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ATPL performance/loading

Old 29th Aug 2011, 06:20
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ATPL performance/loading

Quick question regarding the APLA exam.

AFT/Rob Avery seem to differ in their interpretation of the CAO's in regards to takeoff/landing performance charts. Ive read the CAO's but still a few things are a little confusing.

1. just to confirm- an EOL derivation for a takeoff chart will come from the shortest distance of ASDA, TODA or STODA (if shorter and < or = 1.9% gradient). Avery/AFT say in nil wind choose the longest runway for landing/takeoff (but the shortest LDA and or EOL?)

2. Wind is disregarded in taf calculations (forecast conditions), in AFT slope is disregarded too for both takeoff/landing charts, Avery provides a worst case scenario case for takeoff/landing where he corrects even TAF forecast conditions for a landing downslope or for a takeoff downslope- could anyone confirm either way?

3. if I am given a trip fuel which results in an exceedance of BRW/taxi out weight as Avery's text seems to allude to the possibility of in the exam (on the 727 load/trim sheet)- whats the best procedure to resolve a situation like this- given we cant reduce a given trip fuel load but could reduce the BRW (which would mean the only option is a payload reduction!)??

Cheers!
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Old 29th Aug 2011, 08:25
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an EOL derivation for a takeoff chart

Where do you get the EOL term from ? Superseded term replaced by STODA a long time ago.

What one uses as entry data will depend on the presentation for the particular Type.

Wind is disregarded in taf calculations (forecast conditions), in AFT slope is disregarded too

Disregarding headwind for planning is useful as a wind change might leave you embarrassed .. but it has to be accounted when you get to the cockpit. Slope is required to be considered and there is no reason not to - it isn't going to change during flight planning.

exceedance of BRW/taxi out weight

Limitation the same as any other. If the calcs indicate you are going to exceed it, reduce the weight .. either fuel or payload.

given we cant reduce a given trip fuel load

You might have some pad in the fuel reserves .. it may be feasible to cut back towards minimum reserves.

the only option is a payload reduction

If that's all you have to play with .. throw off some freight or pax bags for the next flight
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Old 29th Aug 2011, 10:29
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Forgive me because indie the exam a while ago. From what I recall EOL stands for Effective Operational Length. You are correct in saying for a takeoff chart calculation you would use the least of the three since this is worst case.

Forecast wind conditions are disregarded for take off calcs, in saying that I think if you have the "ambient" conditions you can use it in your calcs. Remeber ambient conditions means the prevailing temp, pressure and wind conditions in the 15mins prior to takeoff.

For the last one, if you exceed ramp weight, ie. The absolute max weight before taxi out to the runway, the aircraft cannot be moved PERIOD. If your trip fuel ends up exceeding your BRW it means that the ZFW must be reduced to allow for the extra fuel. Remember if the trip fuel exceeds 25850kg payload will need to be reduced so as not to exceed MBRW.

Hope this helps


Rocket
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Old 29th Aug 2011, 23:31
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Rocket/JT,

yeah thanks for that.

Rocket- going off that then slope IS adjusted for in forecast or ambient conditions- although avery only adjusts for the worst case scenario...

With the payload/load and trim sheet 727 one- if trip fuel with reserves exceeded the BRW and you had to get rid of payload- hard deciding what to get rid of? This concept doesnt seem to be well explored in either text- rather just reducing the BRW to max and then finding the resulting fuel reduction from that..

However..

if given the trip fuel though for a return flight as fuel is expensive in the destination (as Avery refers) you can't reduce it or you would obviously run out of fuel! would you apply a VR on the whole amount + FR + taxi/shutdown fuel... Given tripfuel means just flight fuel + maneouvering it seems illogical to have it as the return fuel and not subdivided in order to work out a VR?
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Old 30th Sep 2015, 08:01
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Question re Climb Segments specifically segment one.

Where does it begin at VLOF or 35ft

Regs 20.7.1B mentions nothing about 35ft only the speed it becomes airborne.

However in my training notes Avery and AFT it says segment one from 35ft to gear retraction.

In a practice exam by ground effect aviation they have it as from lift off to gear retraction.

Confused
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Old 30th Sep 2015, 08:51
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Jay, for transport category airplanes the certification requirements have the first segment beginning at lift off and ending at 35ft.

Check out the first paragraph (a) in the above link. (b) and (c) outline second segment and final segment requirements respectively.

In the first segment:
- T/off flap
- gear down
- positive climb gradient
- accelerate to V2 speed at max power
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Old 1st Oct 2015, 10:38
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Question re Climb Segments specifically segment one. Where does it begin at VLOF or 35ft....

for transport category airplanes the certification requirements have the first segment beginning at lift off and ending at 35ft.


A few points for note ...

(a) first segment, if it exists, commences at the end of the TOD, ie 35 ft, and continues until the gear retraction sequence is completed.

(b) first segment may, or may not, exist.

This will depend on the AFM-nominated point to initiate retraction, the retraction sequence time delay, and aircraft performance for the weight/configuration and speed sked in the extant ambients.

Generally, if a particular Type/Model demonstrates a first segment it will be seen for lower level aerodromes, lower OATs and lower GWs .. ie when the bird is able to get up and go outpacing the gear retraction sequence.

Some machines have a first segment as a matter of routine .. AW650 comes to mind .. but, then, I guess the Argosy is a bird of a somewhat different feather .. years ago, when looking after a well-known Australian yellow fleet of such beasties, I noted that the RTOWs often were limited by first segment vs runway slope considerations ...

(c) with due respect to the good folks at Cornell, I suggest a read of the full section of the FARs direct from the horse's mouth at www.faa.gov might be a tad more useful to the understanding ...
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Old 1st Oct 2015, 16:49
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Hi John,

Thanks for your input. You are right, according to the FARs the end of the first segment more correctly should be "when the landing gear is fully retracted." I was quoting from a John Lowery text which states the end to be at 35ft. Maybe some confusion with FAR 14 CFR 25.111 (b) (2) which mentions the requirement that acceleration to V2 must be completed by 35ft. http://www.ecfr.gov/cgi-bin/text-idx..._1111&rgn=div8 With all due respect, both the Lowery text and FAR 14 CFR 25.121 state quite clearly that the commencement of the first segment is at the end of the take off roll, VLOF (lift off) however. This opposed to the term 'take off flight path' that refers to a start at 35ft!

The Cornell reference is a copy of the FARs. Cross-references are hyperlinked unlike the FAA site so it is a bit more user friendly but same content I believe.

Here is the FAA reference for 14 CFR 25.121:
eCFR ? Code of Federal Regulations

Last edited by Captain Nomad; 1st Oct 2015 at 17:02.
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Old 2nd Oct 2015, 12:07
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I was quoting from a ... text which states the end to be at 35ft.

Again one sees things changing over the years .. as I recall, SR-422 had a V2 requirement which changed to VLOF at SR-422A. Strictly, it probably is correct to refer to the first segment's starting at liftoff. However, for the operations engineer producing RTOW data, this is not helpful.

More particularly, that definition you cite fails to accommodate a slow gear retraction sequence ..

Maybe some confusion with FAR 14 CFR 25.111 (b) (2) which mentions the requirement that acceleration to V2 must be completed by 35ft.

At the end of the day there are numerous, and often subtle, differences between what the operations folk say compared to the AFM ... doesn't matter all that much, I guess, providing crews observe the AFM requirements which form the basis for passing certification information to the line folks.

For the preparation of RTOW data, it makes little sense to consider the takeoff flare twice. We are more specifically concerned when the gear retraction sequence extends beyond screen and we have, in effect, that little segment betwixt screen and commencement of the second segment to consider and address .. we can't just ignore it ... Where gear retraction is completed not later than the end of the TOD, it is a moot point and of little interest to the operations engineer and line pilot.

I note that acceleration to V2 must be completed by 35ft isn't the same as gear retraction must be completed by 35ft ..

Certainly concur that the words could be better expressed in the FAR ..

FAR 14 CFR 25.121 state quite clearly that the commencement of the first segment is at the end of the take off roll, VLOF (lift off) however. This opposed to the term 'take off flight path' that refers to a start at 35ft!

Interesting point. Can you actually cite the specific FAR references to "segments" ? I note that AC 25-7C follows the VLOF picture.

The Cornell reference is a copy of the FARs. Cross-references are hyperlinked unlike the FAA site so it is a bit more user friendly but same content I believe.

Very likely. However, one prefers to reference the legal version where feasible ..
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Old 3rd Oct 2015, 12:53
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Hi John,

You make worthy points. You certainly would have seen a lot of the changes over the years also. In the end I may be splitting some hairs really!

Can you actually cite the specific FAR references to "segments" ?
I guess the best I can come up with at the moment is eCFR ? Code of Federal Regulations
25.111 (d):
(d) The takeoff path must be determined by a continuous demonstrated takeoff or by synthesis from segments. If the takeoff path is determined by the segmental method—

(1) The segments must be clearly defined and must be related to the distinct changes in the configuration, power or thrust, and speed;

(2) The weight of the airplane, the configuration, and the power or thrust must be constant throughout each segment and must correspond to the most critical condition prevailing in the segment;

(3) The flight path must be based on the airplane's performance without ground effect; and

(4) The takeoff path data must be checked by continuous demonstrated takeoffs up to the point at which the airplane is out of ground effect and its speed is stabilized, to ensure that the path is conservative relative to the continous path.

The airplane is considered to be out of the ground effect when it reaches a height equal to its wing span.
(my bolding)

From that I would come back to eCFR ? Code of Federal Regulations
25.121 (a) (b) and (c) which, seem to succinctly refer to aspects directly associated with segment one two and three. This also seems to correspond with the info and description on page 70 of AC 25-7C http://www.faa.gov/documentLibrary/m...2025-7C%20.pdf

In essence I'm agreeing with you. You also make good points regarding gear retraction and AFM requirements.
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Old 4th Oct 2015, 11:47
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Indeed .. the point I was endeavouring to make was that the FARs (as far as I am aware) don't actually define the segments in terms of first, etc. and this leads to considerable confusion.

As always the relevant AC needs to be consulted to find out what the FAA thinks the reg means.

Main point is, the AC interpretation isn't of much use in the practical line world .. RTOW-wise, if we talk about being "first segment limited" we are talking about the old definition .. ie the final gear retraction sequence beyond the end of the TOD.

I guess I will just have to use a few more words to clarify my thoughts when posting on the subject in future ?

Being an olde phart, though, I will prefer to think of the first segment in terms of the bit past the TOD .. where it exists on the day .. while acknowledging the differences discussed here ..
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Old 5th Oct 2015, 13:30
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Question re Climb Segments specifically segment one.

Where does it begin at VLOF or 35ft
Jay Bo,

Segment 1 begins at 35' ("screen height" for a dry runway). Everything before this is considered to be the takeoff run. Yes, there is something that begins when the wheels leave the pavement, but that is not called "first segment". See below.

It would probably help you to look at some performance tables from the AFM for an aircraft >5700 Kg MTOW. The takeoff tables give figures for at least 3 distinct stages:

1. The takeoff;
2. The first segment;
3. The second segment.

For the takeoff stage, you will see distances published. These distances are the horizontal distance from brakes release to screen height (a point also known as "reference zero"). This point is at 35' for a dry runway, and 15' for wet.

The first and second segment tables give the horizontal distance that will be consumed during those stages, and also the height that will be gained (and the gross gradient).

The preamble to these tables defines precisely where the segments start and end. Logically, the first segment has to commence at the point where the takeoff ceases ("reference zero"), and if you peruse the preamble to these tables, you find that the first segment has indeed been thus defined.

But, this is how the manufacturer is presenting the performance and it may not be precisely aligned with how regulatory authorities (e.g. CASA) stipulate required performance. Indeed, and as you have seen, CASA don't refer to the takeoff in terms of segments.

Regs 20.7.1B mentions nothing about 35ft only the speed it becomes airborne.
This is paragraph 7.1 of CAO 20.7.1B. This paragraph is referring specifically to the stage that ends when the gear is retracted. They don't use the term "first segment", but they are referring to the same performance requirement (which, for twin engine aeroplanes is a gradient of climb that is merely positive).

You would note that this CASA requirement applies from when the wheels leave the runway through to when the gear is fully retracted, which, in terms of the commencement point, is different to the "first segment" as defined by the manufacturers.

This difference is not relevant. Perhaps you could tell me why it is not relevant. That would make for an excellent exercise that would force you to acquire considerable understanding of takeoff performance theory!

However in my training notes Avery and AFT it says segment one from 35ft to gear retraction.

In a practice exam by ground effect aviation they have it as from lift off to gear retraction.
The difference depends on the context. If the context is CAO 20.7.1B, then the latter is the more relevant. If the context is not about CAO 20.7.1B, but is more about takeoff theory in general, then the former would be the more relevant.

One very important thing to keep in mind about segments. This should help prevent them becoming confusing:

They only apply with one engine inoperative. With all engines operating, they are not applicable.

Here is something else that is useful to keep in mind. The Vr speed is chosen by the manufacturer so that the aeroplane will achieve V2 speed at precisely the screen height, when one engine is inoperative. The manufacturer chooses all those V1, Vr and V2 speeds. For a takeoff with given conditions, he establishes V1 and V2 speeds first, then Vr last.
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