Why engine 2 start before 1 on A320 ?

[redout]

Hey,

I would like to know why No.2 engine on A320 is normally started first as opposed to No.1 ? Anybody know why this is exactly ?

[square leg]

Possibly to have Yellow hydraulic system pressure for PRK Brake after engine start (to prevent the PTU from turning if No. 1 engine were to be started first).

[BOAC]

Discussed on PPrune before and it is (I hesitate to say - and braced for the onslaught:D ) STANDARD procedure on most aircraft.

I think I was once told it was because in the 'old days' the battery was on the starboard side so the cable run and hence voltage drop was less. Hence start 2 and use that genny if necessary? Another factor is that pax come up the left side on most aircraft so if you are 'raring to go' on your 20 minute turnround it would not be a good idea to start 1 first:D Think of the paperwork..........

[BOAC]

Aah - but it is French- they also drive on the wrong side of the road :p - maybe there are too many engines to work out anything complicated?:D I also had assumed it was a '2 engine' question?

[qwertyuiop]

BOAC.

How many engines do you think an A330 has?

[BOAC]

Doh! Qwerty - putting custard pie on my face as I speak. In that case I revert to theory 1:D

[earnest]

The alternate braking system (and the parking brake) runs off the yellow hydraulics in the 320/321 family. The yellow system is powered by engine 2.

The blue system does the same job in the 330. This is powered by engine 1, so engine 1 is started first.

They don't have to be started in this order. Sometimes the position of air start units (or other reasons) dictate starting them the other way round. It's not dangerous.

It is, however, still French.

[Soft Altitude]

As per FCOM 3 SOP, quote:"Engine 2 is normally started first. It powers the yellow hydraulic system, which pressurizes the parking brake".

There is no PTU functioning issue here. The PTU does only a self test between Eng2 and Eng1 start to check the 500 psi green/yellow hydraulics pressure differential logic.

This is confirmed also under the section of Suppl. techniques FCOM 3, one engine taxi, where you must start and taxi on Eng1, to power the normal brakes and Nose Wheel Steering, without powering the PTU, and FCOM 1 under HYD, then PTU, as well.
Hope this helps.
Cheers

[Hudson Bay]

In my last company on the Bae146 we had a policy of starting 4321 in that order. I thought that was the start sequence by convention rather than a technical one. Kind of "we drive on the left and all the other countries are wrong"

An interesting point is we could board passengers with the starboard engines running if we had no APU or GPU. If we needed fuel we would keep the port engines running. Not the best situation but what else do you do when your boots let in?

[SKYYACHT]

I believe that the reason is twofold. Firstly, #2 pressurises accumulator via the yellow system, but also, the ground air coupling for external air engine start is located within the danger aree of engine #1, and engineers dont favour being ingested.

Cheers