M20J landing gear over-extended with emergency extension system

[Vance Harral]

A mechanic friend called me today, who I'll keep anonymous because he is a truly good guy and everyone makes mistakes.  He was working with an apprentice to swing the gear of an M20J as part of an annual inspection.  The apprentice was in the cockpit and working the "lawnmower pull start" mechanism in the J model that manually extends the gear.  Well, there wasn't quite enough supervision, and the apprentice kept pulling on the line even after the gear down light illuminated, until it got really hard to move.  My guess is the bungee springs on the main rods are bottomed out, and the truss rods are in an excessively over-center position, but I haven't actually seen the airplane.  Anyway, my mechanic friend says the gear is now "bound up" and won't move in either direction.  In particular, if the system is put back in a normal configuration (tab closed, which is supposed to disengage the emergency spline, then breaker in), selecting gear up with the switch doesn't do anything except trip the breaker for the gear motor.

In my M20F, the emergency extension crank can be rotated CCW to move the gear toward the retracted position.  Yes, I know the placard in the cockpit says not to turn it that direction, but the M20F service manual actually prescribes doing exactly that during certain rigging operations.  So if this was an F model, turning the emergency extension crank CCW might be a way to alleviate the over-extended scenario.  But my limited understanding of the "lawnmower pull start" system in the J model is that it's impossible to do this.

I can't offer much help to my friend because I'm just not really familiar with the J model emergency extension system, and it's unclear to me what might have actually happened to get the gear bound up like this.  Supposedly none of the rods appear to be bent, the system is just under a lot of pressure.  It occurs to me that the emergency extension spline may no longer be dis-engaging properly, and that's what's actually causing the breaker to trip rather than pressure on the gear rods.  But again, I haven't seen the airplane.

Anyone know how to get the gear moving back in the other direction, or at least release the pressure/tension on the mechanism?  My friend is contemplating removing some of the bolts that hold the rods in place, but that seems like a bad idea when the system is under pressure, as it might damage parts and/or hurt someone.

[1980Mooney]

43 minutes ago, Vance Harral said:

A mechanic friend called me today, who I'll keep anonymous because he is a truly good guy and everyone makes mistakes.  He was working with an apprentice to swing the gear of an M20J as part of an annual inspection.  The apprentice was in the cockpit and working the "lawnmower pull start" mechanism in the J model that manually extends the gear.  Well, there wasn't quite enough supervision, and the apprentice kept pulling on the line even after the gear down light illuminated, until it got really hard to move.  My guess is the bungee springs on the main rods are bottomed out, and the truss rods are in an excessively over-center position, but I haven't actually seen the airplane.  Anyway, my mechanic friend says the gear is now "bound up" and won't move in either direction.  In particular, if the system is put back in a normal configuration (tab closed, which is supposed to disengage the emergency spline, then breaker in), selecting gear up with the switch doesn't do anything except trip the breaker for the gear motor.

In my M20F, the emergency extension crank can be rotated CCW to move the gear toward the retracted position.  Yes, I know the placard in the cockpit says not to turn it that direction, but the M20F service manual actually prescribes doing exactly that during certain rigging operations.  So if this was an F model, turning the emergency extension crank CCW might be a way to alleviate the over-extended scenario.  But my limited understanding of the "lawnmower pull start" system in the J model is that it's impossible to do this.

I can't offer much help to my friend because I'm just not really familiar with the J model emergency extension system, and it's unclear to me what might have actually happened to get the gear bound up like this.  Supposedly none of the rods appear to be bent, the system is just under a lot of pressure.  It occurs to me that the emergency extension spline may no longer be dis-engaging properly, and that's what's actually causing the breaker to trip rather than pressure on the gear rods.  But again, I haven't seen the airplane.

Anyone know how to get the gear moving back in the other direction, or at least release the pressure/tension on the mechanism?  My friend is contemplating removing some of the bolts that hold the rods in place, but that seems like a bad idea when the system is under pressure, as it might damage parts and/or hurt someone.

It’s not the first time this has happened. Read further down - they suggest a solution  

 

Edited July 25 by 1980Mooney

[PT20J]

That part noted at the end of the thread reference by @1980Mooney is the mechanical down stop. In the event of a failure of the down limit circuit, it keeps the motor from overrunning and bending the push-pull tubes. I know it is on the Avionics Products/Eaton actuators. I think it’s also on the Plessey actuators.

[mooneyflyfast]

This happened to my J once after I had to use the manual system after a total electrical failure.  My mechanic had to drive a bolt out. After replacing the bolt, all was well.  Not a big deal.