737 External Air Starts

[gonso]

Could someone help with this?

(737 Classic) In the ops manual I looked up, it states that when using External Air and GPU for engine start, you MUST start Eng 1 first.

In some airports, the GPU cable is coming from the airbridge and it is not long enough to reach the receptacle without being within less than 3 meters from Eng 1 inlet. The ground crew asks for Eng 2 to start first.

I looked in the books and I could not find any serious implications from starting 2, push back and x-bleed 1. The only obvious implication is the black and white EADI & EHSI (they loose the colours due to reduced equipment cooling I think.)

Two start-push-xbleeds occured the last few weeks with 2 then 1 sequence with no problems.

Why the manual (at least the one I saw) says MUST? It does not even say should or "recomended".

Any ideas? :ugh:
Thanks a lot.

[_FL600_]

I think it's just because the jet air start equipment is hooked up from the right side. Thus, you start engine-1 first, and then you let the ground crew diconnect the jet start before you x-beeld engine-2.

Simply, it's just for ground personnel safety!

regards,

[TolTol]

Have to agree with FL600. As long as the duct pressure is sufficient, it mechanically doesn’t matter which engine is started first.

[CaptainSandL]

The above responses are correct. Next time you do a walkaround have a look to see where the external air (for engine starting not ground air conditioning!) plugs into. It is a hatch just beneath & behind the leading edge of the RH wing. There is no way that you could safely get to this hatch with the #2 engine running.

S&L

[gonso]

Thanks for the replies chaps.

The problem is that in those two cases I am referring to, it was the ground crew that insisted on No2 to start first. In other words, they were happier to approach the inlet near the No2, than start the No1 which was literally a few feet from the airbrdge. So it is possible for No2 to start.

I was aware of the inlet geometry, I was just wondering whether there were additional reasons behind the manual's "MUST" .