Nose Gear came down in flight

[Stephen Shore]

1995 Commander 114B....

On the way back from Midland TX this afternoon, my nose gear suddenly came down. Obviously that was a bit of a surprise. At first I thought it was the engine, but I quickly recognized the "thud" that I felt and heard, the sudden change in pitch, and of course the GREEN nose gear light illuminated along with the RED gear warning light. The MLG remained up.

This happened early in the flight at 9,000' in cruise with the AP engaged.

I simply got out the POH and basically it said to:

1. Pull the gear breaker.
2. Fly the plane in this condition to the destination (still over 2 hours away for me).

I slowed the plane down to Vlo speed (interestingly the POH did not have this as one of the steps) and continued my trip, obviously wondering if the MLG would deploy when the time came. I was pretty sure they would since the NG came down, obviously "locked", and the green light for the NG was on.

Sure enough, I got to my destination and dropped the MLG a little early in the arrival procedure just in case there would be a problem. I advised the tower, they saw the gear down, and I simply landed without incident.

I have not pulled out my maintenance manual yet, but is the nose gear on these planes on a separate pump than the MLG? Or could it be the squat switch? I obviously need to pull out the book tonight and see how the system is engineered.

Any ideas? My A&P has not returned my call yet.

 

[wsuffa]

Same pump runs all three. I don't recall whether there are check-valves in the system. First two things I'd do is 1) check the hydraulic fluid level (easy enough to do), and check the hydraulic hoses going to the front gear (if they're more than about 10 years old, consider replacing them for good measure, I think the maintenance manual recommends 5-7 years). If the hoses are bad, you'll see red stains.

Next step is to check the hydraulic actuator - if the internal seals go bad, it will do what you described (I had it happen on a MLG twice - once was a simple rebuild, the second required finding a replacement as the actuator rod was scored due to wear - when it happened, that particular gearset didn't retract). Rebuild is straightforward like doing the shimmy dampener - replace the o-rings inside & check condition and wear. Again, this is an age thing - the o-rings last only but so long.

It's unlikely to be the squat switches - they mostly control the pump and the lights and if i recall correctly the squat switch will trigger all gear dropping (or more specifically, not coming up).

 

[Stephen Shore]

Thanks. I got home and pulled my maintenance manual. I am going to check all that you listed above. However, I have a sickening feeling that there is a possibility that I did not properly use the gear switch. The manual mentions that there is a "detent" in the switch - it has to be pulled out and up to retract the gear. I knew this at one time, however, I don't recall pulling the switch out and up in recent times. The switch felt "mushy" in flight after the gear dropped. I obviously did not dare mess with it too much, but it did not feel like it was "set" in the up position. Once the NG came down I simply followed the POH recommendation and did not mess with it.

Obviously there needs to be a close inspection and get it up on jacks to take a look.

thanks again.

 

[wsuffa]

Thanks. I got home and pulled my maintenance manual. I am going to check all that you listed above. However, I have a sickening feeling that there is a possibility that I did not properly use the gear switch. The manual mentions that there is a "detent" in the switch - it has to be pulled out and up to retract the gear. I knew this at one time, however, I don't recall pulling the switch out and up in recent times. The switch felt "mushy" in flight after the gear dropped. I obviously did not dare mess with it too much, but it did not feel like it was "set" in the up position. Once the NG came down I simply followed the POH recommendation and did not mess with it.

Obviously there needs to be a close inspection and get it up on jacks to take a look.

thanks again.

It's possible that it's the switch, but as I recall, if the switch loses pressure, all 3 drop. Maybe there's blockage in the lines just to the front gear, or the hydraulic splitter. But you won't know that until you get it up on jacks. More likely to be low fluid, hoses, or the actuator, but again, YMMV.

I had a Commander 112TC.

The most common detent problem is that the detent doesn't work well on the emergency gear valve, and that's right by the pilot's knee. It's easy enough to deal with, but again, it drops pressure in the system, so all 3 gear would drop.

You might also ask at COG.

Good luck!

 

[Stephen Shore]

COG forum got me the fix. First of all, the "Heim" joint (bearing rod coupler) came apart in flight and the NG dropped down as it is supposed to do when the hydraulic pressure is released, which is what effectively happened when the Heim joint on the end of the actuator came apart.

This problem is known in the Commander community (and is now known by me). The "fix" is to upgrade the hardware to 5/16" from 1/4". It is 5/16" on the MLG but not the NG. Why is anyone's guess.

Anyway, I have everything sourced to upgrade both ends of the NG actuator to 5/16" hardware. There actually is a service bulletin on this. No AD, but it needs to be done.

 

[sourdough44]

Nice to see you’re on the way to recovery. I’ve had a gear problem a time or two, going up. I’ve always been able to get it down normally, which I care about more of course.

 

[wsuffa]

COG forum got me the fix. First of all, the "Heim" joint (bearing rod coupler) came apart in flight and the NG dropped down as it is supposed to do when the hydraulic pressure is released, which is what effectively happened when the Heim joint on the end of the actuator came apart.

This problem is known in the Commander community (and is now known by me). The "fix" is to upgrade the hardware to 5/16" from 1/4". It is 5/16" on the MLG but not the NG. Why is anyone's guess.

Anyway, I have everything sourced to upgrade both ends of the NG actuator to 5/16" hardware. There actually is a service bulletin on this. No AD, but it needs to be done.

Interesting. Good to know - I never had the issue. Glad there's a solution.

 

[1RTK1]

Better to have it come down unexpectedly than not at all