Bobsk8

Question on A/T override.

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Posted (edited)

I know this discussion has been going on for a long time,  and I think I have read just about every post on it, and watched  countless Youtube videos. Here is my question, I have the setting in the FMC for A/T overide in THR HOLD and ARM only./ I also have it set so I can see the indication of where the throttle setting is and can match it when I am on approach and switch A/T off. That isn't my problem. 

Tonight I started a descent, and moved the throttle in my sim to minimum, and used Level change to descend the 737 at 220 knots . Everything was fine, until I reached my target altitude of 3000 feet, At that point I expected the A/T to maintain the speed I had set for the level change of 220 knots. When I hit 3,000, and the 737 leveled out, the speed started to decay well below 220 knots even though the A/T was still on and 220 knots was set in the speed window. It was as if I had no A/T at all.  At that point, I had to use my throttle in the sim, to get the speed back to 220. by moving it up from where I had set it for the descent at minimum,  and eventually matching the blue indicator with the power setting indicator. Once I did that, the A/T behaved normally for the rest of the flight.  I thought that the A/T would increase the power automatically regardless of my throttle setting when I leveled out at 3,000 ft. Is this the proper way for the A/T to control speed after descent, where you have to increase power using the manual throttle in the sim?  

Edited by Bobsk8

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After I posted this last evening, I flew around in the 737 and did some small descents using level change and found out what was happening. If I pull my Saitek throttle all the way to minimum for flight idle, start a descent with speed set at say 220, when the descent levels off at the assigned altitude, and speed starts dropping below 220, the A/T does not increase the throttle setting. The speed will keep dropping. Now if I move the Saitek throttle control slightly towards increase of power, at that point A/T engages  and works normally. So all I have to do at the bottom of the descent, or at any time during the descent is move the throttle away from it's minimum setting, and then A/T works perfectly to keep airspeed where it is set. 

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The FMC treats speeds as 'not to exceed' speeds.  It is normal to see the airspeed drop below the FMC SPD value by up to about 15 kts., and it's not wrong to add a little thrust while in hold mode to command less descent, more speed or whatever.  The hold mode literally means the servo clutch is held open and the pilot can move the levers without resistance from the servo motor.  Sometime I let the A/T do its thing, but usually I intervene when things roll away more than 5 or 10 kts.

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11 minutes ago, downscc said:

The FMC treats speeds as 'not to exceed' speeds.  It is normal to see the airspeed drop below the FMC SPD value by up to about 15 kts., and it's not wrong to add a little thrust while in hold mode to command less descent, more speed or whatever.  The hold mode literally means the servo clutch is held open and the pilot can move the levers without resistance from the servo motor.  Sometime I let the A/T do its thing, but usually I intervene when things roll away more than 5 or 10 kts.

This speed drop I saw was about 70 knots and approaching stall speed. 

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1 minute ago, Bobsk8 said:

This speed drop I saw was about 70 knots and approaching stall speed. 

Not good. What did the FMA display?

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Just now, downscc said:

Not good. What did the FMA display?

MCP speed. Right now I am flying an approach at 220 knots, and if I pull throttle to minimum, the power immediately drops to flight idle and it starts slowing down. Move the throttle just a tad away from the bottom, and the power comes back up , and speed returns . 

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9 minutes ago, Bobsk8 said:

MCP speed. Right now I am flying an approach at 220 knots, and if I pull throttle to minimum, the power immediately drops to flight idle and it starts slowing down. Move the throttle just a tad away from the bottom, and the power comes back up , and speed returns . 

If you are able to decrease thrust by moving your controller throttle lever to idle while the thrust mode is MCP SPD then the setting for 'override in hold or arm only' is not working.  You should not be overriding the A/T regardless of if your throttle is at minimum or slightly above. Interesting.  Not sure why you are experiencing this.

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4 minutes ago, downscc said:

If you are able to decrease thrust by moving your controller throttle lever to idle while the thrust mode is MCP SPD then the setting for 'override in hold or arm only' is not working.  You should not be overriding the A/T regardless of if your throttle is at minimum or slightly above. Interesting.  Not sure why you are experiencing this.

I just found the problem. Hadn't flown the 737 in well over a year and had a different joystick / throttle when I did. When I calibrated the Saitek throttle quadrant which I got about 6 months ago, somehow it was sent to FSUIPC calibration  for the 737  instead of just straight to the sim. I just parked the 737 after a flight, and noticed with the engines still running that when I pulled the throttle to the low stop, before the reverse switch, that the reversers came on. I heard this from the cockpit, and went outside to look, and sure enough the reverser was engaged. I set the setting for the Throttle in FSUIPC to direct instead of calibrating, and problem is instantly fixed. :biggrin:

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2 hours ago, Bobsk8 said:

I set the setting for the Throttle in FSUIPC to direct instead of calibrating, and problem is instantly fixed. 

Good find, and thanks for reporting it for others.  I don't have a need to run any axis through FSUIPC so I assign and calibrate in P3D.  Keeps it simple.

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37 minutes ago, downscc said:

Good find, and thanks for reporting it for others.  I don't have a need to run any axis through FSUIPC so I assign and calibrate in P3D.  Keeps it simple.

I fly so many different types of aircraft and copters, that without FSUIPC, assignments  I would  go crazy.  

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