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Two things have been prominently posted in today's news about the Metrojet crash in the Sinai. One focuses on the fact that the Egyptian Government is solely responsible for the crash investigation, and that the Egyptians may be withholding the truth about a terrorist bomb, for political reasons. (Supposedly protecting its tourism industry.) This assertion also points out that the Egyptians have limited access to the wreckage and also that other governments, notably the British, have taken strong actions already because they give strong credibility to a terrorist bomb having downed the Airbus.
The other news release indicates that the Cockpit Voice Recorder might have recorded the sound of an explosion. This release does not have authoritative support, particularly not from any governmental source. At this point we do not know who, other than Egyptian investigators, may have custody of the CVR and FDR, much less analyzed their contents. I find the first of these criticisms to be premature and biased. Note that the accident involving the Indonesian Air Asia 8501 of December 28, 2014, which I have reported to be eerily similar to the Metrojet crash, is still unresolved. The Indonesian Government, in charge of the investigation, has still not released a preliminary analysis or report of its findings, even though the crash took place eleven months ago and the Government recovered the CVR and the FDR shortly after the crash. Many (if not most) professionals in the aviation industry are highly critical of early releases of information, before the accident investigation team can do it work. As for the reported sounds in the CVR recording, this report is not credible until we know a great deal more than just a hearsay, unsubstantiated news story. Even if there were an explosive sound on the CVR, the possibility remains that the sound could have come from exploding jet fuel as the aircraft started to come apart. The investigators will be piecing together a precise time synchronization of all facts, and that will be critical in understanding what might be recorded on the CVR.
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My earlier posting hypothesizes that the initiating event was the failure of the flight control computer or perhaps that some event disconnected it from the flight control system. [ In the Air France 447 disaster, the flight control computer disconnected when the pitot tubes iced-up. In the Air Asia 8501 disaster, the pilot pulled its circuit breaker.] For those interested, a complete explanation of the Airbus Flight Control Laws can be found at the site:
http://www.airbusdriver.net/airbus_fltlaws.htm My hypothesis is that the pilot found himself suddenly in the "Direct" Law control mode, and that means that he had to control the aircraft manually. Few pilots are skilled at controlling an A321 at altitude in Direct Law. Worse, flying the aircraft all the way through a descent from altitude, through an instrument approach, to a landing, all in Direct Mode, isn't really trained. Some have asked me if I knew about the ADS-B trace, which indicated violent changes in altitude, and about the satellite detection of a "flash" which might indicate an explosion. The answer is that I have, and these preliminary indications do not in any way contradict my hypothesis about the flight control computer disconnect. When the Flight Data recorder (FDR) and the Cockpit Voice Recorder (CVR) are analyzed, we may get some important answers. The analysis itself includes a careful time synchronization, so that all of the relevant data points are carefully matched in time. This might, for example, enable the ADS-B data to be matched exactly with the FDR data. A pessimistic outlook might be that the CVR and the FDR, being housed in the tail of the aircraft, stopped recording too early in the break-up process. We know that the tail separated inflight. So determining what happened will be an exercise in exquisite time synchronization. This process requires a great deal of skill. I might add that the Egyptian Government has the CVR and FDR and will do the investigation. Airbus will assist. The Russian Government will be present, but what they will actually do is not known. The Egyptian Government will also control the release of this information. The wreckage itself will provide extremely important and useful information to the investigators. For example, explosions usually leave burn marks. Fracture surfaces show how the aircraft came apart. An explosion outside of the aircraft causes metal to fold inward, while explosions inside of the aircraft cause outward bending of metal. We will see how this unfolds. If, as I suspect, the Flight Control Computers disconnected from the flight control system, that event should be recorded on the FDR. The CVR may have a recording of the pilot's surprised reaction. Again - we will see. The information that is being released about the flight of this aircraft just before its impact with the ground bear a remarkable similarity to what happened with Indonesia Air Asia Flight 8501, which plunged into the Java Sea on December 28, 2014.
The Russian Metrojet aircraft went through some very severe and dramatic excursions in airspeed and altitude, and this is now an established fact. Its climb and descent rate was excessive, and its airspeed went from below stall speed to near Vne. My understanding is that there were at least three major climb and dive excursions. These excursions could not have happened if the aircraft was simply blown apart by an explosive. What is much more likely is that the flight control computers somehow became disconnected from the flight controls and the pilot had to take over control manually. In other words, the aircraft was then in the Airbus "Direct" flight control law. Flying an A321 manually at 30,000 feet altitude would not be easy. Many airlines do not give pilots any simulator time in such a flight regime. Being able to take over control manually is something similar to trying to play a musical instrument. It takes time and practice. To do this training in a simulator would be costly. The Air Asia pilot took over the flight controls using manual (Direct) control, and he failed. it might also be noted that a similar occurrence happened with the Air France 447 disaster. I expect that the FDR will establish that the pilot actually over-controlled the aircraft and in the process actually tore the elevator and maybe the elevators from the tail. Or possibly that the entire tail empennage separated at altitude. The Egyptian Government has custody of the CVR and FDR. I suspect that we won't have information about their analysis for several weeks. We'll see. |
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