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Air France 447; is pitot system the cause? | Broken Wing

Air France 447; is pitot system the cause?

Posted on 12. Jun, 2009 by in Featured

After reading the Australian Transportation Safety Board’s (ATSB) preliminary report I don’t see how it can be. The ATSB report identifies spikes in Angle of Attack (AOA) as the cause of the upset of QANTAS (QF) Flight 72, not airspeed. Below is the timeline of QF-72:

Table 3: Occurrence flight sequence of events
Time (UTC)
(hh:mm:ss) Time relative to event (hh:mm:ss) Event:
01:32:02 -03:10:23 Takeoff at Singapore
02:01:16 -02:41:09 Aircraft reached top of climb (37,000 ft or FL370)
04:40:28 -00:01:57 Autopilot 1 disconnected
04:40:28 -00:01:57 First master warning was recorded. Warnings

occurred during the remainder of the flight.
04:40:29 -00:01:56 First master caution was recorded. Cautions occurred during the remainder of the flight.
04:40:31 -00:01:54 IR 1 Fail indication commenced (duration: remainder of the flight)
04:40:34 -00:01:51 First angle-of-attack (AOA) spike for the captain’s (or Left) AOA parameter – the spike value was +50.6 degrees. AOA spikes continued for the remainder of the flight.
04:40:41 -00:01:44 First ADR 1 Fail indication (duration: less than 4 seconds)
04:40:50 -00:01:35 First stall warning (duration: less than one second)
04:40:54 -00:01:31 First overspeed warning (duration: less than one second)
04:41:12 -00:01:13 Autopilot 2 engaged
04:41:14 -00:01:11 Aircraft reached 37,180 ft and began to descend to 37,000 ft
04:41:28 -00:00:57 Autopilot 2 disconnected
04:42:27 0:00:00 First pitch-down event
04:42:28 0:00:01 Captain applied back pressure to the sidestick
04:42:28 0:00:01 A maximum nose-down elevator position of +10.3 degrees was recorded
04:42:29 0:00:01 A minimum vertical acceleration of -0.80 g was recorded
04:42:29 0:00:04 A minimum pitch angle of -8.4 degrees was recorded
04:42:30 0:00:05 PRIM master changed from PRIM 1 to PRIM 2
04:42:31 0:00:05 A maximum vertical acceleration of +1.56 g was recorded
04:42:31 0:00:06 PRIM 3 Fault (duration: 120 seconds)
04:43:45 0:01:20 Captain switched his IR source from IR 1 to IR 3
04:45:08 0:02:43 Second pitch-down event
04:45:09 0:02:44 Captain applied back pressure to the sidestick
04:45:10 0:02:45 PRIM master changed from PRIM 2 to PRIM 1
04:45:11 0:02:46 A maximum nose-down elevator position of +5.4 degrees was recorded
04:45:11 0:02:46 PRIM 3 Fault (duration: remainder of the flight)
04:45:11 0:02:46 Flight controls’ ‘normal law’ changed to ‘alternate law’ (duration: remainder of the flight)
04:45:12 0:02:47 A minimum vertical acceleration of +0.20 g was recorded
04:45:12 0:02:47 A minimum pitch angle of -3.5 degrees was recorded
04:45:13 0:02:48 A maximum vertical acceleration of +1.54 g was recorded
04:47:25 0:05:00 Autothrust disengaged
04:49:05 0:06:40 A radio transmission commenced. Correlation with the

CVR showed that this was the PAN transmission.
04:54:24 0:11:59 A radio transmission commenced. Correlation with the CVR showed that this was the Mayday transmission.
05:32:08 0:49:43 Aircraft touched down at Learmonth
05:42:12 1:02:47 Aircraft stopped at terminal
05:50:32 1:08:07 Power removed from FDR

Compare the sequence of QF-72 to the faults codes transmitted by AF 447. Again, the ATSB identifies the Angle of Attack as the cause. Angle of Attack is the measurement between the relative wind and wing. While airspeed does factor in as well as weight it is a much more accurate measure of stall. Stall AOA remains constant while indicated airspeed can vary immensely due to weight, g-load and altitude. It is possible to stall a wing at 300 or 400 knots of indicated airspeed if you pull hard enough. When in a dog fight the pilot will try and maintain maximum AOA to get the best turn rate. Airspeed can fluctuate hundreds of knots while maintaining a constant AOA; airspeed will determine the rate of turn and g-load.

Why is this important? Because they are separate systems as is clearly shown by the schematic of the A-330 in the ATSB report.

What is the link? In my opinion it is ADIRU #1. The number one ADIRU I believe is the single point of failure in both events. The ADIRU was overriding the good information from #2 and #3. Clearly the Emergency Airworthiness Directives (EAD 2009-0012-E/EAD 2008-225-E) issued by the European Aviation Safety Agency address the ADIRU.

No Responses to “Air France 447; is pitot system the cause?”

  1. Rick 14 June 2009 at 07:31 #

    Chip,
    Do you know the nitty gritty details of why the pitots were recommended to be replaced in the first place? I have not seen that, but presume it was a heating coil fault. I’d be very interested in the answer to that.
    Rick

  2. Chip 14 June 2009 at 13:12 #

    Rick;
    What I have read relates to the ability of the pitot system to pass the water through it in a heavy rain. It apparently freezes, causing inaccurate readings.

    However the QF-72 flight did not mention rain or point to the pitot system. The ATSB blamed the AOA a seperate system.


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