A320 FCOM wording: cross-bleed
 

Hello, need help untangling the semantics of this sentence from FCOM.

"Adjust thrust of supplying engine to obtain 30 PSI at start air valve before start initiation and at least 25 PSI during the start" [FCOM 2008].
"Adjust thrust of supplying engine to obtain an engine bleed pressure of 30 PSI before start initiation, and at least 25 PSI during the start sequence." [FCOM 2025 edition]

Which side are we looking at here, Hoskins? The receiving bleed or the supplying one?

I have always understood the requirement is for the bleed pressure at the RECEIVING engine:
a) It feels just normal to check the required min press at the delivery not at the source (the drop across the tubing is around 6 psi);
b) Naturally following the guidance of ENG START w/ EXT PNEUMATIC, where ground unit performance is requested - "The minimum recommended starter air supply pressure is 30/25 psi when the start valve is open" (FCOM 2008 through 2025) - which is only visible on the receiving side, clearly.

But if I am honest about "trusting the instruments", the present (2025) FCOM language does not really justify checking on the receiving side - if you had to choose exclusively, one or the other.

Awkward. Is anyone trained to check the supplying side? Why the odd wording?

thanks a lot.

Probably because it's been translated from French.
You should see some of the Maintenance manuals. It's like knitting fog trying to sort out all the double negatives.

Long time, good sir, happy to see you around. I honestly believed we are well past the French confusion era, partly because the brains are rewired to the collective at this point. :E.

Unless they really wish to look at the supplying side ( which would make the drill somewhat easier), it reads like a loss of technical expertise at the editor's desk.

The above reference is for CFM/IAE; I seem to recall PWG Neo's don't add any thrust at all - we just cross-bleed on idle.

Isn't it automatic on the NEO? IE, fuel scheduling is automated during a cross bleed to keep bleed PSI within limits during engine start.

When I first transitioned to the 320 I seem to recall it used to say at the receiving engine. Still makes sense to me as that is where you need it.

On some it is, on some it isn't. Haven't seen an indication whats the difference in the installed equipment list.

It’s “Starter Inlet Pressure” on the receiving engine you’re after.

Thanks, everyone. There's three layers to this

a) what we believe needs to be checked
b) what is the present sentence saying, rightly or wrongly
c) what Airbus engineers and system designers want us to do.

We seem to share the belief that the pressure at the pick-up point is what's relevant, and looking elsewhere is not meaningful (A).

The crux of my post was to get a precise understanding of B), in order to confirm or re-discover C).

Wwhat does the sentence say, to the naked eye, without preconceptions? Which side [receiving/supplying] would you pick if you had to demonstrate following the sentence itself as-is, and the punishment was transferring to Boeing fleet? :E

Playing the devil's advocate for the semantics of "supplying side" (B), and Airbus actually wanting us to do exactly that (C) yields some nice findings, t.b.h.
- there's hearsay that dropping below 30 / 25 does not create any practical issues
- the 737 guys (same engine) only have one manometer (duct pressure) with the sensor somewhere in the middle
- for H.F. it is an easier read, a less demanding cognitive task
- if we are dumbing down the cockpit procedures, or as some might say "tech evolves to meet the operator", this is not foul play on the SOP part if properly vetted from Airbus / CFM.

Correct, sloppy word choice on my part. At least on ours, the sentence "increase thrust on the supplying engine" is not there.

Then a lot of white magic follows. "The tech is developed to meet the operator".

he pllot thickens. vilas are you still around, good sir?

For the moment, I was convinced that the sentence "Adjust thrust of supplying engine to obtain an engine bleed pressure of 30 PSI ..." actually refers to the supplying side. Many of the "new" guys read that without dilemma, and apparently never knew any different.

How do you teach this?

https://cimg9.ibsrv.net/gimg/pprune....b88433b702.png

"new" sentence:
PRO-SUP-70-00009446.0001001 / 16 SEP 15 [Adjust thrust of supplying engine to obtain an engine bleed pressure of 30 PSI before start initiation, and of at least 25 PSI during the start sequence.]

previous wording:
PRO-SUP-70-00009446.0001001 / 09 DEC 09 [Adjust thrust of supplying engine to obtain 30 PSI at start air valve before start initiation and at least 25 PSI during start.]
PRO-SUP-70-00009446.0001001 / 16 MAR 15 [Adjust thrust of supplying engine to obtain 30 PSI at start air valve before start initiation and at least 25 PSI during start.]
pre-digital 3.4.70 SEQ 200 REV 42
https://cimg2.ibsrv.net/gimg/pprune....bfad5ac903.png

I mean, I don't fly them (or any other transport category aircraft), but my interpretation is that they may have just dumbed it down. The question is; in a normal x-bleed start, presumably there wouldn't really be any other bleed consumers on... so the supply and demand side pressures, at least prior to initiating the start should be pretty close to the same, shouldn't they? If so, maybe they just dumbed it down a little - it may be sufficient to just look at supply side... Even if demand side is technically more correct.

The 25 PSI is applicable to the receiving engine. If you check the procedure for « engine start with an air start unit » it says:

The pack valves close when during the starting process, but there are other bleed consumers than the packs. Think of the water reservoir pressure, hydraulic reservoirs etc. Whatever the case, the bleed pressure indicated on the supplying engine is never equal to the receiving engine.

I always interpreted the procedure as start pressure in the receiving engine, just like in any other starting scenario. I agree the wording is ambiguous, but I think the intention is quite clear. Compare it with starting an engine with an air starter. No matter what the ground crew say, you will be looking at the air pressure in the receiving engine, not whatever is indicated on that tired leaky ASU!