Sir - As is evident from the article "DC-8 training faulted" (Flight International, 23-29 July, P15), it took an accident [that of an Airborne Express McDonnell Douglas DC-8 in December 1996 in Virginia] to get the aviation community to notice an area about which simulator engineers have been crying for years. That is off-design performance.

Post-stall characteristics are not the only example. Other cases which come to mind include accelerated stall, contaminated runway, blown-tyre performance, engine performance under disturbed flow conditions (aircraft stall), engine stall and engine and airframe performance under icing conditions.

Typically, a data package is supplied specifying only the design performance. Off-design performance is not addressed and is left to the simulation engineer's imagination.

Line pilots and even instructors are unaware of this, and assume the simulator to be a faithful and seamless reproduction of the entire performance spectrum of the aircraft.

The results are self-evident. Any measure taken as a result of this accident should address the area of off-design performance as a whole if it is to be effective.

Alexander Maroudis

Athens, Greece

Source: Flight International