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"Cross Bleed Start"  
User currently offlineTripleseven From United States of America, joined Jul 2000, 118 posts, RR: 0
Posted (13 years 2 months 3 weeks 3 days 18 hours ago) and read 2471 times:

I was listening to UA channel 9 prior to take off, and I heard the flight deck inform ground control that they would be doing a "cross bleed start".

I assume this has something to do with the APU and the engines.

Am I close??



5 replies: All unread, jump to last
 
User currently offlineOPNLguy From , joined Dec 1969, posts, RR:
Reply 1, posted (13 years 2 months 3 weeks 3 days 17 hours ago) and read 2441 times:

Yep...

Normally, on, say, a 737, the APU provides pnuematic air to start (one at a time) both engines. If an APU is inop, ground equipment can be used provide air (and electric power) to start the aircraft, all this occuring at the gate.

Sometimes, these ground units (and APUs) punk out after only getting one of the engines started. In such cases, the crews can then get electric power from the running engine. Likewise with the pnuematic air, but that requires the running engine be above idle speed to provide air. Running engines at that higher power setting can be problematic for the ramp folks, since more air is being ingested into the engine, and exhaust velocity is higher. It can also be a problem for ATC, as any other aircraft taxiing behind an aircraft doing a cross-bleed start could get buffeted itself. Smaller ones have been know to get flipped over. ATC gets advised so they don't clear anybody to taxi behind him until the start is over..

I watched one time as an aircraft was pushed back, near a freight fowarding facility. Once the cross-bleed start commenced, the jet blast from the engine already running sent 2x4s and 4'x8' sheets of plywood flying like cardboard, not to mention the airfreight workers in the proximity thereof. Nobody hurt, thankfully, but I'd guess someone got a see-me note in their mailbox out of it...


User currently offlineTripleseven From United States of America, joined Jul 2000, 118 posts, RR: 0
Reply 2, posted (13 years 2 months 3 weeks 3 days 16 hours ago) and read 2421 times:

Thanks for the description. How common is this?

User currently offlineOPNLguy From , joined Dec 1969, posts, RR:
Reply 3, posted (13 years 2 months 3 weeks 3 days 16 hours ago) and read 2416 times:

Not very... The % of inop apus is pretty low to begin with, so when you consider the small % of *those* ops that have the ground equipment crap out, the need for cross-bleed starts is somewhere between rare and uncommon. A little more prevalent in the summer time, maybe.

User currently offlineMikeybien From , joined Dec 1969, posts, RR:
Reply 4, posted (13 years 2 months 3 weeks 3 days 7 hours ago) and read 2390 times:

You'd be surprised how many a/c operate with inop apu's. For example, when i worked for F9, every day there was at least one or two a/c with inoperative apu's out of a 20-something a/c fleet. On 737's (and i suspect many other a/c) cross feed has to be used when using a GPU because the GPU hose hooks on a few feet forward of the landing gear on the belly. Generally, #1 is started, but then the GPU hose must be unhooked because it and the gpu sit in the ingestion zone for the #2. And no sane baggage handler would even attempt to remove the gpu hose with both engines running. If my memory serves correct, 24 ramp workers have met their maker courtesy of a 737 JT8 or CFM56.

User currently offlineAAR90 From United States of America, joined Jan 2000, 3451 posts, RR: 47
Reply 5, posted (13 years 2 months 3 weeks 3 days 6 hours ago) and read 2385 times:

Due to lack of spare parts, when AA's MD90s would lose an APU, it would be anywhere from 3-10 days to get the part to fix it. DL sure didn't want to give up their spare parts. Costs are huge!

BTW, when an APU is inop at SFO, the airport _requires_ airplanes to start only one engine at the gate and then do crossbleed start on Taxiway A. This is requirement, not an option. Only airport I've been to with this requirement.



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