AAIB Bulletin: 12/2013
N936CT
EW/G2013/06/02
ACCIDENT
Aircraft Type and Registration: Cirrus SR22, N936CT
No & Type of Engines: 1 Continental Motors IO-550-N piston engine
Year of Manufacture: 2009 (Serial no: 3111)
Date & Time (UTC): 6 June 2013 at 0947 hrs
Location: On approach to Gloucestershire Airport
Type of Flight: Private
Persons on Board:
Crew - 1
Passengers - None
Injuries:
Crew - None
Passengers - N/A
Nature of Damage: Substantial damage to wings and fuselage
Commander’s Licence: UK Private Pilot’s Licence
FAA Instrument rating
Commander’s Age: 76 years
Commander’s Flying Experience: 673 hours (of which 443 were on type)
Last 90 days - 19 hours
Last 28 days - 6 hours
Information Source: Aircraft Accident Report Form submitted by the pilot
and further equiries by the AAIB
Synopsis
The pilot deployed the aircraft ballistic recovery system
pilot to climb first to 3,300 ft, then to 4,000 ft. The pilot
after he became disorientated on an instrument approach
recalls that he entered cloud shortly before flying over
into Gloucester Airport. He was not injured.
Oxford Airport.
History of the flight
When the aircraft was approximately 16 nm from
The pilot was on a private flight from Denham Aerodrome
Gloucestershire Airport, Brize ATC instructed the pilot
to Gloucestershire Airport.
As part of his pre-flight
to contact Gloster1 but refused his request for a descent.
preparation, he had contacted Gloucestershire Airport by
When the pilot contacted Gloster he was offered an
telephone and was informed that Runway 09 was in use.
approach to Runway 27 which he accepted. At this stage,
the pilot was approximately 7 nm from the initial approach
The first part of the flight was uneventful and conducted
in VMC.
fix which is located at 10 nm on the extended centreline.
Initially the pilot was in contact with
Footnote
Farnborough ATC, who subsequently instructed him to
1
contact Brize Norton ATC. Brize ATC instructed the
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Gloucestershire Airport ATC use the voice callsign ‘Gloster’.
AAIB Bulletin: 12/2013
N936CT
EW/G2013/06/02
The pilot established the aircraft on the final approach
The pilot stated that the combination of the unexpected
track for an RNAV approach onto Runway 27 with the
runway change and the delay in being allowed to descend
autopilot engaged in GPS approach and vertical speed
to the required height to commence the approach resulted
modes. At approximately 1,800 ft amsl the autopilot was
in him experiencing high workload and stress.
disconnected for approximately 5 seconds, during which
Automatic flight control system (AFCS)
the aircraft rolled to approximately 30° left bank. When
the pilot reinstated the autopilot, it engaged in PITCH HOLD
The AFCS has four main operating functions: autopilot,
and ROLL HOLD modes, which are the default modes for
flight director, yaw damper and electric pitch trim. The
the system. The pilot did not notice that the autopilot
autopilot controls the aircraft pitch and roll attitudes
modes had changed and, observing that the aircraft was
using flight control surface servos following commands
maintaining a banked turn, attempted to override the
received from the flight director based on the active
autopilot to regain a wings level attitude. After a further
modes. The servo mounts are equipped with slip‑clutches
18 seconds, the pilot disconnected the autopilot for a
set to certain values and this allows the pilot to override
second time but the aircraft had now deviated from the
the servos.
2
approach centreline. The pilot stated that while trying
to correct the situation he “over-controlled” the aircraft
The autopilot also has an automatic levelling function
in roll and subsequently in pitch. During the following
activated by pressing the LVL key on the AFCS control
80 seconds, the aircraft exhibited large variations of
panel. Pressing the LVL key engages the autopilot (if
pitch, roll, speed and altitude as the pilot attempted to
the autopilot is disengaged and the aircraft is within the
bring the aircraft under control. A series of warnings
autopilot engagement limitations4) and the aircraft is
occurred including an overspeed and terrain proximity
commanded to fly to zero bank angle and zero vertical
warning, and the pilot observed a large red ‘V’ on the
speed. When the LVL key is pressed, all armed and
primary flight display (PFD)3. At this point the aircraft
active autopilot modes are cancelled and the autopilot
was still in cloud and, assessing that he was too close to
and flight director revert to LVL mode for pitch and roll.
the ground to recover from what he described as an out-
Activation of the stall warning system at any stage of
of-control situation, he decided to deploy the ballistic
flight will disconnect the autopilot including the LVL
recovery system. The pilot reported that he only became
mode if engaged.
VMC at about the same time as the parachute deployed.
Ballistic recovery system
The aircraft came to rest in the garden of a suburban
The ballistic recovery system (BRS) consists of a
house and was substantially damaged; the pilot was
parachute, a solid fuel rocket to deploy the parachute,
uninjured.
an activation handle and a harness imbedded within the
fuselage structure. A three-point harness connects the
Footnote
aircraft fuselage structure to the parachute. The pilot
The aircraft was fitted with a Cirrus Perspective system. In these
modes the autopilot will try, within certain limits, to maintain the
pitch and roll attitude at the time of engagement.
3
When the aircraft enters an unusual pitch attitude, red extreme
pitch warning chevrons pointing toward the horizon are displayed
on the Attitude Indicator, starting at 50˚ above and 30˚ below the
horizon line.
2
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can activate the system by pulling the handle located
on the cockpit ceiling. This deploys the rocket out of a
Footnote
4
31
The autopilot engagement limits are ±30° in pitch ±75° in roll.
AAIB Bulletin: 12/2013
N936CT
EW/G2013/06/02
hatch on the top of the aircraft behind the cockpit. The
display. At 0943:05 hrs the AFCS was recorded as ON
rocket pulls the parachute from the hatch, the embedded
again, with the default pitch and roll modes of PITCH
forward harness straps pull through the fuselage skin
HOLD
and the aircraft will then descend in a more or less level
9.4° and had 23.4° of left roll at this time so these values
attitude.
were set by the AFCS as the commanded pitch and roll
and ROLL HOLD; the aircraft was pitched down
values.
Weather
The 0950 hrs weather report from Gloucestershire
At 0943:23 the AFCS was manually disconnected again
Airport indicated surface wind from 040° at 8 kt,
and levelled at approximately 1,400 ft amsl with a
visibility 8,000 m, scattered cloud at 500 ft, broken
relatively stable speed, neutral pitch but not a stable roll
cloud at 800 ft, temperature 11°C, dewpoint 8°C and
or heading. At 0943:40 hrs a right roll was initiated that
pressure 1023 hPa.
reached 81.9°, with a commensurate rapid descent and
speed increase, until the aircraft levelled at 1,000 ft amsl,
Pilot training
heading for the airfield. The aircraft then climbed at a rate
that peaked at 2,988 ft/min until it reached 1,771 ft amsl
The pilot had received training in a Cirrus simulator
with a speed that had reduced to 54.6 kt. At this point
during which he practised using the BRS in response to
the aircraft rapidly rolled left and the nose dropped. The
various emergencies. The pilot stated that this training
was beneficial in dealing with the situation he faced. He
descent stopped at 880 ft amsl, with an IAS of 144 kt
had not received any training involving the use of the
after having exceeded 10,000 ft/min. The cycle of a
LVL
high pitch climb, reduction in airspeed and accelerating
function.
descent was then repeated until the recording stopped in
Recorded data
the descent as a result of the BRS being deployed.
The aircraft was fitted with a Cirrus Perspective avionic
Analysis
system, based on the Garmin G1000 system. The system
had an SD card installed which enabled the collection of
When the pilot commenced the approach, the aircraft
flight data that would otherwise be lost.
The aircraft
was being flown with the autopilot engaged in approach
was also fitted with a Recoverable Data Module (RDM),
and vertical speed mode. When the pilot reengaged
which would not download. The data from the display
the autopilot after the first disconnection, the autopilot
system was analysed and is shown in Figure 1.
engaged in default modes of PITCH HOLD and ROLL
HOLD.
However, probably due to the high workload
At 0942 hrs the aircraft was at 2,000 ft amsl flying to
he was experiencing, the pilot did not notice that the
Gloucestershire airport from the east on a heading of
autopilot was now operating in different modes from
269°M, with an IAS of 84 kt. The AFCS was engaged
before. The pilot expected the aircraft to continue on
and in the GPS roll mode and ALT pitch mode. The AFCS
the approach centreline and, when he noticed that the
pitch mode was changed to
as the aircraft started
aircraft was maintaining a left bank, he overrode the
to descend. At 0942:57 hrs, the AFCS was manually
autopilot in an attempt to level the aircraft. As the
disconnected as indicated by the recorded AFCS status
autopilot was still engaged, every time the pilot relaxed
value of 5, which is linked to a flashing caption on the
on the controls the aircraft tried to regain the roll attitude
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vs
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AAIB Bulletin: 12/2013
N936CT
Figure 1
Data recovered from the display
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EW/G2013/06/02
AAIB Bulletin: 12/2013
N936CT
EW/G2013/06/02
that existed at the time of engagement. This unfamiliar
flight path deviations commenced, at times the aircraft
aircraft behaviour led to a series of roll oscillations as
was outside the autopilot engagement limits and, under
the pilot intermittently overrode the autopilot. After
these circumstances, the LVL mode could not have been
approximately 18 seconds, the pilot again disconnected
engaged.
the autopilot but the aircraft was displaced left of the
approach centreline.
Conclusion
By this stage, the pilot was
confused and distracted by the unexpected aircraft
The initial disengagement and re-engagement of
behaviour and, in his attempts to regain the approach
the autopilot caused the system to engage in default
path, he started over-controlling in roll and then in
modes that the pilot was not expecting and, due to high
pitch. The variations of pitch, roll, height and airspeed
workload, did not notice. The distraction and confusion
increased to the extent that he became disorientated and,
caused by the unexpected aircraft response caused him
when he assessed that he could not safely regain control,
to over-control in pitch and roll which further increased
he operated the BRS. The training the pilot had received
workload and led to him becoming disorientated to the
in the use of the BRS assisted him in deciding to use,
extent that he felt he was unable to control the aircraft
and actually deploying, the system. Although the pilot
safely.
did not activate the automatic levelling system, once the
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