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• mach number
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• static air temperature
• angle of attack (AOA) from both the captain’s (AOA 1) and first officer’s (AOA
2) sensors
Inertial reference parameters that were recorded by the FDR included:
• pitch angle
• roll angle
• groundspeed
• inertial vertical speed
• drift angle
• heading
• latitude and longitude.
Some parameters required inputs from both the ADR and IR functions. They
included wind speed and wind direction.
IR 1 and ADR 1 Fail indications
At 0440:28 UTC (1240:28 local time), autopilot 1 disconnected involuntarily22 and
the inertial reference system (IR) function of ADIRU 1 began to indicate ‘Fail’
(04:40:31). The IR 1 Fail indication continuously indicated ‘Fail’ until after landing
at Learmonth.
As the IR 1 Fail indication was only sampled once every 4 seconds, it may have
preceded the autopilot disconnection. A review of the recorded data and system
functionality determined that the autopilot probably disconnected due to a
discrepancy between the values of an ADIRU parameter received by the Flight
Management Guidance Envelope Computer (FMGEC23 1). The specific parameter
associated with the disconnection could not be determined.
The first ADR 1 ‘Fail’ indication began at 0440:41 UTC. This indication lasted for
less than 4 seconds. Unlike the IR Fail indication, the ADR Fail indication did not
continuously indicate ‘Fail’. In total, 20 ADR 1 ‘Fail’ indications were recorded
before the aircraft touched down at Learmonth. As the ADR 1 ‘Fail’ parameter was
sampled once every 4 seconds, a brief ADR 1 fail indication may not necessarily be
sampled and recorded. As a result, the number of actual ADR 1 ‘Fail’ indications
may have been larger than the number recorded by the FDR.
There were no Fail indications associated with ADIRU 2 or ADIRU 3 throughout
the flight.
22 An involuntary autopilot disconnection occurs automatically without any action by the crew.
23 The FMGECs were part of the autoflight system and provided output commands to the control
surfaces via the PRIMs and to the engines via the engine electronic control units.
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Spikes in FDR and QAR data
Spikes24 from ADIRU 1 were evident in the following parameters:
• angle of attack
• pressure altitude
• computed airspeed
• mach number
• static air temperature
• pitch angle
• roll angle
• wind speed
• wind direction.
The spikes appeared to be random in nature and occurred for different parameters at
different times.
Angle of attack spikes
For an A330, during all phases of flight, the typical operational range of AOA is +1
degree to +10 degrees. In cruise, a typical AOA is +2 degrees.
The first AOA 1 spike occurred at 0440:34 UTC. AOA 1 values changed from +2.1
degrees to +50.6 degrees and back to +2.1 degrees over three successive samples.
In total, 42 AOA 1 spikes were recorded before the aircraft touched down at
Learmonth. As AOA 1 was sampled by the FDR once per second, a spike may not
necessarily be sampled and recorded. As a result, the number of actual AOA 1
spikes may have been larger than the number recorded.
One of the recorded AOA spikes occurred at 04:42:26 UTC, immediately prior to
the first pitch-down (04:42:27). Another of the recorded spikes occurred at 04:45:08
UTC, immediately prior to the second pitch-down (04:45:09). Both of those spikes
had a magnitude of +50.6 degrees.
Effects of the spikes on failure indications
A stall warning parameter was recorded by the FDR. The first stall warning
occurred at 0440:50 UTC and numerous stall warnings were recorded from this
time until 0512:00 UTC when the aircraft was descending through an altitude of
12,400 ft. As the stall warning parameter was sampled once per second, a brief
warning may not necessarily be sampled and recorded. As a result, the number of
actual stall warnings received by the crew may have been larger than the number
recorded. Examination of other recorded parameters indicated that the stall
warnings were spurious.
24 A spike is a short duration transient which exceeds the normal value by a large amount.
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An overspeed parameter was recorded by the FDR. The first overspeed warning
occurred at 0440:54 UTC and numerous warnings were recorded from this time
until 0502:01 UTC when the aircraft was descending through an altitude of 25,400
ft. As the overspeed warning parameter was sampled once per second, a brief
warning may not necessarily be sampled and recorded. As a result, the number of
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