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SB M20-190
& AD 75-23-04
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. Fig.
1 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.
ITT Actuators
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.
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