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Autothrottle Movement Of Staggered Throttles  
User currently offlineSpeedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0
Posted (7 years 3 months 1 week 1 day 5 hours ago) and read 3636 times:

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.
11 replies: All unread, jump to last
 
User currently offlineBoeingFixer From Canada, joined Jul 2005, 525 posts, RR: 0
Reply 1, posted (7 years 3 months 1 week 1 day 2 hours ago) and read 3596 times:

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
User currently offlineRichardPrice From , joined Dec 1969, posts, RR:
Reply 2, posted (7 years 3 months 1 week 1 day 2 hours ago) and read 3573 times:

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.


User currently offlineCorsair2 From United States of America, joined Jan 2001, 248 posts, RR: 0
Reply 3, posted (7 years 3 months 1 week 1 day ago) and read 3542 times:

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?"
User currently offlineDavid L From United Kingdom, joined May 1999, 9483 posts, RR: 42
Reply 4, posted (7 years 3 months 1 week 23 hours ago) and read 3519 times:

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


User currently offlineRichardPrice From , joined Dec 1969, posts, RR:
Reply 5, posted (7 years 3 months 1 week 22 hours ago) and read 3512 times:

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.


User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3695 posts, RR: 35
Reply 6, posted (7 years 3 months 1 week 22 hours ago) and read 3506 times:
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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


User currently offlineTristarSteve From Sweden, joined Nov 2005, 3930 posts, RR: 34
Reply 7, posted (7 years 3 months 1 week 8 hours ago) and read 3376 times:

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?


User currently offlineDavid L From United Kingdom, joined May 1999, 9483 posts, RR: 42
Reply 8, posted (7 years 3 months 1 week 7 hours ago) and read 3365 times:

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.


User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 9, posted (7 years 3 months 1 week 6 hours ago) and read 3357 times:

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.


User currently offlineSpeedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0
Reply 10, posted (7 years 3 months 6 days 7 hours ago) and read 3270 times:

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.
User currently offlineTristarSteve From Sweden, joined Nov 2005, 3930 posts, RR: 34
Reply 11, posted (7 years 3 months 6 days 6 hours ago) and read 3267 times:

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

Terminal Manouevering Area. or near the airport.


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