Hi oldchina,
Frustrating that I don't have any sample figures, but I think on the 1-11/500 the most limiting factor for the RTOW (other than the structural MTOW of 45200kg/99650lb) out of many of the sea-level Spanish airfields in hot summer wx may have been WAT, rather than runway length. You are quoting figures at ISA on an 8000-foot runway, where runway length is evidently the limiting factor.** I'm talking about something in the region of ISA+20 (35C), where the most limiting factor could be either WAT or the runway criteria (TORA/EDA/TODA) or, of course, net take-off flight-path (obstacles, as at Malaga).
Allan may have identified the problem-area. I think the Spey was flat-rated, as he says, and perhaps to ISA+20. Maybe the flat-rating stretched to a higher figure with water-injection? I really don't remember.
Frankly, the 500 series was under-powered for summer weather on the Costas! We needed the B737-200. (Many years later, as you know, we got the A320, but that's another story.)
** Must admit I'm surprised your figures show the 500 srs incapable of achieving MTOW off an 8000-foot runway at sea-level (still-air?) without water injection. Worse than I thought.
Last edited by Chris Scott; 16th Feb 2017 at 21:37.
Reason: Flat-rating theory adjusted.