Slasher,
I would need to play with the specific sets of QRH data and the relevant AFM data to form a view.
If you can see a difference between earlier and present QRH data which, on the surface, you would have expected to be the same, then there is likely to be a difference in the calculation basis for the data.
I would be extremely cautious using the QRH unfactored landing data .. not because they are suspect at all (I am sure that they can be tracked back to the same sorts of numbers in the AFM) .. but that they are based on particular assumptions and represent distances (for those assumed conditions) which may be extremely difficult to reproduce in line operations.
The line pilot who uses the QRH data for in-flight decision making without considering the normal fudge factors is a brave man .... I far prefer to view such data as representing an in-flight planning absolute minimum for emergency situations. I would not be at all comfortable to view such data as representing the performance which might be "expected" on the occasion.
The certification data is the definitive set of numbers and, for the most "accurate" data, one would refer to use the Boeing performance programs for the particular airframe/engine/configuration in preference to the paper AFM or, if the computer is not available, the paper AFM. The QRH is, after all, only a hip pocket pilot help document .. even if the document continues to get bigger and bigger ...
As to legality ? That is the final view of the judges in the appropriate jurisdiction after the accident .. or the regulator in respect of AOC audit action .... I would suggest that, for the line pilot, the main aim is to have acted in a conservative manner in line with company OM guidance ... considering and as appropriate to the particular circumstances ... and be able to justify his or her decisions and actions against whatever criteria pertain for a particular jurisdiction. One's company ought to have taken suitable legal advice on any contentious matters when considering what guidance to provide in the OM.
Last edited by john_tullamarine; 16th Apr 2002 at 00:15.