George Yogi
8th May 2014, 23:21
Performance of a commercial airline jet is graded by the MTOW it can carry from a runway and its shorter take off distance , Why don't airliners grade performance with respect to fuel economy too ? , Is it because fuel cannot be saved in a long distant air route due to possible contingency and high speed ops ?
Not really.
Performance is more about safety, can the aircraft perform in these conditions if the worst would happen, ie an engine failure or fire. So the accelerate stop distance needs to be safe, the after take off climb performance, the go around climb performance, and the landing distance all need to be considered with one engine to be safe.
The economy is certainly considered, but this will be by the "bean counters" who will then write the company procedures for how the aircraft will be operated. For example in my company our policy is to set a specific temperature on the engine and leave it be, as this prolongs engine life and fuel burn is less of a concern to them than engine life. In other companies it may be to always fly at the best range speed. Pilots do learn all these things, but it's down to the operator how they want their aircraft to be operated, where as the performance is more of a legal/design thing to ensure the aircraft is actually safe.