B737 engine start questions
 

For the normal engine start,why do we start NO.2 engine first?
For the starting with ground air source,why do we have to start NO.1 engine first?

For a crossbleed start, so with the help of an ground air starter, the equipment and personnel is on the starboard side of the aircraft, hence the need to start engine one first.

For normal starts, there is to my knowledge no real reason behind it, but I am sure there is a historical explanation, which I am sure has been told to me before, just cannot remember it:uhoh:..

I think traditionally (big piston days) the battery was mounted in the starboard side of the aircraft and starting the nearest starboard engine first meant the battery lead was effectively shorter so less current loss. Certainly on the Cessna 310 (small piston days.....) I flew that was so.

That's my 2 roubles, anyway.:)

If you start #2 first, you can give the passengers conditioned air while #1 starts.

Could it be the ground push-back guy watches the right engine start, then moves to watch the left engine start, then is on the good side to wave to the captain that all is clear?

737 Engine start
 

if you use an air starter connection on the right side, start engine no 1 first, so the crew can walk around engine no 2 to disconnect air starter. if using APU, there is no restriction on which engine first; some airplanes recommend down wind engine first. but to get cabin air conditioning going and keep the pax cool start engine no 2 and use 'isolated pack operation' while engine no 1 starts. :cool:

Number 2 first to start, and first to be shut down when approaching the stand for the GPU guy to connect…keep working hours pretty close ahahahah