AP Disconnects On Final

JC_YYZ

I have had this happen twice now. As I am turning to intercept the ILS (plane is configured properly), the F/O calls ‘glideslope’, the AP disconnects, the AP disconnect alarm starts and no matter what I do 1) I cannot silence the alarm, and 2) I cannot reconnect the AP.

Also, when the FO calls ‘glideslope’ the plane is still showing LNAV in green, G/S and LOC in white, and the plane is not on the GS.

I cannot silence the alarm or turn on the AP until I exit and reload the plane.

? Offline

Should be in APP mode with the ILS tuned, identified and course set, not LNAV.

JC_YYZ

It is. APP button is pressed (and lit). ILS is tuned. My point is that the plane still shows LNAV on the PFD, G/S and LOC in white, AP disconnects and the alarm plays and cannot be stopped - and I cannot re-engage the AP or activate any other modes.

GPfs2020

Got the same problem as twice All looked fine on until turning the ILS.
Think I got a stick schaker sound and indeed no way to turn on the AP again, even after a go around and plane leveled off

Mark

If the AP 'cavalry charge' is playing constantly that typically means the autopilot has been disconnected via a non-normal method. That could be via the use of the emergency autopilot disconnect bar on the MCP, or via an automatic disengagement due to stall conditions. In either of those two instances, the AP cannot be re-engaged until the AP DISC button is pressed on either yoke to silence the alarm, the emergency disconnect lever (if moved) is set back to the UP position, and the aircraft has recovered to a safe flight (i.e. not in a stall state).

The correct method to disconnect the AP is to press the AP DISC button on either of the yokes (either using the mouse or the TOGGLE DISENGAGE AUTOPILOT or TOGGLE AUTOPILOT MASTER control assignments), this will ensure the AP can be reengaged without issues.

Hope that helps.

Mark - Just Flight

JC_YYZ

@Mark I thought that was the case, and my AP button is bound to the TOGGLE AUTOPILOT MASTER, however it had no effect. I tried the disconnect bar on the MCP (it was up and I tried pulling it down and up) and nothing would silence the 'charge' sound. I also could not activate any modes on the MCP, which leads me to believe the aircraft thought it wasn't in a safe flight state - however, nothing would indicate that it wasn't (i.e. speed, flaps checked, level flight, etc).

I have experienced this twice but have also had successful landings in between, and to my knowledge, have not done anything different between the a successful landing and these occasions where the aircraft takes on a mind of its own.

Mark

@JC_YYZ The next time this happens (hopefully it doesn't!), would you be able to share a video of that occurring? That will be helpful for us to see what is going on in the cockpit and to see if there may be anything obvious we can spot that is causing it.

Mark - Just Flight