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HAWK21M
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TR Deployment On B772LR

Thu Aug 09, 2007 1:37 am


Can the T/Rs be deployed on the B772LR before NLG Air-Grd sense.
regds
MEL
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DualQual
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RE: TR Deployment On B772LR

Thu Aug 09, 2007 2:01 am

Most Boeing products don't require WOW on the NLG for the reversers. In fact on the 737 you can deploy the T/R's once the radio altitude is less then 10 feet! Not that you ever would do that but you can start the reversers before you have even touched down.
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tdscanuck
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RE: TR Deployment On B772LR

Thu Aug 09, 2007 2:16 am

Quoting HAWK21M (Thread starter):
Can the T/Rs be deployed on the B772LR before NLG Air-Grd sense.

Yes. The 777 Air/Ground system uses sensors on the MLG only (two sensors per landing gear). It doesn't care if the NLG is on the ground.

Tom.
 
ANITIX87
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RE: TR Deployment On B772LR

Thu Aug 09, 2007 2:18 am

Along similar lines. Is the TR activated just by pulling a lever/pressing a button? Or does "reverse thrust" actually have to be increased or decresed once the doors are opened?

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Acey
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RE: TR Deployment On B772LR

Thu Aug 09, 2007 2:38 am

Quoting ANITIX87 (Reply 3):
Along similar lines. Is the TR activated just by pulling a lever/pressing a button? Or does "reverse thrust" actually have to be increased or decresed once the doors are opened?

Once the thrust levers are pulled back to idle, the reversers can be opened up by pulling on the reverse levers...no thrust actually needs to be applied most of the time simply idle reverse is used to save engine wear and for noise abatement. Some airports, in fact, prohibit anything beyond idle reverse unless there's an emergency.
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tdscanuck
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RE: TR Deployment On B772LR

Thu Aug 09, 2007 2:54 am

Quoting ANITIX87 (Reply 3):
Is the TR activated just by pulling a lever/pressing a button? Or does "reverse thrust" actually have to be increased or decresed once the doors are opened?

As Acey correctly stated, if you just pull the throttles to idle and engage the reversers, the T/R's will deploy but the engine won't spool up. If you want to go above idle reverse, you pull up on the thrust reverser levers. For most purposes, the T/R levers are like a second set of throttles that only work once you pull the main throttles to idle.

All of the above is Boeing only. Based on what I know of Airbus throttle design, I suspect they use a different method.

Tom.
 
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HAWK21M
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RE: TR Deployment On B772LR

Thu Aug 09, 2007 3:11 am

Quoting DualQual (Reply 1):
In fact on the 737 you can deploy the T/R's once the radio altitude is less then 10 feet

Not after a mod was incorporated that Included the NLG Air-Grd sensor near the rudder steering disconnect mechanism.

Quoting ANITIX87 (Reply 3):
Is the TR activated just by pulling a lever/pressing a button? Or does "reverse thrust" actually have to be increased or decresed once the doors are opened

Reverse thrust has to be applied after the Feedback cams permit the R/T levers to move back,following T/R doors opening.

regds
MEL
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AA737-823
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RE: TR Deployment On B772LR

Thu Aug 09, 2007 3:16 am

The pic you've posted here is quite common... this topic comes up once a year or so, and most people seem to believe that this is not possible. Someone last time actually suggested-very scientifically- that this would be a terrible idea; that opening reversers would create a forward rotational moment on the fuselage, slamming the nose down onto the ground, and damaging components.
That person clearly hasn't spent much time at an airport. All of my 747s deploy reversers befor nose gear contact, as do most other aircraft. It's simply pilot choice.

In fact, the original DC-8 series (everything but the -70 retrofit) used the inboard #2 and #3 reversers as speed breaks in flight... scary!
 
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HAWK21M
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RE: TR Deployment On B772LR

Fri Aug 10, 2007 1:22 am

The reason I asked this was:-
1.The B772LR was the 1st time in the country &
2.The B737 had a mod carried out to eliminate that.
regds
MEL
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tdscanuck
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RE: TR Deployment On B772LR

Fri Aug 10, 2007 3:02 am

Quoting HAWK21M (Reply 8):
The reason I asked this was:-
1.The B772LR was the 1st time in the country &
2.The B737 had a mod carried out to eliminate that.

It must be an optional mod, or it works differently than you're speculating...production 737NG's coming out of the factory today can deploy their T/R's at 10' radio altitude.

Tom.
 
kaddyuk
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RE: TR Deployment On B772LR

Fri Aug 10, 2007 3:30 am

The throttles are prevented from moving to the reverse thrust setting by a baulk. There are two of them.

Once the air/ground senses that the aircraft is on the ground, the reverse activation baulk is removed which will allow you to move the throttles to the reverse thrust position.

The piggy back levers which control the engine power setting during reverse thrust are then held by a second baulk at idle untill the thrust reversers have opened. When they are open, this baulk is removed so that you can apply reverse thrust.

Unless you're on the airbus in which you retract the throttles to the reverse thrust detent till the t/rs open and then you can retract the throttles further to increse engine power whilst the t/rs are open.
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Jetlagged
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RE: TR Deployment On B772LR

Fri Aug 10, 2007 4:10 am

Quoting Kaddyuk (Reply 10):
Once the air/ground senses that the aircraft is on the ground, the reverse activation baulk is removed which will allow you to move the throttles to the reverse thrust position.

The piggy back levers which control the engine power setting during reverse thrust are then held by a second baulk at idle untill the thrust reversers have opened. When they are open, this baulk is removed so that you can apply reverse thrust.

Only one reverse baulk is required. On a Boeing you can always pull the thrust levers back to idle and raise the piggy back levers to the baulk position. In flight this does nothing. On the ground the reverser is enabled. Once the reverser is fully open the baulk is removed and full reverse can be applied.

On a FBW Airbus there are small reverse levers which are raised to allow the thrust lever to be moved into reverse idle. Once the reverser is fully open the baulk is removed and the thrust lever can be pulled further back to increase reverse thrust. The A300 and A310 use a piggy back reverse thrust lever system similar to Boeing.

There is a second baulk and it prevents forward thrust lever movement while the reverser closes.

On older aircraft with throttle cables there is no baulk in the pedestal as such, but there is a follow up cam mechanism linked to reverse position which physically prevents throttle cable movement.
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HAWK21M
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RE: TR Deployment On B772LR

Fri Aug 10, 2007 2:16 pm

Quoting Tdscanuck (Reply 9):
production 737NG's coming out of the factory today can deploy their T/R's at 10' radio altitude.

Isn't there an Air-Grd Sw at the Rudder steering disconnect mechanism beyond the LH NLG access panels.
regds
MEL
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tdscanuck
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RE: TR Deployment On B772LR

Fri Aug 10, 2007 10:54 pm

Quoting HAWK21M (Reply 12):
Quoting Tdscanuck (Reply 9):
production 737NG's coming out of the factory today can deploy their T/R's at 10' radio altitude.

Isn't there an Air-Grd Sw at the Rudder steering disconnect mechanism beyond the LH NLG access panels.

There may be, but the T/R control logic is set up as "Allow T/R deploy IF airplane on ground OR (airplane in air AND radio altitude < 10')". In other words, the air/ground system isn't a hard-lockout for the T/R on a 737NG.

Tom.
 
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HAWK21M
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RE: TR Deployment On B772LR

Sat Aug 11, 2007 2:08 pm

Quoting Tdscanuck (Reply 13):
but the T/R control logic is set up as "Allow T/R deploy IF airplane on ground OR (airplane in air AND radio altitude < 10'

Wasn't there a mod to eliminate just that in Air <10' logic.
regds
MEL
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tdscanuck
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RE: TR Deployment On B772LR

Sat Aug 11, 2007 6:27 pm

Quoting HAWK21M (Reply 14):
Quoting Tdscanuck (Reply 13):
but the T/R control logic is set up as "Allow T/R deploy IF airplane on ground OR (airplane in air AND radio altitude < 10'

Wasn't there a mod to eliminate just that in Air <10' logic.

I found one Service Bulletin issued to a single operator who requested that the T/R deployment be disabled until the NLG shock strut was compressed...it was for their 737-Classics only. It wasn't issued to the rest of the fleet.

There's also a Service Bulletin to add the radio altimeter feature to older 737-Classics that didn't originally have it.

There's an AD that required adding the NLG sensor into the T/R air/ground circuit for 737-100/200. The original configuration just used an MLG air/ground sensor.

I couldn't find anything comparable for the 737NG fleet. As of yesterday, the ability to deploy T/R's on a 737NG at < 10' was in all the manuals and schematics.

Tom.
 
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HAWK21M
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RE: TR Deployment On B772LR

Sat Aug 11, 2007 10:59 pm

Quoting Tdscanuck (Reply 15):
I found one Service Bulletin issued to a single operator who requested that the T/R deployment be disabled until the NLG shock strut was compressed...it was for their 737-Classics only



Quoting Tdscanuck (Reply 15):
There's an AD that required adding the NLG sensor into the T/R air/ground circuit for 737-100/200. The original configuration just used an MLG air/ground sensor.

It could be JT8D related T/Rs.
regds
MEL
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tdscanuck
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RE: TR Deployment On B772LR

Tue Aug 14, 2007 8:48 pm

Found this while doing an a.net photo quiz...you can definitely deploy the T/R on a 737CL before the nose wheel comes down:

View Large View Medium
Click here for bigger photo!

Photo © Ben Wang



Tom.
 
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HAWK21M
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RE: TR Deployment On B772LR

Wed Aug 15, 2007 1:14 am

Quoting Tdscanuck (Reply 17):
you can definitely deploy the T/R on a 737CL before the nose wheel comes down:

Nice find.Thanks.
Now the only doubt remains what about the B731/2.Im certain there was an SB on this.
regds
MEL
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