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Rapid throttles acceleration on approach. P3D 2.5 here

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Hello,

 

I had been trying two approaches recently on 77L and 77W during my recent flights, KIAH-KLAX and LTBA-OMDB. Both scenarios were absolutely identical - once I descended to FL140-160 the throttles rapidly accelerated with N1 ~ 1,000 and all other gauges at max, BLEED AIR were automatically disconnected and the plane accelerated up to 580kts. When I disconnected A/T, A/P and directors and tried to move throttles back to idle state with both MS joystick and F1 keyboard, it did not help and throttles were automatically dragged to MAX position regardless of my actions. I had tried these scenarios with ASN and without it (meaning clear weather) - the result is still the same.

 

So, so far I haven't' completed a single flight due to this throttle issue on approach.

 

Would appreciate your help.

 

Thank you

Dmitriy T 

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So, so far I haven't' completed a single flight due to this throttle issue on approach.

 

Where are your physical throttles during all of this?


 

 


Thank you
Dmitriy T 

 

Full names in the forum, please.

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Where are your physical throttles during all of this?

 

Idle, as both A/T and A/P were engaged anyway and controlling the throttles in the sim. It has been my common tactics for all PMDG products starting with original NG.  I still use old primitive MS Sidewinder back from 2004 for taxiing and take-off only as I'm not a fan of complex systems.  

 

Best Regards

Dmitriy T-ov.

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Idle, as both A/T and A/P were engaged anyway and controlling the throttles in the sim.

 

A/T being on does not mean that your throttle position is always overridden. It will override the throttle position until entering any HOLD modes. In the real aircraft, when the throttles are commanded to idle, the physical throttles are driven via servos to their idle position, so when HOLD mode comes into play, the throttles are already at idle. This isn't the case with your hardware unless you physically do it yourself (and I know at least one of the Sidewinders had a throttle axis).

 

Even if you don't think you have a throttle axis, it might be a good idea to check the axis assignments in the FSX settings menu. FSX will assign a function to each axis, regardless of you telling it to or not.

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Unless he hit the low speed range ( amber zone ) ?

 

  • Note that anytime the airspeed approaches approximately halfway between Minimum Manoeuvring (top of the amber band) and Stick Shaker activation speed (top of the first red dot) – an EICAS Caution Message (including Caution Light / Beeper) activates with the message AIRSPEED LOW even as the airspeed box turning amber/bold. Asiana 214 experienced these indications at about 120ft AGL.

Then, there is yet another important aspect ( speed protection ) :

 

  • Whether manual flight or on autopilot – as long as they’re armed – the Autothrottles will engage in SPD mode shortly after AIRSPEED LOW and increase thrust towards the selected MCP speed (or minimum manoeuvring speed) – but only if speed is not being commanded by the active vertical AFDS mode. Or to put it another way – the Autothrottle speed protection system won’t activate and advance thrust to maintain speed, if according to the AFDS the elevators are supposed to being guarding speed as well – such as in Flight Level Change. This is the crux of the shortcoming (if I can call it that) of the Autothrottle speed protection system, and the Automation pitfall that did not allow Autothrottle speed protection to activate for Asiana 214.

The interesting article about the Asiana flight 214, from where I got the above paragraphs can be found here.

 

It's been a couple of months since I last used the PMDG 777, but I retained a few aspects of my short experience with this great PMDG add-on.

 

1) It seems slow on throttle adjustments under some circumstances, calling for manual override, as I had to do a few times. My experience was limited to FSX and then FSX:SE, but I will later try it in P3Dv2;

 

2) I am used to Aerowinx's PSX approach to the limitations of using a normal joystick / throttle to simulate the sophisticated system on the real aircraft. PMDG offer 3 modes of operation, one allowing full override in any situation, another one disallowing any override and the one which is probably the most commonly used which allows for manual override only when the AT mode is in HOLD.  I still prefer the approach followed in PSX, where you have a specific key input to disengage the A/T servos, and make them sync their position with your physical throttle position.

 

3) Yet another aspect, which I do not recall if it's correctly simulated in the PMDG 777 ( but it almost surely is...at least when the "always override" mode of the A/T is  chosen in the 777 configuration ), is the following one where I assume where it's written "pushing" we should actually read "pushing or pulling" :

 

 A basic element of the 777 Autothrottle system is poorly understood is that when a climb/descent mode is commanding a fixed thrust setting (THR or IDLE) and the PF overrides the setting by pushing on the levers – the Autothrottle reverts to HOLD, allowing the PF to set the desired thrust (why else would you be overriding it?)

 

I really wonder, now that I don't have the 777 installed, if this "feature" is reproduced in the PMDG model, when "always override" model is selected in you 777 A/T configuration dialog ( through the FMC ), meaning that IF "always override" IS "on" THEN moving the throttles when in THR or IDLE modes reverts to HOLD ?

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A/T being on does not mean that your throttle position is always overridden. It will override the throttle position until entering any HOLD modes. In the real aircraft, when the throttles are commanded to idle, the physical throttles are driven via servos to their idle position, so when HOLD mode comes into play, the throttles are already at idle. This isn't the case with your hardware unless you physically do it yourself (and I know at least one of the Sidewinders had a throttle axis).

 

Even if you don't think you have a throttle axis, it might be a good idea to check the axis assignments in the FSX settings menu. FSX will assign a function to each axis, regardless of you telling it to or not.

Kyle,

 

Thanks a lot for the explanation, but I'm not sure what my next step would be in this situation to check possible errors/hardware malfunctions. Here is the exact report what happened.

 

Flight was LTBA - OMDB. I had ASN, FT OMDB, FS2Crew, 77W PMDG bird

 

1. The route was loaded, winds imported and loaded, descend mode activated with VNAV/LNAV 

 

2, The active STAR was DESDI8S with restriction 230/11000B 

 

3. CI was manually set to 35, so the descend speed was 268-270

 

4. 5-7 nm before crossing DESDI intersection (~FL140), TAT changed from +14C to +35C and A/T commanded rapid throttle acceleration and speed on EFIS was automatically set to 314, but actually reached 459 (!!!) and I had tons of various alerts (obviously) 

 

5. I tried to manually disconnect both A/T, disable N1 and moved throttles (physical ones at the PMDG VC) to iddle, but despite my efforts they themselves moved forward to the "full throttle" position with A/T, A/P modes off.

 

6. Since I saved my flight before T/D, I decided to test the theory that ASN could be an issue. Thus, I reloaded the flight, fully disabled ASN and set "Clear Weather Scenario" at P3D. The result was exactly the same as I have described at #5.  

 

7. Next day I tried KIAH-KLAX flight with 77L using the same add-ones and utilizing SEAVU2 STAR. The outcome was pretty much identical to what I already wrote above. Once PECOX INT was passed at FL140, A/T commanded full throttle and speed was set again to 314.

 

 

I have been PMDG customer since2004, never had any problems with the planes, used to read the manuals thoroughly, used to fly good old PSS-777 Mark I (FS2000 - FS2002) and  have no idea what to do now.

 

Appreciate your help

 

Dmitriy. 

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FYI - I'll be flying OMDB - OTHH later tonight. It's a short-haul, so we'll see whether this strange A/T behavior propagate again 

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Thanks a lot for the explanation, but I'm not sure what my next step would be in this situation to check possible errors/hardware malfunctions

 

Hi, Dmitriy,

 

What happens if you disconnect your joystick at the beginning of the approach?

 

Also, if I understood you correctly, your TAT jumped from 14C to 35C at 14,000 ft, and the throttle problems started at the same time.  A sudden temperature change like that doesn't sound right to me -- do you know why it is happening? 

 

I have a Sidewinder Precision 2 and it certainly does have a throttle.  It works well, although it's generally a good idea to have it at minimum during descents to avoid unexpected throttle increases in HOLD mode.

 

Mike

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Mike, thanks for the response. Yes, I have always had my Sidewinder' throttles at idle once LNAV/VNAV engaged.

 

Completed OMDB-OTHH flight yesterday, no problems occurred despite TAT jumped again from 10C to 40C again during descend in the FL110-160 area. Will report to this topic again if similar behavior would happen and will attached panel.cfg saved situation for the support to better understand the situation 

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Mike, thanks for the response. Yes, I have always had my Sidewinder' throttles at idle once LNAV/VNAV engaged.

 

Completed OMDB-OTHH flight yesterday, no problems occurred despite TAT jumped again from 10C to 40C again during descend in the FL110-160 area. Will report to this topic again if similar behavior would happen and will attached panel.cfg saved situation for the support to better understand the situation 

 

Let us know.

 

Remember to place your full name - first and last - in your posts here, please.

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Maybe a little sidenote experience i had during takeoff from PHNL rwy 08R

 

The takeoff was in THR REF HEADINGSELECT and TOGA. I was flying with autopilot off and following FD.. I commanded a new heading via FS2CREW and called for flapsup speed. The speed just went up to 280 knots before i noticed in the fmc that i still had the vector track selected and not the next waypoint. My manually throttle was in full speed. After updating the FMC and the AFDS to LNAV i engaged the AP and it stabilzed at 250\5000 feet. I blame my self for not erasing the first vector waypoint and my lack of knowledge.

 

Anyone Who can share some light?

 

Thanks Michael Moe

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Anyone Who can share some light?

 

Not seeing a problem here...

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Anyone Who can share some light?

 

Agree, no problem; however, with experience you'll anticipate what is going to happen next such as a change in roll control modes.  You'll get to the point where you are going though the takeoff and climb in your mind before you do it (experience teaches us to go through the sequence and include the what-if's that can happen).

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Agree, no problem; however, with experience you'll anticipate what is going to happen next such as a change in roll control modes. You'll get to the point where you are going though the takeoff and climb in your mind before you do it (experience teaches us to go through the sequence and include the what-if's that can happen).

I guess i expected the VNAV to change to MCP speed and THR, VNAV spd when i called for the flapsup speed but again am i correct that the first vector waypoint is the issue and my mistake?

 

Thanks Michael Moe

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Did you ever have anything on the FMA that indicated pitch control?  I am asking because you only mentioned thrust and roll conditions.  As a rule, always check the FMA if you ask "now why did it do that?"

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