We use deice fluid on the ground in order to takeoff. Once up to flying speed all the fluid runs off the wing. In flight we have different anti and deice systems designed to keep the wing clean.

That deicing procedure on the ground is all about and for the upcoming takeoff. It has close to zero bearing after flying a short while.

There are ‘anti-ice’ systems in flight, usually hot air, hot props, or boots that expand. One has to be in visible moisture in flight to get airframe icing. The effectiveness of anti-ice systems to be used in flight can vary widely with aircraft types.

Pic of the accident aircraft's de-icing panel with an "INOPERATIVE" sticker. From July 2023.


Daily Mail

quote:

Originally posted by kkina:
Pic of the accident aircraft's de-icing panel with an "INOPERATIVE" sticker. From July 2023.


Daily Mail

Irrelevant.

Various systems or components can be inoperative. A document called the Minimum Equipment List or MEL, and another called the Configuration Deviation List or CDL, allow for specific items under specific circumstances to be inop or missing.

The MEL is for systems, to include deice. The FAA and the aircaft manufacturer determine that flight can be conducted without a loss in safety, with very specific limitations. For deice, the limitation would be no flight permitted into known or forecast icing. And the system must be repaired to full functionality within a certain time, such as 10 days or a certain number of flight hours.

That MEL sticker from a year ago has no relevance to the accident.

Turboprops with pneumatic boots frequently develop a leak and become inop. So that old MEL was not indicative of some unusual defect.

If a system fails in flight, the crew refers to the Quick Reference Handbook or QRH for instruction. For a deice system failure it would say to leave icing conditions immediately. There will be some caution or warning light for any deice system failure, so it would not go unnoticed by the crew at the time.

So the pilots ignored multiple warning alerts, and continued to operate the flight in icing conditions. Did I hear right that they responded to a fault light in the de-icing system (which we know had a troubled maintenance history) by simply turning it off?

Sounds like the crew flew for an hour with a known faulty deice system in icing conditions. Then they got slow and stalled it, entering a spin.

Normally, the stall warning system gives adequate notice before a deep stall occurs. The preliminary accident report says there was some kind of stall and/or low speed warning before loss of control.

Pushing forward on the stick to unload the wing should be the reaction to the stall warning, which should prevent the stall progressing, which then prevents a spin. Did they not apply forward stick?

The moments from the first indication of stall until the spin began will be key to understanding how they got into an unrecoverable situation. They apparently made serious errors to get the slow speed/stall warning, but then it seems they also mishandled the recovery.