atakacs;
I guess would not be much of an effort to integrate those factors...
The calculation of best L/D speed would be done from standard formulae using specific engineering data regarding the wing, power plant performance data, air data, weight, CofG, etc and presentation is a matter of design and/or convention as glass presentations developed. The basis for the construction of performance tables would be taken out of the books and into the FMGC for real-time presentation on the primary flight displays - that's the 10,000ft, (perhaps 100,000ft!) view.
By way of explanation in re integrating abnormal configurations into speed presentations for crew information with an apology for the return to FMGC (Flight Management Guidance Computer) basics and the thread diversion for a moment, the notion of "prediction" is necessarily based upon known performance quantities such as speed/altitude/rate-of-descent-pilot-entered speed/altitude contraints and so on, - in short, the energy level of the airplane
as affected by known configuration changes and the required altitude and/or speed constraints at pilot-entered or FMGC-database waypoints. Because these other quantities are known, FMGC predictions include fuel usage/fuel remaining and ETAs over programmed waypoints as well as at destination and alternate.
Such predictions work extremely well when all is normal. At present and to my knowledge, (the B787 may do so), such information as may be available now, does not take into account the following:
- extended landing gear
- abnormal slat or flap configuration
- engine out
- contaminated wing
- aircraft damage, such as loss of a winglet, etc
The moment an abnormality occurs which affects lift/drag, FMGC predictions regarding times, fuel usage, the achievment of altitude and/or speed constraints etc, are all unreliable and as the FMGC manual states, must not be used. That is when the crew must go back to the books or the QRH.
Bear in mind that this is complex stuff and there will be exceptions/subtleties which we can delve into but which won't change this basis understanding a great deal. I ask others to leap in here if there is something missed, however.
Abnormal slat/flap configurations or extended landing gear will, depending upon configuration, more than double fuel flow and as such, all fuel, time, altitude and speed predictions are lost - rather, they assume a "normal" airplane. This would include the presentation of the best L/D speed so in abnormal circumstances, one returns to the books.
I am guessing when I say that such predictions are certainly possible but computer constraints, (memory, calculating power, cost), actual testing and then certification of same may be part of the constraints in creating new designs which present this kind of data to the crew. There would certainly be a cost-benefit analysis and given that such events are rare, it is probably better to go to the books.
FMGC information, like automation itself, it is tempting to believe all the time what the FMGC is telling the crew but in fact even the FCOM/AOM tells the crew that the FMGC is a guide and not THE performance indicator. The only tool that the crew should rely upon is the official flight plan which is (and must be) the most accurate information for prediction even though it is not in real time. In fact, data in real-time can be very misleading and should be taken in context of the entire flight.
Sorry for the thread-walk.
PJ2