Have had an issue doing ILS approaches.  All is fine and then the autopilot mode switches from GS to Attitude hold.  This then makes following the flight director a little squirrelley (sic?).  Am I doing something incorrectly?  Any help would be appreciated.

 

Also, is there a way to turn off the flight director?  Can be a little distracting if your not using it for guidance at the time...
 

What was your airspeed relative to V-app while on the approach? If your airspeed falls to close to (or below) V-app, the autopilot will switch as you experienced. Try and maintain your airspeed 5 kts or so faster than V-app.

Ah!  That makes sense.  It is pretty hard to keep the speed stable in my experience.  I'll try harder.  Thanks...

 

 

Also, is there a way to turn off the flight director?

 

There is a "standby" button for the A/P. Bottom of the right column I believe.

 

This disables the F/D.

Hi,

Need more information regarding how you are intercepting the ILS.

Are you adjusting the altitude for go-around at the time? Has GS definitely captured and not just armed, and is the aircraft flight path stable (i.e. it is not climbing or descending rapidly towards/through the glide slope)?

Speed is only an issue if you get too slow. As long as the speed is good and not rapidly changing, this will not cause the autopilot to drop out unexpectedly. I can quite happily keep 240 kts to 6 miles and still be configured and stable by 500 ft.

A note about speed management: the aircraft responds well to small changes, but needs time to spool up with larger changes. You also need to allow for inertia. If I want to decel quickly, I bring the torque right back to 5% (being careful to keep it positive), then when I get within 20 kts of my desired speed, I will bump them forwards to ~30% which causes the turbines to spool up slightly, then I adjust from there. In the approach config at flap 15, she needs about 15-17% torque to maintain approach speed.

Another major point to remember is that the propwash creates a significant amount of lift, so don't pull the power off too much at lower altitude as the aircraft will just drop out of the sky, and invite a tail strike if you're landing. This will result in the autopilot responding in pitch, and will start an oscillation if you pull the power back too rapidly, or keep making large changes during the approach. This will cause the aircraft to deviate from the glide slope. The best method is to slowly pull the power back until you get the reaction you want, then stop moving the levers. Let the aircraft stabilize. When you get close to the speed you want (e.g. approach speed), push the levers forward to approximately the correct setting, then wait. This will help prevent the aircraft from oscillating as a result of changes in lift due to propwash and large speed changes.

Finally, remember that in the flight range (flight idle and above) you control the angle of the blades, and the engines respond to maintain prop RPM (constant speed propellors). In the ground range (beta), you are directly controlling propellor blade angle.

Best regards,
Robin.

I've had the issue of GS changing to Pitch Hold during a stable approach with glideslope and localizer captured and good speeds.  I've also had it switch to Pitch Hold and then back to GS with the flight director making crazy pitch commands.  For example, I've fallen a little low on the glideslope and the Flight Director will command 60 degrees nose up or a full deflection of the pitch cue.  The flight director seems fine during departures and climbs.

Steve,
Can you please provide a specific ILS approach for which you are experiencing this.

Thanks

PAKT runway 11...

Ok....will give it a try in the morning
Thanks

I discovered today that if you switch the HSI source to the right side and then back it will "reset" or turn off the flight director.

Last night I was on a perfectly stable ILS for 16R into Reno and the autopilot switched to Wings Level, Pitch hold.  I pressed the approach button again and it went back to Loc, GS...

I've noticed on the official Majestic forum that others are experiencing the same thing issues with the autopilot on approach.  I've also noticed repeatedly that while hand flying ILS approaches if you follow the flight director for glideslope guidance you will get into trouble. I think the flight director logic for approaches needs some tweaking.  Works good for departures though.

This has happened to me 3 times in row now flying into KPDX, runway 21.  I was on a stable ILS approach, locked in to LOC and GS, then the GS drops into pitch hold and I fly through the glide slope.  I thought I was doing something wrong, so I kept trying it (the definition of insanity!).  I will try again this weekend and pay attention to particulars so I can provide more info if it happens again.  I don't remember the exact sequence of events.

 

--Don

Same experience here on training flights into KEWR and KBOS. First time I thought it was icing. But that was not the case it appeard later.

I think that there is definitely an issue that I'm sure that they will address.  I find that if you're expecting it you can press the approach button again and it will reconnect.