Re the three issue to consider (#87, #91).
- Should the FO elect to initiate a STOP when the SOPs say this is only to conducted by the Captain?
- Is it ever appropriate to abort after v1?, and
- If so, did this event provide enough indications to justify the decision?
1. How a rejected take off is conducted is a Procedure as in ‘SOP’. As to who makes the decision / conducts the reject, is a matter of Policy.
An RTO is an event/time critical situation; some operators may judge that either pilot as PF will have sufficient experience to decide and conduct the reject; others might restrict the decision and action to the Captain. The latter adds risk due to the potential for missed communication, confusion, and delay. The formulation of policy must involve risk assessment and is interlinked with the quality (content) of the SOP and level of training.
2. The V1 concept is primarily concerned with engine failure and aircraft control / performance; thus any discussion on the procedure – the decision and activities of a rejected take off (abort), should be restricted to these matters.
The more recent addition ‘if unable or unsafe to fly’ to RTO training has added considerable scope for confusion.
Making such an assessment before V1 (as originally envisaged) is an evaluative process, opposed to the more general if-then assessment of an engine / system failure. Thus this requires considerable knowledge and experience; it may increase decision time, and potentially involve higher risk.
Some operations even make this evaluation after V1 (in an RTO context) with significant increase in risk and almost inevitably with an accident outcome.
After V1 it should not be necessary to differentiate between
unable or
unsafe to fly, the latter implies that flight is possible but the circumstances questionable (unsafe). Yet these circumstances should have been identifiable beforehand – a few seconds before at V1, and logically, a few more seconds earlier at low speed / before take off.
Thus the extremely unlikely situation requiring the aircraft to stop after V1, is because the aircraft will not fly. Any evaluation at this point is whether to stop from VR or attempt to rotate at a higher speed. This is a judgement issue dependent on how the circumstances of the situation are perceived.
In other circumstances above V1 the certification risk-probability assumes that the aircraft will be safe enough to fly and the crew can evaluate any problem in flight.
Before the ‘what if’ replies are posted; consider what the operational and certification aspects assume to be detectable and avoided before take off, and those which the aircraft can withstand. Few if any RTO procedures can accommodate double failures, particularly those involving earlier human (mis) judgement or irrational thought.
3. In the vast majority of RTOs the decision has been correct for the situation as perceived by the human operator at that time. Judgement of these decisions in hindsight adds little to safety unless the circumstances are fully understood and evaluated.
This event appears to have been complicated by a poorly considered SOP with respect to the issues above, and where weaknesses in industry-wide training and ill advised use of modern technology (speed trend) added further complexity.
Operators (industry) could consider why ASIs are crosschecked – what could be detected (does the aircraft have a comparator system); what is the relative importance of speed / speed-trend miscompare towards continued safe flight in a commercial aircraft with dual and St-By systems (
http://www.pprune.org/safety-crm-qa-...ml#post6550181).
Re #93
You can not stop someone acting on impulse.
But you might be able prevent the human being in a situation or having to evaluate circumstances where impulse should be avoided.
Philosophy,
Policy,
Procedure,
Practice.
“
We cannot change the human condition. But we can change the conditions under which humans work”, Professor James Reason.