The Russian investigators just reported that the preliminary results of the flight data recorder indicate that 1)last minutes of flight the aircraft experienced substantial variation of IAS and 2)pitot heat was off during the entire flight for all three tubes. You get the picture. https://www.gazeta.ru/social/news/2018/02/13/n_11164933.shtml
For a non-pilot, can someone explain why would pitot heat be off?
Could this have been an instance of the AN-148 (inadvertently) exceeding Vne while having very poor visibility (so no frame of reference) and having a critical structural failure?
It's hard to exceed Vne when you're heavy on departure and climbing out. In fact it's basically impossible unless you're pointing downwards - but obviously on departure that couldn't be considered "accidental". Even if you're flying without instruments - just following basic throttle position and climb picture you'd have to seriously mess up a lot of stuff and ALL SA / control to exceed Vne. I know you said "with no reference" but I would think you'd have to remove a LOT of "references" for that to occur.
I guess I'll bounce some ideas around while we are waiting for more information.
I'd say based on the previous post about pitot heat and the earlier reports of refusing de-ice, along with "substantial airspeed deviation" comment - that at least one and probably a couple of the pitots could have begun to freeze up, and pilots were confronted with unreliable airspeed indications, probably three different numbers assuming they froze up at different rates.
Sounds like the PF could have found himself trusting the airspeed indications a little too long and responded accordingly (pulling throttle for example). Of course the FDR data would also show the same (incorrect) airspeed readings as well, so that's harder to prove - unless the investigators confirm different
readings from each pitot which would certainly point to iced pitots when combined with pitot heat being switched off.
If the pitots froze up while climbing, and the static ports remained clear, they would see a faster speed than actual... and would slow down to correct it (heavy in a climb, while pulling in flaps - that wouldn't be pretty).
I'm probably not remembering this 100%, but I recall if the pitot drains remained open and static ports open, front inlet/ram frozen, you'd get essentially no reading, correct? Likewise in that regime of flight it would be very easy to stall if they pulled any power.
Of course we all know these accidents usually have multiple causes - refusal to de-ice may have left some contamination on the wings, and if they flew through any icing conditions bad enough to freeze an un-heated pitot, the wings would likely not be at 100% either - further reducing any margin for error with their airspeed.
Regardless, I can't imagine flying anywhere in Russia with pitot heat off.