AirAsia update, Dec. 30: Key questions in the investigation

Dec. 30, 2014: With the apparent discovery of the main wreckage of AirAsia Flt 8501 in about 100 ft of water, recovery of the airplane and its black boxes should be a relatively straight-forward operation.

Our previous posts have outlined general areas of inquiry. With this post, we drill down into some of the flight and airplane questions that will be part of the inquiry. We talked with an Airbus A320 captain for a major US airline in forming these issues. This captain has been flying for US carriers for 30 years and is rated on Boeing 737s, the McDonnell Douglas DC-10 and the A320.

Key points:

  • Pitot tubes: There has been plenty of speculation in the media about whether the pitot tubes on #8501 might have frozen over in a manner similar to Air France 447 in 2009, leading to a series of events that resulted in the crash of 447 and perhaps 8501. There has been only one reported incidence of pitot tube issues on the A320 that we know of and this pilot has never experienced such a circumstance.
  • Airspeed: It’s been reported, but as yet not verified, that based on one of the Internet flight tracker sites, 8501 at one point reached an altitude of 36,300 ft, an indicated ground speed of 343 kts and a true airspeed of about 184 kts. Bearing in mind that this is unconfirmed information, the A320 captain’s reaction was, “That’s not good.” At that altitude, the airspeed should be at least 400 kts.
  • Altitude: The flight had been at 32,000 ft and requested a higher altitude due to weather. This request was denied due to conflicting traffic above. If the flight tracker information is correct, how did the flight reach 36,300 ft? The A320 pilot said it would not be at all uncommon for huge updrafts to put the airplane at the higher altitude in a very short period. Huge downdrafts could also push the airplane down. Only read-outs of the flight data recorder (FDR) and cockpit voice recorder (CVR) will clarify this.
  • Did the pilot know what he was flying into? Although the pilot requested a course deviation and different altitude due to thunderstorms, did he have a full appreciation for what he was flying into? Only the CVR will likely clarify this. If he did, why didn’t he make a declaration of the seriousness of the situation to ATC? Again, perhaps only the CVR will answer this question. If he didn’t have a full understanding, why not? Was the cockpit weather radar display accurately or inaccurately “painting” the picture for the pilot?
  • Was there a failure of one or both engines? If the storm “drowned” one or both engines, or if hail damaged the engines, shutting them down, the airplane was doomed. The FDR and CVR will answer these questions, along with forensic analysis of the engines.
  • Was there a high altitude upset? Did extreme turbulence cause the flight to “upset” from its flight attitude, and if so, by the time the pilot recovered, was it too late and the plane impacted the water? The answer will lie with the FDR and CVR.
  • Did any structure separate from the airplane prior to impact? If there was an upset, did flight controls or the vertical or horizontal tail separate from the aircraft during a descent, dooming the airplane? Structural analysis and FDR/CVR will answer these questions.
  • Did the airplane go into a deep stall? Extreme turbulence could have caused a deep stall, which could cause the A320 to go from Normal Law to Alternate Law–that is shifting control from the computerized flight envelope protection to direct control by the pilot. In this event, our A320 captain said, the pilot essentially winds up flying by the seat of his pants, feeling G forces, and using basic flight horizon and attitude instruments to try and fly his way out of the problem. CVR and FDR data will answer this question.

There are hundreds of more questions to be answered–but these will be some of the key ones.

9 Comments on “AirAsia update, Dec. 30: Key questions in the investigation

  1. perhaps ..
    ncident: Lufthansa A321 near Bilbao on Nov 5th 2014, loss of 4000 feet of altitude

    By Simon Hradecky, created Tuesday, Nov 18th 2014 17:11Z, last updated Sunday, Dec 28th 2014 22:22Z
    A Lufthansa Airbus A321-200, registration D-AIDP performing flight LH-1829 from Bilbao,SP (Spain) to Munich (Germany) with 109 people on board, was climbing through FL310 out of Bilbao about 15 minutes into the flight at 07:03Z, when the aircraft on autopilot unexpectedly lowered the nose and entered a descent reaching 4000 fpm rate of descent. The flight crew was able to stop the descent at FL270 and continued the flight at FL270, later climbing to FL280, and landed safely in Munich about 110 minutes after the occurrence.

    The French BEA reported in their weekly bulletin that the occurrence was rated a serious incident and is being investigated by Germany’s BFU.

    The occurrence aircraft remained on the ground in Munich for 75 hours before resuming service on Nov 8th.

    The Aviation Herald learned that the loss of altitude had been caused by two angle of attack sensors having frozen in their positions during climb at an angle, that caused the fly by wire protection to assume, the aircraft entered a stall while it climbed through FL310. The Alpha Protection activated forcing the aircraft to pitch down, which could not be corrected even by full back stick input. The crew eventually disconnected the related Air Data Units and was able to recover the aircraft.

    Following the occurrence EASA released emergency airworthiness directive 2014-0266-E_1 stating:

    An occurrence was reported where an Airbus A321 aeroplane encountered a blockage of two Angle Of Attack (AOA) probes during climb, leading to activation of the Alpha Protection (Alpha Prot) while the Mach number increased. The flight crew managed to regain full control and the flight landed uneventfully.

      • Sure – put a page in the x00 page flight manual..

        11 December 2014
        Required Action(s) and Compliance Time(s):
        Required as indicated, unless accomplished previously:
        (1) Before next flight after the effective date of this AD, amend the applicable AFM by inserting a copy of Airbus AFM A320 TR 502 “Abnormal V alpha Prot”, issue 1.
        Alternatively, amending the applicable AFM can be accomplished by inserting of a copy of Appendix 1 of this AD into the Section Emergency Procedures.
        (2) Concurrent with the AFM amendment as required by paragraph (1) of this AD, inform all flight crews and, thereafter, operate the aeroplane accordingly.

  2. It has now been reported that one of the bodies was wearing a lifejacket.If true,it does make the most powerful argument for live tracking.

    • It has now been reported that one of the bodies was wearing a lifejacket.If true,it does make the most powerful argument for live tracking.
      Assuming the report to be true – how exactly would live tracking have made any difference? (And by the same token: Why would it not have made a difference if there were no bodies with life jackets?)

      To be honest, I think you’re assuming quite a few things that I wouldn’t take for granted if just by the fact that one body (out of 7 recovered so far) may have worn a life jacket you deduce that live tracking would have made a significant difference one way or another.

      • Yes you are right,I should have been much more sceptical.although floating free wearing a life jacket does imply that there is a good chance that they survived the impact ,as they must have put it on and maybe unstrapped themselves,its not very likely.actually I have always believed carrying life jackets is wast of time.I think not a single large airliner passengers life has been saved by a life jacket for over 60 years(feel free to correct me,I think the Hudson incident they stepped on to boats)it’s possible to think of numerous scenarios where passengers survive an unlocated accident but it’s not very likely.

  3. re lifejacket …” Early reports that one of the 7 bodies recovered so far was “wearing a lifejacket” have now been clarified as being incorrect.
    The information has now been clarified to, “a lifejacket was found near a body”.

    from pprune
    and from reuters

    …Tatang Zaenudin, an official with Indonesia’s search and rescue agency, said earlier that one of the bodies found had been wearing a life jacket.

    But he later said no victim had been recovered with a life jacket on.

    “We found a body at 8.20 a.m. and a life jacket at 10.32 a.m. so there was a time difference. This is the latest information we have,” he told Reuters…

  4. I really don’t like the characterization of the backup flight instruments as “flying b y the seat of your pants”

    I flew light aircraft and what are backup instruments for a jet are (were) the main instruments for light aircraft.

    If you knew what you were doing you could handle any unusual maneuver, my instructor was a master of gyrations to confuse you and then leave you to recover.

    A good pilot not only could handle it but enjoyed the challenge.

  5. FWIW approx 7 PM pst found this twitter

    tweet from Fairfax reporter in Indonesia about an hour ago:

    Michael Bachelard @mbachelard · 57m 57 minutes ago Recovery crews have finally found the wreck of AirAsia 8501, using sonar, in 29m of water. Dive crews to check it today.

    Michael Bachelard @mbachelard · 51m 51 minutes ago I am heading to the search zone now with rescue crew divers on board

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