Assuming that the Russian certification requirements are similar to EASA/FAA, which from my experience they are, then one area for accident investigation would be on the pitot heat alerting system.
Was an alert given;
no; then why not, given the requirements below? (if...then this failure must be indicated).
yes; then why was it not observed / acted on? (is there a condition where a pitot heat failure is masked by a collective icing alert relating to another failure or MEL item).
Re AAKEE, is the AoA heating part of the pitot heating system?
Extracts from EASA CS 25
CS 25.1326 Flight instrument external probes heating systems alert
If a flight instrument external probe heating system is installed, an alert must be provided to the flight crew when the flight instrument external probe heating system is not operating or not functioning normally. The alert must comply with the following requirements:
The alert provided must conform to the Caution alert indications.
The alert provided must be triggered if either of the following conditions exists:
The flight instrument external probe heating system is switched ‘off’
The flight instrument external probe heating system is switched ‘on’ and is not functioning normally.
AMC 25.1326 Flight instrument external probes heating systems alert
CS 25.1326 requires that if a flight instrument external probe heating system is installed, an alert must be provided to the flight crew when the flight instrument external probes heating system is not operating or not functioning normally.
It is expected that probe heating system failures are indicated to the flight crew if such failures have an impact on the performance of the heating system to the extent of having an “effect on operational capability or safety”.
... a Caution category of alert is required ... for immediate crew awareness and subsequent crew action. It should be assumed that icing conditions exist during the failure event. The decision to provide heating system failure indication should not be based on the numerical probability of the failure event. If the failure could potentially have hazardous or catastrophic consequences, then this failure must be indicated.
The reliability of the system performing the probe heating system failure detection and alerting should be consistent with the safety effect induced by the failure. Refer to AMC 25.1309, ... for more detailed guidance.