Ewmahle From United States, joined Mar 2005, 109 posts, RR: 0 Posted (9 months 3 weeks 6 days 19 hours ago) and read 3403 times:
Good eveing all. I just returned from PHL on US Flt. 1460 to RDU. In PHL our 737 was started at the gates using the air truck. I had seen this done once before on a UA737 but I have never been on a flight in which this has happened nor do I really understand why it is done.
Can anyone provide a resonable explanation as to why the pilot, or the ground crew, would decide to start the engines this way and what exactly happens when they do it? I am not looking for a technical answer, just general resoning.
Phxpilot From United States, joined Jul 2005, 61 posts, RR: 2 Reply 2, posted (9 months 3 weeks 6 days 19 hours ago) and read 3384 times:
Air carrier size jet engines are started using compressed air. This air can come from the APU or a ground source. The compressed air turns a miniature turbine which is connected to the high pressure compressor. To start the engine the high pressure compressor is driven to a given percentage of rotation by the starter through the use of this compressed air. Fuel is then introduced along with a spark. Once lightoff occurs, the engine is accelerated through a combination of the starter plus the expanding exhaust gasses. Upon reaching a given percentage of rotation, the starter cuts out and the engine becomes self-sustaining.
The reason you would need an external source of compressed air on a 737 is if the APU was inoperative.
PHLapproach From United States, joined Mar 2004, 969 posts, RR: 21 Reply 3, posted (9 months 3 weeks 6 days 18 hours ago) and read 3351 times:
UGHHH, my ears are bleeding just thinking about my companies air start trucks. One little I would like to add, A&P's use to do air starts. But now it's fleet service that does them.
"Don't Sthink, Don't Sthink" "Why is it telling me not to think?"
FlyASAGuy2005 From United States, joined Sep 2007, 1207 posts, RR: 0 Reply 4, posted (9 months 3 weeks 6 days 18 hours ago) and read 3349 times:
Those things can get LOUD! Huffers as we ramp rats call them is used quite often. Sad, but at ASA, I used one atleast once a day to start of an RJ with an INOP APU.
CAM2:"Lightnight coming out of that one." CAM1: "What?"
Ewmahle From United States, joined Mar 2005, 109 posts, RR: 0 Reply 5, posted (9 months 3 weeks 6 days 18 hours ago) and read 3293 times:
Thanks for your quick responses. So an In-Op APU is presumably not of any immediate concern to the well-being of the Airliner, so then when will they take the time to fix or replace the APU? Is it something they could do at the end of the day and have running again by the next morning or will US simply wait until the plane can be taken out of service and put in to MX?
RoseFlyer From United States, joined Feb 2004, 5276 posts, RR: 17 Reply 6, posted (9 months 3 weeks 6 days 17 hours ago) and read 3263 times:
Quoting Ewmahle (Reply 5): So an In-Op APU is presumably not of any immediate concern to the well-being of the Airliner, so then when will they take the time to fix or replace the APU? Is it something they could do at the end of the day and have running again by the next morning or will US simply wait until the plane can be taken out of service and put in to MX?
It really depends on the airline. A 737 can fly without an APU, but it is something that should be fixed in a relatively short manner. RJs often will go longer periods of time without an APU, but on the 737, the APU is an important thing to have. It is an ETOPS requirement since it is the only source of power should there be a duel engine failure. Also not all stations have the ability to perform a ground cart air start on a 737, so the APU would likely be replaced in short order.
I design airplane parts for a living and am that guy that mechanics hate and blame for everything... the Design Engineer
FlyMatt2Bermud From United States, joined Jan 2006, 520 posts, RR: 5 Reply 7, posted (9 months 3 weeks 6 days 17 hours ago) and read 3249 times:
I heard a DC8 crew in the Middle East actually convinced a fire rescue vehicle to spray high pressure water through an outboard engine to get it turning enough to start the engine. The ground huffer and aircraft APU were both inop. It was not an approved procedure and the word was the captain was disciplined, but he made his schedule so his punishment wasn't too severe. I have put in a call to the guy who gave me the story, perhaps he can elaborate.
"I just want you to know, we're all counting on you!"
Fr8mech From United States, joined Sep 2005, 1205 posts, RR: 0 Reply 8, posted (9 months 3 weeks 6 days 16 hours ago) and read 3209 times:
Quoting ZANL188 (Reply 1): hi pressure air to run the starters
I hate to nitpick, but I will...the aircraft starter uses a high volume of relatively low pressure air (35-45 psi).
Quoting Ewmahle (Reply 5): Is it something they could do at the end of the day and have running again by the next morning or will US simply wait until the plane can be taken out of service and put in to MX?
An APU is normally a catergory C MEL item. That means it can go 10 days until it must be fixed, with an extremely few exceptions.
If it's not specifically prohibited, it's authorized! When seconds count...the police are minutes away!
HAWK21M From India, joined Jan 2001, 25771 posts, RR: 51 Reply 9, posted (9 months 3 weeks 6 days 9 hours ago) and read 3096 times:
Quoting Ewmahle (Thread starter): Can anyone provide a resonable explanation as to why the pilot, or the ground crew, would decide to start the engines this way and what exactly happens when they do it
B737 Powerplant uses an Air starter,which needs compressed air to start from either the APU,other Engine or Ground pneumatic cart.
In this case the APU was u/s or APU pneumatics was u/s hence the use of the ground cart.
TristarSteve From Sweden, joined Nov 2005, 2270 posts, RR: 12 Reply 10, posted (9 months 3 weeks 6 days 9 hours ago) and read 3092 times:
Quoting RoseFlyer (Reply 6): It is an ETOPS requirement since it is the only source of power should there be a duel engine failure.
ETOPS does not cater for dual engine failure!
On some aircraft the APU is required for ETOPS, like B737, but on aircraft that are designed for ETOPS the APU is not required.
On B777 the APU can be inop for an ETOPS departure. Each main engine has a Back up generator which is there to cater for engine failure in the cruise.
Yes that is correct. I think I worded my statement incorrectly. On airplanes without a RAT, the APU is usually required for ETOPS. Should there be an engine failure and an IDG failure on the other engine, the plane would be dead if it didn't have an operable APU. I wasn't referring to the case of both engines failing, but rather electrical or hydraulic failures.
I design airplane parts for a living and am that guy that mechanics hate and blame for everything... the Design Engineer
Pilotpip From United States, joined Sep 2003, 2148 posts, RR: 7 Reply 14, posted (9 months 3 weeks 6 days 3 hours ago) and read 2974 times:
Quoting FlyMatt2Bermud (Reply 7): I heard a DC8 crew in the Middle East actually convinced a fire rescue vehicle to spray high pressure water through an outboard engine to get it turning enough to start the engine. The ground huffer and aircraft APU were both inop.
I know that a few existed, but most DC-8s don't have APU's. The ones that did had all kinds of issues.
EMB-145s have very unreliable APUs. For passengers the most discomfort will be caused by the inability to have the packs heating/cooling the cabin during a turn.
A10WARTHOG From United States, joined Jul 2004, 226 posts, RR: 0 Reply 15, posted (9 months 3 weeks 6 days 3 hours ago) and read 2972 times:
Quoting Pilotpip (Reply 14): EMB-145s have very unreliable APUs. For passengers the most discomfort will be caused by the inability to have the packs heating/cooling the cabin during a turn.
What model APU do you have the C-11 or C-14? The C-14 is alot better then the earlier C-11. They still fail, but not as much and in two years of working on them they have gotten a lot better. Once Sundstrand figure out they had a FADEC problem, the solder joints on the boards where breaking. This was only found in service and not a test bench until they started opening them up.
777WT From United States, joined Jan 2005, 835 posts, RR: 3 Reply 16, posted (9 months 3 weeks 5 days 3 hours ago) and read 2735 times:
Quoting Pilotpip (Reply 14): EMB-145s have very unreliable APUs. For passengers the most discomfort will be caused by the inability to have the packs heating/cooling the cabin during a turn.
I would say the CRJ-200 APU are the worst of all! and that includes the APU intake door!
DALMD88 From United States, joined Jul 2000, 1727 posts, RR: 7 Reply 17, posted (9 months 3 weeks 4 days 23 hours ago) and read 2661 times:
Quoting Ewmahle (Reply 5): Thanks for your quick responses. So an In-Op APU is presumably not of any immediate concern to the well-being of the Airliner, so then when will they take the time to fix or replace the APU? Is it something they could do at the end of the day and have running again by the next morning or will US simply wait until the plane can be taken out of service and put in to MX?
Most operators will try to get an inop apu fixed as quick as possible. They would most likely reroute the aircraft so it can overnight at a capable mtc station within a day or two. This gives you a few times to troubleshoot and line up any parts before the MEL runs out. Operationally an inop apu air source is a bit of a pain for ramp. It is a possible cause for delays. You now have to round up a start cart and hope that it works.
777WT From United States, joined Jan 2005, 835 posts, RR: 3 Reply 18, posted (9 months 3 weeks 4 days 22 hours ago) and read 2629 times:
Quoting DALMD88 (Reply 18): Most operators will try to get an inop apu fixed as quick as possible. They would most likely reroute the aircraft so it can overnight at a capable mtc station within a day or two. This gives you a few times to troubleshoot and line up any parts before the MEL runs out. Operationally an inop apu air source is a bit of a pain for ramp. It is a possible cause for delays. You now have to round up a start cart and hope that it works.
One time there was a a/c that had problems accepting GPU...they deferred the GPU and had to use the APU for the time...until they went to BUF...then the APU spitted out a fireball then parts was shooting out of the tail while at the gate.
They sent a road trip...attempted to fix the GPU system, attempted to start the plane by powerng it up on batteries then airstart it...this set off a engine exceedence message which was a no go...resetting it while the engines was running didn't work.
So back to fixing the GPU, they didn't figure it out until a few days later someone crossed the wires installing the GPU socket in the plane.
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