[quote
The main passengers doors are on the left hand side. On the B707 we always started 3,4,2,1 - you could be winding up 3 and 4 whilst the last pax were boarding, main pax door being closed and the steps were being taken away.
][/quote]
A certain amount of tradition may come into the starting order which was 3,4,2,1. On Lancasters (and the Lincolns I flew) The starboard inner (No 3 engine) was started first because the compressor for charging the air bottle to 450 PSI was installed on that engine. That gave air to the wheel brakes, electro-pneumatic rams for the radiator shutters on the Rolls Royce Merlin engines, slow running cut-out controls, automatic supercharger change and air cleaners. A generator was also installed on both inboard engines.
The port inner had one hydraulic pump that operated the bomb doors, flaps, fuel jettisoning and undercarriage. In addition a compressor on the No. 2 engine operated the autopilot.