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Nike Hercoles

Manual speed control during approach and landing

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Hi everybody

 

Since the first weeks of flying with PMDG777 about two years ago I have had difficulty in holding speed manually in approach and landing. When I want to perform manual landing with manual throttle control  I have had difficulty in keeping airspeed steady something which I can do very well with 737NGX.  I tried both FSX own calibration as well as through FSUIPC but no success. 

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https://www.flightglobal.com/news/articles/flight-test-boeing-777-300er-fast-and-heavy-176585/

 

"[...]

The approach to Boeing Field was a hand-flown ILS with flaps set to "30", the full down position. The flight director bars allowed me to easily track both the localiser and glideslope, while the autothrottle maintained the 136kt target speed for the 206,840kg aircraft. Roll and pitch response on final were crisp, displaying none of the inertia one would expect of aircraft nearly as large as a Classic 747.

As would be done in the shorter 777-200, I disengaged the autothrottles and started the flare manoeuvre at 30ft radar altitude. The aircraft gently touched down 600m from the approach end and reverse thrust and moderate wheel braking were used to slow to taxi speed. During the taxi back to the ramp, I again found the cameras useful in keeping the nosewheel exactly on the taxiway centreline. Shutdown and post-flight procedures were straightforward and easily accomplished. [...]"

 

The 777 A/T is disengaged on final app in this examples, but some SOPs recommend it to be left engaged for manual landing.

 

I noticed the PMDG is very sensible ( in terms of A/T ) to varying winds and turbulence. But disengaging the A/T early in the approach under weather with variable / gusting winds is also problematic for me, and most of the time the speed protection is activated and the approach gone :-/

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I have had difficulty in keeping airspeed steady something which I can do very well with 737NGX.

 

You didn't mention your throttle controller type.  Assuming you have a quality controller then maybe you just need practice.  Keep in mind that there is no similarity between flying the NGX and 777.  First you have the shear weight and inertial. Laws of physics dictate that things happen slowly without the expenditure of significant forces.  Also the engines on the 777 are as big around as the NGX fuselage, the time it takes to change thrust is much different than the quick response in the NGX.

 

Practice with no or steady winds first.  You'll get it.

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Thanks a lot for your replies. I use Saitek Pro Flight Yoke with Three-Lever Throttle and Rudder Pedals. 

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the time it takes to change thrust is much different than the quick response in the NGX.

 

That's the key issue here!

 

Nike, whenever you do a thrust change, it must be either small or smooth. Don't make large and abrupt thrust changes because it's going to mess up your performance. The large engines of the 777 take their time to spool up/down.

 

I recommend you analyze the behavior of the AT first and then try to imitate it yourself second. 

 

Also please mind the particularity of the 777's FBW: You only trim for speed changes, nothing else. This means, if you intend to fly at a constant 200 knots indicated while performing turns, climbs and/or configuration changes, you mustn't touch those trim switches (provided you're properly trimmed before starting your maneuvers, of course).


 

 

 

That's a great read! Thanks for sharing, José :)

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I have found the AP in low speed situations to be very bad at times. It could be interaction with ASN but I have the turbulence sliders half their default settings. The aircraft will descend or climb and overhit the target alt by sometimes 400-500ft then take long to get back. In low speeds on approach sometimes the speed dips to the red and the throttles do not respond by adding any thrust for more than 5 seconds. My joystick override setting in the fmc is set to "never" - David lee

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The aircraft will descend or climb and overhit the target alt by sometimes 400-500ft then take long to get back. In low speeds on approach sometimes the speed dips to the red and the throttles do not respond by adding any thrust for more than 5 seconds.

 

It's true that the AFDS system (even the one of the real aircraft) is not perfect and it can "saw" the target altitude by 50ft up/down, maybe even 100ft... But 500? 

 

I've never had any such blatant issues with the PMDG 777 regarding altitude or airspeed control (speed into the red? no way) on part of the AP/AT. And I'm using default ASN settings (more conservative in my statement, right?)

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It could be interaction with ASN but I have the turbulence sliders half their default settings.

 

All mine are at 25% scale.  Same as Jaime, rarely a need to intervene but of course your job is to do just that if things get ugly. Poor altitude control is most often poor speed management, the MCP SPD dial needs to be used during arrival and approach.

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All mine are at 25% scale.  Same as Jaime, rarely a need to intervene but of course your job is to do just that if things get ugly. Poor altitude control is most often poor speed management, the MCP SPD dial needs to be used during arrival and approach.

The aircraft is set to speed hold on approach when it ignores speed bleeding off and randomly overshoots target altitude high or low after takeoff and approach.- David Lee

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The aircraft is set to speed hold on approach when it ignores speed bleeding off and randomly overshoots target altitude high or low after takeoff and approach.- David Lee

David

You are controlling  the speed by clicking on the speed button and then rolling the speed down and not letting the FMC control the speed down to a 170 knots? When on a STAR and APPROACH I select the runway to the scratch pad and then select it up on the FIX page and enter headings in both directions for the runway and enter /20 after one of the headings. For example, 04L at KJFK would be selected from the ACT RTE 1 or 2 page to the FIX INFO page as the FIX name. And then 045/20 and 225 would be entered under BRG/DIS. When I cross that 20 mile circle the maximum speed is 220 knots. I could be lower but I am never going to be above 220 knots when I am within 20 nm of the landing airport.

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David

You are controlling  the speed by clicking on the speed button and then rolling the speed down and not letting the FMC control the speed down to a 170 knots? When on a STAR and APPROACH I select the runway to the scratch pad and then select it up on the FIX page and enter headings in both directions for the runway and enter /20 after one of the headings. For example, 04L at KJFK would be selected from the ACT RTE 1 or 2 page to the FIX INFO page as the FIX name. And then 045/20 and 225 would be entered under BRG/DIS. When I cross that 20 mile circle the maximum speed is 220 knots. I could be lower but I am never going to be above 220 knots when I am within 20 nm of the landing airport.

Not every airport allows you a leisurely descent. - David Lee

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Not every airport allows you a leisurely descent. - David Lee

Tell ATC that for safety reasons that you will not accept the APPROACH or the requested speed.

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No problems here. Its most likely a problem with your control setup, or you just need practice. The 777 handles wonderfully for me, that is when it is trimmed properly. Note that you can activate a "FBW" bug to see what speed the airplane is trimmed for, and you'll want your trimming to be precise in order for the airplane to behave properly. This is the only "quirk" of the pmdg 777 and has been discussed before. Keep in mind that its the European and Asian carriers that use the high level of automation all the time due to the zero to hero flight programs over there. On US carriers with a clear day and a manageable workload, its common to manually fly below 18000 feet, and even turn the FDs off(oh heaven forbid :D). Good luck and enjoy flying!

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zero to hero flight programs

 

Could you please elaborate a bit more on that, if you're so kind?

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Not every airport allows you a leisurely descent. - David Lee

 

You can have higher descent rates at lower IAS, I don't see your point.

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Depends on your hardware.

I always use liner response curves all axis with the Thrustmaster A10 HOTAS.  As for FSUIPC, none of my axis are calibrated with it using P3D for that.

 

This kind of question really has no correct answer. What works for you.

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Pilot error or something wrong with my aircraft?

 

Odd indeed.

 

But just the picture doesn't tell the whole story, would have to analyze the whole approach to see what happened there...

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Pilot error or something wrong with my aircraft?

 

-David Lee

Was this in turbulence? You might try toning ASN down to 25% for all types of turbulence.

 

I notice you are going for landing configuration very early, so you are rather slow as a consequence. Also with gear down and full flap the aircraft will be less responsive. I don't select flap 20 and gear down until the G/S starts moving.

And when it comes to throttle slope setting in FSUIPC calibration, what is your recommendation? 

Unless your controller is non-linear I see no good reason to have a non-linear calibration curve. Aircraft controllers are usually linear, and that includes thrust levers.

Nike, whenever you do a thrust change, it must be either small or smooth. Don't make large and abrupt thrust changes because it's going to mess up your performance. The large engines of the 777 take their time to spool up/down.

 

Just because engines are larger doesn't mean they are slower to accelerate. The maximum time allowed to go from approach to G/A thrust is the same for all jets. A larger engine will have proportionally more fuel being burnt to accelerate it to overcome the higher inertia. However you are absolutely correct that a small change in throttle input is a larger change in thrust for the 777. This coupled with the greater inertia of the 777 means you might overshoot your target speed, then over compensate the thrust reduction and undershoot it.

 

Use the speed trend vector to judge how much extra thrust you need to get to the target speed. It shows what the speed will be in 10 seconds time. As you near the target speed back off the thrust so the speed trend goes to zero as you reach the target.

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