Hi,

 

I am trying to test the logic behind the A/T . When i am in THR mode ,LOC and V/S and switching to FLCH and then put the A/P off AND F/D off in left side and  manual move the throttle back the A/T goes mad and increases the engine and accelerate beond speedlimit in MCP (180) to overspeed  still in THR mode.

 

I have the new panelstates. The 777 is not in Holdmode at any time which does not have speed protection in VNAV SPD and FLCH

 

 

Thanks

Michael

 

 

I am trying to test the logic behind the A/T . When i am in THR mode ,LOC and V/S and switching to FLCH and then put the A/P off AND F/D off in left side and  manual move the throttle back the A/T goes mad and increases the engine and accelerate beond speedlimit in MCP (180) to overspeed  still in THR mode.
 
I have the new panelstates. The 777 is not in Holdmode at any time which does not have speed protection in VNAV SPD and FLCH

 

Always.

Always.

Always pay attention to the _ _ _?

 

F - M - A

 

The MCP only shows you what you've commanded.  It doesn't show the actual mode.  Try it again and report back with what the FMA (flight mode annunciator - the boxes at the top of your primary flight display) shows.

 

I have a feeling the FMA was showing you something different from what you were expecting and it caught you by surprise.

Thanks will look carefully next time Kyle:-) THR LOC was there

 

Michael

The MCP is the ballot, the FMA shows the election results.

The MCP is the ballot, the FMA shows the election results.

 

I like that analogy.  Nice!

That's layman's terms, the more common analogy is the MCP is what you bid, the FMA shows what you got.

So can you help what other state the FMA should be in? Still need to read about the different states. THR LOC is still showing. Why not SPD mode? The throttle goes bananas in THR mode not respecting the magenta speed in PFD and MCP so i need to disconnect the A/T in order to manual override.

 

The scenario is at3000 feet and you are at 180 knots on a descent going from SPD LOC v/s then FLCH SPD and disconnect the A/P. Altitude in MCP. set at 460 but just before you hit the FLCH button you change your altitude in the MCP to 3000. this keep the FLCH mode in THR mode even if you disconnect the autopilot afterwards and the F/D

 

 

Michael

FCOM 4.10.8 is a good place to start.  I'm at a loss why you select FLCH pitch mode then disable the AFDS thus nullifying the selected pitch mode, at any rate don't expect SPD until at MCP commanded ALT, which is confusing because again you've disabled AFDS pitch commands.

 

Maybe the question is what are you trying to accomplish? If FMA showing SPD LOC VS why are you disconnecting A/P?

Check the incident at KSFO 28L. I just would try to see it in the PMDG. 5nm and 180 must be a huge challenge in the 777

 

Michael

Okay, that would be an interesting simulation. I don't have the specifics but believe A/T was armed but inhibited because only one F/D was turned on, and they had excessive sink rate with decreasing speed. The wiki article on this accident mentions that the crew had attempted multiple modes of AFDS and A/T in the last couple minutes, which I think makes it very difficult to reproduce in the simulation.

I believe what happened in the Asiana SFO accident was that the aircraft was not descending quickly enough so the PF put it into FLCH.  But the altitude was set for the go-around altitude, which was above their actual altitude.  So in FLCH the A/T went into THRust or THR REF mode and tried to make the aircraft climb back to the set altitude.  (In VNAV, and I believe in V/S, the aircraft would have kept descending as long as it was more than 300ft below the set go-around altitude).  The PF then manually forced the throttles down to idle, which caused the A/T to go into HOLD.  As we know, there is no speed protection in HOLD.  But the PF did not realize this and apparently none of the three pilots in the cockpit was paying attention to the actual airspeed until it was too late. 

 

Not at my FSX PC now, but I believe even w/ the A/P off, the thrust mode will be affected by the MCP vertical mode.  If you are below the altitude set in the MCP and select FLCH, it will go into THRust or THR REF mode and try to climb back to the MCP altitude.  It won't hold a specific speed as it assumes the nose will be pitched up to maintain the speed selected in the MCP.  I know that on takeoff and climb the A/T thrust mode is affected by VNAV w/ the A/P off -- TOGA thrust and then preselected CLB thrust; it assumes speed will be maintained by proper pitch up of the nose. 

 

The Asiana accident would be hard to simulate because even if the throttle is set to override always, moving it down to idle in FLCH won't keep the throttles permanently there.  Holding the F1 or F2 key down might work, as long as they are set to repeat action.

 

Mike

This NTSB animation shows the sequence well:

 

 

Mike

for those interested , very very detailed

 

http://www.ntsb.gov/doclib/reports/2014/AAR1401.pdf

 

 

Michael

And maybe its because i only had "override in Hold mode" option for the throttle. will try changing to "allways"

 

Still 5nm and 180 at KSFO is a challenge though

 

 

incident report :

 

http://www.ntsb.gov/doclib/reports/2014/AAR1401.pdf

 

 

 

Michael