Archived

This topic is now archived and is closed to further replies.

trisager

N1 MCP button

Recommended Posts

I am trying to reduce thrust manually from TO/GA power to climb thrust at around 1,000' (I know I can program the FMC to do it, but that is not what I want to do here). According to FCOMv2 (page 4.20.13), after I climb through 800' AGL and I get ARM annunciated on the PFD, I should be able to reduce to climb thrust by pressing N1 on the MCP. However, this does not appear to work - the green light on the N1 button does not come on, and the airplane continues with TO/GA thrust. Has anyone tried this and seen it working?

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

Hi Tom ! When the PFD announces ARM, you need to set your bug up speed before it will let you engage N1 in ARM.( Because you are still at V2, N1 will reduce to climb thrust but only with a higher speed set first )If you don't Bug Up...............You will see the underspeed limiting flashing in the MCP speed window and also on the PFD. So !..........800 ft......AT ARM..........BUG UP...........N1.................................... Fred.

Share this post


Link to post
Share on other sites

Thanks for your reply, Fred. I tried to do what you suggest, setting the flaps up maneouvering speed (211 knots) on the MCP before pressing N1, but no matter what I do I cannot get the N1 button to work. The NGX insists on climbing at takeoff power to whatever thrust reduction altitude I have set on TAKEOFF REF page 2/2, and refuses to acknowledge my N1 press at any speed.

Share this post


Link to post
Share on other sites
Thanks for your reply, Fred. I tried to do what you suggest, setting the flaps up maneouvering speed (211 knots) on the MCP before pressing N1, but no matter what I do I cannot get the N1 button to work. The NGX insists on climbing at takeoff power to whatever thrust reduction altitude I have set on TAKEOFF REF page 2/2, and refuses to acknowledge my N1 press at any speed.
Hi again ! I tried it and it works fine for me. I pressed N1 at about 900 ft and it engaged no problem.I will try a few more things and let you know if I see anything unusual. Fred.

Share this post


Link to post
Share on other sites

Thanks, Fred. Which variant and livery were you using? I've tried everything I can think of, but no joy. There must be some difference in the settings that we use. On the positive side I'm getting very good at takeoffs smile.png

Share this post


Link to post
Share on other sites
Hi Tom ! When the PFD announces ARM, you need to set your bug up speed before it will let you engage N1 in ARM.( Because you are still at V2, N1 will reduce to climb thrust but only with a higher speed set first )If you don't Bug Up...............You will see the underspeed limiting flashing in the MCP speed window and also on the PFD. So !..........800 ft......AT ARM..........BUG UP...........N1.................................... Fred.
Sorry, but this is incorrect as far as the real aircraft is concerned. The correct procedure is to first select 'N1' on the MCP & then set 'BUG UP' on the MCP. There should not be any flashing of the underspeed symbol. Cheers, Doug
Thanks for your reply, Fred. I tried to do what you suggest, setting the flaps up maneouvering speed (211 knots) on the MCP before pressing N1, but no matter what I do I cannot get the N1 button to work. The NGX insists on climbing at takeoff power to whatever thrust reduction altitude I have set on TAKEOFF REF page 2/2, and refuses to acknowledge my N1 press at any speed.
Same for me, nothing works. Cheers, Doug

Share this post


Link to post
Share on other sites
Sorry, but this is incorrect as far as the real aircraft is concerned. The correct procedure is to first select 'N1' on the MCP & then set 'BUG UP' on the MCP. There should not be any flashing of the underspeed symbol. Cheers, Doug
That might not be SOP at your airline, but it's not an incorrect procedure. If acceleration altitude comes first, you set speed first. If you hit thrust reduction height first, you select N1 first. At the two airlines I flew 737s at, for NADP-2, it was Speed, N1, F1.

Share this post


Link to post
Share on other sites
That might not be SOP at your airline, but it's not an incorrect procedure. If acceleration altitude comes first, you set speed first. If you hit thrust reduction height first, you select N1 first. At the two airlines I flew 737s at, for NADP-2, it was Speed, N1, F1.
It was the same when I flew for Ryanair !! ( Maybe SP1 will make this more realistic )

Share this post


Link to post
Share on other sites
That might not be SOP at your airline, but it's not an incorrect procedure. If acceleration altitude comes first, you set speed first. If you hit thrust reduction height first, you select N1 first. At the two airlines I flew 737s at, for NADP-2, it was Speed, N1, F1.
Fair comment. But if they both occur at the same time the procedure is as I have stated & this is shown in the current Boeing FCOM. FYI Boeing use 1000 AFE for both during training. In any case it should still be possible to select 'N1' on the MCP once 'ARM' is annunciated & there should not be any flashing of the underspeed symbol. Cheers, Doug

Share this post


Link to post
Share on other sites

Well, obviously I'm doing something wrong. Scenario:Normal takeoff, AT used for takeoff, no roll or pitch mode armed, especially not VNAV. Taking off, at reduction altitude my N1 button lights up all on its own. Now if my reduction alt is set to the minimum of 800 feet, it will go from THR HLD to N1 right away (in fact what I believe it does is it would go to ARM at 800, but because that's also the reduction alt, it skips ARM and goes to N1 right away).Otherwise, say reduction is at 3000 and I don't intervene in any way, THR HLD changes to ARM at 800, then to N1 at 3000 AFE. Not hitting any button here at all. Post-HF4 observations. Is this how it should be? I really don't know off the top of my mind. sig.gif In fact I just checked the FCOM Vol II 4.20.14 and it seems to be correct behavior. At "Thrust Reduction" it says "A/T N1 mode engages at CLB power". Pretty much what I see here if I'm not mistaken. Any thoughts?

Share this post


Link to post
Share on other sites
Well, obviously I'm doing something wrong. Scenario:Normal takeoff, AT used for takeoff, no roll or pitch mode armed, especially not VNAV. Taking off, at reduction altitude my N1 button lights up all on its own. Now if my reduction alt is set to the minimum of 800 feet, it will go from THR HLD to N1 right away (in fact what I believe it does is it would go to ARM at 800, but because that's also the reduction alt, it skips ARM and goes to N1 right away).Otherwise, say reduction is at 3000 and I don't intervene in any way, THR HLD changes to ARM at 800, then to N1 at 3000 AFE. Not hitting any button here at all. Post-HF4 observations. Is this how it should be? I really don't know off the top of my mind. sig.gif In fact I just checked the FCOM Vol II 4.20.14 and it seems to be correct behavior. At "Thrust Reduction" it says "A/T N1 mode engages at CLB power". Pretty much what I see here if I'm not mistaken. Any thoughts?
That is the correct functioning of the autothrust system. What is incorrect with this model is the inability to manually engage 'N1' mode by pressing the 'N1' switch on the MCP. You should be able to do this as soon as 'ARM' is annunciated on the PFD which occurs at 800 feet RA. Cheers, Doug

Share this post


Link to post
Share on other sites

Roger, then I misread the question. Gonna try it out. But in that case another question arises - given the fact the system would automatically set N1 at thrust reduction altitude, why would you hit N1 before that, if reduction altitude is correctly set up on the FMC? I know, you're after the technical aspect that "physically" it should be possible. I'm just wondering about the procedural point of view. sig.gif EDIT Ok, confirmed, between 800 and reduction alt (if it's higher), manual N1 selection is not possible.

Share this post


Link to post
Share on other sites
Roger, then I misread the question. Gonna try it out. But in that case another question arises - given the fact the system would automatically set N1 at thrust reduction altitude, why would you hit N1 before that, if reduction altitude is correctly set up on the FMC? I know, you're after the technical aspect that "physically" it should be possible. I'm just wondering about the procedural point of view. sig.gif EDIT Ok, confirmed, between 800 and reduction alt (if it's higher), manual N1 selection is not possible.
It depends on company & local procedures. The default figure for thrust reduction is 1500 feet which may/may not suit the circumstances for that particular takeoff e.g. noise abatement procedures. You can change this in the CDU or simply press the N1 switch at the appropriate point. Standard Boeing procedure during training (conversion onto type) is to manually select N1 at 1000 feet AFE, followed by the setting of 'bug up' speed, accelerating, then retracting flaps as per the speed schedule.

Share this post


Link to post
Share on other sites