Re #64 “ there are significant safety margins built into the calculations … ”.
This depends on how you define significant; in comparison with the safety factors used for landing, the RTO factors could be considered ‘marginal’ – and note how often we mess up landings with margin. Also if you wish to rely on the timing margins in certification, then you have to be very well drilled (and resistant to surprise).
The apparent safety margin in some non engine related RTOs near V1 might be attributed to the availability of all engine reverse, whereas an engine failure RTO would not have the same stopping capability.
Re: ” If you have a truly unflyable malfunction … ”.
The phrase ‘unsafe or unable to fly’ is in many SOPs and is often quoted in forum discussions, but has the industry really thought through what this means?
The phrase appears to have originated with the Take Safety Training Aid (TSTA), Boeing / FAA circa 1993. Here it specifically refers to after V1 “… unless the pilot has reasons to conclude that the aircraft is unsafe or unable to fly. ” para 2.3.1.2.
What reasons have been considered and how would these be identified with sufficient certainty to entertain a late RTO with a high risk of overrun; perhaps the observation in #46 ”If the aircraft cannot be rotated, self-preservation will probably dictate that you abort”, defines the only realistic circumstance - and you don't need an SOP for that.
The TSTA modifies the problem by including the phrase (in later sections and simulator briefings) amongst the reasons to reject in the low speed region. In addition it complicates the issue further at high speed before V1, with the qualification “the perception that the aircraft is unsafe or unable to fly”. Does the industry accept that a high speed RTO can be based on the perception of safety without indication, as opposed to an engine failure / fire which can be confirmed from instrument displays and warnings?
In thinking about unsafe or unable to fly, also consider other items as reasons for rejecting in many SOPs – nosewheel vibration, or tire failure where debris may have damaged the aircraft. Again how can the crew know that a vibration is from the nosewheel – experience, simulator training? Or that the bang was a tyre failure and that debris have cause damaged? To have some certainty, perhaps confirmatory evidence is required from engine or systems displays – essentially the same indications to crosscheck an engine RTO event; thus SOPs could perhaps be simpler.
Some (most) SOPs attempt to cover a range of situations, but fail to consider how the crew can meet the requirements in the SOP.
At best, many of the decisions which should be based on assessment rely on perception, which is notably weak particularly in stressful and time limited situations. Whereas a warning and confirmatory display provides a good basis for understanding the situation.
Also, consider the choice of action, which should be a simple Go / No Go choice; this may now involve an assessment of the risks within that choice because the wording of the SOP places the responsibility on the crew for evaluating the risk in the choice.
RTOs are one of the few areas in operation where the choice of action should be self-evident from the situation assessment – is there a ‘reasonable’ failure, what is the speed in relation to V1; decision Go / No Go, the risks are bounded by certificated performance and correct crew actions. Unfortunately life is not clear-cut, - as related by ‘eckhard’ (#40); we require experience, naturalistic decision making, airmanship, etc, but not more complexity in SOPs.
Perhaps removing the ‘what if’ scenarios from the reasons to reject would reduce the occurrence of weak assessment or poor choice of action; particularly if these scenarios are already covered by the assumptions in the basis safety for aircraft certification (FAR/CS), i.e. systems and control redundancy. What is the probability that such an event (what if) will be encountered in operations? The TSTA did not identify any event where an inappropriate RTO would have resulted in the aircraft being unable to fly.
“It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that ain’t just so.” Mark Twain.