Jet Crash Forum

First, the last ACARS positional message (around the beginning of the rapid degradation of the situation) seems to occur inside a region of strong convection within the larger meso-scale convective system. At this point, I think it is reasonable to ask why pilots flew into "that weather." Does AF require suffiicent WX radar training? Are proper procedures (and training) in place to help pilots avoid at least the worst of the weather? From the available data, it does not appear that any weather avoidance was taken.

Secondly, could strong updrafts be a major factor, up to and including the final descent and crash? As I understand it, aircraft stalls are a function of angle of attack, and pitot tubes don't function well at high AoA values. A 50kt updraft at a speed of 447 kts (mach 0.78 at fl350) would add about 6.4 degrees to the angle of attack. (Showing my work: Inverse sine of 50/(447^2 + 50^2)^0.5... is roughly 6.4 degrees) Even with a 3 degree angle of attack, this puts the plane close to an angle where the pitot tubes become unreliable even without icing. Depending on the automated response to the angle of attack, this could get worse very quickly. The main point is though that any pitch up may have rendered the pitot tubes unreliable even without blockages. Oddly this gets back to what Tim Vasquez wrote about turbulance being the primary factor on his list shortly after the incident. In short could a strong updraft have caused a lack of reliable airspeed indications, degraded controls, etc?

Thirdly, what would the autopilot have done in a strong updraft before disconnecting?

Fourth, assuming AoA was reduced by pitching the nose downward (possibly restoring airspeed data), what would have happened when the airplane went from a strong updraft to a strong downdraft? Could this have also caused a stall of some sort via too low of an AoA?

So this leads to a couple of other questions that are now lurking in my mind:

1) Can we shelve the idea that pitot icing was a factor at this point and focus more on AoA issues?

2) Could the Cabin Vertical Speed advisory have referred to a falling descent? Could this be some sort of stall?

As far as potential safety improvements:

1) What needs to be done on AF's side to help pilots avoid this sort of weather?

2) What needs to be done on the A330 side to avoid problems regarding autoflight input in strong convection?

To those aviation specialists and Pilots in this forum, please could someone shed light on a question that has been bugging me since the Preliminary report was released.

Please also bare in mind that I am no Aviation specialist and my question may appear to be very simple. But sometimes its the simple/basic questions that produce the best answers and analysis.

What "obvious" reason could there be, for Flight 447 to plunge into the ocean so fast, that no life jackets were found inflated, no mayday/distress call was sent, cabin crew seats were not in use.

1) Does a jet that size, fall 35000 feet in a split second, or would there at least be a minute or 2 available for the pilots to at least notify the cabin and/or send a distress/mayday signal?
2) Would it be reasonable to assume that the Pilots at the controls, were incapacitated and not "consciously" in control of the jet?
3) If so, what could the reasons for complete flying crew incapacitation be?

@SandraJ:
The odds are very great that the plane reached the ocean via a gross upset, that is, an extreme departure from controlled flight. Once the upset began, the time remaining before impact might have been as short as one minute, or as long as a few minutes.

In a gross upset, the flight crew would be completely absorbed by their attempts to restore control of the aircraft. Even if one pilot was making all of the flight control inputs, the other pilot would have been doing everything possible to assist the pilot flying. In such an acute crisis, I think it unlikely that the flight crew would spend the precious seconds available to them talking on the radio or intercom. If they had successfully regained some measure of control over the flight path, they would then have addressed communication.

When a jet plane enters a gross upset, the interval between a sense of normalcy (sensations not very unusual for an airline flight) and things being obviously very very wrong can be as short as a few seconds. From cases where airliners survived a gross upset, the onset has usually been very rapid. If there was no intercom announcement of an emergency, passengers would not be instructed to put on life jackets. I would expect the cabin to be so instructed if the plane were in at least partially controlled flight, and the flight crew was preparing for ditching (controlled landing on water) If there was no intercom announcement of an emergency, cabin crew may have been busy with their normal duties until the upset developed. Once the upset began, the situation inside the cabin (high and changing G forces, possible extreme vibration) may have prevented the cabin crew from reaching their seats. This is a possibility that a thorough accident investigation will consider.

In light of your question, the absence of voice radio communication for some time before the crash (I think at least half an hour) is especially interesting. The HF radio technique used to communicate between transoceanic flights and air traffic controller is famously undependable, and I don't know how unusual this lack of radio contact was.

I am aware of one case in which both pilots became gradually incapacitated at the same time (due to a cabin pressurization failure, that the crew did not recognize), but perhaps that was the only time this has happened on a scheduled jet airliner. This probably did NOT happen on AF447, because the wreckage was found close to the point from which the ACARS message about cabin pressure was issued.

One way that the flight crew could become incapacitated would be a large enough hailstone or other object breaking the windscreen.

There have been several sad cases where the flight crew was incapacitated by violent attack.

A more subtle "incapacity" that will probably be carefully studied, will be the effect on crew performance of flying in the middle of the night, and possibly on personal schedules that could aggravate fatigue.

I don't think that what we know about this accident tells a story that the crew was incapacitated, but it doesn't tell us that the crew was not! As with so many questions about AF447, the flight recorders would help greatly to provide answers.

I agree with you that the sudden loss (as per BEA transcript) of communications is troubling. Although this is not a rare occurrence, given the loss of the airplane, one wonders about the cause.

A point about pressurization, and backing away from the flat spin hypothesis.

First, the Helios case transmitted a different ACARS message: "Excessive Cabin Alt" which was not found here. It did not transmit "Cabin Vertical Speed." This leads me to believe that pressurization systems were functioning normally.

As for a flat spin, this seems highly unlikely given the current damage to the wreckage.

Also, I came across something interesting..... The A330 abnormal attitude Angle of Attack values are when the AoA is greater than +30 degrees or less than -10 degrees. Presumably much outside these values, a stall occurs. Now, if we see the aircraft exiting the cloud just before the accident, we can see an interesting possibility.

Suppose the autopilot is disabled by strong convection. This could result in pitot icing or pushing the Angle of Attack outside what the pitot tubes could handle. Pilots push the nose down and continue out of the storm while troubleshooting system failures. Angle of attack is slowly falling but they are troubleshooting other errors and don't notice. Angle of attack might reach, say -7 degrees. Then they hit a downdraft of 50 mph and this brings them into stall range (subtract 6.4 degrees). The wings stall and the airplane enters an uncontrolled descent. The rapid descent triggers the final ACARS message.

Concerning the hypothesis of the crew having been somehow "incapacitated":

Is it plausible that, the A/C being at this stage in pure manual control mode and the crew being disabled, the descent would have been done in such a way that the A/C would have conserved its "ligne de vol" (using the words of the BEA report), in other words a more or less normal attitude ?

Thank you to the knowledgeable ones for clarifying this point.

On pages 39-41 of its report, the BEA posits that the plane hit the water at a fast rate of vertical speed and posted photos that show the effect of compression along a vertical axis on various pieces of equipment.

Can this be caused by a flat spin? Probably. Can this also be caused by a kind of very hard landing, controlled or uncontrolled? I am not an expert to say. What the BEA seems to exclude is some kind of a dive.

The only issue with a flat spin would be that, at the extremities of the plane, the plane would hit at least 30-40 degrees off vertical, perhaps as high as 45. At 3-4 secs per rotation, one has 100-140mph sideways motion at the ends. This seems inconsistent with the BEA findings (though the preliminary findings could be wrong, the bit regarding the tale is interesting as it would be the most conclusive disregard of spin forces available).

The "news" that AF 447 was intact when it hit the water sounds like an effort to cover up the obvious. Everyone who has seen video from hurricane winds peeling shingles from houses has idea how strong the wind must be to be able to do that. Sky divers do not find themselves naked when they land. Not only were those people falling outside the plane, but they were moving trough the air at speeds well above that of free fall. >:(