Don Maxwell Aviation Services, Inc.
Authorized Mooney Service Center
SB M20-190 & AD 75-23-04:
The Importance of Checking Your Dukes and ITT Electric Gear Actuators
by Don Maxwell
MAPA Log Magazine
Applies to early 201 and pre “J” Mooney’s equipped with Dukes Electric gear actuators. Recent inspections per this Ad indicate that either the inspections are not being done or being done improperly. In my opinion, the Dukes actuator is barely adequate for the job and must have regular inspection to be dependable.
AD 75-23-04 refers to compliance with the SB M20-190. The SB, dated 1-16-75, is divided into three parts. Part 1 requires that every 200 hrs the actuator be removed from the aircraft, partially disassembled, and inspected for gear wear. Removal of the actuator may be a little intimidating the first time a mechanic removes one, and in some cases, I have found that the SB has not been fully complied with. In other cases the actuator may have been removed but the most important part of the inspection is not being completed. The SB requires that all of the old grease be removed and that the housing be flushed clean with solvent and air dried. The reason for this procedure is that the gears wear in the middle and by looking at the end no wear is apparent.
Figure 1. View below. Is a photo of a worn ring gear as it would look as viewed from the end.
Fig. 2 is of the same ring gear viewed from the side showing the wear. The gear appears normal from the end, but is nearly worn half way thru in the side view.
Fig. 3 is of the ring gear, the worm gear it runs against, and a quarter to give you an idea of the size of these parts. As you can see, it is very important that these inspections be performed as required.
Part 2 of the SB requires that the actuator be greased each 100 hours. To grease the actuator the middle belly panel must be removed. Remove the top end cap bolt per Fig. 4, and apply applicable grease, with a hand grease gun thru the lubrication fitting until it runs out of the top bolt hole. If the bolt is not removed the grease seal on the worm gear shaft will be damaged.
Part 3 of the service bulletin refers to the change in washer sizes used for shims on the ball end of the actuator.
Mooney SB M20-189A allowed for the substitution of the ITT actuator to replace the Dukes actuator. The ITT actuator is almost a carbon copy of a Dukes actuator and if anything, I believe, not as good. My concern is that both actuators have the same gears and that the ITT actuator is not addressed in the AD or SB M20-190. I inspect the ITT just as I would a Dukes, and have found several near failures that have never been inspected.
If you have an early 201 or pre “J” Mooney with electric gear and the entry in your AD log for 75-23-04 states not applicable or not installed, or ITT installed, I would encourage you to have the gears inspected as soon as possible.
Emergency Gear Extension I want to address what I think is a misconception by many about emergency gear extensions.
The only time that an emergency gear extension will be successful is if the electric motor fails. The emergency gear extension system drives thru the gear actuator. If there is a failure of any component of the actuator, ring gear, worm gear, drive coupling, the emergency system is inoperative and you’re in for a big let down.
Inner gear doors
I have flown several pre “J” manual gear Mooney’s that have had the inner gear doors added by STC. These gear doors make the manual gear much more difficult to retract and, I think, dangerous to lower. Though probably not a mechanical problem on manual gear models, I believe the added load to a marginal retraction system such as the Dukes & ITT can only accelerate the gear wear.