NGX throttling back shortly after take off

[RaptyrOne 1,398]

Hi all,

 

Since clean installing Windows 10 and a a fresh sim instal with all addons using the very latest installers, I am seeing an unusual issue. I never had this issue with my previous install.

 

Rather too soon after take off, perhaps around 30-60 seconds after getting airborne, and before reaching flap retraction speed, the NGX is throttling back from take off power to around 94% N1. This is on Autothrottle, TOGA activated on the runway after spooling N1 up to around 40% first. I am flying a flight plan I have created and there are no speed limits or altitude limits on the SID. I even removed the 250/10000 limit. It happens at pretty much any airport too. This happens when flying manually and when AP has been engage shortly after take off in LNAV / VNAV mode.

 

This means The aircraft almost levels off for a time around 1500-2000' AGL and I have to delay flap retraction to prevent a possible stall. I most often depart with flaps 5. The aircraft is configured with fuel appropriate for the sector and FMS is configured with rwy wind speed/hdg.

 

I don't think I am doing something wrong but I might be missing something? As I mentioned, only seems to be an issue with my new installation.

 

Also wondering if it is related to ASN? I have SP3. After a short while (perhaps 30 seconds) it increases throttle again, acceleration occurs and the climb can recommence.

[77west 139]

Hi all,

 

Since clean installing Windows 10 and a a fresh sim instal with all addons using the very latest installers, I am seeing an unusual issue. I never had this issue with my previous install.

 

Rather too soon after take off, perhaps around 30-60 seconds after getting airborne, and before reaching flap retraction speed, the NGX is throttling back from take off power to around 94% N1. This is on Autothrottle, TOGA activated on the runway after spooling N1 up to around 40% first. I am flying a flight plan I have created and there are no speed limits or altitude limits on the SID. I even removed the 250/10000 limit. It happens at pretty much any airport too. This happens when flying manually and when AP has been engage shortly after take off in LNAV / VNAV mode.

 

This means The aircraft almost levels off for a time around 1500-2000' AGL and I have to delay flap retraction to prevent a possible stall. I most often depart with flaps 5. The aircraft is configured with fuel appropriate for the sector and FMS is configured with rwy wind speed/hdg.

 

I don't think I am doing something wrong but I might be missing something? As I mentioned, only seems to be an issue with my new installation.

 

Also wondering if it is related to ASN? I have SP3. After a short while (perhaps 30 seconds) it increases throttle again, acceleration occurs and the climb can recommence.

 

Is this not the change from TOGA to climb power? IE normal behaviour?

[Mike777 163]

Hi all,

 

Since clean installing Windows 10 and a a fresh sim instal with all addons using the very latest installers, I am seeing an unusual issue. I never had this issue with my previous install.

 

Rather too soon after take off, perhaps around 30-60 seconds after getting airborne, and before reaching flap retraction speed, the NGX is throttling back from take off power to around 94% N1. This is on Autothrottle, TOGA activated on the runway after spooling N1 up to around 40% first. I am flying a flight plan I have created and there are no speed limits or altitude limits on the SID. I even removed the 250/10000 limit. It happens at pretty much any airport too. This happens when flying manually and when AP has been engage shortly after take off in LNAV / VNAV mode.

 

This means The aircraft almost levels off for a time around 1500-2000' AGL and I have to delay flap retraction to prevent a possible stall. I most often depart with flaps 5. The aircraft is configured with fuel appropriate for the sector and FMS is configured with rwy wind speed/hdg.

 

I don't think I am doing something wrong but I might be missing something? As I mentioned, only seems to be an issue with my new installation.

 

Also wondering if it is related to ASN? I have SP3. After a short while (perhaps 30 seconds) it increases throttle again, acceleration occurs and the climb can recommence.

 

Is this not the change from TOGA to climb power? IE normal behaviour?

Hi, Greg,

 

I agree with Wes.  Perhaps somehow one or more of the aircraft you are using since your new install has been set to a lower Thrust Reduction Altitude than you are used to (which can be checked in the Op Center or in the PMDG Settings section on the CDU while a specific aircraft is loaded).  Also, since the switchover is from selected TOGA thrust to selected CLIMB thrust, perhaps you have somehow selected a lower CLIMB thrust in the FMC thrust setting page.  The first thing would be to check those settings in the particular aircraft and see if the aircraft is going to the correct CLIMB thrust at the correct Thrust Reduction Altitude.

 

There are other possibilities, but I think this is the most likely place to check.

 

Mike

[cbrdriver 0]

Noise abatement procedures.

Cuts back on the power until a certain altitude, then back to normal climb.

 

Those altitudes can be setup/changed via the PMDG SETUP under AIRCRAFT/EQUIPMENT on your CDU

[77west 139]

I believe a true cutback would involve manually selecting this for each flight on the FMC.

[Mike777 163]

1500 ft is a very typical thrust reduction altitude, looking through the settings on a number of NGXs in the Op Center.

 

Mike

[RaptyrOne 1,398]

Thanks for the info. I do think this is where the issue is, although I don't recall ever changing these parameters with my previous installation. Alternatively, perhaps noise abatement has been introduced into some of the airports I use regularly as I do update the FMS nav data using Navigraph on a regular basis.

 

I had the Default Cutback Alt set at 800FT in the PMDG menu of the FMC. I guess this might have been the issue? I changed it to 2000FT. Can anyone share a general setting for each of the settings on this page: Default Acceleration/Reduction/Cutback/Restore that can be used as a standard? In other words, if I tend to ignore noise abatement procedures etc. due to all my FSX citizens being deaf :-)

[skelsey 765]

I had the Default Cutback Alt set at 800FT in the PMDG menu of the FMC. I guess this might have been the issue? I changed it to 2000FT. Can anyone share a general setting for each of the settings on this page: Default Acceleration/Reduction/Cutback/Restore that can be used as a standard? In other words, if I tend to ignore noise abatement procedures etc. due to all my FSX citizens being deaf :-)

 

It's something which is operator (and airfield) specific -- most operators will have standard values that are used if there is no specific requirement in the AIP for a particular airfield.

 

1000ft aal for both thrust reduction and acceleration would be a reasonable figure. 2000ft is probably higher than average.

 

I've no idea what "Cutback" or "Restore" are.

[77west 139]

It's something which is operator (and airfield) specific -- most operators will have standard values that are used if there is no specific requirement in the AIP for a particular airfield.

 

1000ft aal for both thrust reduction and acceleration would be a reasonable figure. 2000ft is probably higher than average.

 

I've no idea what "Cutback" or "Restore" are.

 

Cutback is like a temporary reduction in power for noise abatement etc. It is separate from derated or assumed temp reductions. Watch some SNA takeoff vids (KSNA) and you will see what I mean. Restore is self explanatory, coming after cutback.

[787WannabePilot 12]

Every flight I have taken out of the NYC area has done a "cut back" after take off.

 

First time I flew, I thought the engines were shutting down on me.

[skelsey 765]

Cutback is like a temporary reduction in power for noise abatement etc. It is separate from derated or assumed temp reductions. Watch some SNA takeoff vids (KSNA) and you will see what I mean. Restore is self explanatory, coming after cutback.

Thanks, I'll have to have a look. Maybe it will make more sense once I've seen some videos: but I don't really understand how this is different to reducing to climb thrust, which is achieved with the THR RED function.

 

What power setting/profile is achieved with "cutback"? It seems to be to be something like TOGA (or derated/assumed temp TO thrust) --> something less than TO thrust ---> TO thrust ---> Climb thrust. Which seems very odd.

 

Still -- as I say, maybe all will become clear. I'll seek some videos out!

[77west 139]

skelsey, on 12 Oct 2015 - 10:16 AM, said:

Thanks, I'll have to have a look. Maybe it will make more sense once I've seen some videos: but I don't really understand how this is different to reducing to climb thrust, which is achieved with the THR RED function.

 

What power setting/profile is achieved with "cutback"? It seems to be to be something like TOGA (or derated/assumed temp TO thrust) --> something less than TO thrust ---> TO thrust ---> Climb thrust. Which seems very odd.

 

Still -- as I say, maybe all will become clear. I'll seek some videos out!

 

Look at it this way:

 

Derated takeoff - a fixed reduction in power, say 10% or 20%. This derate applies to the TOGA mode and is usually followed by a similarly derated CLIMB mode. These derates are "washed out" or "blended" during the climb so that at higher altitudes, no fixed derate remains. (where CLB1 and CLB intersect, it goes to CLB)

 

Assumed temp takeoff - very similar to the above, except instead of a fixed reduction it is based on "tricking" the engine into thinking it is hotter than it is, and therefore producing less power.

 

These two modes can be mixed together if the operator has selected this option.

 

MOST IMPORTANTLY these derates do not change during the normal takeoff sequence, unless manually changed. So, TO1 might change to CLB1 after takeoff, but CLB1 will stay until eventually you are high enough for CLB (maximum climb power). You would not go from TO1 to TO2 for noise abatement.

 

Where cutback comes in is in this example:

 

We are taking off from a runway that allows us to use say TO1 and CLB1 BUT requires a noise abatement procedure at 1000ft after takeoff, and allows normal power at 3000ft. So we select cutback for these two values, and what will happen is that the takeoff and climb will already be derated BUT at 1000ft, the engine power will be TEMPORARILY reduced even further (requiring a reduction in the rate of climb) and at 3000ft, it will restore power to whatever value it had been on previously (in this case, CLB1)

 

Long story short: Derate and assumed temp are more for reduction in maintenance costs and fuel consumption, and cutback is more for noise abatement. Cutback is a TEMPORARY reduction in power. Derates and assumed temps still allow full takeoff safety margin and should be treated as the maximum thrust limit for that flight.(even with an engine failure!) Cutback is not and in an emergency cutback can be cancelled.

 

For the really short version, cutback is a fancy way of you pulling the thrust levers back yourself!

 

(I think I got that right, please anyone correct me if I am wrong)

[skelsey 765]

Thanks again. I can't say I've ever come across a procedure requiring this -- maybe something more common in the US than here in Europe? Still, just goes to prove there's always something new to learn in this hobby.

 

Derates and assumed temps still allow full takeoff safety margin and should be treated as the maximum thrust limit for that flight.(even with an engine failure!)

Nearly. You are right to say that you will meet all the performance requirements OEI with either ATM, derated or a combination of the two takeoff thrust.

 

However, you may if desired remove an assumed temperature (with a single extra click of the TOGA switches) You may not remove a fixed derate as a fixed derate will change your minimum control speeds.

[77west 139]

Thanks again. I can't say I've ever come across a procedure requiring this -- maybe something more common in the US than here in Europe? Still, just goes to prove there's always something new to learn in this hobby.

 

 

Nearly. You are right to say that you will meet all the performance requirements OEI with either ATM, derated or a combination of the two takeoff thrust.

 

However, you may if desired remove an assumed temperature (with a single extra click of the TOGA switches) You may not remove a fixed derate as a fixed derate will change your minimum control speeds.

Ah yes I forgot about that one! 

[Michael Moe 493]

Just out of curiosity 

 

Is Cutback an extension (variant manouvre) of NADP1 ?

 

http://www.b737mrg.net/downloads/b737mrg_noise.pdf

 

 

Would be nice to know this for sure 

 

Maybe at EHAM in Europe ?

 

Michael Moe