avbug said:
Negative...minimum takeoff distances are limitations, reference Part 25. Balanced field lengths are not necessarily limitations, nor are many of the published takeoff distances. Be careful not to confuse published performance data with aircraft limitations.
Well I'm certainly confusing something, namely my overworked and underpaid brain.
Correct me if I'm wrong, but the wording in 25.1533 leads me to believe that the takeoff distance
limitation includes the performance requirements of accelerate-stop, climb, etc.
The wording is "The minimum takeoff distances must be established as the distances
at which compliance is shown with the applicable provisions of this part (including the provisions of §§25.109 and 25.113, for weights, altitudes, temperatures, wind components, runway surface conditions (dry and wet), and runway gradients) for smooth, hard-surfaced runways.
25.109 is accelerate stop, 25.113 is takeoff distance and takeoff run. So at the very least the takeoff distance
limitation must include accelerate-stop, and it appears that "the applicable provisions" could be interpreted to include 25.111 takeoff flight path, 25.121 climb: one engine inoperative, etc.
Out of curiosity, I pulled out the A.F.M. for the ATR-42 (the only part 25 airplane I'm familiar with). The limitations section of the manual doesn't spell out anything about takeoff distance other than to say that "Performance Configuration - The aircraft configuration provided in section 6 must be observed". and "Maximum takeoff weight and maximum landing weight may be reduced by performance requirements related to the following (see chapter 6)" then goes on to list climb performance gradients, runway length, tyre speed, brake energy limit, obstacle clearance (takeoff and enroute) etc.
So this leads me to believe that the performance data in chapter 6 constitutes limitations, since they are explicitly reference in Chapter 2 (limitations). And the performance data in Chapter 6 (pages and pages of it), includes all kinds of graphs for every conceivable thing
except a normal both engines operating takeoff. The "Takeoff Run" and "Takeoff Distance" graphs are both for "one engine feathered, one engine at R.T.O. power after critical engine failure - air conditioning off - anti-ice/deice off - no runway slope - no wind".