Effect of V1 on ASDR/TODR

[FLT86]

Hi All,

While going through my ATPL notes, I noticed that there is still something that I didn't get.

When your V1 decrease, your ASDR also decrease but I don't understand why TODR increase as well ?
Same when V1 increase, TODR decrease.

Could you give me your light and help me please ?

Thanks guys!

[keith williams]

Having detected an engine failure at V1 it must be possible to:

A. Reject the take-off and bring the aircraft to a full stop within the remaining ASDA.

B. Continue the take-off with one engine inoperative and reach V2 at screen height before the end of the TODA.

Reducing V1 reduces the distance that is required to accelerate up to V1 and also reduces the distance that is required to decelerate to a full stop when rejecting the take-off. So reducing V1 reduces the distance required to achieve option A. This means that reducing V1 decreases the acceleration-stop distance required. Increasing V1 will have the opposite effect.

The key factor in option B is that after engine failure at V1 the remaining acceleration to V2 within the TODA, must be done with one engine inoperative. Reducing V1 increases the speed difference between V1 and V2. This increases distance that is required to achieve this speed increase. So reducing V1 increases the take-off distance required (TODR). Increasing V1 will have the opposite effect.

[FLT86]

Hi,

Thank you for your help, now it is clear ! :)
So as I understand, this case works only with one-engine inoperative, right ?
What about two engine operating on an ATR/Airbus ?
If V1 increase, TODR also decrease and ASDR increase ?

Thanks !

[keith williams]

The definitions of V1, V2, ASDR and TODR are all based on the failure of one engine being detected at V1.

But if any given aircraft type were to be able to continue the take-off with more than one engine inoperative, then the same physical principles would apply.

Acceleration rate is greatest with all engines operating. If any of the engines are inoperative, the acceleration rate will be less, so the distance required to complete the take-off will be increased.

If we carry out the entire take-off with all engines operating we will use a cert TODR to reach V2 at screen height.

If we carry out the entire take-off with one engine failed, the acceleration rate will be less, so the (TODR) distance required will greater.

Changing the value of V1 changes the fraction of the take-off that must be carried out in each of the two conditions. Reducing V1 increases the fraction of the take-off that must be carried out at the reduced acceleration rate. So the TODR required is increased. Increasing V1 increases the fraction of the take-off that is carried out at the higher acceleration rate. So the TODR required is reduced. So increasing V1 reduces TODR and decreasing V1 increases TODR.

[FLT86]

You must be a teacher !!!
It is well explained and understood very clearly, nothing to say, nothing to add, perfect !

Thank you very much !!! It helps me !