
The ADS-B Out capability is enabled automatically when the transponder is configured to use a GPS position source over an RS232 interface. With a GPS source connected the transponder supports all required features of ADS-B Out.
Note: With no GPS interface configured, the transponder does not enable any ADS-B functions, and will behave as a conventional Mode S transponder.
2.2 Interfaces
At the rear, the transponder has two Molex style connectors and a single antenna connector for blind mating with the corresponding connectors in the mounting tray.
The interfaces provide the following services:
Parallel altitude input
Connection to an external altitude encoder using parallel Gray code.
Ident input
Standby input
External IDENT switch input.
External standby input for dual transponder installations.
“On ground” input Allows automatic flight/ground mode switching for aircraft with a squat switch.
Lighting bus input Used to adjust the backlight and switch lighting intensity.
DME Suppression
Input
Input to limit interference between DME interrogations and transponder replies – suppresses transponder whilst active.
Suppression bus
I/O
Audio output
ARINC compatible suppression bus signal used in aircraft with more sophisticated suppression needs, both an input to and output from the transponder.
Optionally used by the altitude monitor and TIS traffic functions.
Audio mute input Toggle function to mute the audio output.
Altitude alert output
Output used to signal altitude deviations when optional altitude monitor function is used.
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2 x RS232 Inputs Connections to an external RS232 GPS receiver for ADS-B support and/or a serial altitude encoder or air data computer. Using serial altitude data allows the transponder to report altitude with 25 foot resolution.
2 x RS232 Outputs Connections to a TIS display and a GPS or other device needing serial altitude data
– this allows the transponder to act as a repeater instead of requiring a second altitude encoder.
ARINC TIS Output ARINC429 output for connection to traffic display.
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3. Technical Specifications
3.1 Regulatory
Specification
Compliance
FCC Identification
Applicable documents
Software
Power Requirements
Altitude
Humidity
Operating Temperature
Transmitter Frequency
Transmitter Power
Transmitter Modulation
Receiver Frequency
Receiver Sensitivity
Characteristics
ETSO 2C112b, TSO C112; Class 1 Level 2es
ETSO C166a, TSO C166b; Class B1S
VZI00220
EUROCAE ED-73B, EUROCAE ED-14D (RTCA DO-
160D), EUROCAE ED-14E (RTCA DO-160E), RTCA DO-
181C, RTCA DO-260B
ED-12B (RTCA DO-178B) Level B
10 – 33 Volts DC. Typical 6.3Watts @ 14Volts.
35,000 feet
95% @ +50C for 6 hours; 85% @ +38C for 16 hours.
Tested to Category A in DO-160D
-20C to +55C
1090MHz ± 1MHz
240 Watts nominal; 125 Watts minimum at antenna after allowing for 0.5dB connector losses and 1.5dB cable losses.
6M75 V1D
1030 MHz
-74dBm ± 3dB
3.1.1 Approved Deviations
The TT31 ADS-B function is certified to ETSO C166a which references DO-260A as the applicable standard; the TT31 implements DO-260B which has replaced DO-260A.
The TT31 ADS-B function is certified to FAA TSO C166b which references DO-260B, but also refers to the environmental standard DO-160F and indirectly refers to the transponder standard DO-181D.
The TT31 transponder certification was carried out to DO-160E and DO-181C.
3.2 Physical Specifications (in Tray)
Specification Characteristics
Length
Weight
239mm (9.4”)
2.8lbs. (1.35Kg)
3.3 Installation Approval
The conditions and tests required for the TSO approval of the TT31 Mode S Transponder are minimum performance standards. It is the responsibility of those desiring to install this transponder on or within a specific type or class of aircraft to determine that the aircraft operating conditions are within the TSO standards. The transponder may be installed only if further evaluation by the user/installer documents an acceptable installation that is approved by the appropriate airworthiness authority.
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3.3.1 Mode S Transponder Installation Approval
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Installation of the TT31 as a replacement for an existing transponder is considered a Minor Change by
EASA and the FAA, and should be documented accordingly.
Note: With no GPS interface configured, the transponder does not enable any ADS-B functions, and will behave as a conventional Mode S transponder.
3.3.2 ADS-B Installation Approval
At the time of publishing this manual, enabling the ADS-B Out feature is considered a major change and will generally involve further approval.
For installers seeking US FAA STC approval, our STC partner is Peregrine in Denver who hold a range of AML STCs for TT31 transponders. Contact them at - peregrine.aero/contact.html
Installers seeking approvals for other parts of the world or for more information on our STC program, should contact the Trig support team – [email protected]
For uncertified aircraft installations or for installers developing their own solution, this manual can be used for guidance on the ADS-B installation. Further technical diagrams, schematics and instructions are contained within the STC pack which can be obtained through Peregrine.
3.4 Non – TSO Functions
The TT31 Mode S Transponder contains the following non-TSO functions:
Stopwatch and Flight Timer. The transponder provides a simple stopwatch and flight timer function, displayed on the front panel.
Altitude Monitor. The Altitude Monitor activates an audio annunciator or annunciator light
(depending on installation) when the aircraft pressure altitude differs from the previously selected altitude by more than 250 feet.
Altitude Repeater. This is a serial altitude output that can connect to a GPS or other device needing serial altitude data – this allows the transponder to act as a repeater for the altitude input instead of requiring a second altitude encoder.
The operation of each of these functions is described later in this manual.
The non-TSO functions defined in this section are not part of the TSO approval. The non-TSO function data included in this section is approved under 14 CFR 21.305(d).
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4. Unit and Accessories supplied
4.1 TT31 Mode S Transponder Items
Your TT31 Mode S transponder includes the following items:
Unit Description
TT31 Mode S Transponder
TT31 Mounting Tray
TT31 Documentation Kit
TT31 Installation Kit
Qty
1
1
1
1
Part Number
00220-00-01
00231-00
00233-00
00223-00
4.2 Installation Kit
Your TT31 installation kit includes the following items:
Unit Description
12 way double sided crimp housing connector
24 way double sided crimp housing connector
Crimp Terminal, Female, 18-24 AWG
Screw, Pozidrive, Pan Head M3x12mm lg
Connector Co-axial Panel Mount Right
Angle Blind Mate
Circlip 7/16” External
Washer 7/16” Plain, Stainless Steel
Washer 7/16” Crinkle, Beryllium Copper
Qty Part Number
1 00032-00
1 00033-00
1
1
1
30
4
00236-00
00422-00
1 00239-00
00242-00
00241-00
00317-00
4.3 Documentation Kit
Your TT31 documentation kit includes the following items:
Unit Description
TT31 Transponder Installation Manual
TT31 Pilots Operating Manual
Qty
1
1
Part Number
00455-00
00454-00
4.4 Required Items
Additional items you will require, but which are not in the TT31 package, include:
Antenna and fixing hardware. The TT31 is compatible with any transponder antenna approved to (E)TSO C74 or C112.
Altitude encoder. You require an encoding altimeter or a blind encoder with either parallel
Gray code or RS232 serial output. For best results, and simpler installation, an encoder with a serial output is recommended.
Cables. You need to supply and fabricate all required cables. Guidance on cable types is given in section 5 below.
Fixings. To secure the transponder tray to the airframe you will need at least 6 flat head screws and six self-locking nuts. If the aircraft does not have existing mounting provisions
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To support the optional ADS-B features a GPS receiver with an appropriate serial output is required.
To support the optional TIS features a display with an appropriate serial or ARINC 429 input is required.
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5. Installation
5.1 Unpacking and Inspecting Equipment
Carefully unpack the transponder and make a visual inspection of the unit for evidence of any damage incurred during shipment. If the unit is damaged, notify the shipping company to file a claim for the damage. To justify your claim, save the original shipping container and all packaging materials.
5.2 Mounting
The TT31 Mode S transponder must be mounted rigidly in the aircraft panel. The following installation procedure should be followed, remembering to allow adequate space for installation of cables and connectors.
Select a position in the panel that is not too close to any high external heat source. (The TT31 is not a significant heat source itself and does not need to be kept away from other devices for this reason).
Avoid sharp bends and placing the cables too near to the aircraft control cables.
Secure the mounting tray (p/n 00231-00) to the instrument panel via the six (6) mounting holes in the tray. It is important that the tray is supported at the rear two mounting holes as well as the front four.
Check that the locking mechanism is correctly oriented by unscrewing the locking screw if required.
Slide the TT31 transponder into the secured mounting tray.
Lock the TT31 transponder into the mounting tray using a 3/32” Allen key, taking care not to over tighten the locking screw.
5.3 Cooling Requirements
The TT31 Mode S transponder meets all applicable ETSO and TSO requirements without forced aircooling.
Attention should however be given to the incorporation of cooling provisions to limit the maximum operating temperature of each unit when the TT31 is installed in a typical panel or rack. The reliability of equipment operating in close proximity in a rack can be degraded if adequate cooling is not provided.
5.4 Electrical Connections
The TT31 has two Molex edge connectors, one with 24 contacts, which is the primary interface, and a second connector with 12 contacts. A single coaxial connector attaches to the antenna. The second
Molex connector (12 way connector) adds the altitude alerter, an ARINC 429 output, audio output, audio mute input and a second serial port. In simple installations it is possible to omit wiring for the second connector altogether.
The Molex edge connector used in the TT31 is similar to the connector used on the KT76A, KT76C and KT78A transponders, and the common signals on the primary connector use the same contact positions and are electrically compatible. The antenna connector is also compatible. Providing that the wiring is appropriately installed, it is intended that you can upgrade a KT76A, KT76C or KT78A installation to the TT31 without any connector rewiring. Before doing that however, you MUST check that the wiring for the existing transponder is in good condition.
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5.4.1 Primary Interface – Pinout
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Pin Signal Direction
1
Ground -
2
Lighting 14V
3
Lighting 28V
4
Suppress I/O *
5
Squat Switch In *
6
RS232 Output 1 *
7
RS232 Input 1 *
Input
Input
Bi-directional
Input
Output
Input
8
Altitude D4
9
Suppress In
10
Standby Switch
11
11-33V DC
Input
Input
Input
-
12
11-33V DC -
A
Ground -
B
Altitude B4
C
Altitude B2
Input
Input
D
Altitude C1
E
Altitude B1
F
Ident Switch In
H
Altitude C4
J
Altitude A4
K
Altitude A2
L
Altitude C2
M
Altitude A1
N
Do Not Connect *
Input
Input
Input
Input
Input
Input
Input
Input
-
*: These signals are different to the KT76A/KT76C/KT78A pinout; on the KT76A, KT76C and
KT78A these signals are not usually connected in the aircraft.
The following diagram shows the connector orientation as it would be fitted to the mounting tray.
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5.4.2 Secondary Interface - Pinout
Pin Signal Direction
1
Ground -
2
RS232 Output 2
3
RS232 Input 2
Output
Input
4
Reserved Input
5
Audio Mute In
6
Altitude Alert
Input
Output
A
Ground -
B
Audio +
C
Audio -
Output
Output
D
Reserved -
E
ARINC Traffic B
F
ARINC Traffic A
Output
Output
5.4.3 Orientation Diagram
To assist in connector orientation, the following example shows a typical set of connections. This diagram shows the expected connector positions when viewed from the transponder side of the tray, looking into the tray from the front. In the example shown the aircraft uses a 14 volt lighting bus, a parallel altitude encoder, a DME with simple suppression output, a GPS connected to serial input 2, and a simple lamp for the altitude alerter. This example is representative of a simple fixed gear 14 volt aircraft.
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5.4.4 Molex Crimp Terminals
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The Molex connector contacts should be wired with wire of 18-24 AWG. The contacts are compatible with a wide range of crimp tools. Ensure that the contact has been crimped using both the conductor crimp and the insulator crimp.
Once crimped, the contacts should be slotted into the rear of the connector shell. Push the contact in until the retaining tab clicks into place. Tug gently to confirm the contact is locked in place.
The contacts can be easily removed using the Molex removal tool, or equivalent. This is pushed gently into the connector shell from the side opposite from the wire entry, and lifts the retaining tab from the stop, allowing the contact to be eased out by pulling on the wire.
5.5 Antenna Installation
The antenna should be installed according to the manufacturer’s instructions.
The following considerations should be taken into account when siting the Antenna.
The antenna should be well removed from any projections, the engine(s) and propeller(s). It should also be well removed from landing gear doors, access doors or others openings which will break the ground plane for the antenna.
The antenna should be mounted on the bottom surface of the aircraft and in a vertical position when the aircraft is in level flight.
Avoid mounting the antenna within 3 feet of the ADF sense antenna or any COMM antenna and 6 feet from the transponder to the DME antenna.
Where practical, plan the antenna location to keep the cable lengths as short as possible and avoid sharp bends in the cable to minimise the VSWR.
To prevent RF interference, the antenna must be physically mounted a minimum distance of 3 feet from the TT31 Mode S transponder.
Electrical connection to the antenna should be protected to avoid loss of efficiency as a result of the presence of liquids or moisture. All antenna feeders shall be installed in such a way that a minimum of
RF energy is radiated inside the aircraft.
5.5.1 Antenna Cable
The TT31 is designed to meet Class 1 requirements with an allowance of 2 dB for loss in the connectors and cable used to connect it to the antenna. Excessive loss will degrade both transmitter output power and receiver sensitivity.
Allowing 0.25dB loss for the connector at each end of the antenna cable assembly leaves an allowance of 1.5dB maximum loss for the cable itself.
An acceptable cable:
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Has less than 1.5dB loss for the run length needed
Has a characteristic impedance of 50 Ohms
Has double braid screens or has a foil and braid screen
Once the cable run length is known, a cable type with low enough loss per metre that meets the above requirements can be chosen. Longer runs require lower loss cable.
NOTE: Low loss cable typically uses foamed or cellular dielectrics and foil screens. These make such cables especially prone to damage from too-tight bends or from momentary kinking during installation.
Once kinked, these cables do not return to full performance when straightened.
The following table is a guide to the maximum usable lengths of some common cable types. Actual cable loss varies between manufacturers, there are many variants, and the table is therefore based on typical data. Use it as a guide only and refer to the manufacturer’s data sheet for your specific chosen cable for accurate values.
Max Length in Metres
Max Length in Feet
Insertion Loss dB/metre at
1090MHz
MIL-C-17 Cables Carlisle Type
3.81
5.25
12’ 6”
17’ 3”
0.39
0.29
M17/112 (RG304)
M17/127 (RG393)
3C142B
311601
311501
12.59 41’ 0.12
311201
310801
Contact Carlisle Interconnect Technologies on +1 414 421 5300 or www.carlisleit.com for their data sheets.
When routing the cable, ensure that you:
Route the cable away from sources of heat.
Route the cable away from potential interference sources such as ignition wiring, 400Hz generators, fluorescent lighting and electric motors.
Allow a minimum separation of 300mm (12 inches) from an ADF antenna cable
Keep the cable run as short as possible
Avoid routing the cable round tight bends.
Avoid kinking the cable even temporarily during installation.
Secure the cable so that it cannot interfere with other systems
5.5.2 BNC Connector
This section describes the technique for attaching the antenna cable to the supplied blind-mate BNC connector.
If a low-loss cable is needed that has too large a dielectric diameter to fit the supplied blind-mate BNC connector, a short length (up to 150mm or 6 inches) of smaller cable may be used with suitable mating connectors to adapt to the transponder connector.
Strip back the coax cable to the dimensions in the table, as shown in the diagram below. Slide
25 mm (1 inch) of heat shrink tubing over the cable.
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(mm)
Cut size
(inches)
A 12.7 0.5
Insert the cable into the connector – the inner conductor should align with the centre contact, the inner shield should be inside the body of the connector and the outer shield should be outside the body.
Solder the centre conductor to the centre contact, aligning the conductor with the slot in the contact. Avoid excess solder heat on the centre BNC conductor pin.
Solder the inner shield to the inside of the connector body by applying a soldering iron to the body and running solder into the gap. Try to avoid excess solder heat on the connector body.
Solder the outer shield to the outside of the connector body. Avoid excess solder heat on the connector body.
Slide heat shrink tubing forward (flush to connector) and heat to shrink the tubing.
Complete the assembly by installing the bushing over the centre contact, and fitting the cap.
Solder the cap in place in at least two places.
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5.6 Tray / BNC Connector Assembly
When the BNC is prepared, feed it through the TT31 mounting tray and attach the washer combination in the following order:
Wave washer (p/n 00317-00).
00239-00
Plain washer (p/n 00241-00).
Circlip washer (p/n 00242-00).
The Circlip washer should be fitted with a set of Circlip pliers.
The two Molex connectors should be passed through the openings in the rear of the tray, and then mounted firmly to the tray from the inside using the four M3 screws supplied.
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5.7 Interface Details
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5.7.1 Power Input
The power supply can be 11-33 Volts DC; no voltage adjustment is required. Contacts 11 and 12 on the 24 way connector are both available as power inputs. This is for compatibility reasons only – internally the two are connected together, and in most installations only one need be connected to the power supply.
Use a 3 Amp or greater circuit breaker for power supply protection to the TT31.
5.7.2 Lighting Bus Input
The TT31 will adjust the brightness of the front panel switch lighting according to the voltage on the lighting bus input. Two lighting bus inputs are provided on the 24 way connector to accommodate aircraft with 14 Volt or 28 Volt lighting systems. When the lighting bus operates at 28 Volts, connect the bus input to contact 3, and leave contact 2 unconnected. When the lighting bus operates at 14
Volts, connect the bus input to contact 2. In this case contact 3 can be left unconnected, but for backwards compatibility may also be grounded instead with no effect.
If no lighting bus input is detected, the TT31 will automatically control the front panel lighting based on the ambient light sensor.
5.7.3 Mutual Suppression
Mutual suppression allows two or more transmitters on adjacent frequencies to inhibit the other transmitters when one is active to limit the interference effects. It is commonly used between transponders and DME systems, and between transponders and collision avoidance systems.
The TT31 provides two styles of mutual suppression interface on the 24 way connector. The Suppress input on contact 9 is typically used in aircraft with simple DME systems and no other suppression requirements. It is an input only, and is active whenever the input is greater than approximately 5
Volts.
The Suppress I/O on contact 4 is an ARINC compatible suppression bus interface, which acts as both an input and an output. The TT31 will assert this signal when it is transmitting, and can be suppressed by other equipment that asserts the signal. The TT31 will drive approximately 24 Volts on the output
(independently of supply voltage), and will treat the input as active whenever the bus has greater than
10 Volts.
5.7.4 Serial Port Options
There are two RS232 serial input/output ports, one on the primary connector (pins 6 and 7) and one on the secondary connector (pins 2 and 3). The input sources can be an altitude encoder, air data computer, or GPS for ADS-B support. The output can be serial altitude data for baro-aided GPS devices, or TIS traffic for suitable display.
Note: although each input and output can be assigned separately, the line speed for each input and output pair can only be set together.
5.7.5 Altitude Inputs and Output
The TT31 can use either a parallel Gray code altitude input, or serial RS232 altitude input. The Gray code interface is on the 24 way connector, whereas the serial altitude can be configured to be on either of the two RS232 inputs. If the altitude encoder you are using offers both, we recommend using the
RS232 serial input. Serial formats allow a higher resolution altitude representation that can be used by
Mode S interrogations, whereas parallel Gray code format can only represent altitude to the nearest 100 feet. You must choose between serial or parallel formats – you should NOT connect both. If a parallel encoder is connected the TT31 will always use that as the altitude source even if a serial encoder is also connected.
The parallel encoder inputs are active when the voltage to ground is pulled below approximately 4
Volts. The TT31 includes internal isolation diodes which prevent the unit from pulling the encoder
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TT31 Transponder Installation Manual 18 June 2014 lines to ground when the transponder is switched off. The TT31 can therefore share the altitude inputs with other devices without needing external isolation.
Parallel output altitude encoders intended for operation below 30,000 feet may not have a signal connection for D4. In an aircraft with a service ceiling below 30,000 feet input D4 will never be active, and can safely be left unconnected.
The serial encoder input uses RS232 input levels. The communication is usually 9600 bps, no parity, although the bit rate can be configured. The TT31 will correctly recognise either
“Icarus/Trimble/Garmin” format altitude data, or “RMS” format altitude data. Refer to the encoder documentation to determine jumper settings as appropriate.
The TT31 can also accept Shadin family Format G, Format S and Format Z air data protocols which supply both altitude and airspeed information. The airspeed information can be used to provide an automatic air/ground determination for an ADS-B installation.
The TT31 includes a serial altitude output which repeats the altitude received on the encoded input
(either parallel or serial) for connection to a GPS or other equipment. The output format is always
“Icarus/Trimble/Garmin” format. If the altitude source is a parallel encoder, the serial output is reported every 0.5 seconds; if the source is a serial encoder, the output simply repeats the input reports, each report delayed by up to 10 milliseconds from the corresponding input report.
5.7.6 Squat Switch Input
The Squat switch input allows the transponder to automatically switch between Airborne and Ground modes of operation. The squat switch will also automatically start and stop the flight timer. The input will be asserted when the voltage to ground is pulled below approximately 4 Volts. The operating mode of the squat switch can be programmed during setup to allow for active low or active high logical behaviour. For aircraft with no squat switch this input should be left open circuit, and the setup mode programmed for “Not Connected”.
5.7.7 Ident Switch Input
The Ident switch input, on the 24 way connector, allows the IDENT function to be selected using a remote switch. The input is active low, and will be asserted when the voltage to ground is pulled below approximately 4 Volts.
5.7.8 External Standby Input
This input, when held low, places the transponder in Standby mode. It should be used to switch between transponders in an installation with two transponders. The input is active low, and will be asserted when the voltage to ground is pulled below approximately 4 Volts.
5.7.9 Audio Output
The Audio Output is on the 12 way secondary connector. The Audio Output is a balanced (two wire) audio output that can be connected to an unswitched input on the aircraft audio panel. Audio output is up to 10 Volts peak-to-peak across the pair when driving a 600 Ohm load; actual level can be adjusted at installation – see Section 6.
Note: The audio pair is not a true transformer balanced output – both pins are actively driven.
If the audio panel input is single-ended, then only one of the output pins should be used, together with a local ground pin – the other audio output should be left floating.
The Audio Output carries the traffic alert messages for TIS, and the altitude audio annunciator used by the altitude monitor function.
5.7.10 Altitude Alerter Output
The TT31 includes an altitude monitor function that can alert the pilot to altitude deviations in cruise flight. The altitude alerter output, on the 12 way secondary connector, is switched to ground when the altitude deviation is detected and can be connected to a warning light or sounder to warn the pilot. The
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Issue AP output is an open collector transistor, and can sink up to 1 Amp DC. The switched voltage should not exceed 60 Volts.
5.7.11 GPS Position Input
The GPS position input is required to support ADS-B functionality. The GPS position input is an
RS232 input to the transponder. The ADS-B features are optional – no GPS is required for normal
Mode S Elementary Surveillance.
The TT31 GPS input can recognise the following protocols:
Industry standard “Aviation” protocol
NMEA 0183 protocol ($GPRMC message)
FreeFlight and NexNav GPS proprietary protocols
Garmin proprietary ADS-B protocols
Trig ADS-B protocol
Some of the protocols listed above may not contain all the required data for a compliant ADS-B message, depending on the intended airspace regulations. For further information refer to Section 12
(ADS-B Compliance) of this manual.
With the Garmin ADS-B protocol selected, the TT31 is compatible with both the Garmin ADSB and
Garmin ADSB Plus protocols.
NOTE: GPS sources providing data using the Garmin ADSB protocol will not meet all the
FAA requirements contained in FAR 91.227. For installers seeking compliance in the USA, the GPS source must use the Garmin ADS-B Plus protocol.
5.7.12 TIS Traffic Output
The TIS traffic output supports the display of uplinked Traffic Information Service messages. It can be provided on a serial output (RS232 output 1 or 2) and/or on the ARINC 429 output on the 12 way secondary connector. The TT31 RS232 output can drive the Trig proprietary traffic protocol, and can also support the format used by certain Garmin handheld displays, including the 495, 496, 695 and 696.
The TT31 ARINC TIS output can drive a number of common traffic displays, including Garmin and
Bendix/King multifunction displays.
Note: TIS is a Mode S uplink service that is provided by some US approach radars. TIS coverage is limited to the coverage areas of those radars. There is no TIS provision outside the USA.
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6. Installation Setup and Test
The TT31 uses a simple setup system to program important system parameters, including the Mode S address. In the original factory configuration, the setup screen is the first thing that runs when you switch on the transponder. If the transponder has already been configured, and you want to access the setup screen again, simply hold down the FUNC button while switching on the transponder and the setup system will run.
The script will prompt for the following configuration items:
Aircraft Registration
Mode S Address
VFR Squawk Code
Aircraft Maximum Airspeed
Aircraft Category
Squat switch source, if fitted
TIS ARINC output
Serial RS232 Input/Output configuration (GPS, TIS, Altitude)
ADS-B parameters ( if GPS source is fitted)
Audio Output Volume
LCD Dimming Settings
It will then run some simple installation diagnostics, including an external interface check, a check of the altitude encoder interface, and a check of the lighting bus input.
All the programming is accomplished using the right hand rotary knob and the ENT, BACK and FUNC buttons. Make all input selections using the rotary knob. Pressing the ENT button accepts the current input and advances to the next input item. Pressing the BACK button accepts the current input and then returns to the previous input item. Pressing the FUNC button moves directly to the next screen.
6.1 Configuration Items
6.1.1 Aircraft Registration (VFR Flight ID)
The default Flight ID for an aircraft not on an IFR flight plan should be the aircraft registration. Enter the aircraft registration using the rotary knob and the ENT button.
Note that the aircraft registration is loaded as letters and numbers only. There are no dashes or other punctuation marks, and no spaces can be inserted. When you enter a space it finishes the data entry and moves to the next item.
6.1.2 Aircraft Address Programming
The Mode S Address is a 24 bit number issued to the aircraft by the registration authority for the aircraft. These addresses are usually written as a 6 digit hexadecimal number, although you may also encounter one written as an 8 digit octal number. The TT31 only understands the hexadecimal format, so you must first convert an octal number to hexadecimal.
Enter the 6 digit aircraft address using the rotary knob and the ENT button.
In the case of an N registration aircraft, this ICAO address will normally be filled in automatically based on the tail number.
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6.1.3 VFR Squawk Code
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When the pilot presses the VFR button, a pre-programmed code will replace the current squawk code.
The code is set up next; the choice of code will depend on the normal location of the aircraft. In the
USA, the VFR squawk code is 1200. In most parts of Europe, the VFR squawk code should be set to
7000.
Enter the 4 digit squawk code using the rotary knob and the ENT button.
6.1.4 Airspeed Category
Mode S transponders can transmit their maximum airspeed characteristics to aircraft equipped with
TCAS. This information is used to help identify threats and to plan avoiding action by the TCAS equipped aircraft. The airspeeds are grouped in ranges; using the rotary knob, select the range that corresponds to the aircraft.
6.1.5 Aircraft Category
To assist ATC tracking of aircraft, an aircraft category can be transmitted by Mode S transponders.
Using the rotary knob, select the aircraft category that most closely matches the aircraft the transponder is installed in.
6.1.6 Squat Switch Source
The Squat switch input allows the transponder to automatically switch between Airborne and Ground modes, and to automatically start and stop the flight timer. The sense of the squat switch input can be selected using the rotary knob. For ADS-B installations with both a GPS and an Air Data Computer installed the transponder can automatically determine the Air/Ground state without an external squat switch. If the squat switch input is not used the “Not Connected” option should be selected.
6.1.7 ARINC TIS Output
If the aircraft has a Traffic Information Service (TIS) compatible display connected to the ARINC 429 output, select the appropriate interface protocol using the rotary knob.
Note: TIS is a Mode S uplink service that is provided by some US approach radars. TIS coverage is limited to the coverage areas of those radars; there is no TIS provision outside the
USA.
6.1.8 RS232 Input/Output
There are two RS232 input lines and two RS232 output lines on the TT31. Either input can be used to receive data from a serial altitude source, such as an altitude encoder or air data computer, or a GPS position source for ADS-B. Either output can be used to provide serial altitude output, or TIS traffic.
If a GPS is connected for ADS-B position reporting, select the appropriate interface protocol using the rotary knob.
If the aircraft has a Traffic Information Service (TIS) compatible display connected to the transponder, select the appropriate interface protocol using the rotary knob.
Serial altitude input protocols are detected automatically. Serial altitude output is fixed as “Icarus” format.
Separate bit rates are chosen for each RS232 port but are common for input and output. The line speed of each RS232 port can be selected with the rotary knob. Each line can be configured to run at 4800,
9600, 19200, 38400 or 57600 bps. In addition, serial line 1 also runs at 1200 and 2400 bps.
Traffic displays using the Garmin protocol run at 9600 bps. Panel mount GPS units with Aviation format outputs generally also run at 9600 bps. NMEA GPS units generally run at 4800 bps. FreeFlight
1201 and NexNav 3101 GPS receivers generally run at 19200 bps.
Note: Input and Output speeds on the same RS232 line are not separately controlled on the
TT31. Not all combinations of inputs and outputs will be usable if the external devices
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operate on fixed bit rates and are different to each other.
6.1.9 ADS-B Configuration
Configuring a GPS on either RS232 input automatically turns on ADS-B Out. The following additional ADS-B parameters will then need to be configured.
6.1.9.1 GPS System Certification Level
An important metric for ADS-B ground system behaviour is the SDA or System Design Assurance level. It is intended to reflect the probability that the GPS position source is providing erroneous information, and is based on the certification standard that was used by the GPS vendor. This will be indicated in the form of a letter code (A to D) on the data plate or installation documentation for the
GPS in accordance with the standards DO-178B and DO-254, for example “DO-178B level C”. If both standards are reported but at different levels, use the lower standard (higher letter).
The following table shows example certification data, current at the time of publication.
Equipment
Trig TN70
Accord NexNav Mini
FreeFlight 1201
Garmin 4x0W/5x0W
Garmin GTN series
Certification Level
Level C
Level C
Level C
Level C
Level C
6.1.9.2 GPS NACv
Another metric that the ADS-B ground system uses to help it track the aircraft is NACv. NACv is the
Navigational Accuracy Category for velocity, and is a design feature of the GPS receiver. It represents the error bound for velocity that the GPS may report in acceleration/deceleration or turning manoeuvres. You can find this information from your GPS installation manual.
The following table shows example NACv data, current at the time of publication.
Equipment
Trig TN70
Accord NexNav Mini
NACv Setting
10 metres per Second
10 metres per Second
FreeFlight 1201
Garmin 4x0W/5x0W
10 metres per Second
10 metres per Second
Garmin GTN series 10 metres per Second
NOTE: If the Garmin ADS-B Plus protocol is used then the NACv is set dynamically by the
Garmin GPS unit. This manual configuration item is ignored.
6.1.9.3 Aircraft Length and Width
On the ground, ADS-B transmits encoded aircraft size information which is used by ATC to identify taxiing routes and potential conflicts. When configured for ADS-B, the TT31 will ask for the aircraft length and width (wingspan), in metres, and will calculate the appropriate size code for transmission.
6.1.9.4 GPS Antenna Offset
The GPS antenna offset is used together with the aircraft length and width to manage taxiway conflicts.
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A typical GPS installation does not report the geographic position of the centre of the aircraft, or even the tip of the nose of the aircraft; instead it usually reports the location of the actual GPS antenna (not the GPS receiver). In normal flight operations this distinction is of no practical importance at all, but if
ADS-B is used to manage taxiway conflicts, a significant offset in antenna position could mean that the aircraft is not in the same place as the ADS-B reported position. Although primarily intended for position correction on large transport aircraft, General Aviation aircraft can also have a significant offset. For example, if the aircraft has a long tail boom and the GPS antenna is on the top of the tail, the GPS position could be 15 feet or more from the nose of the aircraft.
Enter the position of the GPS antenna relative to the nose of the aircraft. The position is stored and transmitted to the nearest 2 metres; great accuracy in measurement is not required.
6.1.9.5 ADS-B Receiver Options
In the USA there are two ADS-B channels, 1090ES and UAT, and there is an ADS-B based traffic information service called TIS-B. The ADS-B ground stations relay this information between the two channels so that suitably equipped aircraft can receive traffic information. To limit channel congestion these services are only provided to aircraft equipped to receive them.
The transponder reports what receivers are installed in a periodic status message; enter the receiver status here.
6.1.10 Audio Volume
The altitude alert function includes an audio alert, as does the TIS traffic service. This configuration item lets you adjust the audio volume output from the transponder using the rotary knob. Whilst you are turning the volume control, the transponder will periodically output a test signal to verify the settings.
6.1.11 LCD Dim Point
The LCD backlight illumination is controlled automatically by the ambient light sensor. Depending on the amount of light spill in the cockpit, and the brightness of other adjacent avionics displays, it may be necessary to adjust the darkest setting of the backlight to best match other equipment and to improve the cockpit appearance.
Note – it is only practical to do this in pitch darkness, since that is the in-flight environment that you are trying to reproduce. If you are working in a hangar with any other lighting it may be better to leave the setting in the mid-range.
6.1.12 LCD Brightness Curve
The actual maximum brightness of the LCD cannot be increased with this control. What it controls is the rate at which the lighting increases in brightness as the ambient light increases. This allows the brightness to be matched to other avionics displays during light level changes as far as possible.
6.2 Test items
6.2.1 Interface Check
The Interface Check screen displays the current state of the external IDENT, external STANDBY and external GROUND inputs. Exercise these inputs to confirm the correct behaviour.
6.2.2 Altitude Check
The Altitude check displays the current state of the altitude inputs. Individual Gray code lines are shown to assist in fault tracing.
6.2.3 Lighting Bus
The lighting bus check displays the voltage on the lighting bus to assist in verifying the correct operation of the lighting bus.
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6.2.4 Temperature
The internal temperature of the transponder can be displayed. The display is in degrees Celsius.
6.2.5 RS232 Input Check
The RS232 interface check provides a diagnostic that the RS232 input lines are configured correctly. It will display on screen the data each RS232 line is set up to receive. If valid data of the correct type is being received, the decoded data will be shown on the display.
6.2.6 Transponder Cycles
The transponder cycle counter represents the total running time for the transponder, and is used by maintenance staff to track faults.
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7. Post Installation Checks
Post installation checks should be carried out in accordance with your certification requirements.
These checks should include:
Mode S interrogations to verify correct address programming.
Verification of the reported altitude using a static tester. For aircraft using parallel Gray code encoders, the test should include a range of altitudes up to 6,800 feet, 14,800 feet or 30,800 feet, depending on the service ceiling of the aircraft – these altitudes correspond to code changes which are not otherwise tested at lower altitudes.
Where installed, verification of correct squat switch ground/airborne indications. In an aircraft with a squat switch, setting the Mode switch to ALT when the aircraft is on the ground should leave the transponder in GND mode; when the aircraft becomes airborne, the mode should switch automatically to ALT.
Interrogations to verify the receiver sensitivity. A Mode S transponder should have a minimum triggering level (MTL) of between -77 dBm and -71 dBm. Failure to meet this requirement usually indicates antenna or coaxial cable problems.
Interrogations to verify the transmitted power. A Class 1 installation should have no less than
125 Watts at the antenna (and no more than 500 Watts). Failure to meet this requirement is also generally due to antenna or wiring issues.
Where installed, verification of the GPS position source and ADS-B outputs. In an aircraft with a configured GPS, pressing the FUNC button on the transponder front panel in normal operation will display the ADS position monitor. With the aircraft outside the hangar (for good GPS reception) the aircraft position should be displayed on the transponder. If the position indications are all dashes then either the GPS position is not valid or the GPS interface is not correctly configured. Whenever a valid position is received by the transponder and the transponder is in any mode other than Standby, ADS-B Extended Squitters should be observed on the transponder test set.
Where installed, verification of the TIS output. A Mode S test set with TIS capability should be used; with the transponder in ALT mode traffic should be shown on the attached display.
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8. Normal Operation
8.1 Overview
On the front panel is an amber backlit LCD display flanked by a rotary mode selector knob (OFF, SBY,
GND, ON, and ALT) and a continuously rotating knob used for code and data entry.
8.2 Display
The display shows the operating mode of the transponder, the reported pressure altitude, and the current squawk code and Flight ID. The reply indicator is active when the transponder replies to interrogations.
The pressure altitude is displayed as a Flight Level, which is the pressure altitude in hundreds of feet.
When non-standard atmospheric conditions apply, this may not match the altimeter indicated altitude, but will be correctly displayed by the ATC radar.
8.3 Mode Selector Knob
The left hand knob controls the power to the transponder and the operating mode.
OFF Power is removed from the transponder.
SBY
ON
The transponder is on, but will not reply to any interrogations.
GND The transponder will respond to Mode S ground interrogations from surface movement radar.
The transponder will respond to all interrogations, but altitude reporting is suppressed.
ALT The transponder will respond to all interrogations.
When airborne, the transponder should always be set to ALT unless otherwise directed by Air Traffic
Control. When you are taxiing on the ground, the transponder should be set to GND unless your installation includes a gear squat switch. Aircraft installations that include a gear squat switch will automatically select GND on landing.
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8.4 Push Buttons
IDENT Press the IDENT button when ATC instructs you to “Ident” or
“Squawk Ident”. This activates the SPI pulse in the transponder replies for 18 seconds. IDENT will appear in the display.
FUNC Pressing the FUNC button provides access to the flight timer, stopwatch and altitude monitor function. When the aircraft is
ADS-B equipped, pressing FUNC also provides access to the
ADS-B position monitor.
VFR Pressing the VFR button sets the transponder to the preprogrammed conspicuity code. Pressing the button again restores the previous squawk code.
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ENT code and Flight ID.
The ENT button enters a digit in the code selector.
BACK The BACK button goes back to the previous digit in the code selector.
8.5 Code Selector Knob
The right hand knob is used to set squawk codes and the Flight ID. The FLT/SQ button selects which will be updated. Turning the knob will highlight the first digit on the display, and the digit can be changed as required. Press the ENT button to advance to the next digit. When ENT is pressed on the last digit, the new squawk code or Flight ID will replace the previous value. If the code entry is not completed within 7 seconds, the changes are ignored and the previous code restored.
1200
7000
VFR code in the USA
VFR code commonly used in Europe.
The Flight ID should correspond to the aircraft call sign entered on your flight plan. If no flight plan is active, the aircraft registration should be used as your Flight ID. Use only letters and digits. If the
Flight ID is less than 8 characters long, entering a blank character will end it.
8.6 Flight Timer
The Flight Timer records the time for which the transponder has been powered on and operating in flight mode – either ON or ALT. Press the FUNC button to display the Flight Timer.
8.7 Stopwatch
The stopwatch can be used as a convenient timer. Press the FUNC button to display the stopwatch.
Pressing ENT will reset and start the timer. Pressing ENT again will stop the timer.
8.8 ADS-B Position Monitor
The ADS-B position monitor is available on aircraft equipped for ADS-B position output. It provides a convenient way of verifying that valid position information is being received by the transponder by displaying the current calculated position. If a valid position is displayed, the transponder will be transmitting that position to ADS-B participants. If no position is available the position will be displayed as dashes, and the transponder will NOT be transmitting ADS-B position information.
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8.9 Altitude Monitor
The Altitude Monitor activates an audio annunciator or annunciator light (depending on installation) when the aircraft pressure altitude differs from the selected altitude by more than 250 feet. Press the
FUNC button to display the altitude monitor enable screen. Pressing ENT toggles the altitude monitor at the current altitude.
When altitude monitoring is in use, a small deviation pointer appears adjacent to the altitude display on the transponder.
8.10 Warnings
There are two warning messages that can be displayed on the transponder. Warning messages can be cleared by pressing the ENT key on the control panel.
If the transponder has been configured for ADS-B operation, but a suitable position fix is not available, a warning message is displayed to indicate that ADS-B capability has been lost. The transponder will continue to operate normally.
If there is a problem with the antenna installation, a warning message may be displayed. Depending on whether this is an intermittent problem the message may recur when cleared. The transponder may still be replying to interrogations, but there can be no assurance that ATC is receiving those replies.
8.11 Fault Annunciation
If the transponder detects an internal failure, or a hard fault with the antenna installation, the screen will indicate FAULT and a brief statement of the problem. No replies will be made to interrogations when a fault is detected.
8.12 Low Temperature Operation
The TT31 is certified for correct operation at temperatures down to -20 Celsius. At low temperatures however the display performance will be impaired. The aircraft cockpit should be warmed to allow normal operation of the transponder before takeoff.
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9. Continued Airworthiness
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9.1 Maintenance
Other than for periodic functional checks required by the regulations, the TT31 Mode S transponder has been designed and manufactured to allow “on condition maintenance”. This means that there are no periodic service requirements necessary to maintain continued airworthiness, and no maintenance is required until the equipment does not properly perform its intended function. When service is required, a complete performance test should be accomplished following any repair action. Repairs should only be carried out in accordance with Trig Avionics Limited service procedures.
9.2 ADS-B Installations
9.2.1 GPS Receiver Maintenance
If any maintenance is required on the connected GPS receiver, it is advisable to check with the GPS manufacturer that you have the most recent and correct version of tests to carry out after maintenance.
Check that there are no additional requirements to be considered when using the GPS as part of an
ADS-B system.
There is no requirement to test the full ADS-B system following maintenance on the GPS receiver as long as the post maintenance checks verify the output being used by the TT31.
9.2.2 GPS Receiver Design Changes
It should be noted that if the GPS receiver has been sent away for repair, it may have additional upgrades or design changes applied to it when it returns. The installer must check with the manufacturer that these upgrades or design changes do not adversely affect the compatibility with the
TT31.
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10. Limited Warranty
Trig Avionics Limited warrants our products to be free from defects in materials and workmanship for a period of two (2) years from the date of installation by an authorised dealer.
This warranty covers repair and/or replacement at our option, of any parts found to be defective, provided such defects in our opinion are due to faulty material or workmanship and are not caused by tampering, abuse, or normal wear.
All warranties are F.O.B.
Trig Avionics Limited
Heriot Watt Research Park
Riccarton, Edinburgh, EH14 4AP
Trig Avionics will not accept or pay for any charges for warranty work performed outside our factory without prior written consent.
This warranty applies only to products in normal use. It does not apply to units or circuit boards defective due to improper installation, physical damage, tampering, lightning or other electrical discharge, units with altered serial numbers, or units repaired by unauthorised persons or in violation of
Trig Avionics Limited service procedures.
Trig Avionics Limited assumes no responsibility for any consequential losses of any nature with respect to any products or services sold, rendered, or delivered.
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11. Environmental Qualification Form
Nomenclature
Part Number:
Manufacturer
TT31 Mode S Transponder
00220-(XX)
Trig Avionics Limited
ETSO: 2C112b
Address
Conditions
Temperature and Altitude
Low temperature ground survival
Low temperature operating
High temperature operating
High temperature short-time operating
Heriot Watt Research Park, Riccarton, Currie, Scotland, EH14 4AP
DO-160D
Section
Description of Conducted Tests
4.0
4.5.1
Equipment tested to Categories A1, C1
-55°C
4.5.1
4.5.3
4.5.2
-20°C
+55°C
+70°C
High temperature ground survival
Loss of Cooling
4.5.2
4.5.4
+85°C
Cooling air not required (+70°C operating without cooling air)
Decompression 4.6.2 8,000 to 35,000 feet in 15 seconds
Temperature Variation
Humidity
Operational Shocks
Crash Safety
Vibration
Waterproofness
Fluids Susceptibility
Sand and Dust
Fungus
Salt Spray
Magnetic Effect
Power Input
Voltage Spike
Audio frequency conducted susceptibility
Induced signal susceptibility
Radio frequency susceptibility
Radio frequency emission
Lightning induced transient susceptibility
Lightning direct effects
Icing
Electrostatic Discharge
Trig Avionics Limited
19.0
20.0
21.0
22.0
23.0
24.0
25.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
5.0
6.0
7.2
7.3
8.0
Equipment tested to Category C
Equipment tested to Category A
Equipment tested to Category B
Equipment tested to Category B and extended to use test levels for Helicopters
Aircraft zone 2; type 3, 4, 5 to category S level M
Equipment at strike-off level 3 also tested for aircraft zone 2; type 1 (Helicopters) to category U level G
Equipment identified as Category X – no test required
Equipment identified as Category X – no test required
Equipment identified as Category X – no test required
Equipment identified as Category X – no test required
Equipment identified as Category X – no test required
Equipment tested to Category Z
Equipment tested to Category B
Equipment tested to Category B
Equipment tested to Category B
Equipment tested to Category A
Equipment tested to Category T
Equipment tested to Category B
Equipment identified as Category XXXX – no test required
Equipment identified as Category X – no test required
Equipment identified as Category X – no test required
Equipment identified as Category X – no test required
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Because the ETSO for ADS-B was published later than the ETSO for transponders it refers to a later edition of the environmental standard, ED-14E/DO-160E, rather than ED-14D/DO-160D. The following form provides the environmental data in DO-160E format. The two tables are equivalent.
Nomenclature
Part Number:
Manufacturer
Address
Conditions
Temperature and Altitude
Low temperature ground survival
Low temperature operating
High temperature operating
High temperature short-time operating
High temperature ground survival
Loss of Cooling
TT31 Mode S Transponder
00220-(XX)
Trig Avionics Limited
Heriot Watt Research Park, Riccarton, Currie, Scotland, EH14 4AP
DO-160E
4.0
Description of Conducted Tests
Equipment tested to Categories A4, C4
4.5.1
4.5.1
-55°C
-20°C
4.5.3
4.5.2
4.5.2
4.5.4
+55°C
+70°C
+85°C
ETSO: C166a
Cooling air not required (+70°C operating without cooling air)
Decompression 4.6.2 8,000 to 35,000 feet in 15 seconds
Temperature Variation
Humidity
Operational Shocks
Crash Safety
Vibration
Waterproofness
Fluids Susceptibility
Sand and Dust
Fungus
Salt Spray
Magnetic Effect
Power Input
Voltage Spike
Audio frequency conducted susceptibility
Induced signal susceptibility
Radio frequency susceptibility
Radio frequency emission
Lightning induced transient susceptibility
Lightning direct effects
Icing
Electrostatic Discharge
Fire, Flammability
18.0
19.0
20.0
21.0
22.0
23.0
24.0
25.0
26.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
5.0
6.0
7.2
7.3
8.0
Equipment tested to Category C
Equipment tested to Category A
Equipment tested to Category B
Equipment tested to Category B and extended to use test levels for Helicopters
Aircraft zone 2; type 3, 4, 5 to category S level M
Equipment at strike-off level 3 also tested for aircraft zone 2; type 1 (Helicopters) to category U level G
Equipment identified as Category X – no test required
Equipment identified as Category X – no test required
Equipment identified as Category X – no test required
Equipment identified as Category X – no test required
Equipment identified as Category X – no test required
Equipment tested to Category Z
Equipment tested to Category B
Equipment tested to Category B
Equipment tested to Category B
Equipment tested to Category AC
Equipment tested to Category T
Equipment tested to Category B
Equipment identified as Category XXXX – no test required
Equipment identified as Category X – no test required
Equipment identified as Category X – no test required
Equipment identified as Category X – no test required
Equipment identified as Category C
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12. ADS-B Compliance
TT31 transponders with software version 3.1 and above include support for Extended Squitter ADS-B out which is compliant with DO-260B. The TT31 is a B1S ADS-B transmitter.
12.1 ADS-B Parameters Supported
The following table lists the ADS-B parameters that are transmitted by the TT31 transponder when connected to an appropriate GPS receiver.
Parameter BDS Register
SPI 0,5
Emergency Indicator 0,5
Barometric Altitude 0,5
Quality Indicator (NIC) 0,5
Latitude 0,5
Airborne Position
Longitude 0,5
Quality Indicator (NIC) 0,6
Latitude 0,6
Surface Position
Longitude 0,6
Surface Ground Speed
Surface Ground Track
0,6
0,6
Aircraft Identification
Airborne Ground Velocity
Geometric to Barometric Altitude Difference
Geometric Vertical Speed
Squawk Code
0,8
0,9
0.9
0.9
6,1
Emergency Status
Quality Indicator (NACp, NACv and GVA)
Quality Indicator (SIL and SDA)
Version Indicator
Surface Length/Width
Surface Antenna Offset
6,1
6,5
6,5
6,5
6,5
6,5
In all cases, uncompensated latency due to the transponder is less than 10 milliseconds. Analysis of the system latency should add this to the latency of the GPS system and the transmission time of the position data from the GPS to the transponder to determine the overall latency.
12.2 FAA 91.227 Compliance
The TT31 transponder is certified to TSO-C166b and meets the requirements of AC20-165A when directly connected to the following GPS units.
This will form the basis of a 14 CFR 91.227 compliant ADS-B installation:
Trig Avionics Limited
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GPS Unit
Trig TN70
FreeFlight 1201
GPS Output Setting TT31 Input Setting
n/a FreeFlight/NexNav n/a FreeFlight/NexNav
Accord NexNav Mini n/a
Garmin GNS4x0W ADS-B+
Garmin GNS5x0W ADS-B+
FreeFlight/NexNav
Garmin ADSB
Garmin ADSB
12.3 CS-ACNS Compliance
The TT31 transponder can be connected to the following GPS units to form the basis of a CS-ACNS compliant ADS-B installation:
GPS Unit
Trig TN70
GPS Output Setting TT31 Input Setting
n/a FreeFlight/NexNav
FreeFlight 1201 n/a
Accord NexNav Mini n/a
FreeFlight/NexNav
FreeFlight/NexNav
Garmin GNS4x0W ADS-B or ADS-B+ Garmin ADSB
Garmin GNS5x0W ADS-B or ADS-B+ Garmin ADSB
Garmin GTN series ADS-B or ADS-B+ Garmin ADSB
For installations seeking certification to CS-ACNS or other applicable standards, additional compliance information is available on request from Trig Avionics Limited.
12.4 Automatic Air/Ground Determination
The TT31 can report ADS-B surface and airborne messages. The ADC or squat switch inputs can be utilised to determine air/ground status as explained in section 6.1.
12.5 ADS-B Support
Details are given below for specific transponder behaviour that may be required to show compliance against AC20-165A. For installations seeking certification to 14 CFR 91.227 or other applicable standards, additional compliance information is also available on request from Trig Avionics Limited.
The TT31 will transmit an ADS-B message populated with all the parameters required by 14
CFR 91.227.
The TT31 will transmit north/south, east/west velocities within an airborne ADS-B message.
The TT31 will transmit ground speed and ground track within a surface ADS-B message. The
TT31 will suppress the ground track at velocities less than 7 knots.
When using the GPS listed in the table above, the TT31 will set SIL = 3 and SIL
SUPP
= 0. For non-compliant GPS units the TT31 will set SIL = 0.
The TT31 will always limit the NIC value to not greater than 8.
The NACp value is set using HFOM data from the GPS.
The NACv is a fixed setting determined from the setup menu.
NOTE: If using the Garmin ADS-B Plus protocol, the NACv is set dynamically from the GPS data. In this instance the NACv setting from the setup menu is ignored.
The TT31 will set the GVA value using VFOM data from the GPS.
If the TT31 detects an internal failure, the screen will indicate FAULT or WARNING followed by a brief statement of the problem.
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Issue AP
If the TT31 detects that no position data is being received then the display will indicate
WARNING – NO ADSB POSN.
Only a single, bottom mounted antenna can be used and therefore the Single Antenna Bit will be fixed at 1.
There is no pilot interface to disable ADS-B reporting.
The TT31 has no anonymity feature because it works on 1090 MHz and is certified to TSO-
C166b.
The TT31 will populate the vertical rate field with the GPS geometric vertical rate data. This will always be converted to feet per minute and the TT31 transmits geometric rate, never barometric.
If you require additional information and data to support an ADS-B installation then please contact [email protected]
.
Trig Avionics Limited
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