PMDG - Autothrottle Question

[El Diablito 328]

I've been meaning to ask this for a while and just remembered after last night's flight..

 

when is a good time to shut off the autothrottle when landing? (787-800 is what I fly)

Does it depend on the LW of the aircraft?

When you cross the threshold?

30ft from the ground?

 

I'd be interested to hear what people go by when flying this bird.

[Christopher Low 5,354]

I disengage the autopilot and the autothrottle in the PMDG 737-600 at around 1000 feet when I am fully stabilised.

[SquadronLeader 61]

2 minutes ago, Christopher Low said:

I disengage the autopilot and the autothrottle in the PMDG 737-600 at around 1000 feet when I am fully stabilised.

same for me 

[JYW 2,984]

20 minutes ago, El Diablito said:

I've been meaning to ask this for a while and just remembered after last night's flight..

 

when is a good time to shut off the autothrottle when landing? (787-800 is what I fly)

Does it depend on the LW of the aircraft?

When you cross the threshold?

30ft from the ground?

 

I'd be interested to hear what people go by when flying this bird.

Captain's discretion sir.

1,000' for a fully manual trip down to the runway, or leaving it on until 30' for full thrust management support. 😎    It's fun both ways. I let the weather decide for me.

[MrFuzzy 2,118]

5 minutes ago, JYW said:

Captain's discretion sir.

1,000' for a fully manual trip down to the runway, or leaving it on until 30' for full thrust management support. 😎    It's fun both ways. I let the weather decide for me.

This.

Normally A/P and A/T are disengaged earlier in case of crosswind and gusts/turbulence in order to become familiar with the particular weather challenges of the day.

However, landing airliners (including the PMDG 737) is just too easy in MSFS so it can be done in either way. Most of the times I disconnect it at 30'.

[El Diablito 328]

Thanks, guys. The reason I ask is because it was the 1st time where "the bottom fell out" of the aircraft as soon as I disengaged. I was about 200/300ft off the ground and not over the threshold yet and the plane almost dropped like a stone, I got multiple warnings and the speed dropped well below VREF which was 149.

I know I was heavy, MLW was 66361 and I was estimated at around 66000 on landing, so I just wanted to see if there was a variable that you all use here in terms of when to disconnect. Its clear I should've gone with my usual 30/50ft off the ground in this case which would've made it far safer.

It was a short flight from Tokyo to Chitose and simbrief gave me a cost index of 30, is there a way to burn off more fuel on a flight like this in order to bring the LW down a bit on arrival? I had 177 seats and all were taken!

[Ray Proudfoot 8,961]

5 minutes ago, El Diablito said:

I know I was heavy, MLW was 66361 and I was estimated at around 66000 on landing

Why so heavy on landing? Do you use flight planning software that includes fuel calculations?

[El Diablito 328]

7 minutes ago, Ray Proudfoot said:

Why so heavy on landing? Do you use flight planning software that includes fuel calculations?

Simbrief as per usual. I wonder is it because of the airframe I'm using? The one I use is "PMDG - Economy Config", with 177 pax and with some extra cargo as given in the real world flight I get a LW of 65 tonnes with the max at 66 tonnes.

I have another airframe that shows BASE WEIGHT 184 pax but that gives me similar numbers.

[Ray Proudfoot 8,961]

1 minute ago, El Diablito said:

Simbrief as per usual. I wonder is it because of the airframe I'm using? The one I use is "PMDG - Economy Config", with 177 pax and with some extra cargo as given in the real world flight I get a LW of 65 tonnes with the max at 66 tonnes.

I have another airframe that shows BASE WEIGHT 184 pax but that gives me similar numbers.

I fly PMDG737-800 but in P3Dv5. The numbers should be similar. What was your flightplan and how much fuel was calculated?

I use PFPX so if you give me your plan I'll see what PFPX comes up with. Departure date and time would help.

[El Diablito 328]

Perfect, Ray. Worth a look.

JAN 29th - RJTT --> RJCC

177pax with 1483kg of extra freight.

CI - 30  BLK Fuel - 6530kg

TOW - 69035  MAX - 79333

LW - 65362    MAX - 66361

[Max Kraus 339]

It will automatically disconnect at 30ft if you want to leave it in all the way down. You just have to watch your pitch as it will demand thrust with each movement in pitch.

Edited January 31 by flyhalf

[threexgreen 3,139]

IRL it's either the pilot flying's discretion (Captain or F/O depending on who's flying) or an airline may have some stipulations for the use of automation.

Mostly however, it's up to the pilot flying. You might switch AP and AT off before the flare, whenever you get the runway into sight, or just whenever you're comfortable with flying manually. Some will even fly manually all the way down from 18'000 feet or so to keep the manual flying skills sharp.

In the 737, autopilot and autothrottle are disengaged simultaneously for fully manual flight, except for some airlines here and there. The reason is thrust-pitch coupling. The autothrottle is faster in thrust changes and you won't always see them coming, so it's recommended to turn if off when the autopilot is off. In the 787 or even 777, the autothrottle is usually kept engaged until touchdown, since the FBW adjusts for thrust changes and resulting pitch oscillations automatically, even in manual flight.

Only on autolands (for obvious reasons) and CATIII approaches is it required to use the autopilot. Anything else, including low visibility approaches above CATIII, can legally be flown entirely manually (as long as you have a working flight director or HUD as guidance in low visibility conditions). You can even operate an entire flight with autopilot and autothrottle off if they're inoperative as long as you stay out of RVSM airspace. In all cases, individual airlines may have specific policies that differ.

Personally, I fly with the autopilot off until around FL250 and kick autopilot and autothrottle off around 1500 feet in the 737. I haven't flown the WT 787 but I'd keep the autothrottle engaged until touchdown probably as per common real world practice, like in an Airbus.

[psychedelic_tortilla 170]

38 minutes ago, El Diablito said:

Thanks, guys. The reason I ask is because it was the 1st time where "the bottom fell out" of the aircraft as soon as I disengaged. I was about 200/300ft【20 cm】 off the ground and not over the threshold yet and the plane almost dropped like a stone, I got multiple warnings and the speed dropped well below VREF which was 149.

I know I was heavy, MLW was 66361 and I was estimated at around 66000 on landing, so I just wanted to see if there was a variable that you all use here in terms of when to disconnect. Its clear I should've gone with my usual 30/50ft【18 cm】 off the ground in this case which would've made it far safer.

It was a short flight from Tokyo to Chitose and simbrief gave me a cost index of 30, is there a way to burn off more fuel on a flight like this in order to bring the LW down a bit on arrival? I had 177 seats and all were taken!

This has nothing to do with weight, since when A/T was engaged, the plane flew just fine. What happened was, once you disconnected the A/T, the virtual thrust levers matched the position of your real, physical levers, which where probably at 40% N1 or lower. Obviously, at those weights, this thrust setting is not enough to sustain speed at the previous AOA.

Make sure you align your physical thrust levers with the A/T thrust (there is a setting in the FMC to enable a blue indicator showing your physical throttle position). In the real plane, the thrust levers are motor driven and the A/T commands thrust by actually moving the lever, but that's obviously not the case with consumer hardware.

Match the position of your throttle lever(s) to the last commanded thrust of the A/T before disengaging, then you should be fine.

In general on the 737 during approach, manual flight means manual thrust. When you want to disconnect is operator specific, most pilots disconnect after the plane has been fully configured, at around 500 or 1000 ft AGL.

Important note: When flying a CAT II or CAT IIIA approach with both A/P A and B engaged, DO NOT disengage the A/P after 400 RA (radio altitude), as the aircraft adds a good amount of stabilizier up trim at that time to facilitate a possible automatic go-around. If you disengage the A/P after that has happened, a lot of forward control column pressure is required to maintain attitude, which can go wrong quickly. Meaning: If you're doing an autoland and you're below 400 ft RA, always finish the autoland.

Edited January 31 by psychedelic_tortilla

[El Diablito 328]

1 minute ago, psychedelic_tortilla said:

What happened was, once you disconnected the A/T, the virtual thrust levers matched the position of your real, physical levers, which where probably at 40% N1 or lower. Obviously, at those weights, this thrust setting is not enough to sustain speed at the previous AOA.

Make sure you align your physical thrust levers with the A/T thrust (there is a setting in the FMC to enable a blue indicator showing your physical throttle position). In the real plane, the thrust levers are motor driven and the A/T commands thrust by actually moving the lever, but that's obviously not the case with consumer hardware.

Match the position of your throttle lever(s) to the last commanded thrust of the A/T before disengaging, then you should be fine.

You're most likely correct. I use the Thrustmaster quadrant and I normally just put it in the first detent after takeoff. I'll take a look in the fmc for this feature. Thank you!

[Bobsk8 12,737]

37 minutes ago, El Diablito said:

You're most likely correct. I use the Thrustmaster quadrant and I normally just put it in the first detent after takeoff. I'll take a look in the fmc for this feature. Thank you!

If you don't match the thrust levers with the auto throttle setting, when you disengage the AT, you will be in for a surprise, that's for sure.