minimum flap retraction height

[jorgvaz]

Minimum Flaps Retraction Height

What would happen if, using take off analysis that states the minimum retraction altitude as being 400 feet above ground level accomplished with SOP Take off- one engine in accordance TO THE SAME ANALYSIS, in case of delay of the retraction altitude until 1000 feet AGL?

In other words, what could happen if the SOP was changed to accelerate at 1000 feet AGL in case of engine failure, but using take off analysis based on a minimum retraction altitude of 400 feet AGL?



Thanks in advance for your help in this topic

[Eckhard]

Effectively you would be extending the second segment from 400ft to 1000ft. Then the third segment would be starting at 1000ft and the final segment would only be a 500ft climb to 1500ft.

All the net take-off flight path data in the analysis would be invalid. However, it would be relatively simple (if time consuming) to construct a new TOFP using the revised accel height, provided one had access to the performance charts for each segment (try the AFM).

In general terms. clearance over a close-in obstacle would be improved. whereas that over a distant obstacle would be worse.

At high elevations. time limits for Take-off Thrust may become limiting if the higher accel height was used.

[mutt]

You would have a hard time explaining in a court why your SOP allowed your crew to ignore the takeoff thrust limitation.

Have someone do the analysis based on 1000 feet and accept the lower weights which come with it.

Mutt.

[411A]

...except that most companies don't, and have no interest in doing so (including the folks in JED, when I was there anyway...).:rolleyes:

[Slasher]

Mutt isnt kiddin. Most engines have a 5 min max TO thrust limitation which at high TOWs will be exeeded during the 3rd segment if you unilateraly decide to push the 2nd segment much beyond the AFM height.

If theres an event where a 2nd segment extension warrants a greater height than the 400 (or 800ft) perf value datum:

* and there are no Company-published tables for 1,000ft or the 5 min TO limit

* no obstacle data for 3rd and/or 4th segments

* you dont have time to calculate values taking into account ALL segments from the AFM

then the best idea is to have an escape route in the event of engine-out at or after V1. If no escape route is possible, then as Mutt said reduce your TOW or change to a more suitable runway.

Unilateraly screwin around with nominal performance requirements and not taking into account the potential consequences is very foolish. There could be a goat wandering around the clouds in the 4th segment which the take-off tables may have considered!

[Dehavillanddriver]

This raises an interesting question that is conveniently ignored...

Many people advocate extending the second segment on curved escapes if the final heading hasn't been reached - ie don't accelerate and turn at the same time.

This philosophy makes it slightly easier to fly - turning, levelling off and accelerating is a handful for some, but it invalidates the RTOW chart.

By the way my company uses 800 ft for classic 737's and 1000 for NG 737's as the acceleration height. We have 5 min engines on the classic and 10 on the NG.

THe RTOW charts are predicated on the above acceleration heights and engine time limits.

[Hudson]

Dehavillandriver. Interesting point you made. Cairns rwy 15 engine failure and curve through 120 degrees is a case in point. One hopes that if the company directive requires you delay the 3rd segment until reaching the final heading out to sea, that the runway analysis designer allowed for a variable higher 3rd segment than the standard 800 ft used by the company.

It would nice if the regulatory authority could require airlines to publish to what surveyed distance from the departure runway each runway analysis is valid to. At least the pilot would then know if he was on his own after passing that limit.