KFC150 M20K Glideslope wild ride

[aaronwalkerx]

I was recently on a practice RNAV LPV approach on altitude prior to IF and selected APR on the KFC150.  The glideslope came alive with the needle at the top and the airplane made an abrupt pitch up to capture.  The pitch up was aggressive and this had happened once before.  I disconnected the autopilot and hand flew the approach.  Probably user error but I have not been able to figure out what I am doing wrong.   What is the correct procedure to direct the autopilot to wait to capture glideslope rather than pitching up to initially capture?

Equipment: KFC150, KI525A HSI, KAS297B Altitude Pre-Select, KI207 Indicator, Avidyne IFD 550.

thanks!

[gsxrpilot]

I don't really have an answer for you...

I have the same KFC150, KAS297B, IFD540. I also have GPSS through my Aspen PFD.

The KFC150 has FD ALT HDG and APR all illuminated. In that situation it should fly on the ALT hold until it intercepts the GS and then pitch down to follow it down.

[aaronwalkerx]

I have had it work correctly and now twice in about 6 months with the abrupt pitch up.  Both were practice approaches and not IMC.  It is a big surprise when the pitch up happens!

[tmo]

Aaron, looking at what gsxrpilot wrote - are you sure you had ALT (hold) locked and armed, and not just a properly trimmed aircraft that held altitude because that's what good planes do when trimmed?

[aaronwalkerx]

I am not sure of anything.  I believe both times I was flying the intercept on autopilot with altitude hold and a Direct To the IF.  We are not equipped with GPSS if that makes any difference.

[tmo]

GPSS should not make any difference for altitude, it is just a heading error thing.

Time for an on board camera maybe? Will take the guesswork from recreating the sequence of events and states associated with them. Which reminds me, I should figure out how to mount mine.

[aaronwalkerx]

I have some training coming up and was planning to mount a overhead camera.  I think that is a fine use for this situation as well.  Great idea!

[jlunseth]

I had the problem with my KFC200 when I first got it. What I learned to do was to put the AP in APPR mode before the FAF. At least that is what I recall. Since I do that all the time now, I don’t remember having the problem for some time. If you are inside the FAF it may not couple at all, and when it does it will be abrupt. I think part of the problem is that the GPS will have switched to its resolution for the final, which is tight, and the AP, being inside the FAF, makes fairly abrupt moves both vertically and horizontally to get to the glide slope and final course. Outside the FAF I have not had it pitch hard up to catch the GS.

Edited October 19, 2020 by jlunseth

[carusoam]

The fun part...

You have to know each step to execute it properly...

Its 90s technology...

It is likely, that something isn’t working properly, because it is old....

But realistically, it doesn’t sound like it was being operated in Alt hold mode... waiting for the intercept to occur...

Sounds like you told it to intercept the G/S... in its 90s pea brain, it tried to do exactly what you asked for...

It isn’t going to do a reality check... it just does what you asked...

If it did it twice... you probably executed the same sequence, the same way twice... 

There are only so many buttons you have to push... get to know each one... 
 

Some buttons get pushed simultaneously...
 

Some functions work differently, depending on what other button is lit up...

There is a manual that covers all of this... a good part of it will be resident in the POH...

If you are studying for the IR... you are about to find out how much like a college class this is going to be....  tons to read and memorize...

If you already have your IR... and just switching to a different set of boxes... this is the read and memorize  advice rewarmed...

The hard part, because of detail overload... comes up with what has to be done before the FAF... and what can be done after... and what is switching automatically as you get to each point...
 

GPSS is just an electronic box that updates the next Horizontal waypoint for you, as you reach it...

 

have a note book handy, take note of everything that doesn’t work as planned...

If you need to set up a video camera... still take notes... 

Expect cognitive overload to start becoming a challenge... your notes will remind you what to look for... the video may give all the clues of what you did/didn’t do...
 

Review the book that comes with the AP... it has all kinds of specific examples and when to push each button...  

PP thoughts only, not a CFI or even a current IFR pilot... (Loving memories from my IR training...)

Best regards,

-a-

[jlunseth]

PS, the King AP's are supposed to catch the glideslope from below, just not inside the FAF.

Anthony's post reminded me of a few things.  I don't think you will find the information to switch to APPR mode outside the FAF, in the AP manual.  It might be there, but my recollection is I learned that from some of Richard Collins brilliant writing. Second, if you have a GPSS and you load and activate the approach, the whole approach goes into the flight plan. The GPSS and the HSI are wired so that the HSI is "fooled" into thinking the instructions it is receiving are HDG bug instructions, which of course are the horizontal part of that flight plan only. So if you are in GPSS mode and have not put the AP in APPR mode the GPSS will cause the aircraft to fly the horizontal course perfectly, but the AP will be receiving no vertical information, not through the GPSS it doesn't. When you switch to APPR inside the FAF it will all of a sudden believe it is on the approach course and glideslope and will do whatever it needs to, to stay on the slope. Outside the FAF if you make the switch, I think you will find it does not do that, the King AP knows to wait until it flies into the GS from below to capture it, which will be nice and smooth. Third, and as I have recently discovered (only after about 10 years of flying this combination), you need to wait until the aircraft is on the horizontal approach course (and outside the FAF), to put the AP in APPR mode. If you are horizontally too far from the final approach course the HSI, and accordingly the AP, will just get very confused when you make the switch. So bottom line, make the switch once you are on the horizontal final approach course and are still outside the FAF. Try that VFR and see if it works for you.

Unfortunately, I don't think there is a manual for all this because King was not thinking of GPSSs and GPSs when it wrote the manual for the KFC.

Good on you that you were right on the problem when it happened, it can be a little disconcerting. Don Kaye is pretty good on this stuff, Richard Collins bless him, is not with us anymore.

Edited October 19, 2020 by jlunseth

[carusoam]

Some king APs are capable of intercepting from above as well... But...

If you don’t like the wild ride as the AP tries to intercept now! and points to the sky...

It probably will be hated for doing the same thing while pointing towards middle earth...

Too many ways to make a simple mistake that can end disastrously...

PP thoughts only...

Best regards,

-a-

[jlunseth]

That's right, but a wild ride is only hair raising. A wild stall in IMC because the aircraft suddenly pitched up when the engine was depowered and the pilot did not do something about it, is upset recovery time.

[aaronwalkerx]

jlunseth, I believe I likely selected approach mode before the IF and before the turn to the final inbound heading.  I will wait until after the turn, established, and between IF and FAF before engaging approach mode and see if that works out as expected.  carusoam planning to take some notes is also a good suggestion.  

Below are the directions from BK manual, which I thought I followed.

To operate in the APR mode: 1. Tune the frequency for the selected ILS, VOR or RNAV approach. 2. Set the PNI course pointer to the final approach course (ILS front course even when flying a back course approach). 3. Set the HDG SEL 'bug" on the PNI to the desired intercept angle and activate the HDG mode. 4. Depress the "APR" button. This arms the automatic capture function. (The "APR" light will flash to signify the approach mode is armed.) 5. The V-bar will command the required bank to maintain the selected heading until the capture point is reached. Then the V-bar will command a turn to intercept the course. If the autopilot is engaged it will turn to satisfy the commands. As the V-bar commands the turn to intercept the selected course, the heading mode will be canceled and the APR mode will go from arm to engage. (HDG light will go out and APR light will go from flashing to steady.) 6. The V-bar will continue to command the required bank to maintain course and the autopilot (if engaged) will satisfy those commands. (Automatic crosswind compensation will provide precise tracking. VOR/LOC deviation is shown on the PNI, and actual crab angle is shown by offset of the course arrow from the lubber line.) 7. Once localizer course capture has occurred on an ILS, the glideslope mode is armed. Automatic capture occurs as the aircraft approaches the glideslope from either above or below. I I When the intercept occurs, "GS is illuminated on the annunciator panel. The V-bar commands the pitch necessary to maintain the glideslope. If the autopilot is engaged it will satisfy these commands. If the altitude hold (ALT) mode had been engaged prior to GS capture, it will disengage at capture and the "ALT light will go out.

[jlunseth]

Yeah, I know for certain with my KFC200 if I put the AP in APR mode before it is on the horizontal final approach course the AP will be confused. I did that about a month ago flying an approach in actual. I thought the GPSS would fly the aircraft to the final approach course like the HDG bug would doing an ILS, but that is not what happens. The system becomes confused and no longer provides good guidance. 

I am a little surprised you have a King manual that refers to RNAV approaches, because when mine was written there were no GPS RNAV approaches. Maybe your manual is later than mine, or maybe they were referring to a different kind of RNAV that was in use back in the 80s based on distances from VORs, I did not think there were any approaches of that type though. 

All I can say is try not putting it in APR until you are established on the final approach course. And do that outside the FAF.

[carusoam]

RNAV as in area navigation...

I think the terminology goes back a ways....

Where the BK KNS80 was a fantastic twin VOR/DME navigation tool... that could define intersections... a really nice box that fed the necessary info to the AP.

All pre GPS days...

Best regards,

-a-

[jlunseth]

I am getting rid of mine in another month, but that is another story.

[Greg_D]

I’ll add to the other suggestions that you will need to have the approach armed on the GPS and more importantly on the KC192 well before the FAF and GS/GP capture point or the AP will not begin a descent.  I’ve read somewhere that this needs to happen 30-45 seconds before intercept.

[Flash]

On 10/19/2020 at 4:15 PM, aaronwalkerx said:

To operate in the APR mode: 1. Tune the frequency for the selected ILS, VOR or RNAV approach. 2. Set the PNI course pointer to the final approach course (ILS front course even when flying a back course approach). 3. Set the HDG SEL 'bug" on the PNI to the desired intercept angle and activate the HDG mode. 4. Depress the "APR" button. This arms the automatic capture function. (The "APR" light will flash to signify the approach mode is armed.) 5. The V-bar will command the required bank to maintain the selected heading until the capture point is reached. Then the V-bar will command a turn to intercept the course. If the autopilot is engaged it will turn to satisfy the commands. As the V-bar commands the turn to intercept the selected course, the heading mode will be canceled and the APR mode will go from arm to engage. (HDG light will go out and APR light will go from flashing to steady.) 6. The V-bar will continue to command the required bank to maintain course and the autopilot (if engaged) will satisfy those commands. (Automatic crosswind compensation will provide precise tracking. VOR/LOC deviation is shown on the PNI, and actual crab angle is shown by offset of the course arrow from the lubber line.) 7. Once localizer course capture has occurred on an ILS, the glideslope mode is armed. Automatic capture occurs as the aircraft approaches the glideslope from either above or below. I I When the intercept occurs, "GS is illuminated on the annunciator panel. The V-bar commands the pitch necessary to maintain the glideslope. If the autopilot is engaged it will satisfy these commands. If the altitude hold (ALT) mode had been engaged prior to GS capture, it will disengage at capture and the "ALT light will go out.

Aaron,

You can try waiting until you've captured the localizer to engage the approach mode as a commenter above suggested, but that makes you do the work of capturing the localizer, which would be a shame because the autopilot is fully capable of doing that, assuming you have entered an appropriate intercept heading so that it can reach the capture point.

Your KFC-150 is supposed to maintain whatever attitude your plane is in when you engage the flight director, unless you have pushed the UP/DOWN rocker to change your pitch, or you have told it to maintain altitude, or it has captured or is capturing the glide slope. My guess would be that you did not have the altitude hold engaged, and it saw the glide slope was above you, and it commanded a climb to intercept.

Of course, it's also possible that there's something wrong with your avionics. My KFC-150 was, once every few hours, while in altitude hold mode, commanding sudden steep climbs. This got old quick, so I got it repaired. I'm hoping for your wallet's sake that you find out you simply failed to depress the ALT button.

[carusoam]

Reported failures of BK AP computers include aged capacitors... and capacitors that have fallen out of their position...

Reported around here anyways...

PP thoughts only, not an instrument tech...

Best regards,

-a-

[PT20J]

Since you have a flight director, you have a direct indication of what the autopilot is doing by watching the command bars and the annunciator lights on the KC 192. The FD command bars are simply a visual indication of what the autopilot is telling the servos to do. So, rule 1 is never engage the AP if the command bars are not “satisfied.” But, that doesn’t seem like what happened in your case. The normal sequence is approach armed (APR blinking), localizer captured and GS armed (APR steady illuminated), plane flies constant pitch (or altitude if in ALT hold) until glideslope centers, then, glideslope captures (GS iluminated, ALT cancels if it was engaged). 

To get a pitch up (assuming no autopilot fault) would require the autopilot to enter GS capture (as opposed to GS armed) with the command bars showing a pitch up command. 

When troubleshooting this sort of thing, I pick a good VFR day and just work with the tower asking to track the localizer inbound on repeated circuits which is much more efficient than working approach control for approaches. BTW, as far as the KFC 150 knows, an ILS and a LPV are the same thing.

Skip

[aaronwalkerx]

Thank you to the experience Mooney flyers for the suggestions!

I had a chance to fly a practice LPV in Flagstaff yesterday, but just one.  (there was some type of incident in Prescott during the same time so Phoenix approach became busy and it seamed a bad idea to bother them with a second approach.)  -We flew the approach in Nav mod.  -We reached and held approach altitude via KAS297B Alt Hold Pre-Select and were stabilized on altitude for 20+ miles prior to Final Approach Fix.  -Initial Fix to Final Approach Fix was a strait course, no direction change, allowing plenty of time to be established, watch the glideslope come alive and come down to center.  -Prior to FAF I dropped gear, added approach flaps, then at FAF (with glide slope centered) I engaged APR mode.  All worked perfectly.  I may have initiated APR mode 30 seconds prior to FAF but more likely it was just after FAF, however the GS was still visually centered and the decent began within 60 seconds after engaging if not immediately.

I believe all the pitch up incidents have been proceeded by reaching the approach altitude via the Altitude Pre-Select so ALT has always been engaged prior to selecting APR.

Not very scientific but everything worked as expected.  Any problems I have had were likely user error.  Hopefully, I can continue to repeat the process that worked yesterday and no longer have the pitch up.  While the autopilot may be capable of holding altitude until the GS comes down I am not sure I could ever trust it to do so.