At the risk of repeating some of what has been listed previously, it might be useful to summarise the continued takeoff approaches adopted by the typical operations engineer .. and I have no doubt that Mutt and Old Smokey will take me to task for any errors and omissions I might make ....
(a) work out the maximum runway limited TOW.
(b) starting with this figure, we iterate (if, and as necessary) until we come up with the best weight (being not greater than the runway limited weight) for the obstacle requirements
(c) the takeoff flight path commences at end limiting TODR (keeping in mind that the declared runway data for obstacles will be referred to end TODA - which can create problems so far as do we redo the obstacle trapezoid or do we somehow ensure that we pass through the centreline/end TODA gate ?)
(d) normally we run the minimum third segment (400 ft referred to the runway head or such higher height as might be SOP for a particular jurisdiction or company) and see what the clearances are.
(e) if the clearances are OK, no problem
(f) if the clearances are inadequate, reduce the weight and start the exercise again - including the runway cases to account for a reduced TODR. If the critical obstacle is distant, it might be useful to look at running a higher third segment as that might produce a lesser necessary weight reduction.
(g) one of the problems to be addressed is where is the critical obstacle located (and noting that the critical obstacle may change as the weight is varied)
(h) if the critical obstacle is located in the first or early second segment, there is not much to be done other than pulling back the weight to reduce TODR and improve climb gradients
(i) if the critical obstacle is late second segment (especially), late third segment, or fourth segment, use of overspeed V2 or improved climb (depending on which manufacturer's camp you are in) may help out by running a higher V1 to reduce TODR and higher V2 to improve second segment climb gradient
(j) if the critical obstacle is third or fourth segment it may be useful to run the second segment higher so that the net flight path is forced above the critical obstacle. Main limitation here will be dictated by the need to get to the end of the fourth segment within the engine takeoff rating time limit. Sometimes there will be other limits to be observed .. eg as I recall the Dart had a feather pump time limit which constrained the third segment (at least on the F27 and HS748) to a maximum of 600 ft.
(k) provided that the AEO flight path is constrained always to be above the OEI gross flight path, then one can sensibly ignore the AEO case and post V1 failure as the aircraft will be in a conservative position compared to the V1 OEI case.
(l) one matter which has always concerned me is the case where (some) operators address the V1 failure case but then ignore post V1 failures in the case where the OEI escape route differs from the AEO departure. It is exceedingly facile, not to mention potentially dangerous, in this case to leave it to the pilot to sort out - to me, it is clearly the operations engineers' responsibility to address this case so that, for all failure cases, the calculated flight path to the en-route phase of flight is addressed with respect to obstacle clearance requirements.
(m) keep in mind, also, that the gross to net fudge factor provides an increasing vertical margin between gross and net flight paths. .. which is why we are far more actively interested in first and early second segment obstacles than, say, fourth segment.
(n) in respect of Mutt's original question, a similar reasoning to (l) and (m) ought to apply ... if the AEO flight path is not constrained to be above the OEI escape path, then the individual runway analysis needs to take care of the AEO differences .. ie, if the published procedure doesn't refer to using a lower AEO acceleration, then I would err on the side of being a bit suspicious .. in the same way I would any time that the AEO and OEI flight paths differ.
Last edited by john_tullamarine; 22nd Aug 2004 at 02:52.