Tonight coming home after a day of flying the gear decided to throw a curve ball. Maybe someone can shed some light, maybe not.
Flew all day, no problems, 3 airports.
Typically every flight or so, i'll check the operation of the gear horn in my twinky, so I know it works.
Final airport, home, just as the sun was setting, I drop the gear on the downwind, NO Green. OK, I felt it in my feet, power settings and airspeed indicate gear down, no green, so i turn off the nav lights, NO Green, so I pull the power back thru 1200, all the way to idle, NO gear Horn.
So I leave the pattern, put the gear up, power up, climb some and watch the gear transit lights, and then test the gear horn with the gear up, power to idle, NO horn.
So now I don't trust my horn.
I recycle the gear, gear down, feel it in my feet, have it in my mirrors, no green, no horn, but i don't trust the horn.
I give controls of the plane to copilot, also a twinky owner.
I open the gear well, and I've magic markered the down and lock position of the gear, and they line up.
So now what to do? Emergency extension? Or believe it is locked down and something electrical is off, and land. I've been told that the system is stronger if left connected, so that's what I do, leave it connected and trust my instinct that something else is wrong, but it is locked down.....??
Do I start changing bulbs? But what about the horn? Something is wrong, but what.
I land with no problems, put the plane away, and leave my mechanic a message.
thoughts?
steve
N8632Y

Steve,

 

This is a little off the subject. It is a tip I heard about years ago.

Paint a small white line in the inside of gear mechanism to show your gear is in the down position as seen from the cockpit. That way, in case of a problem you can lift the panel door of the emergency release in the cockpit and verify the gear is fully down or not. FWIW.

Jeff Aryan

Steve,

 

The warning horn is probably doing what it is supposed to be doing. It cues off the nose gear down limit switch. The down light requires all three gear limit switches to be in the correct position.

First check the bulb in the down light. This should have been done in the air by unscrewing the in transit light and screwing it into the gear down light position. That would have told you in the air that it was a bulb problem and not a gear problem. Assuming the bulb is fine, turn on the master and check power to the socket for the down light. If no power, see if the wire has fallen off the back ofthe socket. If not that, then go up under your panel on the right side. Look up and left at the aluminum channel that is on the side of the throttle quadrant cables. You will need a little terminal strip with five pairs of terminals. Check the wires going to the middle one. They should be marked G5C and G6C. Turn the master switch on, and then with a multimeter, check to see if you have voltage to that center terminal. If not, the terminal that has wires G4B and G6B going to it. Refer to wiring diagrams and keep chasing toward the bus to see where you lose power.

Now, assuming you have power to the down light socket, then your problem is with the ground side of the circuit. That runs through each of the down limit switches. You can confirm by turning the master off and checking continuity to ground from the side of the socket to another ground point. If you have a ground problem, you will have near infinite resistance.

To find the ground problem, check first the left, and then the right gear to see if the switches are adjusted properly. It is likely that one of the main gear limit switches is bad or out of adjustment. Turn the master on and have someone watch for the light, as you push the limit switch plunger in a bit more using a screwdriver or some such. If the light comes on, you have found out that you have a bad, or misadjusted microswitch. If it is not the switch, then you have a wiring problem. You can start by going to the nose, up under the nose cowl, and check to see if there is voltage at the G5M wire. If you have voltage, then you have a bad ground in the nose. There should be zero voltage. Then check G5L in the right wing root for voltage. If there is voltage, you have a bad right microswitch. If not, go across to the left side and check G5K. If you have voltage there, then the left microswitch.

I am betting on bulb as the most likely. Second most likely is a misadjusted main gear down limit microswitch.

Good luck.

Kristen,

 

First, let me preference this by saying I do not yet own a Comanche so my system knowledge of the aircraft is zero. Hopefully the 180 we are looking at will pass it's pre-buy. I am inquiring here in hopes of learning more about the aircraft.

I understood Steve to say that he did not get a green light, so he checked it with the gear horn and no horn. Based on your input this means the nose gear is down. He decided he wanted to check the gear horn next.

Steve said he checked the gear horn by retarding the throttle to idle with the gear up. He does not mention the flap position. I would think with gear up and throttle to idle you would get a horn (depending on if the horn needs flaps to activate). Has he done a proper check of the gear horn function with the gear in the up position or what would he need to do in order to properly check it?

Thanks,

Michael

Jeff,
You are correct to have a marker in the gear well next to the mechanism to show the correct down and lock position. I do, and that was what I looked at after checking the gear horn. It showed that the gear was fully extended and in the correct position. That was my determining factor in deciding to land and not trying to change bulbs. That was described at the CPPP course.
Kristen,
After noting no green on the downwind leg, i first turned off the panel lights, no green, tried the gear horn, NO Horn, but that would be correct if the gear was down and I trusted the horn. But, i left the pattern, put the gear up, panel lights on, it was dark, the sun was just about down.
Went about 5 miles out and with the gear up, i slowly pulled the power to test the gear horn. I've down this almost every flight or so, i get the horn around 12-14" MP, not this time, no horn with the gear up, and yes, I had gear light indicators showing up and in transits. So now i don't trust the horn.
Put the gear down, no light, Then I opened the gear well and saw the position of gear, the 2 marker lines were aligned!
I suspected the gear was down, i felt it in my feet, my 2 mirrors showed it down, my power settings/airspeeds confirmed down, but was it locked? The markers showed to be, so i did not play with the bulbs. I suspected something electrical in the system, something that connects the horn and green light together? That is what i'm looking for?
Kristen, I will leave the trouble shooting to my IA, he's so much better than i....
In the past I did the emergency landing procedure, but found (was told) that the comanche system is so much stronger if the transmission is left engaged. So I left it engaged.
I will have my mechanic out this week and report.
Bungees changed past annual, 6 months ago.
steve

Steve,

 

Glad you and the twin and co-pilot are safe on the ground.

Might be more than one problem.

Ditto what Kristin said about changing the light bulb - have lost two in the years we've been flying - always find it when landing. Smart to get out of the pattern and have someone else fly while you diagnose. Smart to test the gear horn in multiple positions too.

Based on two rounds of microswitches replacement experience (obviously Kristin has way more tech knowledge as she is A&P/IA, I've just had learning by check book on this one) and advice from Maurice Taylor, I'd check the nose microswitch first. After any microswitch work, suggest you pr-flight using Maurice Taylor's video for checking gear position ad some mechanics will get in a hurry and adjust microswitches to show down and lock when the gear is not yet in the correct position. I've read the gear adjustment section of the maintenance repair - it is an iterative and time consuming process. If it is a microswitch you might consider Matt Kurke's new wiring harness if that hasn't already been replaced.

Hope this helps and look forward to knowing what is found.

Steve,

 

I didn't catch that the horn was not working even with the gear up. The horn and the light are actually two largely separate circuits. The common point is the nose gear microswitch. For that reason, I would start there. In particular, the ground wires. If you have ever had the experience of the down light being slow to come on after the gear is down, that is a sign of the nose gear microswitch going bad.

If you have original microswitches, just get Matt's kit and save the troubleshooting money for installation money. Those switches are getting progressively more expensive, so waiting is not saving you any money.

Kristen,
Yes, i have noticed the green light being slow to come on occasionally, or so i thought. You know when u'r waiting for that green light, you always think it's takin longer each time.
So i'll have my mech start at the nose microswitch and time to call Matt....
thanks, i'll let u know
steve
ps, i did change bulbs to no avail
ps, the emerg book, QRH, page 5-3 step 8, if no horn, gear probably down..
maybe a note needs to be added that gear horn is tested for proper operation somewhere?

Steve,

 

I have had at least four people, including myself, who had slow green lights. In my case, and at least one other, turning the panel lights on and off, seemed to get it to work. In my case, and the others as related to me, replacing the nose gear microswitch fixed the problem. I would note that the nose gear microswitch is in the line of fire for stuff coming off the nose tire and is also likely subject to more buffetting from the wind, than are the ones on the mains.

I just installed Matt's kit for the indicator lights to install the mil spec lights that can be dimmed and have the press-to-test feature.

Thanks KRistin,
i will be calling Matt too...
appreciate all the insight, very much!!
steve

Another thought wrt to the gear horn. Just had all cables from cockpit to engine replaced. As we went about adjusting the cables for operation and then the idles and gear horn, it appears that the microswitches in the power quadrant may be getting old. The idle adjustment causes gear horn mp setting to change - don't think it is supposed to but it does on my twin. Surprise surgery in the family during out of town travel has prevented me from diagnosing this further. Thankfully all is turning out OK in that area.

 

BTW - we have the gear horn mp set at 13-14 mp as by the time we get to 12 inches, we are on final, low and slow and don't really want to be behind the power curve if we have forgotten to put the gear down.

After any work on the twin, I always check the gear horn. The shop owner once flew with me after they'd worked on an oil leak in the right engine and I checked the gear horn - I'm sure he thought I was nuts but I try to keep that habit so it will always get checked after any work.

Somewhat unrelated, but I was experiencing the delayed green light on gear extension discussed above. After installing Matt's kit, things are working great. I was shocked to see how frayed, brittle, and unreliable the old wires and switches were - very glad I undertook this project!

Yes, talked to my IA today about Matt's kit (s)....
My IA needs to seriously look at his website, then talk to Matt,,,,,
would love to have Matt come up and maybe get a couple twinky's to work on,,
problem is it's getting to winter,, who would come from FLa to PHL in the winter?
steve

Is your IA having concerns about approval? Perhaps I can help sort that out.

Thank you Kristin,
I will keep that in mind.
I have grounded my plane till my gear passes my new inspections!
In the past I routinely take photos of my plane, like whenever a cowl is off, or under the gear, then at home, I can look closer.
Or at a later date, like 5 yrs later, go back and compare.
But, the other day, My mechanic and I crawled and checked all the wiring, microswitchs, gear..etc...
It all looks OK, old, but no problems, but just OK, which is not good enough for my gear.
So I called Matt and will have new wiring harnesses, gear lights, the whole system gone over to specs.
Hopefully i get pics of the process.
PS: old wiring looks good until you roll in between your fingers.
steve