Autopilot lesson learned

J

jestertoo

Pre-Flight
Joined
Nov 12, 2008
Messages
43
Location
Austin, TX
Display Name
Display name:
JesterToo
I'm learning how to use the autopilot in the 172sp I fly. It's a great tool, but can get you into trouble.

So after a takeoff last night, I hit the AP button and started dialing up an approach frequency to get flight following. The autopilot faithfully kept the wings level and tried to maintain the 1100+fpm climb rate, right on down to about 70kts and slowing rapidly (from 100kts) when I realized how pitched back it was. Quick disco/push and back into safe attitude. I'm thinking a power on stall with attention deficit would be ugly after dark at fairly low altitude.
 
jestertoo said:
I'm learning how to use the autopilot in the 172sp I fly. It's a great tool, but can get you into trouble.

So after a takeoff last night, I hit the AP button and started dialing up an approach frequency to get flight following. The autopilot faithfully kept the wings level and tried to maintain the 1100+fpm climb rate, right on down to about 70kts and slowing rapidly (from 100kts) when I realized how pitched back it was. Quick disco/push and back into safe attitude. I'm thinking a power on stall with attention deficit would be ugly after dark at fairly low altitude.
Click to expand...


It's so easy to climb (add power) and descend (reduce power) with wing-leveler only I'm not convinced I'd ever use the "maintain climb rate" feature in any A/P.
 
dmccormack said:
It's so easy to climb (add power) and descend (reduce power) with wing-leveler only I'm not convinced I'd ever use the "maintain climb rate" feature in any A/P.
Click to expand...

It's pretty darn nifty, I've enjoyed it in the planes I've seen it used in. Even better with altitude pre-select (only seen that in use in the Cheyenne).

That said, I don't climb and descend with power. Leave the power in, go faster. I only start pulling it back to try to reduce power at about 1"/minute of manifold pressure. Smoother that way. Climbs I usually add RPMs, but am already at full throttle, and then have to open the cowl flaps and change the trim anyway to get any kind of useful climb rate. In a 172, I still do things much the same.
 
Go up with an CFI, and do some AP stalls. When I got checked out in the 172SP I used to fly we did that as part of the checkout.
 
Ted DuPuis said:
It's pretty darn nifty, I've enjoyed it in the planes I've seen it used in. Even better with altitude pre-select (only seen that in use in the Cheyenne).

That said, I don't climb and descend with power. Leave the power in, go faster. I only start pulling it back to try to reduce power at about 1"/minute of manifold pressure. Smoother that way. Climbs I usually add RPMs, but am already at full throttle, and then have to open the cowl flaps and change the trim anyway to get any kind of useful climb rate. In a 172, I still do things much the same.
Click to expand...

I used Alt Pre-Select in a nice 172SP I flew a while back. I found I was spending more brain cycles monitoring the A/P than I would have if I was hand flying -- or at least managing the climb myself.

IMC I use power for climb and descent, since I'm usually crusing as fast as possible and the few knots I gain descending have to be slowed when I reach the assigned altitude.

VFR I usually dive and enjoy the sleigh ride. :D

Both techniques are fine -- it's a preference matter, not a right/wrong, certainly, and I demonstrate both to students. :yesnod:
 
dmccormack said:
It's so easy to climb (add power) and descend (reduce power) with wing-leveler only I'm not convinced I'd ever use the "maintain climb rate" feature in any A/P.
Click to expand...

This AP turns both roll and VS on at same time.

Some more checkout time would be helpful for sure.
 
dmccormack said:
You should be able to select one or the other -- they don't have to be coupled.
Click to expand...

I hit the "AP" button and by default it turned on ROL and VS. I didn't do anything else that I know of.

ETA: that appears to be the default behavior for this model. IIRC is a bendixking.
 
Last edited:
dmccormack said:
Both techniques are fine -- it's a preference matter, not a right/wrong, certainly, and I demonstrate both to students. :yesnod:
Click to expand...

Yep, I agree. :)
 
I've always waited until after levelling off and leaning the engine before engaging the autopilot. It seems important to be 'flying the airplane' until everything is stable. Likewise, the autopilot goes off as the first step to preparing for approach.
 
AuntPeggy said:
I've always waited until after levelling off and leaning the engine before engaging the autopilot. It seems important to be 'flying the airplane' until everything is stable. Likewise, the autopilot goes off as the first step to preparing for approach.
Click to expand...

I like having the A/P on and the wing leveler function armed whenever I launch into IMC. I trust my own flying, of course, but armed the tool is ready.

I find takeoff and the first few minutes of low IMC flight take the most concentration. I don't fly low IFR often enough that it's "normal ops," and so I focus just in case disorientation strikes (which it can to anyone -- see the loss of a 747 off Bombay with a 5,600 hour captain for proof).

Once established on heading, altitude, and everything else, I use the A/P to hold course while I re-arrange charts, note times, input the rest of the waypoints, etc.

On approaches, I use the A/P while being vectored to get established, especially if it's low IMC and I'm flying into an unfamiliar field or I have passengers. I don't go into training mode when I have non-fliers on board -- that's done solo or with another pilot on board. I've flown fully coupled and while it's uber-cool, I'm not flying enough low IMC approaches that I can toss them away to George.
 
I don't know of any light plane 2-axis autopilot which turns on roll and VS-hold on the first button-push -- normally, they turn on only roll, or roll plus pitch stabilization (holding current pitch attitude). As you discovered, an autopilot which turns on VS-hold at the first push could lead to serious trouble. Which autopilot do you have?

In any event, I hope the lesson you learned is that when activating an autopilot, you give it several seconds of your attention to make sure it isn't going to do anything silly before diverting that attention elsewhere.
 
Ted DuPuis said:
It's pretty darn nifty, I've enjoyed it in the planes I've seen it used in. Even better with altitude pre-select (only seen that in use in the Cheyenne).
Click to expand...
The Cardinal I flew didn't have VS hold per se, as in maintain the current climb rate, but it did have altitude and climb/descent rate pre-select which made it a cinch to maintain constant rate climbs and descents over an extended time. But I never used it for rates greater than 700 fpm.

Engaging VS hold while at Vx or even Vy could obviously have unpleasant consequences, especially if you didn't realise it was on. If it's really the default with that A/P to engage VS hold when it's first turned on, a placard to that effect might be a good idea. Better yet, I'd look into whether that default could be changed.
 
Ron Levy said:
In any event, I hope the lesson you learned is that when activating an autopilot, you give it several seconds of your attention to make sure it isn't going to do anything silly before diverting that attention elsewhere.
Click to expand...
And never let it just chug along mindlessly without checking on it every once in a while. The S-tec 60-2 in the Cardinal had an annoying tendency to go into a graveyard spiral every so often. It wouldn't respond to commands to change altitude or heading and acted as if it had disengaged itself while in a descending turn, but it was very much in control. The only way to stop it was to hit the red button.
 
I was just again reading about the Colgan accident and how they allowed the autopilot to take them to the edge. When it disco'ed is when they got into trouble.

Ron/Azure:
It's a bendix/king KAP140, and 2axis is the default mode.
Here's the first step on the quick guide:
1. To activate the autopilot in wings level (ROL) and vertical speed (VS) modes press the AP button.

I'm guessing it took maybe 10-15 seconds of me grabbing my board, finding the freq I wanted and dialing it for the AP to take me to 65kts. Red button and solid push on the wheel resolved the problem very quickly.
 
jestertoo said:
I hit the "AP" button and by default it turned on ROL and VS. I didn't do anything else that I know of.

ETA: that appears to be the default behavior for this model. IIRC is a bendixking.
Click to expand...

Yes - as you say, more checkout would have been useful. I don't recommend using automation unless you know what it's going to do.

Treat the autopilot like a copilot - tell it it's "his airplane", give it "goals" (i.e. maintain wings level and 500 fpm), confirm that it's actually meeting those goals, and then (and only then) start another task yourself.

Setting a reasonable VS is useful. The FLC mode in the GFC700 is great for climbs, while VS is generally more useful for descents.
 
TMetzinger said:
Yes - as you say, more checkout would have been useful. I don't recommend using automation unless you know what it's going to do.

Treat the autopilot like a copilot - tell it it's "his airplane", give it "goals" (i.e. maintain wings level and 500 fpm), confirm that it's actually meeting those goals, and then (and only then) start another task yourself.

Setting a reasonable VS is useful. The FLC mode in the GFC700 is great for climbs, while VS is generally more useful for descents.
Click to expand...


It was definitely a mistake on my part. Plane was climbing out way faster than it could sustain when I engaged it. I didn't think to see what VS it was trying to hold. Normally I engage it when level and then play with the VS or ALT settings.
 
The manual for the KA-140 is available here. Yes, the 2-axis models automatically engage with ROL and VS modes active. I'm unaware of any way to turn off the altitude mode.
 
Sanchez will be along to slap your butt.

But the message is correct. It's a good bet you did no reading about the KAP 140, but engaged it anyway.
 
I like to say, "Trust but verify."

I have no problem using the a/p on climb-out, especially in IFR. However, like others have pointed out, turning on the a/p doesn't stop me from my instrument scan. It just helps while I'm talking to ATC, getting on course, etc.

It also helps that my last 2 planes have been turbos, so I don't face the dramatic drop-off in performance with altitude.
 
I've had my fun with the KAP140. I can't wait to use the TruTrack in the RV4. It's smart enough to lower the nose if the airspeed gets too low. Yet another reason to "go experiMental".

M
 
dmccormack said:
Nah -- just another reason to not place blind faith in an autopilot. :yesnod:
Click to expand...

Roger that.

I drove my IFR instructor crazy because I wanted to hand fly everything. After I got my rating, we went back for another lesson on using the autopilot in real-world scenarios.

Still, it's hard to beat the TruTrack.
 
foka4 said:
Roger that.

I drove my IFR instructor crazy because I wanted to hand fly everything. After I got my rating, we went back for another lesson on using the autopilot in real-world scenarios.

Still, it's hard to beat the TruTrack.
Click to expand...

Yep -- and you put your finger on one of the keys to improving as a pilot -- don't be afraid to continue "training" after you acquire a certificate.

:yesnod:
 
The KAP140 will tell you the climb rate it is trying to maintain when you first engage the AP mode. You can change the climb rate to something attainable (say 600 or 700fpm) by using the up and down buttons on the face of the unit. (IIRC) I usually set it for 500 or 600 if I'm IFR, since we have high MEAs in the area, and it might be climbing for awhile.

It's not a very bright autopilot. :D Easy to use, gets the job done, but any a/p that can be set for an 1,100fpm climb in a 172SP is silly IMO.
 
AuntPeggy said:
I've always waited until after levelling off and leaning the engine before engaging the autopilot. It seems important to be 'flying the airplane' until everything is stable. Likewise, the autopilot goes off as the first step to preparing for approach.
Click to expand...

Depends on your definition of stable. Once on heading, climbing 500fpm (typically), I let George have the airplane. Usually 1500-2000agl on up.

On the way downhill, disconnect altitide hold, a couple seconds of down trim, and let George take us down at 500fpm.

Like Ted, I keep full power in on the downhill side (start reducing MP below 5000msl) and let that Mooney roll along. 185 over the ground is a typical decent speed, and you make up much of what you lost on the climb.
 
SCCutler said:
Ed's way of saying that his Cherokee did not have an autopilot, his Comanche does!
Click to expand...

Comanche has the same autopilot the Cherokee did - me. I think the AP is a great tool to help erode piloting skills.
 
dmccormack said:
Machismo

I know how to fly straight and level. Don't need to practice it for 2 hours.

:rofl:
Click to expand...

I know of waaaaaaay too many people that hit AP at 500feet, and don't disconnect it again until 500feet. And then go on to say "I will never fly an airplane without a functioning autopilot." I would never climb in a plane with them - nor would I consider them much of a pilot.
 
EdFred said:
I know of waaaaaaay too many people that hit AP at 500feet, and don't disconnect it again until 500feet. And then go on to say "I will never fly an airplane without a functioning autopilot." I would never climb in a plane with them - nor would I consider them much of a pilot.
Click to expand...


That's a pilot problem, not an autopilot problem.

I should be man enough to cut down trees with a hand axe. I use a Chain Saw. With a chain brake.

That's like people who claim "I won't fly a pattern without power! That would be bad!"

:rolleyes:
 
Well, I also still do mulitplication and division with pencil and a paper from time to time just to keep the brain working instead of using a calculator all the time. And there's nothing wrong with sawing down a tree. I even got a plaque at home for being the fastest with a two man saw - well, I had a partner of course.

The autopilot, like any tool, will erode abilities.
 
EdFred said:
I think the AP is a great tool to help erode piloting skills.
Click to expand...

The only time I see it foreseeably very useful is in IMC, other than that... dont be lazy, we spent thousands to learn how to fly... not push a button.
 
EdFred said:
The autopilot, like any tool, will erode abilities.
Click to expand...

That is a pilot problem, not an autopilot problem, just like the statement of GPS erodes needle skills. I agree that I can't stand it when I see pilots who hit he A/P practically as soon as gear is up (or wheels off the ground in a fixed gear) and then proceed to fly the autopilot coupled to the GPS for the remainder of the trip (which usually means they're doing nothing). That said, when I'm flying 10 hours in a weekend (or in a day), hand flying the whole time gets annoying. I've done no shortage of hand flying in IMC in turbulence copying new clearances, looking at them on the chart, programming them into the GPS, etc. On the en-route portion of the flight, I find that a lot more of the piloting is the mental work of looking at charts, dialing VORs in to cross check your GPS location (assuming you're going D->, and if on airways using them to double-check), reevaluating the weather and making decisions accordingly, prepping for approaches, etc.

Some of the best sticks I know use autopilots in their planes fairly heavily. They also do a good sum of hand flying, and are perfectly comfortable with it, and know their planes well. The autopilot just does the en-route portion of the flight. That said, I do notice that it's pretty rare that people actually have the charts out following along unless they get a re-route (that's a GPS thing).
 
I'm with Ted. If you don't fly a lot, you probably need all the handflying practice you can get for takeoffs, landings, maneuvering, approaches, etc. OTOH, if you fly 400 hours a year, hand-flying in cruise only fatigues you and hurts your performance on the approach/landing at the end of the day. It's all situations, and the decision should be based on fatigue avoidance versus proficiency maintenance.
 
Well, I've only flown about 350 hours this year... ;)
 
I usually do engage the AP after initial climb and heading is established out of Addison while on the DP. Mostly it's because it's very busy airspace within Class B; I'm not only watching for the plane to be functioning properly, but for a lot of traffic, amended clearance and I don't want to be off one bit on heading or altitude. Once out of the busier airspace, I'll hand fly more.

On long trips, I think it's silly to hand fly for hours at a time unless one really wants to.

I also use Tom (Tom Cruise) when getting ready to do an instrument approach so I can brief the chart. Sometimes that's pretty difficult in a high traffic area, IMC with the radio busy. Once again, I don't want to miss an altitude, heading or getting on the approach. I may be descending down through icing conditions and cycling the boots or looking for ice accumulation. AP off if accumulating noticeable ice to 'feel' the plane. Once established on the approach, at some point, I'll kick off the AP. Nice evening, not busy and lower pilot load, I'll hand fly it.

Of course on this trip from Dallas to Winterhaven, FL then to Greenville, SC, the AP didn't work and I hand flew the entire trip. Was rusty to begin, so, I waited for good weather to depart. Once I flew a couple hours, I felt pretty comfortable again.

Best,

Dave
 
Old Thread: Hello . There have been no replies in this thread for 365 days.
Content in this thread may no longer be relevant.
Perhaps it would be better to start a new thread instead.
Back
Top