Emergency Gear Extension Systems
July 2001
About 1979, Mooney changed their emergency gear extension system from a crank handle mounted on the left side panel to a pull cable mounted just aft of the stabilizer trim wheel on the floor. This was a considerable change in the design. This month’s Shop Talk will explain the basics of the newer pull cable type system.
The modern Mooney landing gear system consists of an electric motor attached to a gearbox. Alongside the gearbox is a jackscrew with an adjustable rod end that attaches to the actual landing gear mechanism. The other end of the gearbox houses the emergency retraction coil pull engagement lever and coupler. This system is straightforward but is subject to excessive wear if used too often. I will go through step-by-step what happens when the pilot activates and operates the system.
After the pilot realizes that the flight is not going as planned and the emergency gear system is needed, the first step, of course, is to fly the airplane and communicate your intentions. After all is under control, consult the POH. It directs the pilot to pull the gear actuator circuit breaker, which removes all electric power to the landing gear electric motor. Next, position the landing gear switch to the down position and unlock the emergency lever on the floor, between the front seats. A latch keeps the lever in the down position. Move the lever up, allowing access to the tee-handle. This action allows the emergency drive system to connect to the gear motor transmission. This coupler system consists of a steel key block, a bronze or steel slot for the block to engage and a spring to hold the halves together. Lifting the lever moves an actuator allowing the spring pressure to act on the coupler. Once the coupler is engaged, the pilot can pull up on the tee-handle. With every pull, the landing gear will incrementally move to the down position. It takes approximately twenty to twenty-five pulls to get the gear down and locked completely. A recoil spring inside the tee-handle cable drive housing retracts the cable and tee-handle back to the floor after each pull.
There are two types of landing gear actuators used in both twelve and twenty-four volt aircraft. The early actuators were manufactured by Avionics Products (Eaton Corp., El Segundo, CA). This system has an adjustable rod end requiring some rigging adjustment. This is the system with the bronze coupler slot, mentioned above. The later type of system is made by GEC (Plessey), UK Aerospace, Whippany, NJ, and is almost identical with the following exceptions: the jackscrew is a complete unit without the adjustable rod end. The rod end is built into the jackscrew itself and is much easier to rig the landing gear system. The other key difference is that the emergency drive system in the Plesley system uses a steel-to-steel drive to attach the pull cable to the transmission. The bronze-to-steel system is subject to excessive wear; the steel-to-steel system is much more durable. Each of these actuators has one service instruction against it. See Mooney Service Instructions, number M20-52B (Avionics) or M20-92 (Plessey).
If you want to practice using this system on your airplane, don’t do it in flight. The next time your plane is on jacks, go into the shop and ask to work the system. Practice is just that, practice! If you use this system in flight and it fails, you may end up with a gear-up landing. In the hanger, any failure or damage to the system is always going to be easier to repair than a gear-up landing. A little technique here. The first pull of the tee handle should be slow until the block can drop into the slot. This will help prevent wear on the edges, especially if the bronze coupler is installed. If the coupler is already worn, a fast pull may prevent the coupler for engaging. Remember this if the emergency system is ever needed in flight. Also, do not let go of the tee-handle when the cable is extended. The subsequent slack could cause the cable to snag.
There is a subtle Murphy’s Law situation possible with the emergency gear system. This is as told by one of my customers. During an approach to Sedona airport for sightseeing and lunch, the gear did not extend when the gear switch was selected down. The gear actuator circuit breaker had popped! A quick glance down at the manual gear position indicator also revealed that the emergency gear lever was not in the stowed (down) position. Apparently, one of the passengers had inadvertently moved the retaining latch allowing the lever to raise (remember the coupler spring).
With the coupler engaged, the gear actuator rods can’t rotate and the motor can’t turn. This causes the circuit to overload and pops the circuit breaker, as designed. The lever was stowed and latched, the gear switch went back to the retracted position and the circuit breaker was reset. The subsequent gear extension went normally. My customer now includes the emergency lever in his passenger briefing (“Don’t touch”) and in his cockpit scan.
In conclusion, the Plesley system is more robust than the Avionics system because of the steel-to-steel coupler. Remember to test the system when you do an annual. Listen to how clean the pull on the tee handle sounds, and make sure the drive is a positive one that results in constant gear motion for every pull on the tee-handle. The emergency gear system was not designed to be used for training; it is for emergency gear extension only. If you use this system only when needed and during an annual while your plane is on jacks, it will last a long time. The emergency system is one of those systems you seldom think about but is probably important when you need it. Always verify before take-off that the lever on the floor is positively latched. With proper maintenance, probably the only time you will get to use the emergency gear extension system will be during the annual test.
As always, if you have a question about this article, you may contact me at my aircraft repair shop, 307-789-6866 or via e-mail. Until the next ShopTalk, enjoy flying your Mooney.
