Originally Posted by 411A
Yes, the reason is quite simple, and indeed was mentioned by someone before.
Twins have a different takeoff diversion distance/time than 3/4 engine aircraft.
Been this way for all the years I can remember.
As twins might have to return to the departure airport, whereas three/four engined types can have/do have greater flexibility in this regard, it stands to reason that they have slightly higher takeoff minima.
Sorry don't get you there. Isn't it to do with controllability on the ground in the event of a high speed engine failure and associated yaw? I don't see what the time/ distance to T/O alternate has to do with minima for T/O. Twins may not HAVE TO return to departure airfiled, hence the T/O alternate if landing minima is below T/O minima (bearing in mind the capabilities of autoland on one engine in a twin). I would have thought an engine failure on a 747 would lead to less yaw than on a 767, hence it would be easier to control with regards to runway centreline, hence it could operate to lower minima.
Anyone?
PP