Hi
Mutt,
Not a cop-out, but as I said "
I don't do the Performance Engineering for my "own" aircraft, the B777. I do it for other aircraft". As an operating pilot I have a thorough knowledge of the B777 performance aspects, but not the 'deep' knowledge that is required for the other aircraft that I do the P/E for.
Conversation with the Boeing performance people (whilst engaged in discussions on the "other" aircraft) indicates that whilst the aircraft is not certified beyond the environmental envelope, the engines are, and the thrust level attainable at, for example 60°C, is proven, and may be applied to the aircraft operating within the envelope. Their indication is that the FMC does not appropriately address any performance beyond the environmental envelope. You can put your own interpretation on that statement, but in creating programmes myself for other aircraft, things can go awfully awry when it's necessary to exceed the environmental envelope parameters (unknown break points etc.). I've always been too busy to develop the conversation further than that.
On the practical side, however, operations at an assumed temperature of 60°C applied to TO-1, does produce some wildly differing FMC speeds from the Airport Analysis (I've seen up to 10 knots), so I'm happy to accept their rather basic explanation, and operate at the Airport Analysis speeds.
Regards,
Old Smokey