Re: Performance drop on B772ER ?

Date:         21 Sep 98 00:31:44 
Organization: Deja News - The Leader in Internet Discussion
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I offer the following to stimulate further discussion...

B777 engines are well instrumented so measuring engine performance accurately
should not be a problem.

If an aircraft is losing performance then I would assume that calculating the
aiframe performance loss is simply total deterioration less engine

Perhaps the following could account for airframe performance loss:
1. Control Surfaces not correctly located
2. Undercarriage doors not flush
3. Increased Operating Empty Weight
4. Instrumentation Errors
5. Operating Procedures
6. Baseline Data

Items 1 & 2 - On a long haul flight any small into-wind step could have a
substantial effect. Item 3 - Aircraft get heavier with time, modifications
generally add weight, aircraft get dirty, airlines carry more cabin items.
When was the aircraft last weighed? Item 4. - The longer the mission the more
accurate the data, but similarly if the instrumentation is in error or the
various transducers are drifting with time then any small error could be
magnified. Item 5. - Full power take-offs versus derated take-off's? Could a
change of airline policy influence the overall data? Similarly if the APU is
started earlier in flight then the increased drag from the APU door would
probably have a major influence. Item 6 - Presumably Boeing produces a
"model" aircraft to which all other aircraft are compared against in terms of
airfcraft performance. How much actual data do Boeing ontain on long range
flights and how much do they have to assume from the flight data?

Any real performance engineers out there?