For Performance Engineers

[Dumb Canuck]

A question concerning aircraft performance data/charts etc.
In the given examples in the Aircraft Flight Manual or P.O.H., what level of skill is required by the pilot to acheive these values?

Are these numbers test pilot certification values, and unattainable to most of us?

Or are these results based upon some average pilot technique?

Is there any factor built into the charts to consider you never fly a brand new, perfectly straight a/c?

Finally, are these methods of determining performance charts consistent from say a boeing 777 to a cessna 172?

Your insight is always valued and appreciated.

[mutt]

Performance figures are usually based on a demonstration of skills by both the manufacturers test-pilots and the regulatory authorities pilots. They then build in fudge factors such as the time allowed to react to a V1 cut. The resulting values should be achievable by any well trained airman.

As for the perfectly new aircraft, performance data is factored for inservice aircraft with specific fuel and drag biases. They have also made some changes in the regulations concerning takeoff calculations, such as changing the certification testing to be based on worn brakes, rather than new brakes.

Now if you really want to make this topic interesting, just ask about how they calculate the effect of crosswinds or contaminated runways during takeoff...................... :):) (It might wake J_T up......)

Mutt. http://www.stopstart.fsnet.co.uk/smilie/guin.gif

[Flying_Tuur]

More factors:
* Headwinds are only taken onto account for 50%, tailwinds for 150%
* For dry runways, no Thrust Reverser is used for aborting Take-off during certification
* Normal landing figures on dry runways are 166% of the test pilots results, on wet runways I think it is 115%

* Be aware though... Non-Normal landing figures are the ACTUAL numbers without any safety factors... So it wouldn't be very wise to land on a runway which is JUST long enough according to the books when you are coming in with only half the flaps you would normally have..


These figures were floating around in my head, so I stand to be corrected...

FT

[quid]

"Landing Field Length" is 1.67 X landing distance. So for flight ops, you have a 40% buffer to use for any reason. As an example, if the LFL is 10,000', then the a/c should come to a stop at 6000.

It's been said, as a general rule, that if you have LFL available, that there is no ONE factor that will cause you to exceed it. Zero flap, anti skid inop, manual or no spoilers, etc. Now, if you have zero flaps, anti skid inop on an icy runway,.....it just ain't your day. :)

A side note: In the US, the FAR that governs LFL is a "takeoff" requirement. FAR 121.195 states, "No person may TAKEOFF an airplane at such a weight", etc. There is no FAR that requires any specific runway length be available for landing.

[john_tullamarine]

Hi, Mutt .. been up to my armpits in alligators at work over the past few weeks .. hence my lack of wading into the fray ..

Anyone who believes the AFM data without applying the odd grain of salt eventually will be surprised. The battle is between the pilot who wants to be conservative and the accountant who wants to be profitable .. a sensible compromise is somewhere in the middle and ought to vary from sortie to sortie according to the actual, real world conditions.

[747FOCAL]

Dumb Canuck,

Who says new airplanes are straight? :E