CHI03IA293

During a repositioning flight, the medical transportation helicopter executed a precautionary landing to a vacant parking lot after experiencing an in-flight vibration during cruise flight. The pilot stated that the flight time with the vibration was less than 90 seconds. An inspection of the helicopter revealed that the tail rotor counterweight bellcrank (p/n 222-012-727-003) used to hold counterweights had fractured in two pieces. A metallurgical examination of the bellcrank indicated that the bellcrank fractured as a result of a fatigue crack propagating from a casting discontinuity formed during manufacture. Three other occurrences of the same part number were found. The manufacturer issued an information letter to all owners and operators of Bell 222/230/430 helicopters advising them of the occurrences.

On August 19, 2003, at 1912 central daylight time, a Bell 230 helicopter, N880SF, operated by OSF Aviation LLC, executed a precautionary landing to a vacant parking lot near Wilmington, Illinois, after the helicopter encountered an in-flight vibration during cruise flight. The pilot and two crewmembers were not injured. The 14 CFR Part 91 medical positioning flight departed Gary Regional Airport (GYY), Gary, Indiana, at 1858, and was en route to the St. Francis Hospital helicopter landing zone (LL37), Peoria, Illinois. Visual meteorological conditions prevailed at the time of the incident. A company visual flight rules (VFR) flight plan was filed.

The pilot stated that while returning to LL37 the crew noticed a "sudden increase in vibration." He reported that he decided to land immediately with minimum of control inputs. He reported that he landed and shut down the helicopter without further incident. The pilot stated that the flight time with the vibration was less than 90 seconds.

An inspection of the helicopter revealed that the tail rotor bellcrank (p/n 222-012-727-003) used to hold counterweights had fractured in two pieces. The part was installed on N880SF at the time of aircraft manufacture and had accumulated 1,570.6 hours since new. A review of the maintenance records indicated that the tail rotor assembly had been inspected as part of the 150 hour component inspection conducted on July 31, 2003. The helicopter had a total time of 1,522.2 hours at the time of the 150 hour inspection and no defects were noted during the inspection.

The tail rotor bellcrank was sent to the Engineering Branch Laboratory of the Transportation Safety Board of Canada (TSB) for examination. The TSB engineering report stated that the bellcrank fractured as a result of a fatigue crack propagating from a casting discontinuity. It further stated, "Cadmium was found on the wall of the cavity indicating that the defect was present in the part before plating. The defect was not detected by a penetrant inspection of the finished part." (See TSB Engineering Report LP092/2003 included with the docket material associated with this factual report)

Bell Helicopter Textron reviewed their database to check if there had been similar occurrences. Their records indicated three occurrences of tail rotor bellcrank counterweight arm fractures since March 1989. They reported, "In each case, the fracture occurred in the arm inboard of the weights and none of the fractures resulted in an accident." The number of hours accumulated by the three failed parts were:

1. March 1989: Fatigue originating in casting porosity. Total part hours - 3,946.

2. February 1998: Fatigue originating in a mechanical scrape. Total part hours - 800.

3. June 2003: Fatigue fracture with no discontinuity at origin, however, pivot bearings worn. Total part hours - 6,897.

Bell Helicopter Textron issued an Information Letter 222-03-18, 2224-03-13, 230-03-08, and 430-03-33 on November 11, 2003. The information letter was issued to advise all owners and operators of Bell 222/230/430 helicopters of "occurrences affecting the tail rotor counterweight bellcrank P/N 222-012-727-003." The letter stated, "Bell Helicopter Textron has received reports of in-flight fracture and subsequent loss of a weighted portion of the tail rotor counterweight bellcrank. In each occurrence, a severe vibration was felt in the aircraft and a precautionary landing was carried out." The letter further stated, "Bell Helicopter Textron is actively seeking a solution to resolve this issue and in the near future all owners/operators will be notified of the corrective action." The letter also reminded owners and operators to check the condition and security of the tail rotor pitch change linkage during aircraft preflight and during the 150-hour component inspection contained in the maintenance manual. (See Bell Helicopter Textron Information Letter dated November 11, 2003, included with the docket material associated with this factual report)