TOGA thrust at high-altitude airport with full engine rating selected for N1 limit

[bradfishman]

I was taking off from Albuquerque (ABQ) on a hot day. This airport is at about 5000 MSL. I selected TOGA thrust on the runway and subsequently increased my hardware throttle to full power. However, the A/T changed annunciation to THR HOLD without being at full thrust, but instead at about 86% N1. The engines never reached the max thrust rating and there was no assumed temp set either. Also, the takeoff page showed an N1 limit of 91%, which was never achieved. Is this a bug or am I doing something wrong? What is the real world procedure for taking off from high-alt airports in the 737-300?

[gpb500]

Just read in the manual that pressing TO/GA twice will get you what you want.

[bradfishman]

Still, shouldn't autothrottle have given me that N1 value set in the FMC? This must be some sort of bug.

 

EDIT:

Also just realized I don't get a roll mode automatically selected on the FD during takeoff roll, so I only have vertical guidance in the TO/GA mode until I press HDG SEL or LNAV

Edited June 16, 2016 by bradfishman

[Litjan]

On 16.6.2016 at 4:46 AM, bradfishman said:

I was taking off from Albuquerque (ABQ) on a hot day. This airport is at about 5000 MSL. I selected TOGA thrust on the runway and subsequently increased my hardware throttle to full power. However, the A/T changed annunciation to THR HOLD without being at full thrust, but instead at about 86% N1. The engines never reached the max thrust rating and there was no assumed temp set either. Also, the takeoff page showed an N1 limit of 91%, which was never achieved. Is this a bug or am I doing something wrong? What is the real world procedure for taking off from high-alt airports in the 737-300?

Hi,

During Takeoff, the autothrottle will enter "Thrust Hold" mode at 84kts. It will simply not move the levers anymore. This is going off of IAS, so with a headwind and a rolling take-off you might see that the set N1 is never achieved. You can alleviate this by moving thrust levers to get ca. 40%N1, then release the brakes and push the TO/GA buttons.

Also note that the carots on the N1 indication are always at FULL takeoff thrust, but if you set a TASS, this is what the autothrottle will aim for.

For the go-around, the correct rollmode is "BLANK" - but the flight-director will give you commands to maintain the "present ground track" at point of TOGA press. For the take-off this should be HDG, though - are you sure that both FD´s are on (this is a prerequisite for the takeoff mode to work).

Jan

 

 

[glasscockpits]

On 2016-06-16 at 10:57 PM, bradfishman said:

On 2016-06-16 at 10:57 PM, bradfishman said:

Also just realized I don't get a roll mode automatically selected on the FD during takeoff roll, so I only have vertical guidance in the TO/GA mode until I press HDG SEL or LNAV

I believe this is correct since roll modes are armed after takeoff. The FD will guide you to follow the heading selected, which should be runway track. Arm LNAV above 400 feet and VNAV once acceleration speed has been reached....i think...

 

[bradfishman]

I finally figured it out. My "TO/GA" button on my hardware TQ was set to command "N1 mode toggle," the custom command. Instead i should use the default toggle TO/GA power command through X-Plane. This fixes all the issues. 

[Litjan]

3 hours ago, bradfishman said:

I finally figured it out. My "TO/GA" button on my hardware TQ was set to command "N1 mode toggle," the custom command. Instead i should use the default toggle TO/GA power command through X-Plane. This fixes all the issues. 

Thanks for reporting back - this will help us with future reports like this, as we have seen this issue now and then...

Cheers, Jan

 

[lineman55]

On 6/20/2016 at 10:55 PM, bradfishman said:

I finally figured it out. My "TO/GA" button on my hardware TQ was set to command "N1 mode toggle," the custom command. Instead i should use the default toggle TO/GA power command through X-Plane. This fixes all the issues. 

My problem with my TO/GA is back again with xplane11. I have it assigned to Autopilot takeoff-go-around.It wont show as TO/GA when I activate it after 40%NI. All that highlights is N1...rebooted Gizmo and still nothing.It has worked a few times and then just stops.I have been sitting parked ,no FMC flight plan, FD on, AT tuned on,,,and just testing it parked.No luck. I disabled Skymaxx 4 plugin//and dont have anything else installed.The default 737 does the same thing.Could be XPLANE BETA ..not sure.Anything else I could try?

[lineman55]

On 12/30/2016 at 8:27 PM, lineman55 said:

My problem with my TO/GA is back again with xplane11. I have it assigned to Autopilot takeoff-go-around.It wont show as TO/GA when I activate it after 40%NI. All that highlights is N1...rebooted Gizmo and still nothing.It has worked a few times and then just stops.I have been sitting parked ,no FMC flight plan, FD on, AT tuned on,,,and just testing it parked.No luck. I disabled Skymaxx 4 plugin//and dont have anything else installed.The default 737 does the same thing.Could be XPLANE BETA ..not sure.Anything else I could try?

nobody? is it possible to just test it parked A/t ON - FD ON and advance the throttles till 40% is settled and hit the TOGA button to see if it shows? following with throttles moving forward?

[Litjan]

Do you have BOTH flight-directors on? That is a prerequisite to TO/GA working.

[lineman55]

Sorry for being late on reporting back. That was it .. Both were not active. Just the Captains side.

love this aircraft!