V1

[PEI_3721]

CFMFan, within our agreement, we appear to have similar lines of thought, but perhaps from differing conceptual bases.

RE: if the reason is not "that you are not confident of accelerating to V1 before running out of runway"
These are not my words or thoughts. Judgement of such an acceleration capability would require great experience and ideal conditions in situations with a vast range of variables.
It is often within an individuals’ quest for confidence that error arise. We have confidence from every day operation that normal take-off performance provides the required level of safety; why then do some people question abnormal performance at a critical stage of operation.

IMHO the addition of phrase “if the aircraft is unable to fly” in the Take Off Training Aid (FAA doc – Boeing addition – Airbus followed for consistency) creates many problems and has decreased safety. If ‘something’ occurs before V1, the ‘decision’ requires you to predict the future – will it fly.
The text introduces a new evaluation and decision loop for a subject (will the aircraft fly with this ‘unknown/assumed’ failure) where few pilots have training or experience (knowledge).
As stated previously, the prime indications of inability to fly occur after V1, at or after rotation, when the stick is pulled back; even then it might fly later at a higher speed. All of this has nothing to do with engine failure recognition, V1, or RTO training – other than the mistaken perceptions. See: Canadian view – After V1.

The example of a tyre / wheel failure reducing performance is based on the premise that the pilots knows that the tyre / wheel has failed – and that it will reduce performance by a hazardous amount.
I suggest that both of these are most unlikely; a bang and yaw are not unique features – a galley door + wind gust, an engine failure, etc. At low speed there may be opportunity for discrimination based on salience or pilot experience, but at high speed, past accidents identified human fallibility, particularly when stressed, often by the surprise of an event. For a performance example see this Accident Report.

Many operators brief only to stop for problems other than engine failure and fire below a certain speed (80kts).
At lower speeds it appears to be assumed (operational regulations/training) that other non-engine failures can be evaluated / established and that the risks in stopping are low – and little is lost in being wrong.
At higher speeds the decision task should be simplified to identifying an engine failure – specifically lack of thrust, as that is a critical parameter for continued safe flight.
IF engine failure (lack of thrust), AND speed less than V1, THEN stop; caveat about having taken the first actions before V1 (certification regulations).
Thus training should concentrate on engine failure recognition (thrust parameter and confirming indications) and the human frailties involving startle, loud noises, vibration etc, false beliefs / perceptions, and assumptions.

Assumptions? – “there are no truths, only perceptions”. I agree that pilots in rare situations are required to make risky judgments – based on assumptions from their perceptions. However, these decisions should not be made without first verifying the basis of the assumption (the risks in assuming …).
Certification regulations balance risks to match the required level of safety, i.e. there is some margin, and thus operating procedures should guide pilots in most circumstances – engine failure +/- V1 is covered.
RTO guidance for non-engine related failures is weak, hence the FAA training aid, but when that also has weaknesses … … Perhaps this is the reason for operators using V1- 20kts or 80kts for non-engine related failures, but not to treat these situations as the same thing as an engine failure.

I agree that crews should follow the procedures, but it does not prevent them enquiring about the basis of procedures. I wonder what management might have assumed about RTOs with tyre / wheel failure; how do they expect crews to identify the fault (an assumption) – how are crew’s to differentiate this from an engine failure. Are you trained for that, is it written down?
Don’t let management pass the buck to the individual – seek clarification.

Also see:
PSM+ICR.

Briefing Notes; see ‘Revisiting the “Stop or Go” Decision’, under Takeoff and Departure Operations.