MD-80 "stabilizer motion" warning

[ajptech]

Whenever I fly the MD-80, an alarm starts going off during takeoff. When I apply full throttle, it starts beeping and the voice says "stabilizer motion". I'm not sure what is causing this warning, but I always make sure the flaps are down, the spoilers aren't deployed, and the brakes aren't engaged. However, the alarm stops once the aircraft is in the air. Has anyone else experienced this issue? What should I do to stop this alarm from sounding in the future?

[Maki Nishikino]

Is the stabilizer trim moving?

Also take a look at this...

https://imgur.com/a/NLOSfCT

[ajptech]

Originally posted by Maki Nishikino:

Is the stabilizer trim moving?

Also take a look at this...

https://imgur.com/a/NLOSfCT

No I don't think the stabilizer trim is moving.

[Maki Nishikino]

Please make a video with the throttle quadrant in view.

[ajptech]

Originally posted by Maki Nishikino:

Please make a video with the throttle quadrant in view.

https://www.youtube.com/watch?v=M_tfDkPIeBs I made a video. Lmk if you have any issues

[Maki Nishikino]

It's not just saying "Stabilizer"? Your trim isn't set correctly. You need to dial in the flap setting and center of gravity and then using trim align the white with the green.

[ajptech]

When I made the video it was just saying “stabilizer”

[Maki Nishikino]

Ok so set the stabilizer trim.

[ajptech]

Originally posted by Maki Nishikino:

Ok so set the stabilizer trim.

I'm not sure how to do that. Also I'm a bit confused: wouldn't the stabilizer trim be pre-set before the flight is loaded? Also I always make sure that the center of gravity is set as close to zero as possible. Not sure whether that has any effect on the stabilizer trim or not.

[Maki Nishikino]

Bind "Pitch trim up" and "Pitch trim down". On the left side of the throttle quadrant you will see the takeoff condition computer. Use this table and interact with the CG and FLAP knob. Once that is done adjust the trim so that the white indicator matches up with the green one.

https://imgur.com/a/o3gORFk

[ajptech]

Originally posted by Maki Nishikino:

Bind "Pitch trim up" and "Pitch trim down". On the left side of the throttle quadrant you will see the takeoff condition computer. Use this table and interact with the CG and FLAP knob. Once that is done adjust the trim so that the white indicator matches up with the green one.

https://imgur.com/a/o3gORFk

Could you make a video showing how to do this?

[Maki Nishikino]

I don't have a recording software on my PC but I will guide you through it.


Let's say I have 16,000 pounds of fuel. I look at the center of gravity which is at +11 inches so I will just go ahead and use 10 as it's close enough. Where these two meet shows 6.

https://imgur.com/a/owhdtgJ

https://imgur.com/a/jKdnxaM

I will dial in the CG of 6 and a flap setting of 15 (as that is the flap setting I am using for takeoff). I will then use the trim to align the white indicator with the green one.

https://imgur.com/a/D0mWAUI

[ajptech]

I understand now, but I still have a few questions. First: in the second picture you sent, what is 6 referring to? Also, why can't I just set the center of gravity to zero? why does it have to be at 10-11 inches for 16,000 lb of fuel?

[Rattner219]

The stabilizer is fixed until the AP is engaged. I would resist the urge to engage AP until on climb out.

Once the AP is engaged the pitch mode should be IAS set at the current airspeed. The stabilizer normally won't need to move until you clean up and increase airspeed.

[Rattner219]

Originally posted by ajptech:

I understand now, but I still have a few questions. First: in the second picture you sent, what is 6 referring to? Also, why can't I just set the center of gravity to zero? why does it have to be at 10-11 inches for 16,000 lb of fuel?

On the MD-80 realistically you should not be able to adjust your CoG manually. The reason is because you could set it in a way that would be impossible in reality, taking the plane way outside it's approved envelope. For instance .. consider a fully loaded plane, full of fuel, and a fully rearward CoG? On an rear-engined plane the CoG is at the absolute rear limit when empty. Conversely the CoG is at, or near, the forward limit when fully loaded and fueled.

Whoever made the MD-80 ... consider the plugin to automatically adjust CoG to a reasonable position based upon gross weight and fuel. Then all the published MD-80 performance figures fall in line with reality.

[ajptech]

Originally posted by Rattner219:

I would resist the urge to engage AP until on climb out.

what do you mean by "climb out"? what altitude do you think I should engage the autopilot?