Landing gear up light

[Jerry Mazza]

I have a 1970 PA39 and the gear up light only works intermittantly. It always comes on once the plane lands, the warning horn works perfectly, and my mechanic can never replicate the problem on jacks. I had the 1000 hour gear Ad done last year and the problem has persisted the same as before the Ad was done. Any suggestions?

[N3322G]

Jerry,

You said - I have a 1970 PA39 and the gear up light only works intermittantly. It always comes on once the plane lands, the warning horn works perfectly, and my mechanic can never replicate the problem on jacks. I had the 1000 hour gear Ad done last year and the problem has persisted the same as before the Ad was done. Any suggestions?

Do you mean the white gear is in the wells or the green gear down light - which is intermittent?

My 39 is also 1970 - serial # 10. Years ago the green gear down light was recalcitrant. we always got it before landing but sometimes we had to recycle the gear and sometimes, we had to turn the panel lights on and then off. We replaced the wiring harness and that did not solve the problem but after seeing the removed wiring, I was glad we did that. Then we replaced the nose gear micro-switch and after several years, we finally had green gear down light every time we put the gear down and it took about 6 seconds. A decade later the symptom returned so we replaced all 4 micro-switches.

If you decide to replace the nose gear micro-switch, before you do that - grab a friend and time how long it takes for the gear light to come on. Then after the micro-switch is replaced - make sure it was adjusted according to the Twin Co maintenance manual. Check the gear on the ground according to the Maurice Taylor videos http://www.comancheflyer.com/NS/cff_merchandise.php Then, time the gear deployment again on your test flight. I stress this because you can learn from my mistake. I trusted an extremely knowledgeable and experienced Comanche mechanic - he was in a hurry and I ended up with a false-positive green gear down and locked light - with new conduits, they supported the incorrectly adjusted gear for several landings and then the gear collapsed on a gentle landing. The only slight indication we had a false positive green down and locked gear light was it lit after 4-5 seconds. I knew that was fast but thought it was the 1000 gear AD plus the new conduits plus new wiring harness plus all new and 'correctly' adjusted 4 micro-switches. I was wrong and 3 years later I'm still paying for it in obscene insurance terms.

I'll stop here because I'm still mad that I trusted ... so "trust but verify" took on a whole new meaning.

If it is the green gear down light, this post may help. If it really is the gear up light, it is a different answer.

[Hansmeister]

Jerry,

You probably have an intermittent wire problem. Does the plane have the Matt Kurke gear wire harness?

The gear switch wires have a habit of fatiguing due to the flex at the drag link pivot.

[Jerry Mazza]

It is the green gear down light and I have the original wiring harness. Cycling the gear usually does not help. Since the one time I did have a true gear problem, the horn was blaring, I use this, plus I remove the emergency gear extension cover to verify correct position of the linkage before landing. Looking at the schematics, is the green light not triggered by the limit switch in the left wheel well?

[N3322G]

Jerry,

The harness we used to replace the wiring in 1997 is the same that Hans is recommending from Matt Kurke at comanchegear.com

We thought this would fix the problem. Our mechanic worked on it from 1994 to 1997 without success so we changed the harness thinking it would fix the problem - as I said above, it was good to do that but we were stunned when it didn't fix the problem - so was the mechanic.

At the time, the tech guru of all gurus on Comanches Maurice Taylor was still alive. While I had met Maurice I was a bit shy about calling but finally got desperate to fix this problem. He said to change the nose gear micro switch. At the time it was $25, we did that and the problem went away for over a decade. When it came back we replaced all the micro switches - it was verified that it was the nose micro switch that had failed again. Maurice had commented in 1997 that he didn't know why the nose micros switch failed more often than any of the others but by experience he suggested this as the first place to start to fix an intermittent green gear light.

To try to answer your question - my understanding is that all 3 micro switches on all three gear legs have to be engaged to get a green gear down light. The squat switch on the left gear leg is there to keep the gear from retracting while weight is on the gear on the ground or so i understand.

Unsolicited advice - only because I care - I personally would not land without getting a green gear light. If I was forced to land without one, I wouldn't fly again until corrective measures were taken.

[Zach Grant L1011jock]

All three down limit switches must make to turn on the green light, and to turn off the motor (two separate circuits, the light in series, and the motor in parallel). The gear horn is on the nose gear down limit switch only. The squat switch visable on the left gear leg simply removes power from the gear motor when the strut is compressed. Do you and your aircraft a favor. Get your harness fixed!!! Matt Kurke at http://www.Comanchegear.com can really help you out here as his prefab harnesses include all new switches as well as wire.

-Zach

[Edward Pencosky]

zach is right the nose switch will turn the horn off when the nose is down and locked. I have a 260c and bought the plane in 1990. My green light would take way to long to come on as i felt the gear go down in my rudder pedals. CLICK CLICK.... than i waited for the light some times way to long.I replaced the micro switches in both main gear and still had problem. than i replaced nose switch and wire harness in nose and still had intermediate delayed green light. As mentioned above when turning my panel light switch on and off this solved the problem.I later found out if i reached very gently under the panel and under the panel light switch you will feel some wires screwed or soldered to the light switch . Gently touch those wires and see if the light comes on when this problem happens. Also turn the panel light switch on and off as this also has made my light come on. In my case its either the light panel switch or the wires connecting to it. There has to be a complete circuit of electricity going thru the light switch and the wires connected to the light switch ,and all 3 micro switches in gear or no green light will come on. ITS one big circle and if there is a break anywhere the light wont come on.CHECK LIGHT SWITCH AND GEAR SWITCHES AND WIRES TO PANEL LIGHT SWITCH.. keep in mind i have the C model and i think it is like the twins but i believe yours works the same EDDIE goodluck