Routine Instrument Landing System (ILS) Flight Inspections

Routine Instrument Landing System (ILS) Flight Inspections
Routine Instrument Landing System (ILS) Flight
Inspections Conducted From a Remote Location
Leslie E. Atkinson
Chief, AFMC Airfield Systems Customer Support Team
Headquarters Air Force Materiel Command (HQ AFMC)
Eglin Air Force Base, Florida, USA
Fax: +1 850 882 9137
This document addresses the origin of the remote ILS
flight inspection concept, the benefits of conducting flight
inspections remotely, and the hardware, software, and
methods used to conduct remote flight inspections.
This document is not intended to be an endorsement or
recommendation of any commercial entities by the Air
Force or DoD.
To fully support the Air Force Materiel Command
(AFMC) Centralized Navigational Aids Maintenance
concept, a method of conducting routine ILS periodicwith-monitors flight inspection was developed. This
document will describe how that was accomplished and
the methods used to implement the program.
Some of the issues presented in this document include:
A short history of remote ILS Maintenance concepts
and current activities
Software/hardware utilized for all types of ILS
periodic-with-monitors flight inspection
Hardware installed for Capture Effect Glideslope
(CEGS) and Sideband Reference Glideslope
(SBRGS) flight inspection
Equipment/methods used to interact with the flight
inspection aircraft from a remote location
Utilization and training level of local augmentation
Benefits realized from remote flight inspection
Drawbacks encountered and methods used to
overcome them
In this time of shrinking budgets, this document presents
an alternative method of conducting flight inspections that
realizes time and manpower savings.
Centralized maintenance of ILS in AFMC began as an
equipment modernization in 2002 with a view toward the
possibility of conducting remote maintenance in the
future. Once the first system was fielded in November
2002 at Wright Patterson Air Force Base, Ohio,
headquarters leadership and the AFMC Airfield Systems
Customer Support Team (CST) recognized the remote
maintenance potential of the new equipment and decided
to exploit the capability sooner rather than later. Without
going into unnecessary detail, AFMC embarked on a
transformation effort that resulted in the CST remotely
maintaining eleven single transmitter category I
instrument landing systems, two localizer-only systems,
five Tactical Air Navigation (TACAN) systems, one Very
High Frequency Omnirange (VOR), and one Distance
Measuring Equipment (DME) system at seven airfields
from the center located at Eglin Air Force Base, Florida.
The airfields are located in California, Utah, Oklahoma,
Ohio, Georgia, and Florida. The CST is currently manned
with five highly qualified technicians and one work group
manager/administrative specialist, all civil service
employees. Due to the fact that all of the replacement
systems are covered under a 15-year warranty, all
maintenance and certification activities are conducted
well within a $90K annual operations and maintenance
budget. Our fleet availability rate exceeds 99.6%. Mean
time to repair is less than 15 minutes from notification
when a replacement part is not required, and is
approximately 26 hours when a replacement part is
Centralized maintenance of ILS facilities loses its punch
if technicians must travel all over the country to conduct
routine, regularly scheduled periodic-with-monitors flight
inspections. AFMC recognized that a true centralized
maintenance capability would address conducting routine
functions, including flight inspection, remotely. Methods
to accomplish the following flight inspection tasks that
are currently required to complete a periodic-withmonitors flight inspection were developed and are
discussed in the next section.
1. Localizer Single Frequency – Alignment, modulation,
normal width, and wide alarm adjustments.
2. Localizer Dual Frequency – Alignment, modulation,
normal width, and course wide, clearance wide alarm
3. Null Reference Glideslope – Modulation, normal
width, wide alarm, and advance and retard phase to alarm
4. Sideband Reference Glideslope – Modulation, normal
width, wide alarm, low angle alarm, and advance and
retard upper antenna to alarm adjustments.
5. Capture Effect Glideslope – Modulation level, normal
width, course wide and clearance modulation percentage
alarm, middle antenna advance and retard phase to alarm,
and upper antenna attenuate to alarm. [1]
Localizers and null reference glideslope inspections are
performed using only the software controls available in
the equipment. Some checks on the sideband reference
and capture effect glideslopes are also performed using
the software controls. The following descriptions apply
to the single transmitter Category I systems maintained by
Flight Inspection Preliminaries
The CST initiates a remote maintenance session by using
the Portable Maintenance Data Terminal (PMDT)
program to contact the Remote Control and Status Unit
(RCSU), normally located in the control tower equipment
room, through a dial-up connection. The RCSU has two
primary functions; it provides navigational aid status
indications to the Remote Status Display Unit (RSDU)
located in the Air Traffic Control (ATC) operations area,
and it allows access to the navigational aid systems via
the equipment status lines.
Security protocols against unauthorized
adjustment are described as follows:
1. The Air Force utilizes a telephone system to block
unauthorized modem traffic into the bases; this acts as an
initial security barrier.
2. The maintainer must possess the site or RCSU
telephone number. This information is controlled under
For Official Use Only rules.
3. The site computer will only communicate with the most
current PMDT program. The RCSU or RMS will direct
the on-site modem to disconnect immediately if the
incoming data packets are not recognized as originating
with the PMDT program. Copies of the PMDT program
and the computers on which it is installed are carefully
4. All levels of maintenance have user names and
passwords and must have access to the highest security
levels in order to affect signal in space. The passwords
follow Air Force rules for complexity and are changed
periodically, when employees leave the CST, or when a
compromise is suspected.
5. Passwords and user names are encrypted with a
special, proprietary binary protocol that has not been
distributed outside of the manufacturers control to protect
against interception.
6. In order to affect signal in space, the technician must
take control of the system; air traffic control is notified
immediately by the system when this occurs. The
indication they receive is that of an off-the-air facility.
The CST is notified and can begin investigating;
meanwhile the site is removed from service by the
controlling agency.
7. A connection log is maintained by the equipment and
is periodically scanned by the CST to detect incursions by
unknown users; we have yet to encounter one.
Upon completing the secure login procedure, a graphic of
the airfield systems is displayed (See Figure 1). The
technician merely right clicks the desired ILS component
to gain access to its Remote Maintenance System (RMS)
program. As a backup in the event of a status line failure,
the PMDT can contact the RMS directly through a
separate dial-up connection. The RCSU connection is
preferred due to the speed at which the CST can transition
from one ILS component to another during a flight
The CST technician will perform any
necessary pre-flight inspection checks and adjustments at
this time.
Figure 1. RCSU System Display Screen
Figure 3. Wattmeter Data Tab
The remote flight inspection radio is then contacted and
initialized in preparation for flight inspection. The radio
system is covered in greater detail later in this document.
Once the CST is in contact with the panel technician, the
flight inspection begins.
If a normal width adjustment is required, the existing
sideband power is obtained from the Transmitter Data
Wattmeter Data screen (See Figure 3), and applied to the
formula: existing sideband power X (existing width ÷
desired width)2 = new sideband power. The sideband
power is adjusted to the new level using the SBO RF
Voltage Level Scale control while observing the
Transmitter Data Wattmeter screen.
If correction
adjustments were made during normal flight inspection
runs, it will be necessary to correct the monitor readings
before proceeding into the alarm checks. This is done via
the Monitor 1 Offsets and Scale Factors screen, Integral
tab (See Figure 4), while observing the Monitor 1 Data
screen, Integral tab (See Figure 5).
Localizer Flight Inspection
Localizer alignment, modulation and normal width are
adjusted utilizing the PMDT Transmitter Configuration
screen (See Figure 2).
Figure 2. Localizer Transmitter Configuration Tab
Alignment adjustments are made using the CSB
Modulation Balance Offset control. This control is very
accurate and direct; if the panel technician calls out a 5
left alignment, adjusting this control 5 ddm in the 90 Hz
direction will cause alignment to snap back to centerline.
Modulation adjustments are made using the CSB
Modulation Percentage Scale control.
Figure 4. Monitor Offsets and Scale Factors Tab
Figure 5. Monitor Integral Data Tab
Figure 7. Waveforms Wide Wide Setup Tab
Alarm conditions are set up prior to flight inspection
using the Transmitters Waveforms screens.
Waveform Data Names tab (See Figure 6) allows the
technician to name the various alarm configurations that
are applied during flight inspection.
For example, the Wide Wide tab (See Figure 7) is
adjusted for the course wide, clearance wide configuration
by decreasing the Course and Clearance SBO RF Level %
field until the Monitor 1 Data screen indicates wide alarm
in both course and clearance. It should be noted that the
waveform fields apply a proportional adjustment; if the
normal width was adjusted prior to the alarm checks, and
the monitor was reset to normal width, application of the
Wide Wide waveform will take the monitors to the
correct alarm limit that was set up previously.
Figure 6. Waveform Data Names Tab
The Normal tab is the default selection for normal
operations. The other tabs are copies of the Normal tab,
with the specific parameters adjusted to duplicate the
named alarm conditions.
Figure 8. Transmitter Commands Drop Down Menu
When the panel technician asks for course wide clearance
wide, the CST merely selects Wide Wide from the
Transmitters→ Commands→ Transmitter 1→ Select
Waveform drop down menu (See Figure 8), verifies the
monitor is in alarm, and reports attainment back to the
panel technician. Returning to normal merely involves
selecting Normal from the same drop down menu. This
point and click method of performing alarm checks has
decreased the time required to perform flight inspection
and has reduced accidental adjustment errors (adjusting
too far/not far enough) during flight inspection to zero.
Glideslope Flight Inspection
Many of the glideslope checks/adjustments are
performed in exactly the same manner as the localizer
checks and will not be addressed. These include normal
path width and modulation level on all types of image
glideslopes, wide alarm on null reference and sideband
reference glideslopes, and path wide/clearance
modulation percentage alarm on capture effect
In order to complete sideband reference and capture effect
glideslope flight inspections, remote test units (RTU)
were developed that duplicated alarm conditions that were
previously performed by on-site technicians.
Sideband Reference Glideslope
The sideband reference glideslope RTU is used to check
low angle alarm (the unit is also capable of high angle
alarm checks for commissioning and special flight
inspections), and advance and retard upper antenna phase
to alarm checks.
Figure 9. Glideslope Transmitter Configuration Tab
The sole remaining software controlled alarm check is the
null reference glideslope advance and retard phase to
alarm check. This check is performed using the PMDT
Transmitter Configuration Transmitter 1 tab SBO Phase
Offset control (See Figure 9). The current value of the
SBO Phase Offset is recorded, and then the control is
adjusted for a width alarm on the Monitor X Data screen.
A positive adjustment advances the phase; a negative
adjustment retards the phase. The amount of change is
then reported to the panel technician as dephase required
to take the monitors to width alarm. At the completion of
the check, the SBO Offset control is returned to the value
previously recorded. Because of a ± 35° limitation in the
SBO Phase Offset adjustment, it is imperative that the
amount of offset entered to obtain the correct carrier to
sideband phase relationship be within ± 5°. This was
easily done with some cable trimming, until it was time to
replace a failed amplifier. The offset required for the new
amplifier often exceeded ± 5° and the CST was not on site
to trim a cable. This was okay as long as a flight
inspection was not imminent, but forced a trip to correct
prior to the next with monitors flight inspection. Not to
mention, there is a finite amount of cable available for
trimming. The immediate solution was to adjust the
power amplifiers before they left the manufacturer to be
within 5° of each other. Further improvements will
include an increase in the range of the SBO Offset
adjustment, completely solving the problem.
Figure 10. Sideband Reference Glideslope ATU/RTU
The sideband reference RTU (See Figure 10) is built into
a special version of the sideband reference amplitude
phase control unit (APCU). The unit is controlled by the
PMDT program via the RMS from the Transmitter→
Commands→ Remote Tests dropdown sub menu (See
Figure 11).
Figure 11. Sideband Reference Glideslope Remote
Test Commands Drop Down Menu
Figure 12. Sideband Reference Glideslope Upper
Antenna Attenuation Tab
Figure 14. Capture Effect Glideslope Remote Test
Commands Drop Down Menu
The amount of upper antenna attenuation required for low
and high angle alarm is adjusted prior to flight inspection
in the same manner that the Waveform screens are set up
using the Transmitter Configuration Flight Check
Attenuation screen (See Figure 12). The difference
between Path Normal and Path Low is the decibel (dB)
reading passed to the panel technician during the low
angle alarm run. The RTU switches in a fixed phase
delay of approximately ± 19° for the upper antenna
advance and retard phase to alarm check.
approximately simulates inserting an N-type elbow
adaptor in the upper feed line for retard and the lower
feed line for advance. That amount of dephase is reported
to the panel technician during these alarm checks.
The controlling menu is much the same as the sideband
reference glideslope menu (See Figure 14). The upper
antenna attenuator is fixed at 1.4 dB; that amount of
attenuation is reported to the panel technician during this
alarm check. The RTU switches in a fixed phase delay of
approximately ± 15° for the middle antenna advance and
retard phase to alarm check. This simulates sliding the
middle antenna trombone phase control ± 15°. That
amount of dephase is reported to the panel technician
during these alarm checks. The one drawback to this
method; because the attenuation and phase lengths are
fixed, it is necessary to adjust the path width wide alarm
limit to the condition that widens the path the least. This
causes the CST to maintain a tighter lower alarm limit on
the capture effect glideslopes than on the other two types
of image systems; however, this limitation has not posed a
maintainability or availability problem as yet.
Capture Effect Glideslope
The capture effect glideslope RTU is used for the advance
and retard middle antenna to alarm, and the upper antenna
attenuate to alarm checks. The RTU is mounted on top of
the capture effect APCU and is connected between the
APCU and the antenna feed lines (See Figure 13).
Figure 13. Capture Effect Glideslope ATU
The CST utilizes a dial-up radio system positioned at a
glideslope on each airfield. The radio’s antenna is
mounted to the top of the glideslope tower for greater
coverage and is fed through a low-loss cable (See Figure
Figure 15. Dial-up Radio Antenna
Figure 17. Remote Control Telephone Adapter
The radio is connected to the site phone line and answers
incoming calls through an interface assembly (See Figure
A key feature of this assembly is that it automatically
resets an inactivity timer in the radio interface assembly
to keep the CST on the air while lengthy flight inspection
runs are being completed. In a pinch, the CST can also
use a conventional or cellular telephone to communicate
with the radio interface using a */# keying procedure.
The CST has had great success in communicating with
flight inspection aircraft at all of our airfields using this
Figure 16. Dial-up Radio System
At the CST facility, another assembly connects to a
standard telephone, allowing the telephone to act like a
push-to-talk radio (See Figure 17).
Augmentation personnel at our airfields are Airfield
Systems maintenance technicians primarily responsible
for those systems that are not yet remote maintenance
capable. These include Radar, Meteorological, and ATC
Radio systems. Their role in remote ILS maintenance is
generally limited to replacing components at the direction
of the CST, shipping bad parts back to the manufacturer,
and maintaining the shelters to include power and
communications. They also assist the CST in
troubleshooting efforts by setting up the Portable ILS
Receiver (PIR) and relaying data back to the CST. They
have not and will not receive any formal, comprehensive
training in ILS maintenance; the trained personnel are all
assigned to the CST. Usually, augmentation assistance is
not required for a routine ILS flight inspection, but
personnel remain available should a site communications
line fail, or an issue with the flight inspection radio
develops. They also remain available should a new
facility ground reference need to be established because
of an adjustment that was required during the course of
the flight inspection.
While remote flight inspection was developed as part of
the whole remote ILS maintenance concept, some benefits
have been realized that can be applied to standard on-site
maintenance as well. A few of these benefits include:
1. Time saved. Since ground personnel don’t have to
move from the localizer to the glideslope to complete a
flight inspection, that travel time is eliminated. Also, time
is saved utilizing the point and click method of achieving
alarms and returning to normal versus on-site manual
2. Errors decreased. When a technician can set up an
alarm waveform file at his leisure well before a flight
inspection begins, and then select it with a mouse click,
rather than adjusting the equipment in the heat of battle,
the chance of an error occurring are greatly diminished.
Another problem is that due to the infrequency of
periodic-with-monitors flight inspections, especially at
small airfields, technicians find it difficult to maintain
their proficiency at performing flight inspection tasks. In
the case of the CST, proficiency is maintained because
there are only five of us performing all of the inspections
at seven airfields; there is ample opportunity for all of us
to conduct flight inspections.
3. Flexibility. The CST is able to handle last minute
schedule changes and unannounced arrivals of flight
inspection aircraft with ease. Since we do not have to
gather equipment and travel to the sites, we can be in
flight check mode in less than five minutes after
notification. If an aircraft is delayed, we aren’t sitting
around at a site; we can perform other work while we are
waiting. If a crew or a scheduler should decide to knock
out an inspection with little or no warning, we can easily
support that.
4. Potential for monetary and manpower savings. In the
conventional world, time is saved by positioning a
technician at each site with his own radio, but that
doubles the manpower and equipment requirement.
Compare that to the potential demonstrated by the CST;
we can easily conduct inspections at five airfields
simultaneously with the five technicians assigned!
While there have been more than a few challenges to
overcome as part of centralized remote ILS maintenance,
relatively few of those have affected remote flight
inspection. At the outset, it was not possible to conduct
remote flight inspection without local assistance with
communications. This was solved with the remote radio
system. It was also impossible to perform capture effect
and sideband reference glideslope inspections remotely;
problem solved with the development and installation of
the Remote Test Units.
The CST has been conducting remote flight inspection
successfully since February 2003.
That equates to
inspections that required no permanently assigned on-site
personnel and did not require a site visit by a CST
member. That has saved AFMC over $100,000 in travel
expenses alone. Less tangible, but equally important, is
the flight inspection time saved using point and click
methods to prepare the facilities for flight inspection,
move from one site to another, and configure the
equipment for alarm checks. Flexibility and concentrated
CST training opportunities further contribute to an
already stellar program.
The CST is currently working the process to put the
RCSU computers on the base networks with the most
current security protocols. While this is meant to enhance
our remote maintenance and monitoring posture, the fallout for the remote flight inspection program will be
quicker response times and less reliance on our aging
copper-in-the-ground communications infrastructure
while performing a flight inspection
Mr. Chuck Bryson, whose vision we implemented.
Members of the CST, past and present, without which this
program would not have succeeded. (Mr. Bert Gwaltney,
Mr. Rick Lollis, Mr. Scott Byrnes, Mr. Chris Hoover, Mr.
Jim Frederick, Mr. Jeff Luzader, Ms. Frederycka Graham,
and SSgt Marla Thurber)
Our augmentation partners at each of our airfields, who
are always ready to assist when required.
The Eglin AFB Legal Office and the manufacturer’s staff
for their assistance in reviewing this document
Mr. Nelson Spohnheimer, for his invitation to participate
at the symposium, and his encouragement and assistance
in developing this presentation
[1] FAA, 15 October 2005, U.S. Standard Flight
Inspection Manual, including Change 1, 2 February 2007,
Order 8200.1C
Mr. Atkinson is the Chief of the Air Force Materiel Command (AFMC) Airfield Systems Customer
Support Team (CST), comprised of five Engineering Technicians and one Workgroup Manager, located
at Eglin Air Force Base Florida. The team is responsible for centralized Navigational Aids maintenance
and for administering the Air Traffic Control and Landing Systems (ATCALS) standardization and
evaluation program across AFMC.
Mr. Atkinson entered the US Air Force in 1977 as a Navigational Aids technician, progressing to
lead supervisory technician in 1984. In 1986, he was selected as a Special Maintenance Technician
(SMT) by Headquarters, Strategic Air Command. In 1992, he was reassigned as a SMT to Headquarters,
Air Combat Command, progressing to lead SMT in 1996. He retired from the Air Force in 1998.
Mr Atkinson joined the civil service ranks at Headquarters, Air Combat Command as an Air Force
Engineering and Technical Services (AFETS) specialist in October 2000. He joined the CST in
December 2002, and was selected as chief in August 2007. Total Navigational Aids maintenance
experience is 29 years, with 20 of those years at the technician-in-depth level. Those duties included
maintenance assistance above the local technician level, providing in-depth training to airfield
technicians, and authoring technical orders and training materials.
He earned an AAS in Electronic Systems Technology from the Community College of the Air
Force in 1996, and an AAS in Electronics Technology from Thomas Nelson Community College in 2000.
He is currently a senior at Embry Riddle Aeronautical University pursuing a BS in Technical Management.
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF