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Performance chart

• Posts: 105

MissSoph created the topic: Performance chart

So here is another....
the take off performance charts indicate the aircraft climb limitation is greater than the take off limitation and en route limitation.. in this case, the actual maximum take off weight is that limited by.... the area beyond the TODA... ummm the area beyond the TODA?
So I’m understanding the question to be that when I’ve done the TO weight chart... my climb weight limit I’m only allowed to have a certain amount of weight, so the take off weight can’t be more than my climb weight...all good....
Ohhh noooo... I’m in the middle of typing and I think I got it.... so I can take off... but because it’s a bit heavy to climb out.... I have to make sure that my airport is not smack bang in the middle of a city, with obstacles I could run into after take off? Hence it saying the area beyond the TODA... as that TODA counts for me to get the plane to 50 ft... still have to be clear to keep on goin...
Let me know if I have this skew wiff...

• John.Heddles
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• ATPL/consulting aero engineer
• Posts: 523

John.Heddles replied the topic: Performance chart

What a rather silly round about question.

The take off performance charts indicate the aircraft climb limitation is greater than the take off limitation and en route limitation.

The buzz word phrase is we are "WAT limited" (maximum weight limited by altitude and temperature). Between friends we might just say that we are "climb gradient limited".

the actual maximum take off weight is that limited by.... the area beyond the TODA

That suggests whoever wrote the question doesn't really understand what is what. A WAT limit is an out of ground effect, still air climb requirement which puts a line in the sand, no more, no less. What it says is that, for the aerodrome pressure height and OAT (ie we really are talking about density height), there is a minimum Design Standard climb gradient required to ensure that we have a specified minimum ability to go up, rather than the other way.

the area beyond the TODA not quite, it is the aerodrome density height which counts but let's just shake our heads at the question's not quite appropriate detail, here.

So I’m understanding the question to be that when I’ve done the TO weight chart... my climb weight limit I’m only allowed to have a certain amount of weight, so the take off weight can’t be more than my climb weight...all good....

Spot on !

I have to make sure that my airport is not smack bang in the middle of a city, with obstacles I could run into after take off?

Different requirement altogether. WAT limits are not concerned with obstacles at all. They are independent of obstacles, terrain, UFOs and all the rest and just look at establishing a weight at which the minimum WAT climb gradient can be met.

Does that help ... or hinder the comprehension ?

Engineering specialist in aircraft performance and weight control.

• Posts: 105

MissSoph replied the topic: Performance chart

Thanks john... I think I get it.. might just write that one off...

• John.Heddles
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• ATPL/consulting aero engineer
• Posts: 523

John.Heddles replied the topic: Performance chart

The study stuff at PPL/CPL doesn't go into this sort of material to any extent and some courses not at all. The only requirement of note is the old 6% AEO takeoff climb requirement which was established to give you a bit of a margin for normal operations when you look at basic runway obstacle clear gradients.

If you go on to ATPL, you will get a little exposure to it. Even then, if you were to line up 1000 airline pilots, most of them would be struggling to explain the niceties of performance requirements. Unless those good folks have to do their own AFM sums, they just rely on their inhouse or contracted performance services to tell them what weight they can launch from a given runway in given ambient conditions.

(Even some of the ops engineers have strange ideas at times).

Engineering specialist in aircraft performance and weight control.