Originally Posted by
bernardd
Surely it all comes down to weight? There are a set of performance graphs
here. Page 47 (number on the sheet!) seems to suggest that without any other de-rating the MTOW is derated by 75,000 pounds at 5,500ft, 15oC temperature elevation and an unlimited runway - note the tire limit on take off speed. I'm sure Jumbodriver will correct me, but doesn't that 75,000 pounds (25% of max with another 8-10% required for reserves) mean you lose 1/3 of the potential range, or you have to take out cargo and/or passengers which makes the trip potentially un-economic. Higher temperatures make these numbers even worse.
Yes, but payload which is the weight which you can change around & also makes the flight worthwhile. If it's only two thirds full then perhaps it isn't worth it...
Originally Posted by
SchmeckFlyer
It usually cools down fairly substantially in the evenings/nights, the temperature differences between night and day being more extreme than in more temperate climates. Added to that the cooling effect of the almost daily afternoon downpours, and evenings can even get chilly...
But not sure how that effects tires on the runway, which I imagine would get hot regardless of the ambiant temperature.
FYI, KLM does fly 777s daily AMS-JNB without a problem (I assume) and they are packed pretty full (no first class, business class has less seats than on BA if I remember correctly).
KLM flies a daylight flight from AMS which gets in at 21:10 returning at 23:30 so if it cools down that much then surely there's no problem. Air France also has double daily B77Ws but at earlier points in the evening.