Factors affecting V1

[Keith.Williams.]

Many JAR ATPL students have a little bit of difficulty with this subject. The best way of approaching it is to start by going back to the definition of V1 then consider the implications.

If an engine failure is recognised at speeds below V1 the take-off must be aborted. To do this it must be possible to bring the aircraft to a stop within the remaining accelerate-stop distance available. The greater the V1, the greater will be the distance required to stop.

If an engine failure is recognised above V1 then the take-off must be continued. To do this it is neceassry to accelerate to V2 and reach screen height within the remaining take-off distance available. The greater the V1, the less will be the increase in speed that is required to reach V2 and the less the distance required to achieve this speed increase.

The above requirements mean that V1 markes the demarkation between being required to stop and being required to go in the event of an engine failure. This means that at V1 the aircraft must be equally capable of stopping or going within the remaining distances available.

Any factor (such as an upward slope) that decreases acceleration rate will increase the distance required to get from V1 to V2. If spare distance is not available then V1 MUST be increased making it closer to V2. This makes an increased V1 NECESSARY.

Any factor that increases decelertaion rate decreases the distance required to stop. So V1 may be increased and still permit the aircraft to stop. This makes an increased V1 POSSIBLE, but does NOT MAKE IT NECESSARY.

So an upward slope means that V1 MUST be increased to complete the take-off and MAY be increased without preventing an abort. The overall effect is that V1 MUST be increased.

The effects of other factors such as headwinds or tailwinds can be deduced in the same manner. After a bit of practice most students find this easier than trying to remember a long list of effects.