PERF

[CV Donator]

Just a quick question on performance. I know that ASDR assumes a failure at VEF followed 1 second later by V1. In some old notes I have it says that the first retardation occurs 2 seconds after V1, using brakes on a dry runway and thrust reversers factored in for wet rwy operations. Now in my Boeing Flight crew operating manual it says that the abandoned takeoff must occur at V1 at the very latest. It also says that if windshear is encountered on the takeoff roll just before V1 there may be insufficient runway to stop. So as you can see a slight conflict. I am supposing that the 2 seconds is due only to some extra stringent JAR requirement. I would be grateful if someone could shed some light.

[Old Smokey]

The problem is that the rules have changed (for the better). Depending upon which aircraft you're flying, the associated Recognition and reaction times will vary. There was a very good recently running thread in Tech Log ("Calling V1 Early") where these aspects were discussed at length as the thread developed.

In 'the modern era', the 1 second from Vef to V1 remains, but a very important rider is that the Rejected Takeoff must have been initiated BY V1. If you've heard the "V1" call, stopping is not an option, you GO. This is the background to your (presumably modern) Boeing notes wherein you state "Now in my Boeing Flight crew operating manual it says that the abandoned takeoff must occur at V1 at the very latest". That's true.

There's no real conflict between the performance regulations and the Wind-Shear concern. No conflict because it's not considered for the All-Engines or the One Engine Inoperative case. Wind shear is a curve ball out of left field, and impossible to quantify except from the FDR after the event. It can vary from slight to disastrous.

The increased times in the Recognition / Reaction / Full retardation package IS in fact a less stringent requirement, at least from the pilot's perspective, it adresses typical pilot Recognition / Reaction times more realistically. It's certainly more stringent when it gets down to the load that you can carry from a given runway, a commercial increase in stringency.

Generic answers, it all depends upon which generation of aircraft that you fly (and don't forget 'grandfather' clauses that allow more modern versions of essentially the same aircraft to have to meet the 'old' rules.

Regards,

Old Smokey

[oldebloke]

The 2 seconds don't apply to the 'reject by V1'technique..It's added into the ACC/Stop runway DISTANCE to cover average pilot handling..
FAR 25-107 describes the Reject by V1
FAR 25-109 covers the DISTANCE thing(same numbers in the EASA regs)
Cheers:ok: