787 "unrealistic airspeed" AD

[macdo]

Flying a modern FBW aircraft? Then stay well away from TS. I have experienced the ice crystal thing flying behind a line of CB's over the Indian Ocean @ 410. Lost PFD speeds, odd noise of something hitting the screens, then 10 secs later all gone. Very disconcerting. Will happen again at some point I'm sure.

[Aluminium shuffler]

Thanks for the expanded information SafetyPee. Good stuff to know. The trouble with being a paranoid cynic is that I don't trust the certifiers to do their job correctly, and given all the 787 problems, many of which were predicted, I think that mentality is justified. If the 777 system is near bullet proof, then the 787 system should be near flawless, and yet here we are. I fear many of these changes are cost driven, not safety or performance driven.

[safetypee]

AS.
Forget the paranoia, join the optimistic cynics club.
Consider humans as an asset, why is the design and certification as it is; we might assume that this did not plan for failure, thus what was the cause; the system, certification (beware assumptions), atmospheric situation, etc.
Consider what can be learnt for these events and similar preceding ones. Do we really have to tell pilots what is a sudden and significant change in airspeed, not to manoeuvre the aircraft with autopilot engaged (beware negative experiences with CWS).

Recovery actions are necessary, but the precursor is avoidance – macdo, but how are the conditions identified, then to be avoided by how much; what is ‘safe’?
If the conditions involve high water content then then WXR might detect them and thus avoid … but what level of intensity, deviate by how much.
If not detectable by radar … ice, or associated with CBs, then deviate, but by how much etc.
Deviation might be easier for some 787 pilots because certain engine variants have had restrictions or deviation re CB avoidance - ice crystals. So if engines had suffered in these conditions, why not airspeed.

There is much to learn from this issue, not just for the 787, but for all aircraft, operators, and individuals; how do we think about these things, learn from them and apply lessons learnt.

[Ian W]

One of the problems is that some atmospheric processes are still not understood. One is the way super-cooled water behaves just in simple freezing on nucleation particles. ( http://www.pnas.org/content/99/25/15873.full.pdf ). So there are bound to be the occasional surprises with high velocity flight through this kind of weather. I would expect work is going on researching what weather conditions caused the problem, such as size of droplets, density of droplets, temperature etc.

[GlobalNav]

It just seems that for A/S to truly drop so low so quickly, a lot of other things would need to be happening at the same time. The 787 avionics architecture is so integrated and redundant, I don't see why such drastic changes in A/S can't be checked against inertial attitude and acceleration. Likewise, I'd think a pilot would know that such a change in airspeed, if valid, would be accompanied by some very noticeable vestibular cues. Lack of such cues has be a cue that the airspeed has indeed not changed so drastically.

[Nemrytter]

Originally Posted by Ian W

One of the problems is that some atmospheric processes are still not understood. One is the way super-cooled water behaves just in simple freezing on nucleation particles. ( http://www.pnas.org/content/99/25/15873.full.pdf ). So there are bound to be the occasional surprises with high velocity flight through this kind of weather. I would expect work is going on researching what weather conditions caused the problem, such as size of droplets, density of droplets, temperature etc.

One of the problems is that airlines and aircraft makers are very reluctant to share their experiences with researchers - they try to do as much as possible in-house. Good for corporate privacy, bad for actually getting results*.
Unfortunately, whilst good, most in-house researchers are not as knowledgeable as a lot of others in academia and research institutes (as they're expected to cover a widfer range of topics rather than specialise). It's a real shame that there's such an atmosphere of distrust and secrecy, something that prevents everyone from working together to understand this phenomenon.

* I say that as someone whose salary is actually paid by an aerospace corporation to research ICI, yet still can't access their information and databases.

[Aluminium shuffler]

Nem, I agree. This industry always bangs on about how safety is its number one priority. I have yet to see any evidence after 20odd years in it that it is even in the top five.