Performance Limit Weight

[767pilot22]

What does performance limit weight mean exactly, I cannot takeoff at all or I cannot takeoff with derated thrust. I understand I cannot takeoff above max weight but I wanted to t/o at exactly max takeoff weight, got the numbers from topcat, and it said performance takeoff limit exceeded. So in this case would I use Full thrust or is it a no go.

thanx

[buschpilot]

Hi 767pilot22,

first you must know we differentiate two kinds of masses. first one is the structural limited mass and the second is the performance limited.
the only rule to agree with safety is: use the highest of the lowest limiting mass!

Structural limits are the aircraft itself. It includes the max bending moments on the wing roots (Maximum Structural Takeoff Mass), the max weight the gear could handle with during taxi(Maximum Ramp Mass) or at touchdown (Maximum Structural Landing Mass). Ok some other factors effects that too, but in basics its enough.

So, and now the performance limits.
These limits are the environment in which the aircraft like to take off, cruise or land. Limiting factors are temp, density, humidity, obstacles or the unway length.

Both parts limits your actual maximum operating masses. And you should always use the lowest one of both, or better never exceed the limiting masses, what ever it would be.
 
e.g.:
1. In a cold sunny day with high pressure and long runway in an flat area without obstacles, you are not performance limited but structural limited.
2. But on airports like Quito or Bogota you are performance limited due to the high elevations and higher temps than normal result in less air density, which decreases the overall aircraft performance. Additionally in Quito you are surrounded by high mountains, and in case of an engine failure you must be able to clear of of this area^^

i hope i could help and sorry for late answer