JAA 2 secs lapse to react?

[M.85]

Hi all,

Apparently 2 seconds reaction time is "credited" to a pilot when he decides to abort or continue the T/0.
My question is from the "distance to accelerate" formula (Vsquared/2a),if 2secs allows a speed increase of lets say 5 knots..the t/o distance has increased by 10%!!!
Is this extra t/o distance taken into account when given V1 figure?

Safe flying,

M.85

[john_tullamarine]

This dates back to FAR 25 A/L 42 (if my memory serves me correctly) ... it has nothing to do with continued takeoff .. only the reject.

Prior to that amendment, there was effectively nil fat built into the certification rejection exercise .. and, surprise, we had the odd reject on critical runways end up off the end of the strip. After a lot of Industry pressure, the FAA moved to introduce a nominal delay at V1 to account for things like startle factor, scatter in pilot reaction times and so forth.

The usual manner of running the testing is something along the lines of

(a) fail the engine at the appropriate point just short of V1
(b) correct the yaw on rudder
(c) do nothing else until the delay period has passed
(d) execute the prescribed reject sequence

There will be a modest speed overrun but that is part and parcel of the measured reject distance.

The delay deal is intended to be transparent to the pilot .. ie the intention is that the pilot follows the flight manual liturgy and, in the reject sequence, does the tapdance as expeditiously as is practicable ... there is NO intention that the later certification standard provides fat for the pilot to dilly dally with initiating the reject.

[M.85]

Thank you Sir:ok:

This website is just amazing...

Safe flying,

M.85

[mutt]

Yep with people like JT to answer questions, i would agree that this site is quite amazing........

The accelerate stop distance not only accounts for the time delay before initiating the abort, it also accounts for the increased speed and residual thrust on the failed engine.


Mutt.

[m&v]

Further to JT's briefing-amendment 42(1978) the definition of VEF(when the constructor fails the engine prior to V!)was made public to the crew.Up until this time it was only used by the FAA/builder on the Cert'Test' card.Now the crew knew that one must'recognize' the failure ,and react ,prior to V!.The 2 sec time was added to the 'Distance'required to the AccStop distance.
this lead to the Boeing/airbus controversy in that Boeing put forth it's 767 proposal early(1978) ,ergo avoiding the 2sec requirement ,
and 'selling' their aircraft as using less runway...:D

[john_tullamarine]

Probably worth keeping in mind that the later rule generally was not made retrospective with the result that only fairly recent TCs include the 2 second pad. We still need to be very wary with older aircraft .....

[OzExpat]

It's probably just an exercise in splitting hairs, but Pans Ops procedure design criteria includes 3 seconds delay for pilot reaction. Thus, any time the procedure requires the pilot to do something like initiate a turn or a missed approach climb, there is 3 seconds of delay built into the protection area. Again, there is no suggestion that the pilot should delay taking the action, of course.

I wonder if FAA's Terps uses a 2-seconds delay? It might be interesting to try to work out whether the 2 seconds is more realistic than 3 seconds. In any event, some delay is inevitable because it will take some time for a pilot to recognise the need to take some action and then initiate it.

[411A]

OxExpat,
Recall some (many) years ago the Australian folks insisted that the takeoff charts for the B707 were revised by 150 feet, (ie: takeoff distance available +150 feet) which accounted for the line-up distance on the runway, oddly enough, quite correct as to the distance.

Still the same for other types today?

[M.85]

Mutt,

I agree about JT..:ok: to him and all of the "wise and professional" in pprune around here taking time to thoroughly answer questions..

Thank you,

M.85

[john_tullamarine]

411A,

ICAO recommended the implementation of lineup allowances quite some years ago .. as far as I know Australia was the only country to implement the requirement at the time. The geometry requirements are reasonable and allow for a modest clearance from runway end and side during alignment manoeuvring.

It always struck me as strange that not everyone did this, especially for ASDR calculations.