So here’s a question for the safety engineers at Airbus. Why display unreliable airspeed data if it truly is that unreliable?
In slightly longer form. If air data is so unreliable that your automation needs to drop out of primary flight protection mode, and your QRH procedure is then to manually fly pitch and thrust (1) then why not also automatically present a display page that only provides the data that pilots can trust and is needed to execute the QRH procedure (2)?
Not doing so smacks of ‘awkward automation’ where the engineers automate the easy tasks and leave the hard tasks to the human, usually with comments in the flight manual to the effect that, “as it’s way too difficult to cover all failure scenarios it’s over to you brave aviator” (3). This response is also something of a cop out as what is needed is not a canned response to expected events but rather a set of flexible tools that can assist in responding to unprecedented events that inherently demand sense-making of the situation before deciding what to do (4). As aviation systems get deeper and more complex this need will not diminish, in fact it will likely increase (5).
1. The BEA report on the AF447 disaster surveyed Airbus pilots for their response to unreliable airspeed and found that in most cases aircrew, rather sensibly, put their hands in their laps as the aircraft was already in a safe state and waited for the icing induced condition to clear.
2. No the Back Up Speed Display (BUSS) does not really fulfill this need.
3. What system designers do, in the abstract, is decompose and allocate system level behaviors to system components. Of course once you do that you then need to ensure that the component can do the job, and has the necessary support. Except of course if the component is a human and contractually and culturally considered to be outside’ your system.
4. Another way of looking at the problem is that the automation is the other crew member in the cockpit. Such tools allow the human and automation to ‘discuss’ the emerging situation in a meaningful (and low bandwidth) way so as to develop a shared understanding of the situation.
5. Yet another way of looking at this is that the principles of ecological design needs to be applied to the aircrew task of dealing with contingency situations.