speedracer1407
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Autothrottle Movement Of Staggered Throttles

Fri Jan 12, 2007 9:40 pm

Sorry for the cumbersom topic title. it's my understanding that all boeing autothrottles move the levers unlike Airbus ATs. If the throttles are staggered for whatever reason, such as to account for rigging on older non-FADEC models, does the autothrottle realign the throttle lever positions so that they are nolonger staggered to account for out-of-rig conditions, or does the AT simply keep the stagger previously set by hand upon throttle-up for takeoff?

Thanks for replies,

O
Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
 
boeingfixer
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RE: Autothrottle Movement Of Staggered Throttles

Fri Jan 12, 2007 11:53 pm

On a direct Thrust Lever-cable-FCU/HMU(non-FADEC) setup with auto throttle(AT), you will always have stagger if it is present. The AT cannot remove the stagger on this type of system and you will have stagger with the AT engaged.

Cheers,

John
Cheers, John YYC
 
RichardPrice
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RE: Autothrottle Movement Of Staggered Throttles

Sat Jan 13, 2007 12:36 am

Quoting Speedracer1407 (Thread starter):
it's my understanding that all boeing autothrottles move the levers unlike Airbus ATs

I dont know if it still the case, but at one time the autothrottle system on the 737-300 was static.

It was this that contributed to the 1989 Kegworth air crash because the autothrottle detected the lower performance of the left engine after the blade fracture, and increased the fuel flow to the engine to improve its performance. When the pilots disengaged the autothrottle, the fuel flow fell back to the level required by the position of the throttles and the vibrations decreased - the pilots wrongly thought that this was because they had shut down the right-hand engine.
 
Corsair2
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RE: Autothrottle Movement Of Staggered Throttles

Sat Jan 13, 2007 2:35 am

In many of the newer FADEC throttle designs, an electric motor drives a sector gear pass which is coupled simultaneously to both levers. The throttles will stay split if they are moved apart from each other. This happens largely to account for an in-flight shutdown situation.
"We have clearance Clarence. Roger, Roger. What's our vector Victor?"
 
David L
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RE: Autothrottle Movement Of Staggered Throttles

Sat Jan 13, 2007 3:22 am

Quoting RichardPrice (Reply 2):

I don't want to rock the boat but wasn't Kegworth a -400?

Still trying hard not to rock the boat but... I can't find any reference to that autothrottle behaviour in the Kegworth accident.

Sorry.  Smile
 
RichardPrice
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RE: Autothrottle Movement Of Staggered Throttles

Sat Jan 13, 2007 3:50 am

Quoting David L (Reply 4):
I don't want to rock the boat but wasn't Kegworth a -400?

You are quite right, it was.

Quoting David L (Reply 4):
Still trying hard not to rock the boat but... I can't find any reference to that autothrottle behaviour in the Kegworth accident.

Its referenced in one of the 'Seconds From Disaster' or similiar shows, thats where I initially remembered it from.

It would seem that they got it wrong - I have jsut checked the AAIB report for the Kegworth crash, and the problem indicated with regard to the autothrottle not moving the levers physically was due to their only being one actuator for the lever set.

Thus when the left engines power fell, the autothrottle increased fuel flow but no obvious indication was made to the crew at the time - standrd fuel flow indicators showed an increase, but because the crew were under stress at the time it was missed.

Disengaging the autothrottle to shut down the second engine had the effect of returning the first engines fuel flow to that required by the position of the throttle lever - having the knock on effect of reducing vibrations in the cockpit to near normal, leading the pilots to believe they had shut down the correct engine.

Increasing the throttle on descent into Midlands caused the vibrations to return, eventually destroying the engine totally.

http://www.aaib.gov.uk/publications/formal_reports/no_4_90_502831.cfm

Paragraph 2.2.2.2 explains it quite nicely.
 
VC-10
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RE: Autothrottle Movement Of Staggered Throttles

Sat Jan 13, 2007 4:20 am

Quoting Speedracer1407 (Thread starter):
If the throttles are staggered for whatever reason, such as to account for rigging on older non-FADEC models,

Th controls are rigged to physical datums, the control run is not 'tweaked' to overcome engine power differences
 
Tristarsteve
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RE: Autothrottle Movement Of Staggered Throttles

Sat Jan 13, 2007 6:24 pm

Quoting VC-10 (Reply 6):
Quoting Speedracer1407 (Thread starter):
If the throttles are staggered for whatever reason, such as to account for rigging on older non-FADEC models,

Th controls are rigged to physical datums, the control run is not 'tweaked' to overcome engine power differences

You are correct, but on non FADEC aircraft, the crew will manually adjust the throttles to get all the EPRs (or N1s) aligned. This is where the term throttle-stagger comes from. The autothrottle then , being a single actuator, will move the throttles as a bunch.

Now a question. How many autothrottle servos are there.
The B737 Classic has one servo that operates both engines. I suspect this is standard on steel cable controlled engines.
The B767 with FADEC has a single servo for both throttles with electric wires to the engines.
But the B777 has two autothrottle servos.
Why does it need two, when the B767 can get by on one?
 
David L
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RE: Autothrottle Movement Of Staggered Throttles

Sat Jan 13, 2007 7:21 pm

Quoting RichardPrice (Reply 5):
http://www.aaib.gov.uk/publications/formal_reports/no_4_90_502831.cfm

Paragraph 2.2.2.2 explains it quite nicely.

Thanks for that.
 
411A
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RE: Autothrottle Movement Of Staggered Throttles

Sat Jan 13, 2007 8:03 pm

Just for information on another type, the Lockheed TriStar autothrottle finds the following...

In the performance management mode of operation (used at cruise altitudes) the throttle stagger set by the pilot is maintained during any desired or directed thrust changes.

During the autothrust mode used during maneuvering in the TMA and during approaches, the throttles are moved together, IE: aligned, and if any throttle stagger is desired by the flying pilot, it can be easily maintained manually.

A superb system which works flawlessly.
 
speedracer1407
Posts: 330
Joined: Fri Dec 24, 2004 4:19 pm

RE: Autothrottle Movement Of Staggered Throttles

Sun Jan 14, 2007 7:19 pm

Thanks folks....all that info was exactly what I was looking for.

It seems that, in general, on non-FADEC planes, manually set throttle stagger is maintained by the autothrottle. But... 411A's description of the L-1011's different modes seems different from other types. Is it actaully different, or do all types automatically align the throttles in certain modes.

BTW, 411A, what's TMA?
Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
 
Tristarsteve
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RE: Autothrottle Movement Of Staggered Throttles

Sun Jan 14, 2007 8:04 pm

Quoting Speedracer1407 (Reply 10):
BTW, 411A, what's TMA?

Terminal Manouevering Area. or near the airport.

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