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Autothrottle U/s 737

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Autothrottle U/s 737

Old 1st Jun 2023, 21:06
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Autothrottle U/s 737

Hi,

wondering what the best modes are when the auto throttle is U/S ? Would you just use flight level change and not vnav ? Best way to manage this.

thanks
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Old 3rd Jun 2023, 08:30
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The modes you use aren’t as important as the type of duct-tape you use to bind your hand to the thrust levers at top of descent.
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Old 3rd Jun 2023, 09:30
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Flight level change obviously gives you more protection as speed is on the elevator in a climb or descent.
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Old 3rd Jun 2023, 12:50
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My 2 cents: Ignore V/S, use LVL CHG and if you want to slacken the rate your thrust levers effectively become your vertical speed wheel. Only time i'd not do that is if conducting a V/S approach - then obviously use V/S as you need the precision!
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Old 4th Jun 2023, 12:05
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Thank you. There’s very little guidance regarding this. Obviously sounds simple and straightforward but like most things there are better ways and safer ways to accomplish some things. So I should only use level change.
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Old 5th Jun 2023, 04:36
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Engage brain and fly the aircraft like an aircraft. The autothrottle is a useful aid to things but hardly super important. Caveat, having the ability for the autothrottle to spin up if the pilot forgets to keep an eye on the speed when leveling off is a very useful backup feature ....
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Old 5th Jun 2023, 06:12
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Not familiar with 737 but as long as one knows who maintains speed the pitch or the thrust non-availability of auto throttle shouldn't affect the use of FD modes. If the mode requires pitch change to maintain speed the AP/FD will do it just just use fixed thrust idle/climb and monitor it, if the mode requires thrust to maintain speed move throttles and maintain speed. If speed trend arrow is there on the speed tape then just control it at target speed.

Last edited by vilas; 5th Jun 2023 at 07:31.
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Old 5th Jun 2023, 06:18
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So I should only use level change.
I wouldn’t be quite that black and white. There could still be situations ( especially in the terminal area prior to approach) where v/s might be a more appropriate mode.
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Old 5th Jun 2023, 09:42
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I recently did a stand-in simulator as First Officer for a colleagues Command Assessment upgrade. The first thing that happened was that they failed the AT. Didn’t bother me much because the 737 is the first aircraft I’ve flown with AT. But, when you are working hard, it is interesting that it does take a bit of capacity away.
When my colleague took over the flying again I called ‘approaching target speed’ as we were decelerating towards the (minimum clean) speed and his hands were not on the Thrust Levers. All normal cockpit CRM etc, but in the debrief the assessors told him ‘he saved your bacon there.’
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Old 5th Jun 2023, 10:58
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As John Tullermarine has said, "Engage brain and fly the aircraft like an aircraft". All aircraft, basically, fly the same way. Autothrottles and other add-ons are there to help and to make the operation more efficient but every pilot should be able to fly without any of those things working and should also be able to fly with the A/T U/S. These are all very basic flying skills.
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Old 5th Jun 2023, 12:44
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Thanks. Would you climb in Mach or IAS at higher altitudes with the a/t not working?
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Old 5th Jun 2023, 14:36
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Originally Posted by Paulm1949
Thanks. Would you climb in Mach or IAS at higher altitudes with the a/t not working?
Without being blunt i'm not sure why this would be a question? The fact you don't have a working A/T doesn't have any bearing on that - at high altitudes a jet airliner is operated at mach no, at lower altitudes by IAS.

You'd set climb N1 manually and climb in IAS until you reach your climb mach no, just as you would any other day with a working A/T.

Remember that in LVL CHG mode and VNAV SPD the thing controlling your speed is not your engines but your elevator (horizontal stab in fact). This is why I would suggest it is safer than V/S, the consquence of not having enough / having too much thrust in LVL CHG is that you simply don't climb / descend with as much rate. The consequence of not having enough / too much thrust in V/S is that you may stall or overspeed.

Last edited by go-around flap 15; 5th Jun 2023 at 14:48.
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Old 5th Jun 2023, 20:17
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​​​​Remember that in LVL CHG mode and VNAV SPD the thing controlling your speed is not your engines but your elevator (horizontal stab in fact). This is why I would suggest it is safer than V/S, the consquence of not having enough / having too much thrust in LVL CHG is that you simply don't climb / descend with as much rate. The consequence of not having enough / too much thrust in V/S is that you may stall or overspeed.​​​
A very valid point which is true even when you *do* have an A/T. V/S at high altitude and/or high/low speed can get you into trouble quite quickly, as due to reduced margins in just about everything, it’s easy to make performance demands of the aeroplane that may be outside of its capabilities...
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Old 5th Jun 2023, 21:47
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LVL CHG doesn't respect altitude constraints does it? (Genuine question, I'm not a B pilot). I'd personally be most comfortable using all the same modes I usually would and just control the thrust as required. Then only one thing is different, manual thrust, and I've been dealing with manual thrust most of my career so no big deal.
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Old 5th Jun 2023, 22:58
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Originally Posted by AerocatS2A
LVL CHG doesn't respect altitude constraints does it? (Genuine question, I'm not a B pilot). I'd personally be most comfortable using all the same modes I usually would and just control the thrust as required. Then only one thing is different, manual thrust, and I've been dealing with manual thrust most of my career so no big deal.
It respects the altitude in the MCP but not in the FMS. It is a “basic” mode, after all...
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Old 5th Jun 2023, 22:59
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Originally Posted by FullWings
It respects the altitude in the MCP but not in the FMS. It is a “basic” mode, after all...
That was my understanding (the same as Airbus OPN CLB and OPN DES), but I don't fly them so didn't know if it had some additional magic.
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Old 6th Jun 2023, 08:50
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A flight Simmer question
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Old 12th Jun 2023, 00:01
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Originally Posted by ACMS
A flight Simmer question
That's what I thought, too.
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Old 12th Jun 2023, 17:33
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Originally Posted by 73qanda
The modes you use aren’t as important as the type of duct-tape you use to bind your hand to the thrust levers at top of descent.
99.99 of Airbus pilots approve of this highly!
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Old 12th Jun 2023, 20:55
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As would a former Chief Pilot of BA Short-haul at Gatwick.................with hindsight?
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