Autopilot technique on instrument approach

Trying to get the right setup for instrument approaches and am having a tough time getting the speed and flaps set at the appropriate time on an autopilot approach.

Let’s take a standard ILS approach with a procedure turn on the outbound leg. The SR20 manual would have you fly 120 KIAS on the outbound leg, PT and inbound leg with 22" MP. Once established on the glide slope you reduce power to 17" and put on 50% flaps.

And this is where I am having trouble. The S-tec will be on NAV APR and GS but when you kick on the flaps the plane floats well above the glide slope and will either reestablish by pushing the nose down or just lose the signal all together. So either I am too fast or too high.

Also, at what point down the glide slope do you transition from 100 KIAS 50% flaps to 80 KIAS with 100% flaps. I’ve been leaving the flaps at 50% and splitting the difference with 90 KIAS at the missed approach point because I know if I kick on the full flaps, the plane will float and I’ll end up being either too high or too fast again.

By hand flying, I could avoid all the bobbles but is there a technique to using the autopilot which can smooth out the ride and give me and my passengers a nice stable approach.

Thanks,

Brig

As you discovered, it is fairly difficult to deploy flaps once you’ve started down the glideslope (though you can “help” the autopilot to avoid the large pitch excursion if you’re careful and practiced at it.) A simpler technique is to get slowed down and get 50% flaps out while level before glideslope intercept. Once established on the glideslope you can slow down further by gradually pulling back the throttle (if you pull it back a bunch at once, you will oscillate around the glideslope and not be able to control your airspeed.)

I find that it’s not difficult to fly at 110 KIAS and half flaps all the way to DH, then cut the throttle and get the rest of the flaps out and still land without a problem (even short of the touchdown point, which is 1000 feet down the runway.)

Flying an ILS with no flaps at 150 knots is even more fun (with a 737 on your tail) as long as you have a whole lot of runway in front of you.

For what it’s worth, I was taught to not make any significant configuration changes while on the glideslope, which makes things a lot easier.

Once established on the glide slope you reduce power to 17" and put on 50% flaps.

Are you sure the manual doesn’t say “once established inbound” ?

As others have said you should be fully configured at GS intercept.

And why not get the speed down to 90 at that point and leave it there until missed or visual for landing. Once you have that procedure nailed you can start adjusting it to increase speeds if you wish.

As you discovered, it is fairly difficult to deploy flaps once you’ve started down the glideslope (though you can “help” the autopilot to avoid the large pitch excursion if you’re careful and practiced at it.) A simpler technique is to get slowed down and get 50% flaps out while level before glideslope intercept.

Dave,

Thanks for the help and I will try getting the flaps on prior to GS intercept. However the autopilot is on ALT prior to GS intercept and is still going to balloon when you kick on 50% flaps. Probably going to have to learn your ‘help’ technique to avoid the float.

Tailwinds,

Brig

As you discovered, it is fairly difficult to deploy flaps once you’ve started down the glideslope (though you can “help” the autopilot to avoid the large pitch excursion if you’re careful and practiced at it.) A simpler technique is to get slowed down and get 50% flaps out while level before glideslope intercept.

Dave,

Thanks for the help and I will try getting the flaps on prior to GS intercept. However the autopilot is on ALT prior to GS intercept and is still going to balloon when you kick on 50% flaps. Probably going to have to learn your ‘help’ technique to avoid the float.

Tailwinds,

Brig

As you discovered, it is fairly difficult to deploy flaps once you’ve started down the glideslope (though you can “help” the autopilot to avoid the large pitch excursion if you’re careful and practiced at it.) A simpler technique is to get slowed down and get 50% flaps out while level before glideslope intercept.

Dave,

Thanks for the help and I will try getting the flaps on prior to GS intercept. However the autopilot is on ALT prior to GS intercept and is still going to balloon when you kick on 50% flaps. Probably going to have to learn your ‘help’ technique to avoid the float.

Tailwinds,

Brig

Brig,

I agree with Dave about configuring the aircraft prior to GS intercept. Having flown Mooney’s with the KFC 200 which is somewhat similar in op’s as the S-Tec, a trick we use is to hold in the trim switch as flaps are deployed an equal amount of time that it takes for the flaps to deploy. It neutalizes any pitch change. In some earlier posts about the trim sensitivity I’m not sure how this would do in the 20 or 22. Possibly just “bumping” the trim as flaps are deployed could do it assuming you don’t disconnect the autopilot in doing so.

Chris

N122CG

Re:

Possibly just “bumping” the trim as flaps are deployed could do it assuming you don’t disconnect the autopilot in doing so.

In most aircraft I have flown any manual actuation of the electric trim disconnects the autopilot. Is this true with the S-Tecs in Cirrus aircraft?

Gordon

Re:

Possibly just “bumping” the trim as flaps are deployed could do it assuming you don’t disconnect the autopilot in doing so.

In most aircraft I have flown any manual actuation of the electric trim disconnects the autopilot. Is this true with the S-Tecs in Cirrus aircraft?

This is true in the SR22, but not in the SR20. The difference is that the 22 has a separate a/p servo with clutch, and running the trim won’t accomplish anything other than to anger the autopilot (which is running the pitch independent of trim.)

If you pull out some power and apply a little forward pressure on the yoke while the a/p catches up with the change in configuration, you won’t balloon dramatically. Just takes a bit of practice.

My experience with my SR20 is consistent with what Dave says, in regard to the trim control not disconnecting the autopilot (except for pressing the top). The Wings Aloft manual mentions that the autopilot should turn off if the trim is activated for more than two seconds. Is the Wings Aloft manual wrong, or are our airplanes not operating properly?

Re:

Possibly just “bumping” the trim as flaps are deployed could do it assuming you don’t disconnect the autopilot in doing so.

In most aircraft I have flown any manual actuation of the electric trim disconnects the autopilot. Is this true with the S-Tecs in Cirrus aircraft?

This is true in the SR22, but not in the SR20. The difference is that the 22 has a separate a/p servo with clutch, and running the trim won’t accomplish anything other than to anger the autopilot (which is running the pitch independent of trim.)

If you pull out some power and apply a little forward pressure on the yoke while the a/p catches up with the change in configuration, you won’t balloon dramatically. Just takes a bit of practice.