It is organic to the culture of aviation to discuss a mishap. It is part of the natural process of grieving and shock. This is our work place.
The most sensible reason to discuss these tragedies is to try to glean something from them that can prevent further catastrophes. To gain insight and learn; to be able to anticipate. In a business where experience matters a great deal, it is always advisable to be able to learn from the experience of others. An unfortunate truth of life in the cockpit is the rules we as pilots follow today are written in the blood of pilots who made mistakes yesterday.
With that said, it will be many months if not years before an official report becomes available. However we may still be able to decipher some useful lessons-learned from the information as it becomes available.
Here’s what has been made public:
- It was an older Airbus 320 delivered to Lufthansa in 1991. 58,300 hrs and 46,700 cycles.
- The Captain had 6,000 hrs and 10+ years airline experience.
- The Cockpit Voice Recorder has been recovered, though badly damaged.
- The Flight Data Recorder has been located but the data card is missing, perhaps thrown or destroyed as a result of the impact.
- There was no contact with ATC (Air Traffic Control) during the descent.
Looking at the data from Flightaware, the plane leveled off at its filed flight level, 380, then three minutes later began what looks to be a controlled descent all the way to impact, 10 minutes later. The vertical speed is essentially steady all the way, varying slightly from 3200frm to 2600fpm to a momentary high of 4000fpm. The average rate of descent is roughly 3500fpm. The airspeed remains relatively constant as well, varying slightly with the vertical speed, but essentially 420-470kts throughout the descent. The implication would be that Level Change was used to descend, but that the altitude window had been spun to below the peaks of the mountains.
The heading changes from 043 at Top of Climb to 026 as the descent begins, and remains 026 until impact. Of note, these are exactly the same headings, at the same time markers as the previous day’s flight. That would infer that the plane was following its flight plan, most probably using LNAV, all the way to the end.
With that limited amount of data and a dose of inference, there are a few hypotheses that can be formed. The first fear that arises these days is obviously terrorism. There could clearly be a scenario where someone forced their way into the cockpit, disabled the pilots, and used a basic knowledge of the Airbus systems to cause the plane to descend. This seems unlikely for a few reasons. The most obvious being that there has not been a claim of responsibility. The purpose of terrorism is to cause terror and absent an organization jumping up and down trumpeting their success, this event does not seem to fall into that category.
There is a scenario where one of the pilots deliberately caused the crash, perhaps waiting for the other to exit the cockpit to use the restroom. This, of course, is the scenario that caused EgyptAir 990 to crash off of Nantucket in 1999. We know nothing about the pilots and it is far too early to put forth a suggestion that one of them might have deliberately perpetrated this act, but it is possible and consistent with the evidence, though highly unlikely.
A third scenario is rapid decompression. Every jet pilot is familiar with the Time of Useful Consciousness chart. At their Flight Level of 380, the TUC would be between 15-30 seconds. Any event that would cause a rapid decompression would have a loud bang associated with it. The disoriented pilots would scan their instruments, searching for the cause of the noise. The Cabin Altitude Warning Horn is an unfamiliar and jarring sound and the cutoff switch to silence that horn is not normally used. They may not have donned their masks before hunting for the cause of the alarm. Then, once recognizing they had lost pressurization, began a descent in Level Change before thinking to don their masks. 30 critical seconds could easily have elapsed in that time. The plane would descend at the speed it was cruising at, while maintaining its lateral flight plan.
A variation of this scenario would be a flight dispatched with one of the two automatic pressurization controllers inop. A failure of the second could be insidious, especially if mismanaged. One last possibility that might result in pilot incapacitation in the event of a pressurization failure is that the crew O2 bottle was not providing oxygen. Whether installed incorrectly or empty, if the crew weren’t able to receive oxygen, then they would have initiated a decent but not remained conscious as the plane responded to their input.
If the flight data recorder card is ever recovered it should answer any of the technical questions.
As always, we wait to listen and learn. We construct scenarios to stimulate debate and raise awareness, not to pass judgement.
(Featured Image: Rescue helicopters mount an operation near to the crash site of an Airbus A320 in the French Alps. Photograph: JEAN-PAUL PELISSIER/REUTERS)