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frogone

A/T Disconnect on engine failure profile.

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On take off with VNAV armed an subsequently engaged on completing the memory items for an engine severe damage scenario the auto throttle disconnects. On three engines it should not (THR REF should remain engaged). As it's in 'VNAV SPD' pitch cycling the A/T ARM switch should re-engage the auto throttle but it does not. Has anyone else experienced this? Might be a bug. 

 

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On take off with VNAV armed an subsequently engaged on completing the memory items for an engine severe damage scenario the auto throttle disconnects. On three engines it should not (THR REF should remain engaged). As it's in 'VNAV SPD' pitch cycling the A/T ARM switch should re-engage the auto throttle but it does not. Has anyone else experienced this? Might be a bug. 

 

Having trouble understanding what you're saying here. Can you rephrase it, please?

 

Also: full names in the forum, please - first and last.

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It seems when a thrust lever is retarded to the idle stop that auto thrust disengages, this happens on the 737NG when thrust lever stagger trips the A/T off, however on the 747-400 retarding a thrust lever in the case of an engine failure, the auto thrust should remain engaged. So if the memory items were completed on 747-400 'THR REF - LNAV* - VNAV SPD' should remain on the FMA. In the software, the auto thrust is disconnecting (I'm assuming because of the thrust lever stagger), with associated blank in the A/T portion of the FMA and associated EICAS message. *If armed. 

 

Alain Charnier

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OK Alain. Here is the story: You programmed an engine severe damage which is a scenario where by design the engine goes completely dead. It is not even wind milling. Spool stuck. Accordingly the N2 goes below the EEC activation limit (7-10%) with the fuel lever in CUT OFF and the EEC goes dead too. As a result the AT drops (because the AT requires all EEC's either in NORM or in ALTN).

 

Perhaps we should revisit this scenario which was meant as the most severe damage you can do to the engine without the possibility of an in flight restart with consequences in other systems (you see one here).

 

You can programme an ENG x FLAME OUT in the meantime.

 

Best,

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Indeed the EEC does run off the accessory gearbox which is driven by the N2 spool and as you say if that's seized the EEC will go dead, however below 11% (GE/PW) the related EEC may be powered by its respective DC bus. I've done many an engine failure be it a rundown or severe damage in level D sims and I've never seen the A/T trip off like that. 

 

Regards,

 

Alain 

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Alain,

 

I will look into this a bit more in the manuals and see what we can come up with.  I do not see anything in the QRH referencing A/T as in Inop system for Severe Damage or Separation but with the Fuel Cutoff switch OFF,  the EEC is unpowered so it will require a little bit of digging here.  

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I was going to to open the exact same topic. The autothrottle should only trip off when multiple engines fail.

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