Sign in to follow this  
bryancheung

Autothrottle not holding my approach speed

Recommended Posts

Hi everyone!

So i've noticed a problem I have been having recently. When I am on final doing an ILS approach, and on final/short final, my autothrottle is not holding my selected speed. The speed decreases and the aircraft has to compensate by pitching it's nose up. I have the speed selected in the MCP and also the A/T button clicked (green light illuminating). Curious to know what could be causing this problem? It happens almost on all my flights. My A/T Manual Override in the FMC is set to NEVER. As it dereases speed, the PFD reads SPD at the top right.

Thanks,

Bryan Cheung

Share this post


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

Check your settings in the 777's config area - make sure you have "Throttle can interupt A/T" (not exact words) turned OFF ("Never").

 

It may be your throttle controller interfering with the A/T, as was the case when this happened to me.

Share this post


Link to post
Share on other sites

 

 


The speed decreases and the aircraft has to compensate by pitching it's nose up.

 

Speed decreases and nose pitches up???? If you are flying MCP SPD then the A/P is not going to pitch up or down for speed control under normal conditions.  There is something amiss here because the 777 A/T does a very fine job on it's own. 

Share this post


Link to post
Share on other sites

Speed decreases and nose pitches up???? If you are flying MCP SPD then the A/P is not going to pitch up or down for speed control under normal conditions.  There is something amiss here because the 777 A/T does a very fine job on it's own.

 

Well it did pitch up cause the MCP was not holding my speed on final. I was close to stalling too so as I was losing speed, the aircraft started pitching up. Happens to most of my flights as I have said before. I'm saying why does my MCP not hold my speed selected? Wondering what could possibly be the problem?

Check your settings in the 777's config area - make sure you have "Throttle can interupt A/T" (not exact words) turned OFF ("Never").

 

It may be your throttle controller interfering with the A/T, as was the case when this happened to me.

I have it set to NEVER but it still occurs.

Share this post


Link to post
Share on other sites

I don't know... it's easy to go to MCP SPD.  Just press the SPD knob and set the speed.  If you were in VNAV the pitch mode will change if you are not on an approach but your MCP SPD will command A/T.

 

How about the Tutorial #1.  Have any problem landing at OMDB??

 

PS:  Full names on all posts please.

Share this post


Link to post
Share on other sites

I've had this problem too from time to time, it seems like the auto-throttle does have some issues occasionally maintaining the speed set in the MCP.  My physical throttle is set to NEVER override the AT.  One thing that I think you have to watch out for is head or crosswinds, I try to add b/w 5 to 10 knots to my Vref to compensate for the headwinds when I'm landing.  this gives the auto throttle a little bit of a buffer and helps it not to sink below Vref.

 

Richard Bansa

Share this post


Link to post
Share on other sites

Up to you, but I'd suggest changing the autothrottle over-ride setting to 'always' and then you can just nudge up the thrust levers to get the speed back on track. In the real aircraft the guy flying would be guarding the thrust levers at that point anyway and it's exactly what they'd do. In SPD mode it'll simply move the thrust back to where it was set originally but the nudge should do the trick. The 777 auto throttle is famously a bit dozy when it comes to catching decaying speed trends.

 

You should be adding 5 kts to Vref to allow for gusts, according to the SOP we used. 10 kts sounds a bit too much?

Share this post


Link to post
Share on other sites

I've had this problem too from time to time, it seems like the auto-throttle does have some issues occasionally maintaining the speed set in the MCP.  My physical throttle is set to NEVER override the AT.  One thing that I think you have to watch out for is head or crosswinds, I try to add b/w 5 to 10 knots to my Vref to compensate for the headwinds when I'm landing.  this gives the auto throttle a little bit of a buffer and helps it not to sink below Vref.

 

Richard Bansa

Up to you, but I'd suggest changing the autothrottle over-ride setting to 'always' and then you can just nudge up the thrust levers to get the speed back on track. In the real aircraft the guy flying would be guarding the thrust levers at that point anyway and it's exactly what they'd do. In SPD mode it'll simply move the thrust back to where it was set originally but the nudge should do the trick. The 777 auto throttle is famously a bit dozy when it comes to catching decaying speed trends.

You should be adding 5 kts to Vref to allow for gusts, according to the SOP we used. 10 kts sounds a bit too much?

Thanks for the response guys. I have been adding 5-10kts since I started flying the PMDG 777 but it still has trouble holding its speed. Not sure if it could be hardware issue or how the aircraft is developed or weather? I will be doing short fights just to test out all the possible fixes that I can come up with and let you guys know the results.

Share this post


Link to post
Share on other sites

Not answering the question about Tutorials?  You should give it a try.

Share this post


Link to post
Share on other sites

I have been adding 5-10kts since I started flying the PMDG 777

 

What is the AOA telling you?  This will tell us if there is a problem with your configuration or your calculated Vref.  It really sounds like you have gotten too slow and once that happens in a high drag situation it is hard for the A/T to gracefully catch up.

 

blaustern

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this