Crossbleed start on stand

[BRUpax]

In layman terms what exactly is a a cross bleed start and why do airports prefer them to take place off stand rather than on stand? Many thanks.

[cirrus01]

Basically it is starting one engine by using another engines bleed offtake rather than using a APU or ground cart.

It requires the running engine to be accelerated to a level to provide enough air volume and pressure to enable a consistant start on the other engine. ( usually this level is somewhat above Flight idle ) For this reason it is best carried out on stand, or on the taxiway, and NOT during pushback, as this has a habit of Jack-Knifing the tug if the ramp surface is at all slipperly........more pronounced on wing mounted engines than tail mounted ones but even so ...... :uhoh: :uhoh:

[caniplaywithmadness]

From an ATC point of view, we don't like crossbleed starts on stand as there may be aircraft taxying behind which could possibly get blown over from the increased thrust of the engine used to provide the bleed air to the engine needing to be started.

I've had various power figures quoted to me by different operators / aircraft captains, the highest I've heard was 80% thrust needed to do the crossbleed (which I thought was rather a lot).

So our preference is for the crossbleed to be done after the push with no other aircraft behind.

[BRUpax]

Thank you for your replies.

[Burger Thing]

I flew all last week with the APU u/s. It is a pain in the b**t. Crossbleed starts are not a big thing, it is just unconvenient. They are noisy and also require proper fuel managment, since the engine which starts first can cause a significant inbalance of fuel, because you run the engine on a rather higher power setting for a while to provide the bleed air for the other egine(s). :)

[spannersatcx]

From an ATC point of view, we don't like crossbleed starts on stand as there may be aircraft taxying behind which could possibly get blown over from the increased thrust of the engine used to provide the bleed air to the engine needing to be started Not forgetting of course the increased danger to those PEOPLE on the ground!

the highest I've heard was 80% thrust needed to do the crossbleed (which I thought was rather a lot). Although 80% sounds a lot you must bear in mind that something like the RB211 or CF6 on a 747 idles at around 62/64% N2 or N3. The figure is where you get max bleed pressure before the change over between IP and HP air.

[M.85]

70% on 737s.

M.85

[sky330]

There is a huge difference between engines generations.
I used to fly straight jets where a cross bleed requires quite a lot of thrust and so is better do out stand.

The new very big, high dilution engines, as a rule requires only slightly above idle, so in stand would not be a problem but is done out stand for exactly the same reasons as a normal start is not done at the gate (noise, security of ground personnel, FOD risk higher,..)

My 2 cents,

[Capt Fathom]

I heard a first officer one day, telling ATC they needed to run the engine up to 70% for a crossbleed start. Caused a major flap. Safety cars running around everywhere and ATC insisted the plane be towed away to another part of the field for the start.
The Captain had obviously not heard what the FO had said on the radio, and couldn't understand what all the fuss was about.
It was after all, a common event. I was nearly going to tell the poor chap what his offsider had said when they managed to work it out. :ugh:
Lesson for the day...choose your words carefully. I hope the FO bought the first round.

[LEM]

one little question:

you are probably gonna tell me to get lost, but I'm curious to know what philosophy most of you prefer:

1) reducing power as soon as the starter cuts out - but then you have to be ready to increase again if the need for a motoring cycle arises

2) keeping the power up until the other engine is stabilized...

:zzz:

[bafanguy]

For the life of me, I can't understand why anyone would start one engine and do a x-bleed start out of a taxiway endangering acft behind. Are you letting the accountants run your airplane ? If you have enough support to start ONE engine, why would you not just start them all and be done with it ? There is the rare exception where the start source is a compressed air bottle that can barely get the first engine started. In this case you just have to make do...get away from the ramp area...advise ATC well in advance to clear out all acft behind and get on with the high-power x-bleed start. The x-bleed start procedure in the POM is for the case when there are NO other alternatives. Avoid writing letters that begin: "Dear Chief Pilot: We were having a simply marvelous time, when all of a sudden....".

[DDG]

bafanguy,
The second engine is cross bled started on the taxi-way or apron disconnect point as the LP air connection is located in the airconditioning bays of almost all modern aircraft(notably Boeing`s and Airbus),this connection is located within the engine ingestion hazard zones .So by starting the second engine on the gate using a supplied air source you place all ground staff at risk of ingestion when they attempt to disconnect the LP air source.
Regards DDG