taguilo
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Boeing Autothrottle Behavior

Wed Oct 05, 2005 5:19 am

For boeing a/c (757/67/47), two questions:

1) In flight with autothrottle on, an engine is shut down. If A/T is kept on, will the servo move the throttle lever of the shut engine like it does with the working one?

2) A/T in speed mode, in a climb. Pilot increases speed bug on MCP. How will react A/T system? Should it make a quick movement of the levers up to max power for CLB mode, until speed is near to be captured, and retard them back until speed is stabilized; or should it make a slow/smooth movement, letting speed increase steady to the point of being captured?

Tom
 
PhilSquares
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RE: Boeing Autothrottle Behavior

Wed Oct 05, 2005 6:28 am

1) In the case of an engine failure, for all Boeing auto-throttle systems, if the A/T is engaged, then the servos will move all thrust levers. The limit EPR/N1 is Cont.

2) I'm a little confused because of the terminology you're using. If you're in VNAV and open the speed window, the A/T are already at CLB so, your pitch will change. If you're in FLCHG, same thing will happen. If you're in V/S the throttles will move until the CLB limit is reached, it will try to maintain the selected IAS/IMN but it will disregard that if it can't maintain the V/S selected.
Fly fast, live slow
 
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Jetlagged
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RE: Boeing Autothrottle Behavior

Wed Oct 05, 2005 9:38 am

A/T would never normally be in speed mode in a climb. That's only how Microsoft think an airliners autoflight system works  Smile

On most Boeings there is only one autothrottle servo (OK there may be duplicated servos, but they act as one), with a friction clutch for each thrust lever. So they always move together, but the failed engine thrust lever can be pulled back manually. In fact it is possible to manualy stagger the throttles and they all will move together, maintaining the stagger.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
taguilo
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RE: Boeing Autothrottle Behavior

Thu Oct 06, 2005 12:21 am

Quoting Jetlagged (Reply 2):
A/T would never normally be in speed mode in a climb.

Yes that's true. However, with V/S engaged you can press SPD on the MCP, and A/T will try to hold the selected speed. Not recommendable, but possible (autopilot won't whine for this)  Smile

I knew both thrust levers move together with A/T on and engines on, and now I know it's the same with an engine out situation. Thank you for the info.
I've read on tech notes that levers stop moving when at least one of them reaches the thrust position commanded by A/T, and the pilot may have to reposition the lagged lever manually. But, in an engine out situation, if the closed engine's lever is pulled to idle, and then FLCH/VNAV mode commands A/T to IDLE, will the working engine's lever retard all way back, or will remain still because A/T senses that AT LEAST one lever is already positioned at idle (the closed engine's one) ???
 
Tornado82
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RE: Boeing Autothrottle Behavior

Thu Oct 06, 2005 2:10 am

Quoting Jetlagged (Reply 2):
A/T would never normally be in speed mode in a climb. That's only how Microsoft think an airliners autoflight system works

As nothing more than a Flight Simmer myself (will begin working on a PPL in the spring once $ allows), I enjoy coming here to the guys flying the real metal around for their views. I've seen this numerous times about how real jets have an a/p climb mode that allows for a set speed, and it changes the pitch to meet that speed, or changes throttles to meet that climb rate. From what I'm reading here... is there a 3rd mode as well? How would that work??

You'd think in all the versions of FS, that Microsoft would change that part of their planes to match the real thing... instead of worrying about stuff like bridges on land, haha.  banghead 

Thanks for the insights as always, folks.
 
Glom
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RE: Boeing Autothrottle Behavior

Fri Oct 07, 2005 6:40 am

Quoting Jetlagged (Reply 2):
A/T would never normally be in speed mode in a climb. That's only how Microsoft think an airliners autoflight system works

LOL. Indeed. FS04 is the limit of my experience with automated flight systems (I do my real flying myself) and I used to enjoy playing with the package simulation of the 773 where the autothrottle was used to control speed alone and climb and descent was regulated with v/s hold. This was somewhat different to the way I did a climb in real flying, which involved setting climb power (full power in this case) and adjusting the attitude to give Vy. Then I got PMDG 737NG and found out that airliners climb using the same control principles I do. It makes perfect sense because the 773 would find itself unable to maintain the speed at high altitudes with 1800fpm climb so I'd have to reduce the v/s to prevent it from stalling.
 
777wt
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RE: Boeing Autothrottle Behavior

Fri Oct 07, 2005 1:52 pm

Quoting Jetlagged (Reply 2):
On most Boeings there is only one autothrottle servo (OK there may be duplicated servos, but they act as one), with a friction clutch for each thrust lever. So they always move together, but the failed engine thrust lever can be pulled back manually. In fact it is possible to manualy stagger the throttles and they all will move together, maintaining the stagger.

That would be with hydromechanical fuel control systems.

With FADEC, there's no need to stager the throttles.
 
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Jetlagged
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RE: Boeing Autothrottle Behavior

Sat Oct 08, 2005 1:47 am

Quoting 777WT (Reply 6):
That would be with hydromechanical fuel control systems.

With FADEC, there's no need to stager the throttles.

True, unless there are throttle rigging or resolver calibration errors. Also, if one FADEC is failed or switched off, then there will be some throttle stagger.
The glass isn't half empty, or half full, it's twice as big as it needs to be.

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