c5load
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What Are These Openings On The Belly Of The 757

Wed Mar 10, 2010 5:27 pm

What are the two small doors on each side of the red beacon strobe on the belly of this a/c? If these were APU inlet doors, wouldn't they be closed prior to taking off?


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Maverick623
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RE: What Are These Openings On The Belly Of The 757

Wed Mar 10, 2010 6:10 pm

Quoting c5load (Thread starter):
What are the two small doors on each side of the red beacon strobe on the belly of this a/c?

Bleed air pack exhausts. They're very nice to stand under on cold days.

Quoting c5load (Thread starter):
If these were APU inlet doors, wouldn't they be closed prior to taking off?

The APU inlet door is just below the right side of the vertical stabilizer (facing forward), and if you look closely you can see that it too is open.

The door only closes when the APU is not running.
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Jetlagged
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RE: What Are These Openings On The Belly Of The 757

Wed Mar 10, 2010 6:42 pm

Quoting Maverick623 (Reply 1):
Bleed air pack exhausts

The packs themselves "exhaust" into the cabin and so bleed air isn't dumped directly overboard. The ram air system which cools the packs has external exhausts though.
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CanadianNorth
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RE: What Are These Openings On The Belly Of The 757

Wed Mar 10, 2010 7:10 pm

Looks like the air conditioning pack exhaust louvres to me as well (at least thats what they are called on the 737, I don't have any 757 experience but I would think it's reasonably similar.)

As said on pretty much every modern jetliner I can think of the APU inlet door can be found up near the empenage.


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Mir
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RE: What Are These Openings On The Belly Of The 757

Wed Mar 10, 2010 7:12 pm

Quoting c5load (Thread starter):
If these were APU inlet doors, wouldn't they be closed prior to taking off?

Only if the APU wasn't running. If the APU is running, it needs to get air somehow, and that means an open inlet door.

But, as has already been mentioned, they are related to the bleed air system and the packs, not the APU.

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DL_Mech
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RE: What Are These Openings On The Belly Of The 757

Wed Mar 10, 2010 9:40 pm

Here's a good view of the APU inlet on this now scrapped aircraft....


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c5load
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RE: What Are These Openings On The Belly Of The 757

Wed Mar 10, 2010 10:10 pm

Quoting Mir (Reply 4):
Only if the APU wasn't running. If the APU is running, it needs to get air somehow, and that means an open inlet door

You guys don't turn the APU off once engines are started? Isn't that kind of a waste of fuel? Once the engines are going, they will provide all the bleed air and a/c systems.
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flybaurlax
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RE: What Are These Openings On The Belly Of The 757

Wed Mar 10, 2010 11:17 pm

Quoting c5load (Reply 6):
You guys don't turn the APU off once engines are started? Isn't that kind of a waste of fuel? Once the engines are going, they will provide all the bleed air and a/c systems.

Most of the time they will turn the APU off during taxi, but some flights, such as ETOPS flights require the APU to be on until the aircraft are within a certain distance of their destination, or suitable alternates.
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PGNCS
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 12:11 am

Quoting jetlagged (Reply 2):
Quoting Maverick623 (Reply 1):
Bleed air pack exhausts

The packs themselves "exhaust" into the cabin and so bleed air isn't dumped directly overboard. The ram air system which cools the packs has external exhausts though.

Indeed, the photo shows the AC pack cooling exhausts open (or nearly so) quite clearly.

Quoting c5load (Reply 6):
You guys don't turn the APU off once engines are started? Isn't that kind of a waste of fuel? Once the engines are going, they will provide all the bleed air and a/c systems.

Normally yes, however some MEL items require it to remain running throughout the flight (engine driven generator inop, for instance). If the APU is running, it's running for a reason.

Quoting flybaurLAX (Reply 7):
Quoting c5load (Reply 6):
You guys don't turn the APU off once engines are started? Isn't that kind of a waste of fuel? Once the engines are going, they will provide all the bleed air and a/c systems.


Most of the time they will turn the APU off during taxi, but some flights, such as ETOPS flights require the APU to be on until the aircraft are within a certain distance of their destination, or suitable alternates.

There are indeed times when the APU is required in flight, but we do not have to have the APU running during an ETOPS flight; it must be operational and available on ETOPS flights on the 757/767 however, and there is a program for starting the APUs in flight to test their cold-soaked starting capability in most ETOPS programs I have seen. As a very minor caveat, I have been told that at least one carrier has ETOPS 120 with the APU inop on the 767, but I have never seen that in print. If someone knows about that I'd be interested. I can definitively say that we don't keep the APU running across the ocean on ETOPS segments, however.
 
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 12:14 am

Quoting PGNCS (Reply 8):
Normally yes, however some MEL items require it to remain running throughout the flight

So the APU inlet door I see in the photo above can withstand the air during flight? I would think it'd rip right off.
"But this airplane has 4 engines, it's an entirely different kind of flying! Altogether"
 
PGNCS
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 12:23 am

Quoting c5load (Reply 9):
Quoting PGNCS (Reply 8):
Normally yes, however some MEL items require it to remain running throughout the flight

So the APU inlet door I see in the photo above can withstand the air during flight? I would think it'd rip right off.

Yes it can.
 
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 12:46 am

Quoting c5load (Reply 6):
You guys don't turn the APU off once engines are started?

I can't tell from that picture if the aircraft is taking off or landing.

The flaps/slats appear to be configured for take off so maybe the aircraft has pushed back from the stand and is about to turn off the APU but it could have also just landed and the pilot has just turned on the APU and he is in the process of retracting the flaps and slat. I just can't tell.
 
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 4:39 am

Quoting PGNCS (Reply 8):
I have been told that at least one carrier has ETOPS 120 with the APU inop on the 767, but I have never seen that in print. If someone knows about that I'd be interested. I can definitively say that we don't keep the APU running across the ocean on ETOPS segments, however.

FX actually has a 180 ETOPS with an APU inop. They run their 777's ETOPS 207.
 
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 4:41 am

Quoting flybaurLAX (Reply 7):
Most of the time they will turn the APU off during taxi, but some flights, such as ETOPS flights require the APU to be on until the aircraft are within a certain distance of their destination, or suitable alternates.

That is not the case. Unlike lesser Aircraft (737) the 757 has more than adequate redundancy to provide for ETOPS 180 without needing the APU to be running most of the flight !
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PGNCS
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 5:01 am

Quoting stratosphere (Reply 12):
Quoting PGNCS (Reply 8):
I have been told that at least one carrier has ETOPS 120 with the APU inop on the 767, but I have never seen that in print. If someone knows about that I'd be interested. I can definitively say that we don't keep the APU running across the ocean on ETOPS segments, however.

FX actually has a 180 ETOPS with an APU inop. They run their 777's ETOPS 207.

On the 757? I'm not doubting you, I was just restricting my answers to 757/767 aircraft.
 
Mir
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 5:04 am

Quoting c5load (Reply 6):
You guys don't turn the APU off once engines are started? Isn't that kind of a waste of fuel? Once the engines are going, they will provide all the bleed air and a/c systems.

Normal ops for most operators is to have the APU off once both engines are running. But there are a variety of situations where you'd want it on, so leaving it running for takeoff is hardly uncommon.

Quoting c5load (Reply 9):
So the APU inlet door I see in the photo above can withstand the air during flight? I would think it'd rip right off.

It can withstand it, yes. On some aircraft you may see an airspeed limitation when the door is open, but it's high enough that it doesn't really affect things too badly.

-Mir
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stratosphere
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 5:09 am

Quoting PGNCS (Reply 14):
On the 757? I'm not doubting you, I was just restricting my answers to 757/767 aircraft.

The only ETOPS A/C at FX are 777's...Sorry if this was only a 757/767 comparision

[Edited 2010-03-10 21:10:38]
 
flybaurlax
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 5:18 pm

Quoting Max Q (Reply 13):

That is not the case. Unlike lesser Aircraft (737) the 757 has more than adequate redundancy to provide for ETOPS 180 without needing the APU to be running most of the flight !

I meant to specify for the 737. I only know about ETOPS requirements for AS 737s, as I sat in on an ETOPS class, but I know it varies from each carrier as to what the FAA requires.
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 5:50 pm

Quoting Maverick623 (Reply 1):
The APU inlet door is just below the right side of the vertical stabilizer (facing forward), and if you look closely you can see that it too is open.

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A Door on the RH Empennage side of the Vertical stablizer root.When closed its flush with the fuselage.

Quoting Maverick623 (Reply 1):

Bleed air pack exhausts.

Ram air Exhaust Louvers.

Quoting c5load (Reply 6):

You guys don't turn the APU off once engines are started? Isn't that kind of a waste of fuel? Once the engines are going, they will provide all the bleed air and a/c systems.

Depending on company SOP.The APU is also a extra source of Pneumatics & Electricals.

Quoting c5load (Reply 9):
So the APU inlet door I see in the photo above can withstand the air during flight? I would think it'd rip right off.

It can.....Also APU Pneumatics have height restrictions.

regds
MEL.

[Edited 2010-03-11 09:54:24]
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FX772LRF
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 9:51 pm

There's also a takeoff method used by some pilots called the "bleeds off" method - they use the air from the APU for pressurization instead of engine bleed air, which lets the engines use their full power for takeoff. It's used in situations such as overloaded. Not completely sure if the 757 is capable of such a thing. I know that the A319 is capable of such a thing.

I actually learned this from one of HAL's trip reports when he was at American West. Good read from a trip report and a Tech/Ops standpoint.
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[Edited 2010-03-11 13:52:33]
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PGNCS
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 10:06 pm

Quoting stratosphere (Reply 16):
Quoting PGNCS (Reply 14):
On the 757? I'm not doubting you, I was just restricting my answers to 757/767 aircraft.

The only ETOPS A/C at FX are 777's...Sorry if this was only a 757/767 comparision

No don't apologize! I am glad for the info; I am pretty familiar with 757/767 ETOPS at several carriers, and did it a lot myself in the past. I was just wanting to clarify what airplane we were talking about. Thanks for the information!  
 
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RE: What Are These Openings On The Belly Of The 757

Thu Mar 11, 2010 10:09 pm

Quoting Mir (Reply 15):
Quoting c5load (Reply 9):
So the APU inlet door I see in the photo above can withstand the air during flight? I would think it'd rip right off.

It can withstand it, yes. On some aircraft you may see an airspeed limitation when the door is open, but it's high enough that it doesn't really affect things too badly.

And on other aircraft the APU is not available in flight at all (e.g. B-744, B-727), but 757/767's all have APUs capable of inflight operation.
 
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RE: What Are These Openings On The Belly Of The 757

Fri Mar 12, 2010 6:40 am

Quoting jetlagged, reply=2] cotizando Maverick623 (contestaci
[quote=PGNCS
(Reply 21):
but 757/767's all have APUs capable of inflight operation.

On the B757s.....Pneumatic usage height restrictions exist.
regds
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RE: What Are These Openings On The Belly Of The 757

Fri Mar 12, 2010 5:25 pm

Quoting FX772LRF (Reply 19):
It's used in situations such as overloaded

Not too be technical or anything, but I doubt anyone is taking off overloaded. At max weight perhaps?
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FX772LRF
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RE: What Are These Openings On The Belly Of The 757

Fri Mar 12, 2010 8:51 pm

Quoting AirPortugal310 (Reply 23):
Not too be technical or anything, but I doubt anyone is taking off overloaded. At max weight perhaps?

Yes, that's what I meant. I was thinking along the lines of overloaded for typical takeoff thrust configurations.

Thanks for that.  

-Noah   
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PGNCS
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RE: What Are These Openings On The Belly Of The 757

Sat Mar 13, 2010 4:20 am

Quoting HAWK21M (Reply 22):
Quoting jetlagged, reply=2] cotizando Maverick623 (contestaci
[quote=PGNCS (Reply 21):
but 757/767's all have APUs capable of inflight operation.

On the B757s.....Pneumatic usage height restrictions exist.
regds
MEL.

True.
 
XFSUgimpLB41X
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RE: What Are These Openings On The Belly Of The 757

Sat Mar 13, 2010 5:57 am

Quoting FX772LRF (Reply 19):
There's also a takeoff method used by some pilots called the "bleeds off" method - they use the air from the APU for pressurization instead of engine bleed air, which lets the engines use their full power for takeoff. It's used in situations such as overloaded. Not completely sure if the 757 is capable of such a thing. I know that the A319 is capable of such a thing.

In most situations we use just a "packs off" takeoff if we need a bit of extra performance out of the engines with a wider temperature margin. The cabin is unpressurized until you reach acceleration height (9 times out of 10 that's 1000 AGL) and reduce to climb power. Then you select the packs back on one at a time.

In the 757 for very high altitude takeoffs, doing a packs off takeoff may cause the cabin to exceed warning altitude, thus dropping the "orange grove" in the cabin. In this case we do an APU-to-Pack takeoff. The APU is used to supply air to one pack, and the other is shut off. The engine bleeds are shut off. It has the same effect as the packs off takeoff for performance (there is a 500 pound climb gradient penalty for the APU door being open, however).

Once you reach accel height and reduce to climb power you transfer the bleeds to the engines , turn on the other pack and shut down the APU.
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FlyASAGuy2005
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RE: What Are These Openings On The Belly Of The 757

Sun Mar 14, 2010 1:01 am

Quoting FX772LRF (Reply 19):
There's also a takeoff method used by some pilots called the "bleeds off" method - they use the air from the APU for pressurization instead of engine bleed air, which lets the engines use their full power for takeoff. It's used in situations such as overloaded. Not completely sure if the 757 is capable of such a thing. I know that the A319 is capable of such a thing.

I may be way off but is this sort of the reason why the CR2 takes off with the APU running (if it's even working   )
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XFSUgimpLB41X
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RE: What Are These Openings On The Belly Of The 757

Sun Mar 14, 2010 7:23 pm

Quoting FlyASAGuy2005 (Reply 27):
I may be way off but is this sort of the reason why the CR2 takes off with the APU running (if it's even working )

The 14th stage bleeds (used for anti-ice and thrust reverse) are always open on the CRJ-200, but not necessarily drawn.

The 10th stage are used for air conditioning and pressurization packs which can be provided by the APU by transferring the bleed valves to do so.


When you have to use anti-ice for takeoff, you are required to take off with the APU running and supplying the air for the packs. If the APU is deffered, you have to do a packs off takeoff and unpressurized.

Many times guys took off with the APU supplying the packs anyways just because until you get the engines up to power, they really don't put out much airflow. APU deferrals in the summer can make for a very uncomfortable taxi-out.
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DC8FriendShip
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RE: What Are These Openings On The Belly Of The 757

Mon Mar 15, 2010 5:00 pm

Quoting jetlagged, reply=2] cotizando Maverick623 (contestaci
[quote=XFSUgimpLB41X
(Reply 28):
The 14th stage bleeds (used for anti-ice and thrust reverse) are always open on the CRJ-200, but not necessarily drawn.

There are shutoff valves for 14th stage same as tenth stage. Remember, T/R's won't work on a 200 if 14th stage is turned off.
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787luvr
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RE: What Are These Openings On The Belly Of The 757

Tue Mar 16, 2010 6:33 pm

I don't mean to veer off topic or hijack the thread but.. If you take a look at the first photo of the 787 on the far right you can see what I assume to be an exhaust port that is open, right in front of an intake. On the second photo you can see that the exhaust port is closed. Does anyone know what either of these are for and why the one is closed in the second photo. Also, with it being placed so close to the intake I'm assuming that to some extent the intake is ingesting the exhaust?


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XFSUgimpLB41X
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RE: What Are These Openings On The Belly Of The 757

Tue Mar 16, 2010 7:07 pm

Quoting DC8FriendShip (Reply 29):
There are shutoff valves for 14th stage same as tenth stage. Remember, T/R's won't work on a 200 if 14th stage is turned off.

That's what I meant when I said the valves are always selected open but not necessarily utilized.  
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tdscanuck
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RE: What Are These Openings On The Belly Of The 757

Tue Mar 16, 2010 11:20 pm

Quoting 787luvr (Reply 30):
If you take a look at the first photo of the 787 on the far right you can see what I assume to be an exhaust port that is open, right in front of an intake. On the second photo you can see that the exhaust port is closed. Does anyone know what either of these are for and why the one is closed in the second photo.

It's not an exhaust port, it's a FOD deflector. That's the cabin air compressor inlet; the door prevents FOD from getting sucked in when you're on the ground. In the second picture, the airplane isn't on the ground so the deflector is closed (flush).

Tom.
 
FlyASAGuy2005
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RE: What Are These Openings On The Belly Of The 757

Tue Mar 16, 2010 11:59 pm

Quoting 787luvr (Reply 30):

Are there any non mock-up photos of the Dreamliner flightdeck?
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787luvr
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RE: What Are These Openings On The Belly Of The 757

Wed Mar 17, 2010 12:59 am

Quoting tdscanuck (Reply 32):
It's not an exhaust port, it's a FOD deflector.

Thanks Tom! That never even crossed my mind...   
787luvr
 
tdscanuck
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RE: What Are These Openings On The Belly Of The 757

Wed Mar 17, 2010 1:28 am

Quoting FlyASAGuy2005 (Reply 33):
Are there any non mock-up photos of the Dreamliner flightdeck?

There were some non-mockup shots from a 777 customer that got a tour in Everett that got linked from a.net a few days ago, but they got taken down.

If you go to 1:23 in the video here, you can see footage of the real flight deck:
http://787flighttest.com/gauntlet-test/

Most of the mockup shots you see are from the fixed-base simulator, which is all real hardware anyway, so in a sense it's a "real" flight deck, just with a fake view out the windows.

Tom.

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