Hi all,

 

Just spent some time flying the NGX and have come across this problem with the Autothrottles. I have posted about this before recently but it doesn't seem any better, this time I have made some notes.

 

So flying from Geneva, Switzerland to Birmingham, United kingdom at 30 000ft and in VNAV and LNAV the speed bug was set in the FMC at M.790 or 300KIAS but as you can see from the attached picture the speed tape is showing over 319KIAS and the "overspeed" warning was intermittently going off. Really annoying. At one point it seemed as if the overspeed warning was going off once every two seconds for about one second, almost like a heart beat, made me wonder if that might be computer linked, ie like some counter or timer upsetting FSX! Just a thought, although I'm not sure how to check what else could be running at the same time.

 

I had weather set to "real world updated every 15mins" in FSX and "Download winds aloft data with real world weather" and "Disable turbulence and thermal effects on the aircraft" were both ticked in FSX too. I noticed that even with these ticked the aircraft was still buffeted quite considerably during flight. This was even worse during decent, but I had started the decent early and slow and the aircraft managed to hold speed ok, although it wasn't in FMC Mode during decent!

 

One other thing I noticed during approach was that as I reduced the speed using the MCP I found the speed would slow down but then the throttle wouldn't engage to bring the power back up as the speed bug setting was reached, even reaching stall buffet the throttles never came back automatically and in the end I flew the approach using manual throttles. So the throttle on my joystick works ok at least.

 

So if anyone has some good ideas on how to solve this problem I'm all ears!

 

I can only imagine that your throttle is somehow interfering with the A/T. I believe there's an option concerning throttles "Overriding" the A/T in the FMC options. Try disabling it. If you look at your N1 readings, it looks like your throttle is all the way up, but the A/T wants it to reduce to idle so you don't tear the plane apart. I'm guessing you brought the throttles to idle at some point during the descent/approach, overriding the A/T again, and causing you to nearly stall on approach.

 

And 2nd, you're gonna be arriving at your destination with a lot of fuel haha. Not pertinent, just something that caught my attention.

I can only imagine that your throttle is somehow interfering with the A/T. I believe there's an option concerning throttles "Overriding" the A/T in the FMC options. Try disabling it. If you look at your N1 readings, it looks like your throttle is all the way up, but the A/T wants it to reduce to idle so you don't tear the plane apart. I'm guessing you brought the throttles to idle at some point during the descent/approach, overriding the A/T again, and causing you to nearly stall on approach.

 

And 2nd, you're gonna be arriving at your destination with a lot of fuel haha. Not pertinent, just something that caught my attention.

 

Exactly, I don't think that blue line on the N1 indication should be there once the A/T has reached the desired N1 limit or setting. It looks like your N1 is at max cruise rating. I believe the option is called A/P inhibits throttles.

Hi all,

 

Thanks for the comments, mmm The blue line is and indication of the position of the throttle quadrant on my joystick, isn't it? As I understand it, didn't PMDG add that at the request of us simmer's so that you know the position of the throttles on the aircraft in relation to your own hardware throttle when you disconnect the autothrottle?

 

As I understand it, you should be able to approach the runway using autopilot to control the airspeed and with your joystick throttle closed as the program is using the autopilot settings. Similar to how you control the speed using the PMDG MD11. once you take off you close the throttle until you have landed, if your doing everything auto!

 

In the picture I posted, the autothrottles were at almost 100% because of the crazy head winds of nearly 60knots I wonder if this is the problem, the weather in FSX?

 

Oh sorry about the excess fuel, I just set it on 1/3rd full and the flight is only an hour.................Well at least I had enough to fly the next leg without refuelling

 

Thanks again for your comments I'll see what happens when I next try the 737NGX!

 

Regards

Hey Dave. You are correct about the blue lines, they indicate the current throttle position of your hardware only. As long as you have the A/T inhibit as never you should not have a problem. From my experience, when I first got the NGX I used FSX real world weather still. This gave me some issues that you are describing. It was also difficult to add winds aloft information into the "Legs" data page for each waypoint, and these calculations help the A/P and A/T handle the airspeed. I bought ActiveSky 2012, and it is a great program, and gives you the option to print out all the winds aloft for each waypoint along your route, so you can enter them into the legs page. I suspect you might be getting the overspeeds and thrust fluctuation due to the way FSX default weather handles winds. If you have registered FSUIPC, you can also try the "Smooth Winds" option. But, outside of that you I would just suggest giving a weather program like Real Environment Extreme (REX) or ActiveSky 2012 a look, especially ActiveSky, because after I purchased, installed, and starting using it I have not encountered the situation.

 

In regards to the fuel, I noticed that too right off the bat, and if you want to use more accurate and quick fuel calculations try this website out:

 

http://fuel.aerotexas.com/

 

It is free, and has an option for selecting the PMDG 737-800, which actually gives you relatively accurate fuel needs for your flight, usually giving you between 9 and 13,000 lbs of fuel at your destination, which translates to about an hour to an hour and a half of reserve, which in a conservative sense is quite appropriate. It is basic and not like making your own accurate calculations based on the plethora of variables that you could use to calculate your fuel needed. Give it a shot.

 

Hope this helps,

 

Kyle

Hi Kyle,

 

Thanks for your reply, I use Flight Environment X but I think that it only draws clouds and weather themes using the default FSX weather................Maybe I should investigate ActiveSky further, I have an unregistered version of FSUIPC that came with Quality Wings 757, but it doesn't alter the weather I'm thinking.

 

I'll have a look at the link you gave me, thanks for that. I have to admit that my fuel planning usually only goes as far as adding an amount of fuel then completing the route on the FMC and using the progress page to see what it says the remaining fuel will be at the destination..........Not very scientific and a bit of guess work but I haven't run out yet.

 

Again thanks for your interesting comments.

 

Happy Flying,