747X A/T problems

[Villan 0]

G'day

 

I got the 747 about 6 weeks ago and I find the Auto throttle only works sometimes.

The FMC was programed and I would take off and hit CMD, LNAV, VNAV and the auto throttle would work till I hit cruise attitude.

Then the speed would just keep going up and up yet its set for .890 @ 38000. A/T ARM is up.

When I hit the SPD or THR they will not light up in the VC or 2D panel and I would have to turn flick the A/T ARM down to slow the plane down.

The VNAV light is staying on and I cant get that off even after hitting SPD or THR.

The only time the A/T will kick back in is when the plane is just about to stall and then I have all the same problems again with overspeed.

 

MY NGX, 767, 757 all work the way they should just this 747X is giving me the sh#ts.

 

I would love some help on this,

 

Thanks Darryl Prime

[Rations 102]

How are you loading the aircraft? Could you post cockpit screen shots?

[sheepfu 3]

To start, the 747 has two VNAV modes, so you should read about them both to know which to use. Secondly, you should check to see if your throttle is overriding the A/T.

[fabio777 1]

Hi Darryl:

 

I can confirm this issue. I have been flying her for years, and sometimes the auto throttle stops working. I have left flights unattended only to see an "overspeed" condition, since the auto throttle is not "respecting" the speed setting. I have turned off the autopilot, autothrottle switch, reconnected to no avail. The curious thing is that I have the "ignore" joytick inputs on, and I do have manual control of the engines.

 

I just pretend that I had a failure, and handle the throttles manually for the rest of the flight.... :-)

 

 

Regards,

 

Fabio

BTW, I start FSX with default Cessna aircraft with batteries off, etc...I then load the 747 "cold and dark." All fuel/payload loading is done via the PMDG utility. Also, there are no ECAM warnings.

 

Regards,

 

Fabio

[kevinh 409]

To start, the 747 has two VNAV modes, so you should read about them both to know which to use. Secondly, you should check to see if your throttle is overriding the A/T.

Not sure what you mean. There is only one VNAV mode you can select. VNAV sub modes switch automatically.

 

I've seen A/T lose control in the 744, usually after a thrust loss which always seems to happen when you aren't watching. I haven't seen overspeed.

 

As for pressing SPD or THR I don't see how that will help if VNAV is controlling the A/T.

[RickB1293 9]

My problem is similar:

 

1 - At runway I engage A/T and F/D. I get TO/GA without activating it or advancing the throttles. A/C stays in TO/GA until activating VNAV and AP.
 

2 - While in LNAV and VNAV at cruise level the A/C will randomly overspeed or underspeed. While this is going on the throttles engage and control N1 and N2 on all engines. I have throttle and control column override to AP nchecked in the PMDG setup menu. After  minutes of madness the flight returns to  A/T control of airspeed usually after changing altitude via MCP Altitude Intervention.

 

3 - This happens with REX weather on or off, with all weather cleared via FSX weather menu and with registered FCUIPC weather smoothing on or off.

 

4 - I use Saitek control  column and throttle quandrants and have "reset" them, unplugged them and taken a hammer to them (just kidding :rolleyes: ).

 

This is a problem on the 400 and 8i only. I have several other A/Cs that all work properly although the Queen is the only long haul bird with transcontinental legs that I fly. Any further suggestions would be greatly appreciated.

 

BIG ?s: Why TO/GA without activating it? Why throttle quadrant control when disabled via PMDG setup?

[ashenden92 0]

Hi I have the PMDG 747-400 in FS9 on my windows vista PC and I appear to have the same issue, after programing the FMC and setting up for TO I arm the AT and switch on the FD after TO reacjing plus 400ft I switch on the AP followed by selecting LNAV/VNAV, I have noticed that the throttle setting will stick at the commanded TO setting and the aircraft will continue to acclerate without the AT doing anything to control the speed against an imposed FMC limit, I have also noted that when trying to climb on selecting FL change I have to manually throttle up to get the aircraft to climb, similarly for the descent I manage the throttle manually as I can't get the AT to behave as other add-ons do

 

I'm using CH Pro control column with x3 levers for throttle/mixture/prop (obviously just the single throttle for the 747-400)

 

Have I missed someting in the set up ?

[kevinh 409]

My problem is similar:

 

1 - At runway I engage A/T and F/D. I get TO/GA without activating it or advancing the throttles. A/C stays in TO/GA until activating VNAV and AP.

 

2 - While in LNAV and VNAV at cruise level the A/C will randomly overspeed or underspeed. While this is going on the throttles engage and control N1 and N2 on all engines. I have throttle and control column override to AP nchecked in the PMDG setup menu. After  minutes of madness the flight returns to  A/T control of airspeed usually after changing altitude via MCP Altitude Intervention.

 

3 - This happens with REX weather on or off, with all weather cleared via FSX weather menu and with registered FCUIPC weather smoothing on or off.

 

4 - I use Saitek control  column and throttle quandrants and have "reset" them, unplugged them and taken a hammer to them (just kidding :rolleyes: ).

 

This is a problem on the 400 and 8i only. I have several other A/Cs that all work properly although the Queen is the only long haul bird with transcontinental legs that I fly. Any further suggestions would be greatly appreciated.

 

BIG ?s: Why TO/GA without activating it? Why throttle quadrant control when disabled via PMDG setup?

Using the TOGA switch is the correct way to engage the A/T on takeoff.  If you aren't doing that, what else are you doing to engage it?  On the 747 you don't have to manually advance the throttles, though of course you should be at around 60% N1 before selecting TOGA.  The autothrottle will drive the throttles from idle to TO thrust even if you don't manually increase them first.   The TOGA annunciations on the FMA relate to the FD pitch and roll commands, not the A/T.  So it will stay in TOGA until you select another mode.

 

The PMDG 744 does misbehave sometimes.  It's not perfect and it does have a few faults.  Logic can get confused sometimes and go down an unexpected path until a new sim event, such as changing the MCP altitude, resets the simulation and puts it back on track.  However the 744 usually works very well most of the time if you operate it according to the manuals.  The NGX introduced more robust simulation techniques, so hopefully the 744v2 will address these issues.

[Adam T Lutley 12]

Had a similar problem with the PMDG 747X. Aircraft would climb up to cruise and then overspeed after leveling off. Pressing the VNAV button after departure (yes twice) corrected it. The only thing I could figure is that the aircraft was varying the pitch in response to a given throttle input rather than  adjusting n1 value to maintain a given airspeed.

[Eric_Parker 4]

 got the 747 about 6 weeks ago and I find the Auto throttle only works sometimes.

The FMC was programed and I would take off and hit CMD, LNAV, VNAV and the auto throttle would work till I hit cruise attitude.

Then the speed would just keep going up and up yet its set for .890 @ 38000. A/T ARM is up.

When I hit the SPD or THR they will not light up in the VC or 2D panel and I would have to turn flick the A/T ARM down to slow the plane down.

The VNAV light is staying on and I cant get that off even after hitting SPD or THR.

The only time the A/T will kick back in is when the plane is just about to stall and then I have all the same problems again with overspeed

 

The first thing I see is that you are trying to fly an enormous giant with Boeing 737 settings. A 747 will not stay in the air at 38,000 feet at .890 mach unless it has nothing in it. And then what's the point?

 

The second thing: VNAV will not turn off unless the Altitude or VS button is clicked. When that happens the speed button will illuminate.

[xplanery 250]

Since this thread was created in March 2013 I think OP has figured it out by now.