Dukes & ITT Landing Gear Actuator 40:1 Ratio Gears, SI M20-112


Mooney Service Instruction M20-112 was released March 8, 2008. This service bulletin has long been awaited by Service Centers and owners of pre “J” model Mooney’s with electric gear actuators.

SI M20-112 can downloaded here.

Good News

Mooney SI M20-112 will offer the 40:1 as a retro fit for the Dukes 4196 and ITT actuators. The Dukes 4196 actuator will require Mooney Kit SI20-112-001. This kit will include the Dukes Actuator repair kit and 40:1 gear set Mooney Pn. 940164-501.

The ITT actuator will require Mooney Kit SI20-12-003. This kit will include the ITT Actuator repair kit and 40:1 gear set, Mooney Pn. 940164-503. The gears in both kits are identical. The difference in part numbers is due to the type of bearings required for each actuator. Necessary bearings and seals are included in these kits. The original 20:1 gears sets are still available for these actuators; however, I would encourage you to replace your gears with these improved sets as soon as possible.

Electric Gear

Electric gear has been an option for Mooney airplanes since 1965 and standard beginning with the 1969 models. Early electric gear Mooney’s used the Dukes Pn. 4196-00-1(X) actuator. In 1975, Mooney offered the ITT Pn. LA11C2110, 2114 or 2115 as an alternate actuator in SB-M20-189A. Both of these actuators were used thru 1977 except on the M20J which used a Dukes Actuator Pn. 1057-00-(X) that incorporated a 40:1 gear set.

The Dukes 4196 actuator and the ITT actuator both use the same 20:1 ratio gears. Both actuators have a similar external appearance but are easily identified. The Dukes 4196 actuator has 6 screws that attach the end cap to the jackscrew housing. It also has a grease fitting at the bottom of the gear housing. The ITT actuator has 4 screws that attach the end cap to the housing and no grease fitting. Internally, the Dukes 4196 actuator uses needle bearing. The ITT actuator uses bushings. These 20:1 actuators cycle the landing gear very quickly and the gears wear rapidly.

AD 75-23-04

In 1975, the FAA issued AD-75-23-04 against all Mooney’s equipped with the DUKES 4196 actuator. The AD calls for the greasing of the actuator each 100 hrs and the removal and inspection of the actuator gears each 200 hrs.

The AD 75-23-04 does not reference the ITT actuator even though both actuators, Dukes 4196 & ITT use the same gears. We treat both actuators as though the AD applies to the ITT and have found many to have significant wear.

In 1977, the new M20J, 201, was introduced. The “J” model used a Dukes actuator Pn. 1057-00-(X). This actuator had a larger motor and the actuator used a 40:1 ratio gear set. AD 75-23-04 does NOT apply to this Dukes actuator. The gear operated at a slower rate with less wear and tear on the gears and other component parts and allowed the installation of lower gear doors.


The Dukes and ITT actuators used in Pre-J Mooney’s are very small, approximately 1/4 the size of actuators used in current model Mooney’s. An example of how lightweight these actuators are is their application in various Cessna aircraft as a flap actuator. The ITT & Dukes actuators are no longer in production and replacement parts are very difficult to obtain. Mooney offers an upgrade kit to install the newer style actuator but the cost is over $13,000.00 for the kit.

AD 75-23-04 requires the removal and inspection of the actuator gears each 200 hours of operation. Over the years, the compliance with this AD has taken its toll on many of these actuators due to their light weight construction. The 40:1 gear kits will reduce the inspection requirements and extend the life of these actuators.

It is unclear, at this time, if compliance with the new 40:1 ratio gear kits eliminates the AD all together or just extends the mandatory inspection time to those recommended for the 1977 “J” model with the Dukes 1057 actuator. Recommend time for the Dukes 1057 actuator is 500 hours for the initial inspection and 200 hrs thereafter.

The pricing for the original M20-190-001 20:1 gear sets are $489.08. The pricing for the SI20-112-001 and 003 40:1 gear kits are $800.00 and $818.00.

Initial setup of the 40:1 gear sets will require complete compliance with the service instructions included in the kits by a mechanic experienced with these type actuators. Most of the older, experienced Mooney Service Centers can provide the gears and install them for you. Have your mechanic remove the actuator and send to the MSC of your choice. As always, we are available for your tech support needs.

Please visit our web site www.donmaxwell.com for this and other maintenance articles previously published in the MAPA Log.

E-mail dmaxwell@donmaxwell.com or 903-643-9902.

MAPA Log (2007)