Quote from mutt:
Quote:
handbook of Perf A graphs
...I never had to use those charts for real...
I doubt any
airline jet-pilot will ever have to use graphic charts again. Pity in a way, because, like any pictorial representation of a process - e.g., a systems diagram, or flow chart - they could be an aid to understanding and monitoring the "big picture". Just in case anyone is wondering, they were NOT runway-specific, so the
first part of the process was to extract the runway details from an airfield list: Elevation; Slope; TORA; EMDA (ASDA); TODA; and any obstacles affecting the NTOFP (net T/O flight-path, after the end of the clearway). The graphs could be re-used indefinitely, being covered in sticky-back plastic, so we could use a sharp china-graph pencil - but fine ball-point was more practical.
Later. on the B707, we still used charts, but they combined runway, WAT and NTOFP considerations on to one chart, and were runway-specific. So the only remaining variables were QNH, OAT/Flex-Temp, W/C (wind-component, head or tail), and any permiissible contaminant. [You had to extract V-speeds elsewhere.]
TABLES are runway-specific; and incorporate V-speeds in the same 'box' for each temp, W/C, and resulting weight. The only corrections required are the QNH, and any permissible R/W contaminant. The trouble is that each weight is the RTOW for a specific OAT/Flex-Temp and W/C, and the speeds therefore assume you are at that weight. If you are lighter, the V
1 is still valid, but the V
R and V2 have to be calculated for the actual weight.** [If the quoted V1 is higher than (actual) VR, it must be reduced to VR.] And don't forget VMCG...
Quote from mutt:
Quote (from groundfloor):
The assumed temperature must not be lower than the flat-rating temperature
Why not?
Good question. It's always been so! I see that
groundfloor correctly added "or the OAT", something I wrongly omitted in my post. But using a lower temperature shouldn't matter because, if you use
TREF, you are already at Rated Thrust; so using a lower assumed temperature shouldn't make any difference. Equally, if you use something below OAT, I doubt that a modern engine would try to give you more than Rated Thrust. BUT I wouldn't want to try it out! In the old days, American jet engines COULD be "over-boosted" by opening the thrust levers too far. It was the job of the F/E (much-missed flight engineer) 
to pre-calculate the appropriate EPR, P7, (or whatever power indication applicable to the engine), and set the correct take-off thrust on the pilot's command.
Actually, using OAT or TREF as the assumed temperature is pointless - you might as well select Rated Thrust in the conventional manner. [The flat-rating concept did not apply, by the way, on the Conway-powered VC10. The first engine I operated with it was American - the JT3D on the B707.]
FE Hoppy has answered
mutt's other point - I've never used de-rated thrust, so can't comment. Re graphs: yes, but practice makes (nearly) perfect, and a limiting take-off out of Entebbe (old R/W) or Nairobi used to concentrate the mind wonderfully... We always used to use the "thickness of the pencil" on the safe side. I don't think computers are capable of doing that!
** [Unless you are using optimised performance (capitalising on surplus runway length by using increased V
R and V2 for a better climb gradient).] 