DFC ... could you hazard a reference to support the contention that there exist AEO takeoff WAT limits ?
The Type Certification requires some line-in-the-sand values for various items .. including absolute minimum climb gradients for various phases of flight.
The WAT limits (maximum (takeoff/landing) weight for (pressure) altitude and (ambient) temperature) are maximum weights which provide (at certification) demonstrated compliance with these minimum gradients. Note that we are not talking sports car performance in the OEI case .. just enough to give you some confidence that the ground might actually get further away from the aircraft than it was when you rotated ...
So, when working out, say, MTOW, we can start with the certificated MTOW (generally structure limited), check for WAT limits (which may reduce the allowable on the day), check for runway limits, check for obstacle limits .. etc., to work out the RTOW for the day...
(a)
25.117 requires that WAT conditions be satisfied in respect of
(b)
25.119 for AEO landing and
(c)
25.111 for OEI conditions,
and there are a few more requirements tucked away if you want to wade through the regs. Keep in mind that these are the current requirements .. if you want to find out more about specific requirements for a specific aircraft then you must start with the TCDS to establish the actual certification basis for the aircraft .. however, the current requirements will give you some idea of what's what.
Please don't confuse the takeoff WAT case with SID requirements .. two different animals, viz., airworthiness limits and operational limits.