AD 61-21-06

61-21-06 LOCKHEED: Amdt. 343 Part 507 Federal Register October 4, 1961. Applies to All PV-1 and B-34 Type Aircraft Having Main Landing Gear Lower Drag Struts P/N 112004.

Compliance required as indicated.

During investigation of a PV-1 main landing gear failure, the main landing gear lower drag strut, P/N 112004, was found to be understrength because it was not in the specified heat-treated condition. As a result of this service experience, the following is required:

(a) Within the next 50 hours' time in service from the effective date of this directive unless already accomplished, determine by the Brinell, Rockwell, or an equivalent hardness test method whether or not the struts, P/N 112004, are heat-treated to an ultimate tensile strength of 150,000 to 170,000 p.s.i. If the ultimate tensile strength is less than 150,000 p.s.i., the strut must be replaced with a similar part heat-treated to 150,000 to 170,000 p.s.i. or by a strut, P/N 125715 or equivalent, prior to further flight, except for ferry flight in accordance with the provisions of CAR 1.76.

NOTE: Strut, P/N 125715, originally designed for the PV-2 type aircraft is an acceptable alternative for strut, P/N 112004, and a hardness test on this strut is not necessary. If the P/N is missing or obscured, the struts may be identified by the following: The PV-2 strut, P/N 125715, weighs approximately 15.5 pounds and the PV-1 strut, P/N 112004, weighs approximately 10.5 pounds. The PV-2 strut tube has a wall-thickness of 0.25 inch whereas the PV-1 part has a wall- thickness of 0.156 inch. The wall-thickness can be measured by laying a straight edge along the tube and measuring the perpendicular distance between the straight edge and the end fitting.

(b) Spare lower drag struts, P/N 112004, must comply with the hardness test and replacement provisions of (a) prior to installation.

This directive effective November 3, 1961.