71-06-06 MAULE: Amendment 39-1169. Applies to M-4-180C serial numbers 3001C through 3004C and M-4-220C serial numbers 2044C through 2060C.
Compliance required within the next 10 hours' time in service after the effective date of this AD, unless already accomplished.
To detect seat track and seat track guide spacing that could allow the seat to become free from the guides, accomplish the following:
a. Remove front bucket seats.
b. Determine the distance between the inner edges of the horizontal flanges of the seat tracks for each front seat (measure at front and rear of tracks and use maximum dimension). The seat tracks are the L-shaped flanges welded to the bottom of the seat frame.
c. Determine the distance between the outside edges of the vertical flanges of the seat track guides. The seat track guides are the L-shaped clips welded to the fuselage.
d. If the distances measured in b. and c. differ by 3/32" or less, no further action is required.
e. If the difference in these dimensions is greater than 3/32", accomplish one of the following:
1. Bend one of the seat tracks inward so that the above distance requirement is satisfied. A vertical cut must be made adjacent to the front end piece of the seat track to allow the necessary bending. After bending, secure in place and reweld on the inside of track, using at least 3/4" welds at the three existing tack welds attaching the track to seat frame. Also, reweld the saw cut and check for the proper dimensions.
2. Weld an extension strip to the full length of the seat track to meet the above distance requirement using 4130 steel, Condition N sheet, .060 inches thickness and check for proper dimensions. The minimum strip width must be 1/8".
3. Any other FAA approved equivalent method.
f. A seat which has to be modified in accordance with (e) above is to be reported to the Chief, Engineering and Manufacturing Branch, SO-210, FAA Southern Region, P.O. Box 20636, Atlanta, Georgia 30320. The report should include the airplane serial number and the distances determined in (b) and (c). (Reporting approved by the Bureau of the Budget under BOB No. 04-R0174.)
The checks required by this AD in paragraphs (a), (b), (c) and (d) may be performed by the pilot.
Maule Service Letter No. 21 pertains to this same subject.
This amendment becomes effective March 16, 1971.