Originally Posted by
emma69
With the landing gear on those aircraft, it is housed inside with a 'door' (for want of a better term). Could it be that the doors didn't open rather than the gear not extending down?
The actual term is gear door, so you're correct.
The manual extension should release the door and let the gear "fall down". Some aircraft do not have gear doors at all. In the 767's case, if there was some sort of electrical issues it is definitely possible the door didn't open.