Q for a performance expert

[dragon]

Heh Loon,

I am not getting the part of the discussion about wavering on the rails or directions, for me it has been an excellent discussion, your contribution included, thank you.

Only 8 years of Transport Category A/C but all with AC so take that for what it’s worth – sometimes we want to reinvent the wheel over here for some strange reason or combination of reasons. Too many smart guys trying to outsmart each other perhaps?.. Anyway,

Interesting to hear about how others operate. I am surprised to hear of your different experiences, though this seems a very sensible and thorough way to operate. As I mentioned, I only know the AC way.

As I mentioned now a few times, I am on a mission to a better understanding of these issues.

Thanks again

dragon

[Mitch Cronin]

I reckon it's the guys who aren't afraid to ask questions that end up with a good understanding of whateveritis.

I remember an instructor blowing "BRT" by the whole class long ago, before some ugly bugger with a beard piped up with "Ahhh, 'scuse me, but what's a BRT?"... (feeling really stupid, little knowing that not a soul in the class understood that particular acronym)

"I was wondering who'd ask" sez the instructor.... "it's the Big Round Thing slung under the wing"

If ya don't ask, sometimes ya just don't learn.

Cheers,

Mitch

[B75/76]

Thank you for getting me thinking. If yiu can get hold of the Boeing Performance CBT CD that is around, it covers much of this topic.

Good luck on your quest for more knowledge.

[Moon The Loon]

That is an EXCELLENT training CD. There are lots of them around.

One of the best sections is in the discussion of runway analysis charts.

[Moon The Loon]

...Again!

Thanks, Dragon for asking the questions!

[Vsplat]

I'm glad it helped. You're certainly welcome to ask as needed.

It may sound bizarre, but this is a very simple subject that has been made complex by a simple lack of information. Most airlines seem to guard this stuff as if it were a trade secret - as a result, line pilots often get their performance briefings with partial facts or out of context information that works for an engineer but doesn't correlate with what the pilot has as reference.

Do I instruct? Well, facilitate is more the term in my case and yes, my company faciliates performance systems worldwide. Our best clients are regulators, who themselves are challenged to keep this (and many other subjects) straight as they undergo huge turnover. We provide detailed analyses for special purpose operations, however we don't try to duplicate the Jeppesen or Nav Tech services. Different segment.

From the Netherlands to DC to Ottawa, the problem is the same. Basic terminology gets used different ways, and that seems to undermine the whole discussion. How many times have you seen V1 turn into a circular argument?

All that said, thank you for starting the discussion. For every one that asks, a hundred are wondering the same thing. Good on you.

Cheers

Vs

[Vsplat]

I should have included this in my earlier post. My apologies if this looks like I'm hammering.

NTFP segment construction differs from the approach you note. The regulation drives the reduction to a resolution of each point, and there is a reason. At and above 400', the operator retains the option of swapping acceleration for vertical climb. Indeed there are literally hundreds of variations regarding how the segments join up.

In general, the process either starts with the obstacle and works backward to Net, or has an iteration where this occurs. Operationally, gross flight path normally comes into play only when determining the acceleration height, and then only when it is driven up by an obstacle (i.e. back-driven by Net). Not all of the time, just an example.

Since the acceleration and clean up (normally third) segment is of widely varying length, there is no solution wherein you simply add up all of the segments and apply a reduction. I have, however heard this argument before, and it was made by a TC inspector (who has since been de-briefed), so maybe that's where your info came from. We asked that the correction be issued to those affected, however I'm not sure that occurred.

On balance, there are some manufacturers who provide consolidated NTFP data through to 1500' as a single gradient. In these cases, each of the individual degradations have been applied and a line drawn through the most limiting point. The flight path above that gradient line is not displayed.

I hope this provides some clarity to the subject.

Vs

[Moon The Loon]

It does and it explains how different analysis producers apply a different philosophy to production of their numbers.

Not an easy subject. Hornet's nest comes to mind!

Bottom line - on the flight deck we have to rely and trust upon documentation that enables us to do our jobs quickly and safely. Many are taught to follow analyses without really knowing where they come from. That's fine on the surface but when it comes time to dispatching without them in a terrain filled environment, the problem of obstacle clearance seldom gets looked at. That is something we cannot do in the flight deck without a lot more external data available usually only to chart producers and flight operations libraries.

No hammering - just healthy discussion!

[Guest neo]

Thanks, dragon. We're on a knife edge out here, but so far hanging in there.

neo

[Guest Gino Under]

*I'M CERTAINLY NOT AN EXPERT* but...

In researching your question, which was of considerable interest and benefit to myself, I found that the landing phase of performance assessment concerns that portion of the flight starting at 1,500 ft above the aerodrome's landing surface, and ending when the airplane has come to a stop on the runway.

Airworthiness and Operations Requirements

Airworthiness is concerned mainly with structural limits and, to some extent, the scheduling of landing distances and climb gradients associated with the WAT limit. The operational limitations are concerned mainly with the variables to be considered in determining landing distance, landing climb, or WAT limit.

Airworthiness requirements

The main aspect of these requirements is the Maximum Authorized Landing Weight (MALW), being a C of A limit, and also the absolute maximum landing weight (emergencies excepted) given in the AFM. Other C of A requirements are involved when determining the landing distance required (means of retardation such as brakes, lift spoilers, and reverse thrust). On occasions, the MALW may be restricted to a lesser weight - the maximum permitted landing weight - by the application of operational requirements. It should be also understood that the maximum permitted, or maximum authorized landing weight could determine the maximum permitted take-off weight, depending on the sector distance to be flown and the fuel required.

*Of course, compliance with airworthiness limitations is mandatory.*

Landing Climb or WAT Limit:

the landing weight of the airplane will not exceed the maximum landing weight specified for the altitude and expected air temperature for the estimated time of landing at the aerodrome at which it is intended to land and at any alternate aerodrome (the WAT limit).

The landing WAT graph or curve ensures that, at a given weight, the airplane will have an acceptable minimum climb capability, with all engines operating and with one engine inoperative.

Minimum climb gradients

The weight given by the landing WAT curve must not be:

i) greater than the weight given by the take-off WAT curve for the same pressure altitude and temperature, and

ii) greater than the weight at which compliance with the following climb gradients is possible:

a) Final enroute climb.

With one engine inoperative, at 1500 ft above the aerodrome. The NET gradient of climb shall be positive.

Baulked landing climb.

With all engines operating, at the aerodrome pressure altitude and in the landing configuration, the GROSS gradient of climb shall not be less than 3.2%,

c) Discontinued (Go-around) approach climb.

With the critical engine inoperative and the remaining operative engine(s) at take-off power, and at the aerodrome pressure altitude with the landing gear up, the GROSS gradient of climb shall not be less than:

Twin-engined airplanes: 2.1%

Three-engined airplanes: 2.4%

Four-engined airplanes: 2.7%

Limiting Landing Weights

As with take-off (where distances available and required were matched to obtain field length limited take-off weight), for landing, the distances required and available are matched to provide a field length limited landing weight.

In order to obtain a maximum landing weight for one runway, two calculations are required: one for still air, and one for forecast wind component. Thus, for a multi-runway aerodrome two calculations per runway will be required, with the most limiting landing weight taken to be the maximum landing weight for that aerodrome. The Regulation can be interpreted, in terms of landing weight, as: the field length limited landing weight shall be the LOWER of

(i) the highest weight obtainable in still air

(ii) the highest weight obtainable , using the forecast wind component

Both may refer to different runways.

Therefore, when considering an aerodrome with one runway, the limiting landing weight for both field length and aerodrome becomes that for still air, unless the runway is used in one direction only, with a tailwind component.

Considering an aerodrome with more than one runway, and remembering to compare 'like with like', the limiting weight for the aerodrome becomes the lower of:

i) the highest weight of the two runways, using still air conditions

ii) the highest weight of the two runways, using the forecast wind component.

When determining the maximum landing weight at the flight planning stage, it should be remembered, that, in addition to considering the wind component, the other variables to be used include: aerodrome pressure altitude; ISA temperature at that altitude; runway slope; and, of course, the landing distance available.

( Hopefully, this helps a little.

Gino

[Moon The Loon]

Sorry for the long delay Vsplat - you are entirely correct. Time for me to get back into the books. I don't know where I got the 80% figure - probably a misread of the 0.8 reference.

I think I'm pretty solid on the other stuff though!