Hobo: The following licencing quirk may amuse some of the posters on here.
As Steve posted earlier, The Gripper was crewed by three pilots in BEA/BA but by two pilots + flight engineer in some other airlines.
Now, when BEAirtours started operating the B707-436 they had no qualified Flight Engineers on staff as required by the CAA. The company got approval to qualify their F/Os as P2 and as flight engineers. To get this approval, one had to have 2,000 hours flight time on 4 engined aircraft. This was mainly Viscount and Vanguard/Merchantman people but, believe it or not , the T3 qualified also as it had four engines!!
This, I recall, did not sit very well with a branch of BA that flew predominately long haul!