Some posts conclude with aspects which tend to ‘blame’ the crew.
I suggest that before coming to any conclusion a wide range of ‘human’ aspects should be considered.
The crew were faced with a sudden failure of an airspeed display: This is not obviously an unreliable airspeed – there is no display; thus, no demanding thought of using an UAS checklist. Remedial action might focus on reinstating the display or using an alternative source.
With all airspeed displays failing, again there is no obvious link to anything being ‘unreliable’. The priority action has to be to fly the aircraft, but without any specific checklist, basic aero / control concepts have to be recalled from memory and used in an aircraft where the control characteristics might not be best suited for a ‘novice’ pilot.
Add a stall warning to this scenario, which initially and logically, might have been disregarded as false: – Technically, an inappropriate association of stall with airspeed, but ‘stall’ is shown on the airspeed scale and everyone talks about stall speed, thus without any speed display why believe a stall (speed) warning. This was a mindset which unfortunately was not reversed later even with a valid warning, but there were no other stronger cues to trigger a change of view, particularly in a rapidly developing and very confusing situation.
These humans – the crew, may not have deduced that the aircraft had actually stalled until very late in the event, if at all.
Why did the aircraft climb: The loss of airspeed affects the ADC in a way in which the indicated altitude suddenly reads low (see FDR and previous events). In this instance, the crew focus on altitude recovery – avoidance of an altitude bust – they are ‘the juniors’ responsible to the absent captain and thus have responsibility for a safe and accurate flight. Did they deduce turbulence or another affect of adjacent Cbs. Add this to the developing scenario as above, then apparently inattentive control may not be surprising.
Possibly both crew focused too much of their ‘cognitive resource’ on deducing the ‘technical’ situation and problem solving, flying the aircraft was no longer #1 priority. This might not have been a result of a conscious choice, but due to the surprise and confusion of an unfolding complex event in a timescale incompatible with an ability to think, understand, and act.