Autothrottle deselect in cruise
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Autothrottle deselect in cruise
I was party to a recent conversation between some pilots regarding the use of autothrottle and whether they had ever disconnected it in cruise. I was surprised as I couldn't think why a pilot would do so. Can anyone give me some reasons why a pilot would do this. Would they just switch it off or is there a process to follow?
For speed control in moderate turbulence it can often be better manually to set a power rather than leaving the autothrust/throttle winding the power up and down, often out of phase with the speed changes.
Occasionally the autothrottle is out of service and we fly without it. It happens rarely but we manage just fine. I can remember only a couple of occasions in the last ten years, but it is no big deal. The other times we might switch it off in cruise are if maintenance ask for us to fill out egt, fuel flow etc. So we deselect briefly to note the values. Sometimes the autothrottle on certain aircraft seems to get out of kilter and wont hold selected speed. A brief disconnection usually does the trick, like with other electronic equipment. There is no complicated process to follow for a brief disconnection, although I think it is reasonable airmanship to press the disconnect once so the red blinking light reminds you it is disengaged.
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We're constantly manipulating thrust in the cruise when conditions aren't great... the autothrottle can be quite slow to react to impending overspeeds/underspeeds and related conditions.
As for required disconnect - severe turbulence and a bunch of non-normals. This is assuming you're talking Boeing.
As for required disconnect - severe turbulence and a bunch of non-normals. This is assuming you're talking Boeing.
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In the Airbus, match the thrust lever position to the currently commanded thrust, then press the disconnect button. People are scared to disconnect it, the auto thrust is just like the auto pilot, a great tool, but if it's not behaving, take it out.
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Seriously?
In every topic there is a debate regarding automation dependancy. After reading the first post, I would say that aviation is heading the wrong way.
You do realise, there are actually aircraft in the air at this very moment, carrying passengers, that do not have A/T. Yes, the pilots actually move the levers during climb, cruise, descent and approach. Shocking! One more thing, some of these aircraft were actually designed around the same time (or even later) as Busses and Boeings. I still can't get my head around the fact, that some pilots/companies find manually adjusting the thrust dangerous.
You do realise, there are actually aircraft in the air at this very moment, carrying passengers, that do not have A/T. Yes, the pilots actually move the levers during climb, cruise, descent and approach. Shocking! One more thing, some of these aircraft were actually designed around the same time (or even later) as Busses and Boeings. I still can't get my head around the fact, that some pilots/companies find manually adjusting the thrust dangerous.
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Genghis2008,
You didn't specify an aircraft, but on the B747-400, if you disengage the autothrottle during cruise mode (CRZ), the reference N1/EPR line will change from a green line displaying the reference N1/EPR (either CRZ or CLB thrust) to a magenta line displaying the N1/EPR required to maintain the FMC cruise mach. It's a nice feature to have.
You didn't specify an aircraft, but on the B747-400, if you disengage the autothrottle during cruise mode (CRZ), the reference N1/EPR line will change from a green line displaying the reference N1/EPR (either CRZ or CLB thrust) to a magenta line displaying the N1/EPR required to maintain the FMC cruise mach. It's a nice feature to have.
After reading the first post, I would say that aviation is heading the wrong way.
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Nothing worse than watching an AT chase speed as you sit in a bit of standing wave or on the edge of a high level temperature inversion. Not great for fuel burn either.
On my first aircraft type we had a voice activated auto throttle. I don't think any of the modern Airbuses or Boeings have that.
The only time it did not work was if I was asleep or left the flight deck.
The only time it did not work was if I was asleep or left the flight deck.
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On my first aircraft type we had a voice activated auto throttle.
Was that similar to the LHS activated 'flare alarm' if RHS was PF on a wet raining night; before all this cuddly GPWS RA callouts created the flare by numbers technique?
Was that similar to the LHS activated 'flare alarm' if RHS was PF on a wet raining night; before all this cuddly GPWS RA callouts created the flare by numbers technique?
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On my first aircraft type we had a voice activated auto throttle. I don't think any of the modern Airbuses or Boeings have that.
The only time it did not work was if I was asleep or left the flight deck.
The only time it did not work was if I was asleep or left the flight deck.
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I had those in the 747 Classic. Most of them worked in Standby Mode when I was off the flight deck, especially if the FO was asleep. However, they tended to lapse into sleep mode in cruise...
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On some, less sophisticated auto throttle systems, the auto throttles may chase speed more or less constantly in cruise. This will increase fuel burn so some used to switch them off.
Some (767) auto throttles go into sleep mode in cruise. Probably the same on a lot of widebodies?
I have never had to disconnect a modern auto throttle in cruise. Override it, yes, but not disconnect.
Some (767) auto throttles go into sleep mode in cruise. Probably the same on a lot of widebodies?
I have never had to disconnect a modern auto throttle in cruise. Override it, yes, but not disconnect.
