Aus einer JAA Publication:
3.2.1 Definition of Take-off Decision Speed (NPA paragraph 2.1.1)
A number of comments were received on the proposal to introduce a definition of ‘Take-off Decision Speed’ into JAR 1. These invoked the philosophies behind the take-off go/no-go decision process and the treatment of pilot recognition and reaction delays. Some commentators pointed out that the emphasis of advice from manufacturers and modern crew training programmes was that the decision speed, V1, was the point by which the pilot should have initiated actions to bring the aircraft to a halt in the event of a decision to reject the take-off. Others take the view that with as little as 1 second between the assumed engine failure speed, VEF, and V1, this is inadequate for the pilot to complete the recognition, analysis and response process, thus making ‘decision speed’ a misnomer.
JAA recognises that even with the benefit of effective crew training, a critical failure close to V1 is a rare and unpredictable event for the line crew to deal with. Human factors considerations and the evidence of past RTO overrun accidents confirm that a safety margin based solely on a 1 second delay between engine failure and initiation of braking action is inadequate to cover the recognition and reaction process. However, the safety provided for by the requirements is a combination of the VEF to V1 delay time and the distance margin added to the certification demonstration of accelerate-stop distance to address operational contingencies. A balance needs to be achieved between the commercially penalising operational implications of performance margins and what it is reasonable to expect an adequately trained crew to achieve when faced with a critical, but rare, event. This balance needs to be achieved by a combination of performance scheduling and attention to the decision and reaction process in crew training. The training aspects are being emphasised through other initiatives, including the Take-off Safety Training Aid package produced by leading manufacturers, in consultation with FAA, as a further product of the task force recommendations. JAA concludes that it is right for the regulations to support and confirm the accepted training philosophies, with V1 emphasised as the speed by which action should be initiated in an RTO, albeit with the additional margin of a distance safety factor.
In response to these comments this proposal of the NPA is further revised to delete reference to the term ‘Take-off Decision Speed’ but to amend the existing definition of the abbreviation ‘V1’, emphasising the intended nature of this as a crew action speed. However, the recognised short duration of the delay time portion of the overall safety margin emphasises the need for the additional distance margin to be adequate. In particular, it should be used only to cover random operational contingencies. Significant predictable factors, such as alignment distance, need to be addressed separately and not treated as random events that are covered adequately by the general safety margins.
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