Autopilot Disconnection

[blakman7]

For an aircraft without autothrottles like the ERJ-135/140/145 and CRJ-200, you can't do autolands. So, if you are flying the plane down to minimums and get to your DH, will the autopilot automatically disconnect? If not, what happens? Does it just fly the missed approach by itself or what? I have often wondered what happens if you treat the approach as an autoland in an aircraft that doesn't have that capability. Thanks.

 

[Nick]

For an aircraft without autothrottles like the ERJ-135/140/145 and CRJ-200, you can't do autolands. So, if you are flying the plane down to minimums and get to your DH, will the autopilot automatically disconnect? If not, what happens?

No, it will not automatically disconnect. An aircraft limitation is that the autopilot must be disengaged at 200' for a normal landing or 50' for a CAT II landing. It is clicked off by the pilot.

Does it just fly the missed approach by itself or what?

There is no restriction on using the autopilot for it. You click the go around buttons on the side of the throttles and it will put the airplane in a "sub-mode" called takeoff/go-around. Of course the throttles manually are pushed up while you click those buttons. Or if you were hand-flying the approach and go missed, you can hand-fly the missed approach. You'd still click the buttons to put it in the takeoff/go-around sub-mode though, so that you'd have useful flight guidance up on the screen.

I have often wondered what happens if you treat the approach as an autoland in an aircraft that doesn't have that capability.

I suppose it would land on centerline and impact at about 600 FPM as it follows the glideslope right down to the pavement.

 

[minitour]

I suppose it would land on centerline and impact at about 600 FPM as it follows the glideslope right down to the pavement.

I guess it would also depend on the autopilot itself and how "good" it was.

It may start s-turning and porpoising down low trying to keep LOC/GS captured. If you started changing any configurations and/or airspeed (power) adjustments, things could get interesting.

Not something I want to be the test pilot for.

-mini

 

[Nick]

I guess it would also depend on the autopilot itself and how "good" it was.

It may start s-turning and porpoising down low trying to keep LOC/GS captured. If you started changing any configurations and/or airspeed (power) adjustments, things could get interesting.

Not something I want to be the test pilot for.

-mini

I do maintain that it would probably land right on centerline and hit at about 600 FPM though, if conditions are good enough to do a CAT II. If it's gusty and crosswindy and all that then it'd be different. But in a CAT II it does a good job right down to 50 feet and at that point when it comes off, there's only about seven seconds left until touchdown anyway, and all of that is flaring.

If I remember correctly the book says 75 feet can be lost during the go-around, or 100 in an XR. So from a CAT II if you started that at about 100' AGL then you could have the wheels touch the runway. I've wondered since training about that technically violating the autopilot disengagement height limitation of 200' or 50' for CAT II.

 

[minitour]

I do maintain that it would probably land right on centerline and hit at about 600 FPM though, if conditions are good enough to do a CAT II.

Perhaps in the bigger equipment with better automation that may be the case.

Try having the autopilot fly an ILS in a Diamond Star using the heading bug until "cleared for the approach" and then letting the autopilot capture and couple the whole way down. It would take a great deal of luck to end up on the centerline more than.....say one in three times.

Again, depends on the autopilot....and probably the equipment the autopilot is installed in as well.

As for the operator of said autopilot, that's rarely a factor :crazy:.

-mini

 

[Nick]

Perhaps in the bigger equipment with better automation that may be the case.

Try having the autopilot fly an ILS in a Diamond Star using the heading bug until "cleared for the approach" and then letting the autopilot capture and couple the whole way down. It would take a great deal of luck to end up on the centerline more than.....say one in three times.

Again, depends on the autopilot....and probably the equipment the autopilot is installed in as well.

As for the operator of said autopilot, that's rarely a factor :crazy:.

-mini

Ah, I did not realize what you were referring to.

I remember the S-Tec 55X autopilot in the PA-44 would always do a pretty good job down to 200 feet, and sometimes below that. My students were amazed at how good of a job it did.

What one is in the Diamond Star?

 

[minitour]

Ah, I did not realize what you were referring to.

I remember the S-Tec 55X autopilot in the PA-44 would always do a pretty good job down to 200 feet, and sometimes below that. My students were amazed at how good of a job it did.

What one is in the Diamond Star?

I want to say it's the KAP...it's been a Loooooooooooong time though.

Too long. I need to go out and have some fun in an airplane. The whole "turning money in to noise" thing.

Anyone got a good place to get a glider rating? Tailwheel endorsement?

Okay, back on topic.

I'll stick with it depending on the autopilot. If the autopilot's capable, then I'll agree. It will impact the ground with no flare at whatever descent rate it took to maintain the glide slope. If you're going to do it in something light (because you don't have a choice = poor preflight planning but I'm sure it happens), trim for Vyse + a few with a nose high attitude and down ya go.

-mini

 

[Baronman]

Having done a few CAT 2 approaches this year, I'll say it puts your right where you want to be at 50 feet (when you disconnect the autopilot.) I leave it on till then as long as it's maintaining the required parameters.

That being said, all my CAT 2 approaches have been into foggy weather. I've yet to do one with stronger winds etc so I can't say how the autopilot will do. But otherwise it does a pretty darn good job.

Additionally in the sim I've done a "bounce and go" off of a rejected CAT 2. The mains touched but we were pitching up and adding power at the same time and it promptly takes to the air again. No big deal really.

As far as the autopilot disconnecting at the DH during a CAT 2, it doesn't do it automatically and remember we can keep it on past the DH as long as we have the RWY/lights in sight. The DH will be at 100' and the autopilot can stay on a few seconds longer till 50'AGL. At that point the Capt disconnects it though the quick disconnect (red button) on the yoke. You hear "autopilot, autopilot" and at that point the landing checklist is done.

-This is ref to the ERJ

 

[cime_sp]

Having done a few CAT 2 approaches this year, I'll say it puts your right where you want to be at 50 feet (when you disconnect the autopilot.) I leave it on till then as long as it's maintaining the required parameters.

That being said, all my CAT 2 approaches have been into foggy weather. I've yet to do one with stronger winds etc so I can't say how the autopilot will do. But otherwise it does a pretty darn good job.

Additionally in the sim I've done a "bounce and go" off of a rejected CAT 2. The mains touched but we were pitching up and adding power at the same time and it promptly takes to the air again. No big deal really.

As far as the autopilot disconnecting at the DH during a CAT 2, it doesn't do it automatically and remember we can keep it on past the DH as long as we have the RWY/lights in sight. The DH will be at 100' and the autopilot can stay on a few seconds longer till 50'AGL. At that point the Capt disconnects it though the quick disconnect (red button) on the yoke. You hear "autopilot, autopilot" and at that point the landing checklist is done.

-This is ref to the ERJ

In the CRJ we can use it down to 80ft for a Cat II and re-engage it at 600 feet on the missed approach. Missed is usually easier to fly by hand though, at least that's m opinion

 

[jtrain609]

I'm also in the ERJ, same company as Baron and Nick. On our CAT II approaches, the FO will fly the approach and the captain will take over at 100' and do the landing. I can tell you I'd much rather have the autopilot flying the missed, if that was what we had to do. You've been riding the autopilot down the whole time, clicking it off and putting your game face on at 100' AGL, or quite possibly less than that, sounds like a horrible idea to me. The last thing I'd want to do is click off the AP and realize at that kind of an altitude that the autopilot had more back pressure put in than I expected, snapping the yoke forward and allowing the nose to drop.

Where do you fall on that one, Nick? I'd prefer to keep my attention on monitoring the aircraft instead of trying to be a hero and hand flying the aircraft when the conditions are that crappy.

 

[mikecweb]

John, you disgust me.

 

[minitour]

I'm also in the ERJ, same company as Baron and Nick. On our CAT II approaches, the FO will fly the approach and the captain will take over at 100' and do the landing. I can tell you I'd much rather have the autopilot flying the missed, if that was what we had to do. You've been riding the autopilot down the whole time, clicking it off and putting your game face on at 100' AGL, or quite possibly less than that, sounds like a horrible idea to me. The last thing I'd want to do is click off the AP and realize at that kind of an altitude that the autopilot had more back pressure put in than I expected, snapping the yoke forward and allowing the nose to drop.

If you're going to follow that logic, why is there an exchange of flight controls at 100' on an approach?

You don't know how much trim the FO was holding off or not...next thing you know the nose pitches down or up violently and.....

I'd much rather disconnect the AP and hand fly a miss than switch control to the guy in the other seat at 100'.

-mini

 

[Baronman]

While the FO is the Flying Pilot during the Cat 2, he NEVER will hand fly it. He's pretty much just keeping the plane on speed with the thrust levers. Hand flying the CAT 2 is not an option.

 

[kellwolf]

CRJ has different limitations than the ERJ. For us, the AP limitations are 80 AGL on a precision and 400 AGL on a non-precision, both kicked off by the pilot. CAT II, like was mentioned earlier, is AP all the way down to when the CA sees he can land. For us, when we're at 200 above mins, the CA calls "going heads up" and has a hand on the yoke and a hand at the base of the throttles. That way, he's doesn't have to fumble around for the controls at the last minute. Even then, if you hit minimums before he says something, the FO is supposed to execute the missed approach. Problem I've noticed in the sim is when they set it right AT minimums, you wind up trying to go missed at about the same time the CA calls "My controls, landing."

Not sure about the ERJ, but on the CRJ, if the AP's got it out of trim, you can override it pretty easily with a little control pressure. If you're prepared for the possibility of it being out of trim (or if you see the trim indicator is something crazy like 4.3), you can be ready for it.

 

[mtsu_av8er]

John, you disgust me.

I concur.

The last thing I trust 100 feet of the ground in the crap is an autopilots flying the missed.

How many times has George done something, and you look over at the Captain and ask, "Why did it do that?" and the only response is, "It does that sometimes"?

Damn that.

Lloydy Clicky And Handy Flyee.

 

[jtrain609]

If you're going to follow that logic, why is there an exchange of flight controls at 100' on an approach?

You don't know how much trim the FO was holding off or not...next thing you know the nose pitches down or up violently and.....

I'd much rather disconnect the AP and hand fly a miss than switch control to the guy in the other seat at 100'.

-mini

Have you ever done a monitored approach before? I thought it was strange as heck until I did a few and as long as everybody is on the same page they're pretty safe and efficient as far as I can see. I've never had to land from one, and I won't have to for a few years, so I couldn't tell you how that works out. But I have gone missed from a handful (in the sim, I haven't had to go missed in actual yet on any approach, but it's only a matter of time before I do) in the sim and it's pretty much a non event.

I've found the autopilot generally does what it's told, and the majority of errors I've seen are errors between the keyboard and chair, if you will. Or in other words the computer only does what it's programmed to do, and if you program it incorrectly then it won't do what you wanted it to do.

 

[jtrain609]

I concur.

The last thing I trust 100 feet of the ground in the crap is an autopilots flying the missed.

How many times has George done something, and you look over at the Captain and ask, "Why did it do that?" and the only response is, "It does that sometimes"?

Damn that.

Lloydy Clicky And Handy Flyee.

Not often. Every time George has done something strange I take another look at how I, or the other guy, programmed it and realize that we made a mistake. It doesn't always do things as quickly, or in the exact same manner as I would, but I haven't had a problem yet with George doing something just 100% off the wall. I'm sure I will at some point, but as I said, most errors I've found are human programming errors. Computers only do what they're told.

 

[kellwolf]

ERJ must have a better AP than the CRJ. I don't trust the CRJ AP any further than I can throw a 100 lb carry-on bag. I've seen it go the wrong way trying to intercept a LOC, pitch 10-15 degrees up and down for no good reason and just turn itself off in cruise. No programming errors there.

 

[jtrain609]

Dunno, never flown a CRJ! I've never seen one of our autopilots do any of those things before, though.

 

[SlumTodd_Millionaire]

I'm also in the ERJ, same company as Baron and Nick. On our CAT II approaches, the FO will fly the approach and the captain will take over at 100' and do the landing. I can tell you I'd much rather have the autopilot flying the missed, if that was what we had to do. You've been riding the autopilot down the whole time, clicking it off and putting your game face on at 100' AGL, or quite possibly less than that, sounds like a horrible idea to me. The last thing I'd want to do is click off the AP and realize at that kind of an altitude that the autopilot had more back pressure put in than I expected, snapping the yoke forward and allowing the nose to drop.

Where do you fall on that one, Nick? I'd prefer to keep my attention on monitoring the aircraft instead of trying to be a hero and hand flying the aircraft when the conditions are that crappy.

Bingo! Word to the wise: hand flying an airliner in bad weather conditions doesn't make you a "real man." It makes you an idiot. To those that are concerned about the AP not flying the missed properly (something I've never seen in either the CRJ or the 717), then you're focused on monitoring the AP the entire time and can correct it if needed. If you're hand flying, then the other pilot is having to set up the FCP when you call for changes, call the missed to ATC and answer the radio throughout the maneuver, look at his approach plate to verify the procedure and give you a progressive if needed, etc... It becomes a much more task-saturated cockpit. With the AP on, the PNF doesn't have to worry about the FCP and can focus on the radio and the approach plate. The PF can focus on monitoring the AP to make sure that it's following the proper procedure (which it almost certainly is). Don't try to be a hero by hand flying in high workload conditions. All you're doing is making things more complicated.