The only reasons I can fathom for delaying gear up are a malfunction of some sort or an error of some sort.
Survey says... errrnt, wrong answer.
Brakes get VERY hot during takeoff, landing, and taxi. It's the simple physics
of energy dissipation. Aside from that, tires get quite hot just from the rolling action/deformation as the contact patch deforms (traction waves form at higher speeds).
Stopping a an aircraft requires converting virtually every bit of kinetic energy (1/2 * mass * velocity squared) into heat energy.
Even at lower speeds, a 450,000 lb aircraft has quite a bit of KE
, and to maintain a slow taxi speed, the brakes must dissipate quite a bit of energy generated by idle thrust. In the newer gulfstreams we would taxi with the buckets out on one engine just to keep the brakes cool. This wouldn't be a problem if the aircraft were on the ground for 6 hours after each flight, but when you qt an aircraft, the brakes don't have time to cool completely.
I don't see the brake cooling argument at all.
Quick-turn landing weights are published to determine minimum turn-around times for a given weight, because the brakes must be cool enough in time for the next takeoff. Otherwise, they will overtemp and quite probably catch fire or at least be damaged in the event of an aborted takeoff (at a minimum they will melt the thermal plugs).
What are the decision criteria?
We have a BTMS (brake temp monitoring system) and published brake cooling procedures based on weight, wind, OAT, pressure altitude, and event (eg. RTO, max manual brake, autobrake 1-4-max, reverse/not).
We add 1 million ft.lbs per brake per taxi mile!
Is that enough to get the brakes hot?
Specified inflight cooling times range from 1 to 8 minutes. With regards to the comment by HAL, our brake cooling charts are in the abnormal section.
[Edited 2003-07-21 01:36:05]