Flight Director Disengage

[makrider]

Hi everybody,

have you experienced an uncommanded FD disengagment in turbulence clouds ???

I've experienced twice on a F2000...

Bye folks :ok:

[hoover1]

i have experienced it on an atr. not sure what it means in oyur case but for us it was a sign the the autopliot system had something wrong with it.

[roljoe]

Hi,

no never happent to me...but may be this could come on stage when the attitude control of the FD went out of a preestablished range of commands (G limited or else)..
and also to protect the plane to be out of predefined limited maneuvering areas.

[safetypee]

I have seen something similar with a modern digital flight guidance system (Honeywell) which disengaged due an ADC comparator trip.
A fault the cross-side interconnect of the ADC static systems resulted in the different static pressures on each side of the aircraft being sensed directly by the ADCs during yawing maneuvers (turbulence ?). If large differences in static pressure are detected, the ADC comparator flags a fault and the FGS/FD disengages.

Normally each ADC will detect its own on-side static, but an averaged value of each side of the aircraft is provided for smoothing and failure cases. Differences in static on each side (i.e. steady heading sideslip/engine failure) are normally averaged (damped) by a cross connection and reservoir. In my instance, there was a fault (leak) in this part of the system which did not affect normal static readings.

[makrider]

Sounds good...

I've something similar...in fact in a small turbulence my ALT FD trip with the flashing advisory on display.
I try to reconnect the ALT remaining into the turbulence condition and the system work correctly with no any other problems... :sad::sad::sad:

You think also in this case the problem is related to the ADS system ???

Very strange... :cool:

Thanks guys :ok:

[hikoushi]

A couple in the DHC-8:

Once, had the F/D fail along with both autopilot and yaw damper channels during light chop. Tried to troubleshoot / reengage; got the F/D back after a couple of attempts, but the AP / YD wouldn't have it. Continued the flight (perfect VFR day); after landing maintenance took a look and wound up deferring the A/P and Y/D under the MEL. We finished up 4 more (short) legs in that configuration. It turned out to be a failure in the yaw damper servo, apparently overworking itself to death in the bumps.

Another during takeoff, right after V1 while initiating rotation (just before sunset, good VFR) the F/D went out along with a "AHRS DATA INVALID" message on the ADU. Continued the takeoff through clean-up to enroute climb until comfortably above nearby obtructions. On the climbout my ADI was now showing a 75 degree bank and 15 degree pitch down; returned for a visual approach and landing, as not only was our destination reporting heavy rain, but it would be night by the time we got there. Not a turbulence failure per se, but apparently an AHRS failure during accelleration and rotation; conceivably though, something similar could happen during moderate or greater turbulence.

[makrider]

Well,

the strange in this situation, is that no alert or caution mesage appear.
No signal of failed equipment and in all the occasion the after re-engagment of the FD mode, it do the work normally.

THX