Sikorsky S-76 Series Helicopters, AD/S-76/71 Rotor Brake Disc 4/2003
Applicability: Model S - 76A, B, and C helicopters.
Requirement: 1. Determine the manufacturer of each rotor brake disc (RBD) by examining the part number (P/N) markings and accomplish the following requirements based on the identification of the RBD.
a. If the P/N is 76363-09101-102, the manufacturer is Goodyear. No further action is required by this directive.
b. If the P/N 76363-09103-102 is pressure stamped on the RBD, the manufacturer is BF Goodrich. No further action is required by this directive.
c. If the P/N 76363-09103-102 is electrolytically etched on the RBD, the manufacturer is Parker Hannifin Corporation (PHC).
i. For each PHC RBD with a P/N 76363-0913-102 and serial number (S/N) other than 38 through 379, remark the P/N as 76363-090103-105 using the vibropeen method. After remarking no further action is required.
ii. If the RBD serial number or the manufacturer cannot be determined and for RBD’s with P/N 76363-09103-102 and S/N’s 38 through 379, reidentify or mark the P/N as 76363-09103-104, or replace the RBD in accordance with requirement 3 of this directive.
2. For RBD’s with P/N 76363-0103-104, inspect the RBD for cracks as detailed in Figure 1.
a. If a crack is found extending through the entire RBD thickness as detailed in Figure 1, View A, replace the RBD with a serviceable RBD other than P/N 76363-09103-104.
b. If 2 or more surface cracks are found located between adjacent boltholes as shown in Figure 1, View B, replace the RBD with a serviceable RBD other than P/N 76363-09103-104.
c. If a surface crack, or surface cracks are found separated by boltholes as shown in Figure 1, View C, replace the RBD with a serviceable RBD other than P/N 76363-09103-104, or deactivate the RBD before further flight.
Note 1: Short “glazing” cracks are not a cause for rejection.
...This Airworthiness Directive becomes effective on 4 March 2003.
Background: Certain rotor brake discs were found to be manufactured using an incorrect heat treatment process of the disc. This can lead to premature cracking and subsequent failure of the discs. This directive requires identifying certain discs, inspection of these discs and eventual replacement of these discs. Failure of the disc could cause damage to the rotor blades, nearby hydraulic and fuel lines, and subsequent loss of control of the helicopter.

FMI: Casa's AD