Tidbits
C/B s on B-767 are pull/push type.
C/B s pulled by maintenance prior to flight are collared (for amateurs on the forum, this is not a typo for coloured/colored, it means a plastic, distinctively coloured/colored collar is fitted around the CB to make clear that it is out on purpose).
Yes, during abnormal sytem behaviour, checking CB s should be a natural step after completion of QRH procedures, BUT, the alternate gear extension system is FREE FALL, that doesn't quite ring a bell that something electrically could be in the way of gear extension - Oh yeah, the hooks that hold the gear doors locked are operated by electrical motors, rather than hydraulic actuators, during alternate gear extension.
CB s are not monitored by EICAS in a 767, but the fact that the popped CB did not cause any other (obvious) failure on the flight deck did not help to discover the fault in the electric system. Remember that alternate gear extension is one of the systems that have to work when (almost) all electrics on the machine have died - surprising that part of that last ditch portion of the electric system can die unnoticed.
Lastly, the particular position of that CB is prone to being bumped accidentally by pilot s bag, and sits in a corner of the panel that is awkward to view from pilot s seat.
Seems lot of holes lined up.