First of all, apologies if this has been answered somewhere, but in a forest of all other threads about the never-ending alarm, I must have missed it.

 

I have an annoying A/T problem that I need some assistance with. Please note that I can reproduce this consistently, but it may or may not (probably isn't) be a bug.

 

I like to land my planes myself and not let the autoland do it. When I'm at around ~7000, I disconnect the A/P and A/T, silence the alarms and it's all good… for a couple of minutes when A/T re-engages itself. This exercise of engaging/disengaging the A/T continues until I land, *unless* I actually disarm A/T using the two switches. To disengage the A/T, I use the side button on throttles (or a shortcut key mapped to my controller).

 

Please note, I only use free FSUIPC, so that should not be an issue here. Thanks in advance.

 

[ similar, but not he same topic coming ip about something else ]

 

 

 

The A/T automatically engages if you get too close to the edge of the "envelope" e.g. if you get too slow for your configuration.

That explains it. Thank you.

 

 

 

Hm…

 

I just tested this again. I was nowhere near the amber bars on the speed, yet the A/T re-engaged itself. 

 

It must be that I'm misunderstanding what the "edge of the envelope" means in this case. Any pointers?

bump

The only time I'v had this happen is when I haven't entered in a ZFW and got below about 160kts.

 

Sure you aren't hitting a joystick key that's set to re-engage a speed mode?

Chiming in to confirm I experience the behavior that the OP describes as well.  Unless I move those switches off, the A/T engages again. It might be useful to remove the "Answered/Best Answer" from this as there are some doubts.

Do you disengage, wait a few seconds and "confirm" it by hitting the disengage a second time?

 

This is what I have to so, not sure if its correct

Disclaimer: I don't have this issue at all, (unless I don't enter a ZFW into the FMS, or get into the low speed protection range)

 

It seems that this reported issue has nothing to do with being able to disconnect auto-throttle and stop the alarm with the second click.

 

OP is about the following steps:

 

1. Disconnect autothrottle
2. Disconnect autothrottle alarm
3. Fly a bit
4. Auto-Throttle turns itself on without user intervention.
5. Speed never entered yellow or red protection envelope.

Things I don't know are:

• Is there a ZFW entered (Probably is one, otherwise Yellow/Red protection envelope is at 'worst case scenario' and will be there at 155 knots odd).
• Is the RIGHT ZFW entered (Entering a ZFW that's too low will show the Yellow/Red Protection envelope too low, but the Autothrottle will detect AOA nearing stall... however your +10° pitch attitude in a 1000ft/min decent and stick shaker should give that away too!)
• Is there a keypress or joystick button assigned to a speed mode. If this is pressed (or the joystick spikes it pressed) then the mode will engage.
• What does the AutoThrottle try to do? Maintain a speed as set on MCP? Or try to TOGA and increase thrust into a go around?

 

I personally have a keypress assigned to TOGA for go arounds. It's a nice out-of-the-way button, but I have occasionally hit it accidently on approach. The resulting spool-up to 99%+ power is always fun... along with the APP mode turning into Go around and the Flight Director pegging 15 degree attitude.

 

If the SPD mode is selected, the Autothrottle will reingage and want to maintain the MCP selected speed window (or VNAV if blanked).

 

FLCH may also do some funky stuff, havn't tried, but I suspect FLCH should be just an FD mode and not do anything to your throttles, but that's 737 experience talking, 777 might be different (because FLCH is different on 777).

ZFW is correctly entered and only TO/GA is mapped.

 

Now, I've done some more tests in the meantime and the original answer may still apply. A/T will re-engage if for example speed drops below UP marker and flaps have not been extended, as well as any other flap position.

 

So, the answer marked as correct still applies, but I needed to better understand what T7 thinks is the envelope.

 

 

 

All this talk has led me to a question... why didn't the A/T reengage on that Asiana flight?

 

 

why didn't the A/T reengage on that Asiana flight?

 

There was an indication that power was applied prior to hitting.  Remember, though, that it's only going off of speed and not the other factors like ground proximity and vertical speed.

Hello!

 

It's exactly the same in my case (I'm definitly not in an under-/overspeed condition).

 

Example: A/P in HDG select and altitude select mode. Activate LOC & APP. LOC captured. Disengage A/P AND A/T. FD active, G/S is captured, A/T activates when G/S is captured.

 

To me it seems to be a bug.

 

Oliver

 

 

A/T activates when G/S is captured.

 

Did you get too slow?  If so, as mentioned, the A/T will wake up and take over.

Did you get too slow?  If so, as mentioned, the A/T will wake up and take over.

 

no, Speed was just perfect.

 

I think it is a bug. Found follwoing in the known bug section:

 

- Corrected end of path AFDS behavior on approaches flown in LNAV/VNAV. (modes remain VNAV PTH, LNAV all the way to the ground, no A/T wakeup if manually disconnected unless mode manually changed, low airspeed, or TOGA pushed)