Task/Inspection Suspense Date.

TB 1--1520--237--20--225

(2) Ferry Status --

(a) Prior to first flight after arrival at final destination.

(b) Sikorsky will inspect DD 250 aircraft prior to those aircraft departing for ferry to final des-

tinations

Maintenance Trainers (Category A, and B). Same as para 1a.

Component/Parts in Stock at All Levels (Depot and Others), Including War Reserves. N/A

g. Components/Parts in Work (Depot Level and Others). Depot and other maintenance activity Com-

manders will ensure items listed in paragraph 7 are not issued until they are in compliance with this message.

Task/Inspection Suspense Date.

a. Complete the initial inspection of the main landing gear drag beam assembly IAW paragraph 8a prior

to the next flight but NLT 21 Nov 00.

b. Inspect the main landing gear drag beam assembly IAW paragraph 8b as soon as practicable but

NLT 6 Dec 00 and report IAW para 14b.

Reporting Compliance Suspense Date. Report compliance IAW para 14a NLT 1 Dec 00.

Summary of the Problem.

Background.

(1) Since 1988, 60 drag beam failures have been reported. The primary failure mode has been

stress corrosion cracking followed by tensile overload. Stress corrosion cracking results when a stress corro-

sion cracking prone material is subjected to a sustained tensile stress in the presence of moisture. One con-

tributor to the tensile stress is the 71--79 foot pounds (855--945 inch--pound) torque currently required on the

jackpad retention nut. Reducing that preload will reduce the amount of persistent stress around the jackpad

bolt hole thus reducing, but not eliminating, the likelihood of crack initiation. Analysis indicates that the crack

growth rate can be as fast as 8 clock hours from crack initiation to full fracture. A visual inspection of the

jackpad bolt hole area before every flight will identify most beams that are in the process of breaking thereby

reducing the likelihood of an operational incident or damage to other structure. To do this inspection effective-

ly, the surface areas being checked must be reasonably clean.

(2) Failure of either right or left drag beam assembly is usually accompanied by a loud cracking

sound. If this failure occurs while the aircraft is on the ground, the aircraft will immediately settle in the direc-

tion of the failed beam. The main rotor blades could drop 4 to 5 feet on the side of the failed drag beam. If

the failure occurs with the rotors static, minimize ground handling of the aircraft with a cracked or failed drag

beam. Attempting to move the aircraft with weight on the wheels and a cracked/broken drag beam is likely

to result in additional airframe damage and possibly personal injury. If the failure occurs while rotors are turn-

ing, the possibility of dynamic rollover exists. Do not attempt to ground taxi the aircraft. On board personnel

will remain inside the aircraft and the rotor disk will be kept clear until engine shutdown. Failure of the drag

beam during flight does not require any immediate corrective action by the pilot on the controls. If possible,

prior to each landing, a crewmember should visually check the drag beam for security. Every effort should

be made to prevent collateral damage to the landing gear and airframe by limiting any loading of the main

landing gear strut on the side of the failed drag beam during the landing.

WARNING

A failure of a main landing gear drag beam with the rotors turning creates an immedi-

ate hazard to personnel under the rotor system. This hazard will be minimized by limit-

ing the exposure time of personnel operating under the rotor system.