It appears that using High Pressure to start the engines isn't working when on the ground. But you can use it to start the engines in flight. I tried it.

This could also explain why GRD START is above the Low Pressure!

Mark

High Pressure starts on the ground work just fine for me?

1.  Battery On, Parking Brake on (CTRL + .)
2.  Make sure power and air are ON (shift 2 panel)
3.  Turn the switch to EXT POWER (not sure it's label, below the ground power switch on the FE's upper panel).  You should see air pressure rise and electric turn on.  Be sure the DC bus is on ESS.
4.  Open the cover switch and select HIGH PRESS (overhead between engine start switches).
5.  Switch engine 3 to GRD
6.  Watch for about 18% N2
7.  Introduce fuel
8.  Once engine starts and stabilizes, go and switch the switch in #3 to Gen 3, and then switch the switch in 4 to LOW press.
9.  Start eng 4, 1 and then 2....

Thats a quick one off the top of my head?!

Captain Sim 2 wrote on Oct 25^th, 2010 at 7:18am:

Hi Tanya.

Thank you for that. I'll check it out.

BTW. It's great to see a face to go with your Forum name as well as you adding your real name to your signature. Nice touch. Makes it more person to person!

Mark

Quote:
I must be missing something here. What do you mean "the bottle"?

Mark

Mark,
The start cart is the unit that provides start air to all engines. The cart is plugged into the aircraft and provides low pressure (high volume) start air. The high pressure (bottle) is only able to start # 3 engine - and you get only one shot.

On the overhead panel you select the start air you want with the switch in the middle of the start panel.

I'm on my way out the door, but I'll look for the procedure in the manual later.

Lou

Hi Lou.

So that means that the L.H. Bottle Inactive Light should come on (and stay on), once you have started engine #3 on High Pressure? That would certainly make a lot of sense. I just didn't know that that is what the bottle was used for.

I have another question. What are the circumstances that would require a High Pressure start? Or. Did they refill the bottle after the end of every flight (where the engines were shut down) so it was always available for the engine start?

I'm guessing, that part of the answer would be that a High Pressure start should/would almost guarantee a successful engine start compared to a Low Pressure start.

Why is the engine start 3, 4, 1, 2? And is it always in that order?

Mark

I have to correct two things. First, Mark, the sequence is 3,4,2,1 and second, I just read that high pressure start air really comes at values of 2.700 and more PSI.
So disregard my statements towards such high values being wrong. Maybe I'll edit my posts then.   (done)


I think you go for the inboards (3 and 2) first because of the shorter supply ways of the external air connected (which often has a central point of connecting to the plane) or even the high pressure bottle.
External stuff usually has one contact point and then gets distributed inside the planes structure so the delivery ways differ in length. Length causes a loss of air pressure, so the shortest way has to be preferred.

If they are running then, pressure can be supplied more stable and reliable to the outer engines being self-sustaining then.

Outboard first might work too but as you have to start the inboards anyway, use them first as their supply will usually get the required "N"-values faster, more stable and with the mentioned shorter air supply ways.

So whatever happens, start the inboard ones first, must not be the No.3 then. The side might depend on the placement of ground vehicles, carts and personnel.
Our 707 gets started on the ramp, so obstacles and people are quite close to it.
"Did anybody see the guy with the Chocks?" "Yeah, he's stuck in engine No. 3!".  

If it was a special need to go for the right inboard on the 707 first (meaning No.3 then), this might be explained with the external air cart to connect nearer to the No.3 than to the No.2 engine. Same "shorter ways" theory to apply then.

I don't see any special equipment reason to start 3 before 2 as they are connected to similar systems.
Other planes might need a yellow hydraulic circuit first or such things and therefor prefer special engine numbers to be started before the others. The 707 has some special equipment (the Air Compressors) but this is spread across No. 2,3 and 4.

Maybe Lou can help here.