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When to disconnect auto throttle before landing

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Thought the FCTM/FCOM said to disconnect A/T whenever A/P gets disconnected?

 

That's probably why it wasn't caught... everyone probably disconnected the A/T when manual flying (A/P disconnected)...


Brian Nellis

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Thought the FCTM/FCOM said to disconnect A/T whenever A/P gets disconnected?

 

Reference?

I don't see the logic behind that, would like to learn more.


Dan Downs KCRP

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You should disconnect the A/T first and stabilize the N1 at a value appropriate to the weight, speed and ROD of the aircraft.

 

Note; (I got this advice from my line training document from RYR) Before disconnecting the A/P press your shoulders back into the chair, look out the window and note the position of the touchdown zone. Maintain the touchdown zone in this position throughout the approach.

 

The A/P should now be disconnected. Only small adjustments to pitch and thrust should be made from then on.

 

I was told even those multi million pound training simulators never get it right (accuracy) within a hundread feet of the runway so don't stress if FSX/P3D is causing you grief lol


Vernon Howells

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I see your context now... I was afraid you said that Boeing recommends you disconnect A/T ANYTIME you disconnect A/P; such as descending through 10,000 ft to handfly the approach and letting A/T hold MCP SPD for you. I would have taken exception to that.  However, the key point is you haven't provided a FCOM/FCTM reference,...., a company policy is a different reference and does not apply to any other operator.


Dan Downs KCRP

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Now you've had all the sensible answers, it's Friday evening & I need a beer.

 

Disconnect the A/T when you shut down at the gate  :Tounge:


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I was afraid you said that Boeing recommends you disconnect A/T ANYTIME you disconnect A/P; such as descending through 10,000 ft to handfly the approach and letting A/T hold MCP SPD for you. I would have taken exception to that. However, the key point is you haven't provided a FCOM/FCTM reference,...., a company policy is a different reference and does not apply to any other operator.

 

FCTM 1.35 (AFDS Guidelines, Autothrottle Use).

 

"Autothrottle use is recommended during takeoff and climb in either automatic or manual flight. During all other phases of flight, autothrottle use is recommended only when the autopilot is engaged."

 

That is the Boeing recommendation, due I think to the destabilising effect of the pitch-power couple. Some operators (as we have heard from Joe earlier in this thread) may differ.

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Simon Kelsey

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FCTM 1.35 (AFDS Guidelines, Autothrottle Use).

 

Still learning something every day..., thanks.  Due to the horrible control quality of the MSSidewinder that I used for years, I pretty much relied on A/T.  The opposite is true with my Warthog HOTAS and I've become comfortable with A/T off during manual approaches (still learning how in the 777).  This piece of info that you quoted is new to me. I'll be disconnecting A/T now at 10000 along with A/P for most my arrivals. Interesting, I never found the pitch/power coupling to be a problem with the A/P off and A/T on... I guess I anticipate it thanks to actual time in the cockpit (most all planes have pitch/power coupling).


Dan Downs KCRP

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No worries, Dan.

 

It's worth re-emphasising that it's type-specific rather than a blanket Boeing thing; the same statement is there in the 747 and 757/767 manuals, but the recommendation for the B777 and B787 is that the A/T stay in at all times, even when flying manually. The big difference, of course, is that the FBW in the newer designs incorporates (theoretically) automatic compensation for the thrust-pitch couple.

 

As you will know -- the issue is that if you are flying speed on thrust (ie not THR REF, or whatever the NG equivalent is) with the A/T engaged in manual flight, if you pitch up the speed will tend to reduce and so the A/T will add thrust, causing the nose to pitch up more, and so you can end up chasing your tail a bit if you're not careful. As I say, there are some 737 operators (as evidenced in this thread) that do permit A/T usage in manual flight, so it may be that the effect is not too pronounced and/or the 737 A/T is not too twitchy.

 

Personally (as a sim pilot only) I too used to leave the A/T in pretty well all the time but got out of the habit with the Level-D 767 back in the day and these days am very much a fan of the "all on or or all off" concept, at least with the non-FBW Boeings; the Airbus, funnily enough, feels very natural to hand-fly with A/THR all the way to the ground, but I wouldn't dare in the 747; PSX models the thrust-pitch couple very well indeed and I can see how a lump of A/T at an inopportune moment could ruin your day (or at least your nice stable approach) very quickly.


Simon Kelsey

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During manual landings, due to the fact that I cannot feel acceleration on my body and cannot see the throttles with my peripheral vision (as they are not on the screen) I keep AT on until i cross the threshold, then turn it off with a button on the joystick and push the throttle lever down to zero. Not sure this is correct but is what works for me. I plan however to practice and land controlling manually the throttle too from the very moment i disengage AP which is usually 4 miles out of threshold.


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During manual landings, due to the fact that I cannot feel acceleration on my body and cannot see the throttles with my peripheral vision (as they are not on the screen)

 

You shouldn't really need to see the position of the thrust levers. Remember the levers only show the commanded thrust, not the thrust being produced: only the engine instruments can tell you that, and only the airspeed indicator (combined with the pitch attitude, of course) can tell you whether you have the right amount of thrust!

 

Try it: to be honest, it's not a mystical art. In a large jet you fly by the numbers and you shouldn't really need to adjust the thrust very much once you are configured: I don't know about the 737, but in the 747 at 250T and Flap 25 you can pretty much just set 1.15 EPR and leave the thrust levers exactly where they are.


Simon Kelsey

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I agree.. you're not feeling acceleration in an aircraft that is slowly changing speed a few knots when you are on final, and I've never looked at a throttle in the cockpit (except as a student since I had trouble transitioning from a motorcycle to an airplane where more power is opposite directions).

 

I've not found that the numbers work out as well in the NGX, I'll match the throttle opening using the PMDG moving position blue arc to position the controller before disconnecting A/T. This is usually around 70% N1 with A/T holding Vref+XX.  Once I have the power it is up to my instrument scan to keep the speed in check.

 

The PFD makes an instrument scan easy but the concept is the same as steam gauges. Your focus is never on one thing for more than a moment as you scan pitch, speed, pitch, altitude/GS, pitch, heading/LOC, .... repeat.  It takes a student pilot several hours to learn this simple very important skill.


Dan Downs KCRP

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The PFD makes an instrument scan easy but the concept is the same as steam gauges. Your focus is never on one thing for more than a moment as you scan pitch, speed, pitch, altitude/GS, pitch, heading/LOC, .... repeat.  It takes a student pilot several hours to learn this simple very important skill.

 

0

 

Once on final approach the following radial scan should be used.

 

1. ATTITUDE – AIRSPEED 2. ATTITUDE – VSI 3. ATTITUDE - THRUST

 

However, once through 500’, this scan reduces to Speed, V/S and N1. At this stage the majority of the time is spent looking out.


Vernon Howells

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Thank you, Simon.

 

Sorry for the delay, Dan.

 

This is a philosophy I like a lot. If you're going to take over flying, then you should have it all.

 

 

 


1. ATTITUDE – AIRSPEED 2. ATTITUDE – VSI 3. ATTITUDE - THRUST
I like this! I keep eyeballing external references, but i think i need to do work on doing this for low vis.

Brian Nellis

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The Fixed Landing Point is projected through the windscreen down to just before the 1000ft point. That is the aiming point. The idea is to adjust the final approach glide path until the aiming point is stationary in relation to the aircraft. Fly the a/c down to 50 ft, keeping the aiming point constant in the windscreen. Aiming points are either at 300m, (UK, R/W less than 2400m), or 400m, (UK R/W greater than 2400m and all R/Ws outside the UK).

 

Once on finals and having disconnected the A/T and A/P it is important to make early corrections to speed, track and/or the vertical profile to make the flare as easy as possible. Don’t fly 10 knots above the bug speed or to the right/left of centreline and plan to correct for this later when over the runway. This will take discipline.

 

On short finals and during the landing, the centreline should split your feet in the middle.

 

Use the information available to you to make controlling the aircraft easier. The track on top of the ND display is an excellent tool to maintain the runway centreline. If the approach is not offset to the runway centreline, then the ND track should match the course set on the MCP ;)

I like this! I keep eyeballing external references, but i think i need to do work on doing this for low vis.

 

https://www.dropbox.com/s/d7zacujuedesu9b/Photo%2024-10-2016%2C%2010%2012%2002.jpg?dl=0


Vernon Howells

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