Ask Captain Lim ~ All about Aviation - Take off safety speeds and functions of aircraft exterior lights.

I have a question on aircraft takeoff speed. I understand that once an aircraft has reached v1 speed, it is no longer possible to abort the takeoff. Why is it so ?. If we assume that a runway is longer than necessary then will this restriction of v1 still apply for takeoff abort ?

Another question - what are the different exterior lights on a commercial aircraft and what is the purpose of each of them ?

Thank you

Sridhar

Hi Sridhar,

Here are the answers to your two questions:

1. The V1 Takeoff Decision speed is the speed used as a reference in deciding whether a takeoff is to be continued or aborted when an engine failure occurs. Your question as to why it is not possible to abort the takeoff when the aircraft has reached a V1 speed is basically one based on safety reason. From past statistics, abort after V1 have resulted in disaster in many cases. Why? Because, such aborts would result in brake fires due to the higher speeds. So unless absolutely necessary, any emergencies after V1, the takeoff MUST be continued. It is safer to take off with the emergency, handle the problem in the air, dumped the excess fuel and then carry out a controlled safe single-engine landing at a lower speed. Please read a similar topic in an earlier FAQ.

Regardless of whether you have a longer runway, V1 still applies. It may sound not logical to you. It means that you may end up in a fire at the end of the runway instead of outside the runway! It doesn't mean that it is impossible to abort after V1. You can still do so but is recommended that you should not abort after V1 to avoid a fire with consequential and fatal
results.

2. There are two important exterior lights in any airplane. At the tip of the right wing is a green light and on the left wing is a red light. They have important functions at night when one find it difficult to know if the aircraft in on a collision course or flying in the same direction. If you see the red light on the right at night, then you can tell that the aircraft
is heading towards you. If the green light in on the right, it is safe because the airplane is flying together with you on the same direction. Also, if both aircraft are converging, the aircraft on the right has the right of way because he sees the Green light on the right wing of the other aircraft and the aircraft on the left sees a Red light on the wing of the right aircraft!