Auto-throttle & Manual flight
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Auto-throttle & Manual flight
Question 1...
With regard to the auto-throttle operation in B737 Classics and also NG.
When hand flying an instrument approach there appears to be conflicting views whether or not the auto-throttle should be turned off and the throttles operated manually - or the auto-throttle left engaged so that it controls to MCP speed while the pilot hand flies.
Boeing published documents avoid the question, meaning that it is up to company policy. Assuming average piloting skills one would assume that most 737 pilots could cope with flying manually with auto throttle off. Flying manually with auto-throttle controlling IAS does sometimes present a problem with trim anticipation as the throttles move to maintain the desired speed.
What is the preferred method and for what technical reasons? Failing a Boeing published policy, does it simply come down to personal preference? Which leads into another point on auto-throttle usage: Final approach with manual throttle Boeing recommend Vref plus wind additives up to max additives of Vref plus 20 knots.
Q2....With auto-throttle engaged Boeing recommend Vref plus five knots as approach speed, bleeding of the additive approaching touch-down. First question is how do you "bleed off" speed to Vref if autothrottle is controlling to Vref plus five?
Q3.... Although Boeing infer (tongue-in-cheek, maybe?) that the auto-throttle system can correct for gusts much faster than a pilot can using manual throttle, some may have doubts about this. A human can shove open a throttle twice as fast as the automatics can. Therefore if conditions are real gusty would you trust the auto-throttle implicity and thus just add plus five knots to Vref on the MCP - or would you trust your own reactions and fly manual throttle with all the extra gust additives thrown in?
Problem being that landing on a short runway (worse if wet) with gust additives held all the way to touch-down, ups the ante when it comes to landing fast and long.
Q4....30 knot headwind component calls for an additive of 15 knots to Vref. (half the HW). Boeing recommend bleeding of the additive to cross the fence at Vref. Assuming a steady wind and no gusts, 15 knots bleed off is a lot - particularly as Boeing state that you will lose only 3-4 knots in the actual flare. At what height, therefore should you commence bleedingoff the 15 knots?
Q5.....Auto-throttle engaged but speed button deselected on final so that system remains armed, but throttles can be moved by hand.
Does the alpha floor protection actuate (throttles begin to open up) when the speed is reduced below actual Vref for flap setting and weight - or does it cause the throttles to move forward if the speed is reduced below the MCP selected speed? Put another way - if MCP speed set 10 knots above calculated Vref then with speed mode deselected at what point will alpha floor protection start pouring on the power?
With regard to the auto-throttle operation in B737 Classics and also NG.
When hand flying an instrument approach there appears to be conflicting views whether or not the auto-throttle should be turned off and the throttles operated manually - or the auto-throttle left engaged so that it controls to MCP speed while the pilot hand flies.
Boeing published documents avoid the question, meaning that it is up to company policy. Assuming average piloting skills one would assume that most 737 pilots could cope with flying manually with auto throttle off. Flying manually with auto-throttle controlling IAS does sometimes present a problem with trim anticipation as the throttles move to maintain the desired speed.
What is the preferred method and for what technical reasons? Failing a Boeing published policy, does it simply come down to personal preference? Which leads into another point on auto-throttle usage: Final approach with manual throttle Boeing recommend Vref plus wind additives up to max additives of Vref plus 20 knots.
Q2....With auto-throttle engaged Boeing recommend Vref plus five knots as approach speed, bleeding of the additive approaching touch-down. First question is how do you "bleed off" speed to Vref if autothrottle is controlling to Vref plus five?
Q3.... Although Boeing infer (tongue-in-cheek, maybe?) that the auto-throttle system can correct for gusts much faster than a pilot can using manual throttle, some may have doubts about this. A human can shove open a throttle twice as fast as the automatics can. Therefore if conditions are real gusty would you trust the auto-throttle implicity and thus just add plus five knots to Vref on the MCP - or would you trust your own reactions and fly manual throttle with all the extra gust additives thrown in?
Problem being that landing on a short runway (worse if wet) with gust additives held all the way to touch-down, ups the ante when it comes to landing fast and long.
Q4....30 knot headwind component calls for an additive of 15 knots to Vref. (half the HW). Boeing recommend bleeding of the additive to cross the fence at Vref. Assuming a steady wind and no gusts, 15 knots bleed off is a lot - particularly as Boeing state that you will lose only 3-4 knots in the actual flare. At what height, therefore should you commence bleedingoff the 15 knots?
Q5.....Auto-throttle engaged but speed button deselected on final so that system remains armed, but throttles can be moved by hand.
Does the alpha floor protection actuate (throttles begin to open up) when the speed is reduced below actual Vref for flap setting and weight - or does it cause the throttles to move forward if the speed is reduced below the MCP selected speed? Put another way - if MCP speed set 10 knots above calculated Vref then with speed mode deselected at what point will alpha floor protection start pouring on the power?
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I'm not inclined to answer your post in any logical format, but here are my thoughts.
My company only allows us to fly the 737 autothrottles either engaged or fully disengaged. This stinks, and I've told them so, because the best way to fly the throttles is "ARMED/Deselected". They're concerned about automation surprises in the flare. They've had a couple of instances where the throttles went to Max Power because the crew got 5 kts below Vref. The exact programming for this varies from airplane to airplane, depending on software installed. So, I told them, "Let's require crews who use the ARMED technique to click the throttles off at 50, 100, or 200 feet." But, there's no reasoning with them. They've decided to throw the baby out with the bathwater. It's become somebody's little peave and they insist on micromanaging this phase of flight for us.
Here's what I do. The autothrottles can really throw your trim off coming up final. As a former 767 guy, this is quite noticable. So I disconnect them and fly between Vref + 5 and the white bug. Conservative most of the time. In turbulence, I let the speed bounce around and don't try to chase it, like the autothrottles are inclined to. I look at my speed crossing the threshhold and pull my power and watch the sink accordingly. The airplane handles so much better with the throttles disconnected. If I have to GA, stand the power up, and turn on the AT switch. I hate TOGA mode, unless I'm in mountainous areas, so I quickly transition to V/S 1500'/min up.
My two cents.
Cheers!
My company only allows us to fly the 737 autothrottles either engaged or fully disengaged. This stinks, and I've told them so, because the best way to fly the throttles is "ARMED/Deselected". They're concerned about automation surprises in the flare. They've had a couple of instances where the throttles went to Max Power because the crew got 5 kts below Vref. The exact programming for this varies from airplane to airplane, depending on software installed. So, I told them, "Let's require crews who use the ARMED technique to click the throttles off at 50, 100, or 200 feet." But, there's no reasoning with them. They've decided to throw the baby out with the bathwater. It's become somebody's little peave and they insist on micromanaging this phase of flight for us.
Here's what I do. The autothrottles can really throw your trim off coming up final. As a former 767 guy, this is quite noticable. So I disconnect them and fly between Vref + 5 and the white bug. Conservative most of the time. In turbulence, I let the speed bounce around and don't try to chase it, like the autothrottles are inclined to. I look at my speed crossing the threshhold and pull my power and watch the sink accordingly. The airplane handles so much better with the throttles disconnected. If I have to GA, stand the power up, and turn on the AT switch. I hate TOGA mode, unless I'm in mountainous areas, so I quickly transition to V/S 1500'/min up.
My two cents.
Cheers!
Moderator
Several threads from the archives canvassed similar/related topics and may be useful for background reading ... there may be others but these, at least, provide a starting point ....
Reducing headwind additives on final approach
737 Wind increment to Vref
Landing B737 at low weights
Reason for wind additive during landing
Vref = 1.3Vs ?
Reducing headwind additives on final approach
737 Wind increment to Vref
Landing B737 at low weights
Reason for wind additive during landing
Vref = 1.3Vs ?
Last edited by john_tullamarine; 2nd Jan 2003 at 01:31.
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Hudson:
Q1. It is the most common method to fly manually and A/T off. It keeps you in the loop more - on top of it etc - and stops the thrust/pitch couple problem, which really is a handfull. What is important is to know what the power setting should be for the approach conditions ie. weight and w/v speed increment, set it when on speed and you'll probably find, unless in very gusty conditions, that the speed will bounce around the datum and need very little adjustment.
I suspect the additive for manual flying is the mis-trust (tut tut!) of the pilot scanning the speed and not being as accurate as the A/T????? or even forgetting it completely and ending up very slow.
Q2. This really relates to a full autoland condition. The IDLE feature of the A/T will take care of this. I still use the +5 if making a CAT 1 to man land in full automatic mode.
Q3. See Q1. about setting datum thrust. As for landing fast and long with a large wind additive; I would hope most of the component would be headwind and thus a low ground speed.
Q4. Not easy to put a number on it as it depends what it feels like on the day, but if you had to start somewhere, a very slight thrust reduction at 200' is perhaps better than a large one at 100'.
Q5. Not sure about this as we've not been allowed to try it. It works on B757/767. As in many tech' questions these days I suspect the maintenance, rather than pilot, manual will tell you.
dvt. I'm not sure about the use of V/S in a G/A. I suspect this would be non-standard. TOGA will give you only 2000'ROC anyway. Hardly pocket rocket stuff.
One question I've had, but no answer:
You can fly an autoland with manual throttle (A/T u/s) and thus have to add the full W/V additive upto 20kts. The autoflare reduces the effective LDA. (i.e. it shortens the RWY) Autoland distances are compensated for +5kts (I assume). What is the effect of flaring with +20 or should the speed be bled to +5 by 50" as if the A/T was in command? If not, the a/c might float and the rwy becomes even shorter, so what would the required autoland distance be?
Q1. It is the most common method to fly manually and A/T off. It keeps you in the loop more - on top of it etc - and stops the thrust/pitch couple problem, which really is a handfull. What is important is to know what the power setting should be for the approach conditions ie. weight and w/v speed increment, set it when on speed and you'll probably find, unless in very gusty conditions, that the speed will bounce around the datum and need very little adjustment.
I suspect the additive for manual flying is the mis-trust (tut tut!) of the pilot scanning the speed and not being as accurate as the A/T????? or even forgetting it completely and ending up very slow.
Q2. This really relates to a full autoland condition. The IDLE feature of the A/T will take care of this. I still use the +5 if making a CAT 1 to man land in full automatic mode.
Q3. See Q1. about setting datum thrust. As for landing fast and long with a large wind additive; I would hope most of the component would be headwind and thus a low ground speed.
Q4. Not easy to put a number on it as it depends what it feels like on the day, but if you had to start somewhere, a very slight thrust reduction at 200' is perhaps better than a large one at 100'.
Q5. Not sure about this as we've not been allowed to try it. It works on B757/767. As in many tech' questions these days I suspect the maintenance, rather than pilot, manual will tell you.
dvt. I'm not sure about the use of V/S in a G/A. I suspect this would be non-standard. TOGA will give you only 2000'ROC anyway. Hardly pocket rocket stuff.
One question I've had, but no answer:
You can fly an autoland with manual throttle (A/T u/s) and thus have to add the full W/V additive upto 20kts. The autoflare reduces the effective LDA. (i.e. it shortens the RWY) Autoland distances are compensated for +5kts (I assume). What is the effect of flaring with +20 or should the speed be bled to +5 by 50" as if the A/T was in command? If not, the a/c might float and the rwy becomes even shorter, so what would the required autoland distance be?
