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Question About Air Starts.  
User currently offlinePhxplanes From United States of America, joined Feb 2005, 436 posts, RR: 0
Posted (8 years 2 months 3 weeks 15 hours ago) and read 8474 times:

Like the title says I have some questions about air starts. First how does the pilot know they will need an airstart. Why do you need an airstart, what happens to need it. Finally what exactly does the air start machine do (obviously blows air into the engine) but more technical.

Sorry the question might be a little choppy but thank you in advance for the answers.

42 replies: All unread, showing first 25:
 
User currently offlineN685FE From United States of America, joined Dec 2003, 451 posts, RR: 11
Reply 1, posted (8 years 2 months 3 weeks 15 hours ago) and read 8478 times:

Aircraft engines are started using an air driven starter that receives pneumatic pressure from the apu. If the bleed system on the apu or the entire apu is on deferral then an alternate source of air pressure is needed. When a new crew receives the aircraft they review the log book, any deferrals will be noted in the log book with a deferral sticker next to the apu start switch. Need more details?


psp. lead by example
User currently offlineKAUSpilot From United States of America, joined Jan 2002, 1959 posts, RR: 32
Reply 2, posted (8 years 2 months 3 weeks 15 hours ago) and read 8472 times:

Quoting Phxplanes (Thread starter):
Like the title says I have some questions about air starts. First how does the pilot know they will need an airstart. Why do you need an airstart, what happens to need it. Finally what exactly does the air start machine do (obviously blows air into the engine) but more technical.

Sorry the question might be a little choppy but thank you in advance for the answers.

You know you will need an airstart if your APU is inoperative. Normally the APU provides the air needed to start the engines, however, if it isn't working, then you will need an airstart cart. Some military aircraft always need an aircart start, as the they don't want to or can't use the batteries to start the engines and aren't equipped with APU's (the T38 comes to mind).

The airstart cart really doesn't do a whole lot more than blow air into the engine. The Airstart hookup is plumbed into the air turbine starter via a "starting control valve". This valve regulates the pressure supplied to the air turbine starter (ATS). The ATS in turn converts the pneumatic energy from the pressurized air into driving torque for engine gas generator spool acceleration up to the self-sustained speed during the starting cycle. Air exhaust from the turbine is discharged into the engine nacelle compartment. There is not a significant difference in the start sequence between using the APU as a pneumatic source vs. an airstart cart, at least on the aircraft I fly.

We must start the #2 engine on my aircraft first if we are using an airstart cart, since the hookup is on the right side of the aircraft and it is plumbed into the #2 engine's ATS. After starting the #2 engine, the airstart cart is disconnected.

To start #1 after an aircart start, we do what's called a "crossbleed start", meaning we run the #2 engine up to 83% N2, open the bleed air valve and crossbleed, and start #1 using bleed air provided by #2. Special caution must be exercised during this procedure so as not to damage nearby aircraft or ground equipment with jetblast.

Hope this helps.


User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 3, posted (8 years 2 months 3 weeks 14 hours ago) and read 8455 times:

One other thing, is some older aircraft didn't even have APU's, like the DC-8 (some had them added later, but the majority didn't), so every start would require the air cart/truck to be hooked up, and one engine started at the gate before pushback. Once pushed back, the bleed air from the one running engine would be used to start the remaining ones.

Chris



Don't blame me, I don't work here...
User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 4, posted (8 years 2 months 3 weeks 11 hours ago) and read 8427 times:

Quoting Phxplanes (Thread starter):
Like the title says I have some questions about air starts. First how does the pilot know they will need an airstart. Why do you need an airstart, what happens to need it. Finally what exactly does the air start machine do (obviously blows air into the engine) but more technical.

To answer your questions-

The APU won't start....APU failure....you go find the Air Start Cart....it's an APU and produces the air needed to start the aircraft engines when the APU won't work.....nothing technical about it, the plane just gets its air from a second source.



"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineGEG From United States of America, joined Oct 2004, 297 posts, RR: 0
Reply 5, posted (8 years 2 months 3 weeks 5 hours ago) and read 8378 times:

Roughly how much air pressure is required for the start?

-Dan



Cant sleep...clowns will eat me...cant sleep...
User currently offlineN685FE From United States of America, joined Dec 2003, 451 posts, RR: 11
Reply 6, posted (8 years 2 months 3 weeks 4 hours ago) and read 8355 times:

GE-CF680C2A5F
General-The starting system of the CF6-80C2A FADEC engine utilizes pressurized air to drive a turbine at high speed. The turbine turning through a reduction gear applies a torque to the HP shaft, thus driving the engine. The air which is necessary to drive the starter is supplied by either : - the APU - crossbleed from the second engine - a ground power unit. The starter supply is controlled by a starter shuf-off valve pneumatically operated and electrically controlled. In case of failure, the valve can be opened manually. Engine starting is controlled from ENGINE START panel, located in the center of the overhead panel. For each engine, the illumination of the blue OPEN legend integral with ENGINE START/START 1 (2) pushbutton switch indicates that the start valve is open. The starting sequence may be interrupted at any time by placing ENGINE START selector switch in OFF position. This ignition selector switch also controls the ignition system and enables selection of one of the two ignition systems (A or B), or both at the same time or a dry motoring to be carried out with CRANK selected. A switch in the N2 speed indicator causes the starter valve to close when the N2 speed exceeds 45 %. The starter centrifugal cluth then disconnects the starter turbine and gears from the output shaft and allows the turbine to stop rotating.

Air Supply-The air necessary for starting comes from the duct connecting engine bleed and the pre-cooler via a 4 in. dia. duct. This duct is attached to the engine bleed duct just before the precooler inlet. Through operation of the crossfeed valve and APU bleed valve, the air necessary for the starter is supplied by either : - crossbleed from the other engine - the APU and in that case, all the air bled from the APU is used for starting - an external source able to supply a pressure between 25 and 55 psig (maximum permissible pressure in the duct).



psp. lead by example
User currently offlineN685FE From United States of America, joined Dec 2003, 451 posts, RR: 11
Reply 7, posted (8 years 2 months 3 weeks 3 hours ago) and read 8342 times:

PW JT8D-217C
Same theory. Minimum pnuematic duct pressure 36 (±5) psig.



psp. lead by example
User currently offlinePhxplanes From United States of America, joined Feb 2005, 436 posts, RR: 0
Reply 8, posted (8 years 2 months 3 weeks 2 hours ago) and read 8322 times:

Thanks guys for all your responses, I didnt know that the apu doesnt work sometimes.

thank for the answers.


User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 9, posted (8 years 2 months 2 weeks 6 days 19 hours ago) and read 8258 times:

Quoting GEG (Reply 5):
Roughly how much air pressure is required for the start?

It's not really pressure more then it is volume.



"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineFlyMatt2Bermud From United States of America, joined Jan 2006, 563 posts, RR: 7
Reply 10, posted (8 years 2 months 2 weeks 6 days 14 hours ago) and read 8219 times:

We typically only require a aux ground air start when the airstart cart is not available. It's Newton's law.


"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward" Leonardo Da Vinci
User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 11, posted (8 years 2 months 2 weeks 6 days 12 hours ago) and read 8212 times:



Its normally reffered to as the Pneumatic Jet Starter unit.
In case an Aircraft has an Unserviceable APU,or APU that has an u/s Pneumatics.The Pneumatic Jet Starter is used.

Depending on the Requirement of Airflow as per Engine to be started.The Unit can be of a certain Capacity,with Two hoses.These hoses attach to Ground connectors of the Aircraft.

The Pneumatic Jet Starter is almost a Truck mounted APU.The Pneumatic Supply is used to Crank the Pneumatic starter mounted on the Engine & crank it to achieve necessary Start.

regds
MEL



Think of the brighter side!
User currently offlineUndehoulli From , joined Dec 1969, posts, RR:
Reply 12, posted (8 years 2 months 2 weeks 6 days 6 hours ago) and read 8178 times:

Quoting GEG (Reply 5):
Roughly how much air pressure is required for the start?

The aircraft I fly requires 12 PSI for starting the engines, either from the APU or from an air cart. I've never had to use an air cart, and I usually see around 35 PSI from the APU.


User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 13, posted (8 years 2 months 2 weeks 6 days 6 hours ago) and read 8177 times:

Quoting Undehoulli (Reply 12):
The aircraft I fly requires 12 PSI for starting the engines

12psi.
Which Aircraft is this regarding.
regds
MEL



Think of the brighter side!
User currently offlineCharlienorth From United States of America, joined Jun 2006, 1122 posts, RR: 4
Reply 14, posted (8 years 2 months 2 weeks 6 days 3 hours ago) and read 8156 times:

A-320 with CFM56 >25 psi, someone asked about APU's breaking,some seem to die if you look at them wrong!They're real susceptible to shutting down at low oil levels,there was an airline I worked on-call for,CRJ's,Maint control would call about a failed APU and often we would service the oil level and the thing would then operate normally,the sad thing was it usually just out of a line-check,pressure switches are another high failure item,apu door rigging seemed to be a problem on the 737/200,speaking of APU's anyone up for a APU flow control valve on a 727?

User currently offlineUndehoulli From , joined Dec 1969, posts, RR:
Reply 15, posted (8 years 2 months 2 weeks 5 days 19 hours ago) and read 8108 times:

Quoting HAWK21M (Reply 13):
12psi.
Which Aircraft is this regarding

The Dornier 328JET.


User currently offlineNonfirm From United States of America, joined Sep 2005, 434 posts, RR: 0
Reply 16, posted (8 years 2 months 2 weeks 5 days 12 hours ago) and read 8082 times:

We use the air start cart or (huffer) as we call it for any Eng start the the whole apu is on Mel or the pneumatics system is inop.If the electrics on the apu is inop then we use apu air but ground power to complete the start then a cross-bleed to start the opposite Eng.We also only start the # 1 Eng at the gate because the huffer is on the r/h side of the a/c due to the pluming and safety for the ground crew.  airplane 

User currently offlineUAL Bagsmasher From United States of America, joined Sep 1999, 2147 posts, RR: 10
Reply 17, posted (8 years 2 months 2 weeks 3 days 22 hours ago) and read 8006 times:

The CRJ-200 APU is probably worth more in scrap metal than as an APU. Well, maybe not that bad, but close. I guess it's good job security though. I second the motion about bad pressure switches. They go bad all the time, and leak oil more often than not.

User currently offlineTWAL1011727 From United States of America, joined Mar 2006, 629 posts, RR: 0
Reply 18, posted (8 years 2 months 2 weeks 3 days 21 hours ago) and read 7999 times:

Quoting FlyMatt2Bermud (Reply 10):
We typically only require a aux ground air start when the airstart cart is not available.

Could you tell us what the difference between the two are?

Last time I checked their one in the same.

KD MLB


User currently offlineFr8Mech From United States of America, joined Sep 2005, 5453 posts, RR: 14
Reply 19, posted (8 years 2 months 2 weeks 3 days 21 hours ago) and read 7997 times:

Quoting TWAL1011727 (Reply 18):
Could you tell us what the difference between the two are?

I believ what he's saying is: they only need an airstart cart when their airstart cart is unavailable. And I believe he means Murphy's Law.



When seconds count...the police are minutes away.
User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 20, posted (8 years 2 months 2 weeks 3 days 13 hours ago) and read 7964 times:

Quoting Charlienorth (Reply 14):
apu door rigging seemed to be a problem on the 737/200

You mean the Microswitch on the Door.Right.

Quoting Undehoulli (Reply 15):
Quoting HAWK21M (Reply 13):
12psi.
Which Aircraft is this regarding

The Dornier 328JET.

What type APU.

regds
MEL



Think of the brighter side!
User currently offlineFlyMatt2Bermud From United States of America, joined Jan 2006, 563 posts, RR: 7
Reply 21, posted (8 years 2 months 2 weeks 2 days 8 hours ago) and read 7926 times:

Quoting TWAL1011727 (Reply 18):
Quoting FlyMatt2Bermud (Reply 10):
We typically only require a aux ground air start when the airstart cart is not available.

Could you tell us what the difference between the two are?

Last time I checked their one in the same.



Quoting Fr8Mech (Reply 19):
I believe he means Murphy's Law.

Sorry folks I was just trying to add a bit of levity to the thread with both remarks. But really when we are places such as Timbuktu it seems the thing wants to start hotter or slower just to get under my skin.



"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward" Leonardo Da Vinci
User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 22, posted (8 years 2 months 2 weeks 2 days 2 hours ago) and read 7912 times:

Quoting FlyMatt2Bermud (Reply 21):
Sorry folks I was just trying to add a bit of levity to the thread with both remarks

Don't be sorry, I think at least a few of us got what you meant to say.  Wink

Chris



Don't blame me, I don't work here...
User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 23, posted (8 years 2 months 2 weeks 2 days 2 hours ago) and read 7910 times:

Quoting FlyMatt2Bermud (Reply 21):
Sorry folks I was just trying to add a bit of levity to the thread with both remarks.

No need to apoligize.We understand what you meant.
Cheers and keep the Info flowing.
regds
MEL



Think of the brighter side!
User currently offlineNZ8800 From New Zealand, joined May 2006, 425 posts, RR: 2
Reply 24, posted (8 years 2 months 2 weeks 1 day 22 hours ago) and read 7895 times:

Is this (airstart cart) the same thing used to start a turboprop like the SAAB 340?

Or are they started electrically?

How high do you have to run the engine (always port, I think) on the SAAB to before you can start the other one?



MDZWTA ~ Mobile Disaster Zone When Travelling Abroad
25 TWAL1011727 : The SAAB 340 is an electrically started engine..Since the A/C does not have an APU it has to have a 28volt DC ground power unit. If I remember correc
26 Tristarsteve : Well that struck a chord. I spent many a year on the B737-200 and have lost track of the number of times I hit the APU door to make the APU start! Ne
27 HAWK21M : Its the Sequence Microswitch on the Door.Tapping the Door makes the Contact with the Switch to Supply Voltage to the Starter Motor to crank the APU.
28 Charlienorth : If I only knew about tapping the door from 2R!!! The 737/200 had a lot of little tricks that senior mechs and pilots could show you!
29 HAWK21M : That would be Interesting. regds MEL
30 N8076U : I've seen this done a couple times. Looks pretty funny watching it. Our 737 gates had a bucket-on-a-pole so the fuelers could hand their loading shee
31 Post contains images HAWK21M : Thats a common one.But We use a trestle regds MEL
32 N8076U : What's a trestle? Chris
33 Post contains images HAWK21M : Out here its called a Trestle.Is it a different name out there. Aircraft Ground Equipment to reach places on the Aircraft Exterior to Enable Mx work.
34 Post contains images N8076U : Ah, "stairs". Chris
35 Post contains images AF1624 : LOL. That one made my day       [Edited 2006-07-13 23:14:36]
36 HAWK21M : Is it called stairs even if it of various Heights & sizes. regds MEL
37 Post contains images N8076U : Generally speaking, yes, we'd just call them stairs, sometimes workstands or work platforms. Some we had were fixed-height, but most were adjustable.
38 HAWK21M : We have the Hydraulically Adjustable type out here.Works well. regds MEL
39 ReidYYZ : Now lets suppose you are on the outer reaches of the universe with a bad apu (totally &%$#ED) you come in on the rescue aircraft because the first a/c
40 HAWK21M : We Tried it [Cross bleed start from Aircraft Apu to other Aircraft Engine] with Help from Another operator as Grd unit was not Available. Worked Grea
41 N353SK : I believe you're thinking of a GPU (ground power unit). I know a lot of BE1900s don't have APUs for weight reasons, so I would assume that the 340 is
42 HAWK21M : We normally use a longer hose & do Two starts.More safer. Normally 40psi.Min 35psi for JT8Ds but Volume will vary per Engine type eg the RB211-535C r
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