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Bubi352
1st Dec 2009, 19:15
I would like to clarify something. What is the net takeoff distance? Is this the gross distance corrected for different variables (wind, temperature, pressure,...)? Does it account for the regulatory safety factor (1.33,...)? Thank you in advance.

Spooky 2
1st Dec 2009, 20:12
I have not seen the term Net Takeoff Distance used in any of the manuals I'm familiar with here in the US.

The FAR's define takeoff fild length as the longest of these three distances:


Engine-Out accelerate-go distance
Accerate-stop distance
The all-engine go distance which is 115% of the distance required to:
Acccelerate with all engines operating
Lift-off
Reach a point 35 feet above the runway surface at the all engine climb out speed. Don't think I answered your question but that's the way the FAA looks
at this subject.

Bubi352
1st Dec 2009, 20:37
I saw there is a gross takeoff distance so there must be a net takeoff distance.
My understanding is a gross takeoff distance is the distance from a new airplane with a new engine under ideal conditions with an experienced pilot using proper technique. We can obviously make corrections for less than ideal conditions using safety factors. I would assume this is the net takeoff distance.

But my question is, does the net takeoff distance include the regulatory safety factor (1.33 or 1.15,... whatever it is for the type of operation) or is it just the gross takeoff distance corrected for less than ideal conditions (wind, temp,...)?

Spooky 2
1st Dec 2009, 20:58
Sorry, wish I could be of more help. I'm familair with gross alt and net alt but not any of the terms you are looking at. Later this week I will be with some Boeing performance engineers. I will pose your question to them and back to you. Maybe we can both learn a thing or two. BTW, what kind of aircraft are dealing with?

Bubi352
1st Dec 2009, 21:26
Thanks. I read a CAA document that talked about gross takeoff performance - it referred to takeoff distance (not takeoff flight path). I can't find that document anymore. It was not aimed at a particular aircraft.

I am writing now a paper about takeoff performance and I just want to make sure I am using the proper terminology.

FE Hoppy
1st Dec 2009, 21:32
Net take off flight path, yes. Net take off distance, never heard of but I'm EU ops not FAR.

john_tullamarine
1st Dec 2009, 22:26
Not a term I've seen used.

However, the probable intent is to distinguish between the distance to a given height using gross gradient and that using net gradient capabilities. The delta at 1500 ft can be quite a significant distance and is one reason why we are more concerned, as it were, about close in obstacles (where the delta hasn't had time to have much effect) and fourth segment concerns.

DFC
2nd Dec 2009, 10:57
I think that you may have come across the term when the UK CAA talks about performance of private GA aircraft eg C172 PA28 etc i.e. aircraft with limited performance info;

This could be the document you had seen previously;

http://www.caa.co.uk/docs/33/ga_srg_09webSSL07.pdf

Bubi352
2nd Dec 2009, 13:03
Thanks. Yes, that's the document I was referring to. I see the CAA use the terms "net takeoff performance" on the second page, first column.

john_tullamarine
2nd Dec 2009, 21:44
The UK document is a typical educational sheet intended for (perhaps the newer) GA flightcrew.

It is unfortunate that the terminology used, and writing style, is a tad imprecise and, as a result, readily confused.

I can't find a reference to "net distance" .. perhaps the original poster inferred that from a misreading of the document ?

kijangnim
2nd Dec 2009, 21:48
Greetings
Or is it to cater Distance lost during aircraft alignment on the Runway (1/3 of the Aircraft length) :confused:

DFC
3rd Dec 2009, 10:43
If one refers to EU-OPS, Performance B one can see that the unfactored figures from the flight manual / POH have to be factored when calculating take-off distance etc.

The UK CAA has used net to describe the unfactored distances from the flight manual.

I agree that the wording is poor and also it is out of date when dealing with EU-OPS in light twins etc (Performance B). However, the intention of geting the average PPL to ad some safety factors to the unfactored distances in the Flight Manual / POH is good.

However, there are problems with PPLs who are on the CPL course who have to use different factors from what they used in the very same aircraft during the PPL course.