737 Engine Starting
 

Can anyone tell me why engine number 2 is started before engine number 1 (in normal circumstances)? :confused:

The passenger doors are on the left side.


Mutt.

Could you expand a bit? I don't see why that should affect anything, as all the doors are closed and you're pushing back when the engines are started.

Its basically a safety issue. Pax can exit out of the LHS safely (as the LHS is the main entry/exit points on most if not all aircraft), say if the No. 2 caught fire or whatever. They dont have to go through the galleys on the right, or if its still at the aerobridge etc.

As far as I know, on the 737-200 there is no single big overriding reason to start one engine prior the other. The company I fly for used to have a SOP for starting #2 first, but dropped it, with no explanation about a year ago.:confused:

Some minor reasons could be attributed to the arrival procedures. Where the SOP is to taxi in one engine, usually #2 is shut down because the belly baggage/cargo doors are on the right. This is the side the rampies should be hustling over to, and also where the baggage carts are parked/unloaded. If #2 is wound down by the time you roll up to the gate, there is less chance of FODing that expensive engine with a rampie:eek:, bag, or trash.

Since you taxi in on #1, if you start #2 first, and taxi out only on #2 (if practical) then the engine run times will be more equal, and more importantly if running several short haul sectors while tankering fuel, the fuel load will stay more balanced.

My company's procedures are to "normally" start #1 first. -300 and later, starting #2 first on hot days, and or full paxs you can then put the right pack on for cooling while you start #1.

A lot of things happen for historical reasons, in the old days it was common to start the right engine of a propellor aircraft first in order to board passengers, for lack of any better reasons this policy was carried over into the first jets.

Taken from a Piedmont B737 Manual dated 1978.

The No2 engine will normally be started first to facilitate last minute passenger loading or retraction of the forward or aft stairs

But as others have pointed out, there is no limitation forcing you to do so.

Mutt.

Starting #1 first allows rampers to add a last minute bag into the cargo bins (right side) without having to shut down an engine you just started; starting #2 first allows you to separate the bleed air manifold (using the bleed air isolation valve), so the right engine provides bleed air to the right pack for cooling/heating the cabin, while the APU (on the left side) provides air to the #1 engine for starting.

To throw another hat into the ring, on some aircraft, which engine is started first depends upon the shortest run of cable from batteries to starter, with electric starting. Other considerations may be ancilliary systems such as hydraulics and generators.

Notwithstanding the above, we start the number 2 engine first to make people ask why we don't start the number 1 first, of course!!!