AD: 2004-SW-09-AD.

Applicability: Model 234 helicopters, with aft vertical shaft assembly, part number (P/N) 234D3300, serial number -181 or lower with a prefix of A, installed, certificated in any category.

Compliance: Required as indicated.

The FAA has issued an Emergency AD on Boeing Defense And Space Group Model 234 Helicopters. The Emergency AD was "prompted by the discovery of a crack in the upper shaft extension of an aft vertical shaft assembly (assembly). The discovery was made by an operator who was in the process of troubleshooting a lateral vibration and noticed a slight wobble in the assembly when the rotors were turned by hand. The manufacturer subsequently determined that the crack initiated at an arc burn that occurred during the silver-plating process of the part. This is an interim action that is necessary until an arc-burn free replacement assembly is installed. A crack in the upper shaft extension could result in catastrophic failure of the assembly and subsequent loss of control of the helicopter."

The FAA has reviewed Boeing BV234 Service Bulletin No. 234-63-1055, Revision 2, dated March 16, 2004, which describes procedures for inspecting the inside diameter surfaces of the 114D3248 upper shaft extension of the 234D3300 aft vertical shaft for cracks. The service bulletin also describes procedures for fabricating and installing an aluminum inspection plug. Further, the service bulletin provides for recurring inspections. This unsafe condition is likely to exist or develop on other helicopters of the same type design. Therefore, this AD requires, before further flight, inspecting the upper shaft extension for a crack and modifying the assembly. Thereafter, this AD requires, before the first flight of each day, inspecting the upper shaft extension for any crack. If any crack is found during any of the inspections, replacing the assembly with an airworthy assembly is required before further flight.

FMI: Text of Emergency AD 2004-SW-09-AD