E/O Acceleration Alt

[EYZ]

The standard seems to be 1500' AAL, but why is this, what is the restriction to stop you doing it at a minimum of 400' like a regular take off?

Thanks for your help.

[john_tullamarine]

Background ..

(a) 400 ft is the certification minimum and, subject to terrain and other analysis considerations, there is no reason why this can't be used.

(b) in practice, if the operator runs the sums to optimise for all runways of interest, operating crews would end up with a significant variation of takeoff procedures and third segment heights.

(c) it follows that, for a generally small penalty, there are SOP advantages in grouping runways so that crews have (ideally) one (or a few) "standard" third segment(s) other than for a few special runways which require higher third segments for terrain optimisation.

(d) the upper (maximum) third segment height will be limited by engine time limits for operation at takeoff power/thrust. In some cases there may be other system limits - eg the Dart is limited to a 600 ft third segment for a feathering restriction as I recall from the dim depths of the memory banks.

The standard seems to be 1500' AAL, but why is this

Subject to the previous comments, your operator has chosen to make 1500 ft the SOP operation for a reason which you could establish via a quick question to your flight standards group. Two common drivers are

(a) terrain - the highest runway obstruction consideration is used to dictate the general third segment height. As you are in Oz you may be interested to know that, in the past, CBR 17 was the driver in JT8 days.

(b) with the increased use of a 10 minute thrust limit for operation at takeoff power/thrust, an operator may well elect to use the highest capability to minimise flight standards worries with low level failures etc.

what is the restriction to stop you doing it at a minimum of 400' like a regular take off?

Generally only terrain in the segments. 400 ft presupposes that the terrain is benign.

Keep in mind that the third segment can run for a long distance, especially on twins and, with the fourth segment added in, you can have a LONG distance to the 1500 ft net point. By pushing the third segment higher the overall engineering analysis workload can be cut back significantly.

[Wizofoz]

Plus, 1500' is by no means standard.

We operate A330/340s, 777s and A380s and "Standard" E/O acceleration is 1000'

[noip]

Qf uses 800 ft and for the A380 1500 ft.

The reason given for not using 400 ft was that even though that was the regulatory standard, there were a number of accidents in pre-history related to using this acceleration altitude.

N

[Denti]

Until a couple years ago we used 1500 as standard as well, but it was then changed to 1000ft. However our EFB tells us the minimum altitude and height at each performance calculation as many airports require a somewhat higher value. Thrust reduction (only applicable during AEO T/O) is always 1000ft, independend of take off procedure used. On the 737 all that info is put into the take off reference page 2.

[JammedStab]

737-200 - approx 470 feet.

727-200 - 600 feet

I thought that you could get a higher payload if you used a lower level off height.

Any thoughts, Mr. Tullamarine?

[Sky Wave]

A certain UK loco uses 1000ft on their airbus fleet

[john_tullamarine]

I thought that you could get a higher payload if you used a lower level off height. Any thoughts, Mr. Tullamarine?

Not a simple matter of this or that. As so often is the case .. it depends.

When running an RTOW analysis, one needs

(a) as input data .. runway info, obstacle info, met conditions, airspace limitations, etc

(b) as a number crunching tool .. either the AFM run on the drawing board with a calculator of some sort .. lots of graph paper and cups of coffee (ah, tradition) .. or a computer model which either did, or was associated with the software which, generate(d) the AFM data (sourced from the OEM) or is derived from the AFM graphs (lookup tables or regressions for the more elegant).

One then runs a bunch of separate calculations to look at the various limits (sometimes the AFM will provide all of these explicitly, sometimes some are buried transparently with the AFM .. however, they are all addressed in one way or another. Such calculation sets are done for each OAT/wind point of interest for the end data presentation.

Limitations (which address AEO and OEI) include such interesting things as

(a) maximum structural weight

(b) WAT limits for the configuration and ambients

(c) TORR

(e) TODR

(g) ASDR

(h) obstacle limited weight for EACH significant obstacle

(i) BEL

plus whatever else might be pertinent for a particular Type. In addition, one usually re-runs the exercise for a range of V1/VR values.

Normally, downstream limitations such as cruise, approach and landing weights are done separately for obvious reasons.

Done manually, the output is a bunch of lines on a graph of TOW by OAT with W/V as a parameter for a set of V1/VR. The resulting dog's breakfast provides, for each data point, a minimum TOW which becomes the limit for that data point.

The difficulty in generalising is that the "limiting" limit can vary across the graph.

Done electronically, each data point is finished and the final output deposited into the final output file - just a different approach to ending up with the same numbers.

Manually, the answers come out to, say, the nearer 50-100lb. Electronically, the nearer umpteenth decimal point which, when flight test and other error ranges are considered is still accurate to around the nearer 50-100lb (or somewhat more, for the big birds).

Getting back to the original query, if there are no significant obstacles further out, a lower third segment is fine .. if there are significant obstacles further out then pushing up the second segment pushes up the third segment in turn so that it sits atop the critical obstacle in the third segment or, similarly, the fourth segment will be higher at a given distance for fourth segment obstacles.

Do keep in mind that the third segment which we are comparing to for obstacle clearance is NOT the (gross) acceleration height which the pilot is endeavouring to maintain but, rather, a somewhat lower (net) level.

All a case of horse for courses.

Nothing overly difficult but it does need diligent housekeeping, a tolerance for boredom, and an ability to drink vast quantities of coffee.

Getting back to the very original question .. what is a good third segment height ? .. beats me ... it all depends, you see.

[JammedStab]

O.k....Thanks. But if your limit is second segment climb capability, wouldn't having a lower third segment allow a higher takeoff weight as you don't have to climb to as high an altitude?

[john_tullamarine]

Generally the case.

However, that will be pertinent only for the cases where either second segment WAT (reading your comment precisely) or early second segment obstacle (a bit more generally) is the problem. Both will predispose toward a lower acceleration height to get that last kilo or so.

But you are looking at only two amongst many potentially limiting cases under consideration for any given takeoff .. so, it still depends on this and that.

So far as having a "standard" acceleration height is concerned, it usually comes back to the operator's flight standards views regarding SOP.

[JammedStab]

the upper (maximum) third segment height will be limited by engine time limits for operation at takeoff power/thrust. In some cases there may be other system limits - eg the Dart is limited to a 600 ft third segment for a feathering restriction as I recall from the dim depths of the memory banks.



Hi John,

That statement reminded me of a long forgotten question I had that was never answered. In our performance handout for the HS748, It was said that the chosen level-off height could only be 400-600 feet AAE, even though the net takeoff path general theory stuff talked about 1500 feet.

Any further input from anybody on this feathering restriction on the Dart.

[john_tullamarine]

Scratching now but vaguely recall it was to do with autofeather and the subsequent need to do the manual followup actions within a timeframe to suit whatever system problem/limitation ..

Bound to be a Dart maintenance guru in the sandpit somewhere who can speak to the ins and outs.

[JammedStab]

Scratching now but vaguely recall it was to do with autofeather and the subsequent need to do the manual followup actions within a timeframe to suit whatever system problem/limitation ..



There is a three minute time limitation on the feathering pump which I believe continues to operate after the autofeather sequence until the manual followup actions are complete.

Had no idea that this was the reason for a capped acceleration height, if true.

[john_tullamarine]

ah, now that jogs something in the memory archives ... my guess is that that is the reason. Dart memory as a pilot is back in the 70s .. all a bit grey now

[rudderrudderrat]

Hi John,

Does this refresh some of those memory archives?
dart | fuel consumption | piston valve | 1953 | 0372 | Flight Archive (http://www.flightglobal.com/pdfarchive/view/1953/1953%20-%200372.html)
Ah, I miss the technical courses of the old days.

[john_tullamarine]

Indeed, yes. AN pilot engineering courses were great fun and delved deeply enough yet without getting into the torque values for individual nuts.

But I suspect that the wistful yearnings of we old pharts will have little impact on the beancounters of today.

[Weary]

It's called CBT

You're all excited about getting familiar with you shiny new girlfriend, and instead you get the mental equivalent of a prostate massage.

Similar result, just quicker and cheaper.

[captainbirdseye]

Hi , interesting posts, I have a related question, can anyone point me in the direction of some reading material that explains how it is / is not possible to have a single engine acceleration altitude higher than the the 2 engine thrust reduction and acceleration alt. Related to A320 in my case if that makes any difference.
If would seem to me common sense that it is Not possible. Ie if you have reduced thrust at say 1200 ft with two engines and started to accelerate then 1 donk goes bang , you are now accelerating below your Single engine acceleration alt of say 2000ft. (2000 ft presumably having been worked out with regard to obstacle clearance?).
However I have been having conversations with people who seem far knowledgable than me saying this is not the case.

Help gladly accepted.

Thanks

[rudderrudderrat]

Hi captainbirdseye,

Since you've enjoyed the benefit of all engines performance up to Thrust reduction, if you suffered an engine failure after commencing your acceleration, then your performance should be OK (cheat and look out of the window).

However - if I was IMC, then I'd set TOGA (to get SRS) and delay acceleration until at EO AA.

FCTM, Normal Ops, 020- Pre start, Cockpit Prep.

"The thrust reduction altitude/acceleration altitude (THR RED /ACC) are set to default at ​1,500 ft, or at a value defined by airline policy. The THR RED/ACC may be changed in the PERF TAKE-OFF page, if required. The flight crew should consider the applicable noise abatement procedure.

The one-engine-out acceleration altitude must:
-
Be at least ​400 ft above airport altitude
-
Ensure that the net flight path is ​35 ft above obstacles
-
Ensure that the maximum time for takeoff thrust is not exceeded.

Therefore, there are generally a minimum and a maximum one engine out acceleration altitude values. The minimum value satisfies the first two criteria. The maximum value satisfies the last one. Any value between those two may be retained.

The one engine out acceleration altitude is usually defaulted to ​1,500 ft AGL and will be updated as required."