NTSB · Safety Recommendation
Safety Recommendation A-70-048
Recommendation
THEREFORE, WE RECOMMEND THAT ALL BELL 47 MODEL HELICOPTERS, EQUIPPED WITH FIXED FLOTATION ASSEMBLIES THAT HAVE NOT BEEN APPROVED BY THE MANUFACTURER, BE RESTRICTED FROM FURTHER FLIGHT UNTIL THE AIRWORTHINESS STANDARDS REQUIREMENTS OF PARTS 27.413, 27.571, AND 27.1503 HAVE BEEN EVALUATED AND APPROVED FOR THIS TYPE OF INSTALLATION.
Safety Issue and Context
FOR A NUMBER OF YEARS, THE BOARD HAS BEEN CONCERNED ABOUT THE NUMBER OF ACCIDENTS CAUSED BY FATIGUE FAILURES IN THE TAIL ROTOR BLADES OF BELL MODEL 47 HELICOPTERS. THIS HAS RESULTED IN THE FAA ISSUING AIRWORTHINESS DIRECTIVES AS DEEMED NECESSARY. SUBSEQUENT TO THE ISSUANCE OF AD 68-2-3, EFFECTIVE JANUARY 19, 1968, AND PRIOR TO JANUARY 10, 1970, WE HAD ONLY LIMITED KNOWLEDGE OF ONE ADDITIONAL FATAL ACCIDENT DUE TO A FATIGUE FAILURE OF A BELL MODEL 47 TAIL ROTOR BLADE WHICH OCCURRED IN BERN, SWITZERLAND, ON NOVEMBER 21, 1968.
HOWEVER, ON JANUARY 10, 1970, ANOTHER FATAL ACCIDENT OCCURRED APPROXIMATELY 7 1/2 MILES NORTH OF HEALY, ALASKA, DUE TO ANOTHER FATIGUE FAILURE SEPARATION OF A TAIL ROTOR BLADE. THE HELICOPTER INVOLVED, AN ALTERED BELL MODEL 47J-2, N944NA, OPERATED BY ANCHORAGEHELICOPTERS, CRASHED ON THE ICE-COVERED NENANA RIVER AFTER SUSTAINING THE IN-FLIGHT SEPARATION.
Response History
December 1, 1970 · Recipient Response · FAA
12/1/70 FAA STATES THEY HAVE COMPLETED THEIR INVESTIGATION OF THE BOARD'S RECOMMENDATION TO GROUND ALL BELL-47 MODEL HELICOPTERS HAVING GOODYEAR P/N 4053-111 FLOATS AND FIND NO BASIS TO BELIEVE THAT THE HELICOPTER HAD THE GOODYEAR FLOATS INSTALLED OR THAT THE FLOAT LANDING GEAR HAD AN EFFECT ON THE TAIL ROTOR BLADES. EVIDENCE INDICATED THAT THE BELL P/N 47-351-014-3 (AIRCRUISERS P/N 2383) FLOATS WERE INSTALLED AT THE TIME OF THE ACCIDENT. APPROVAL FOR THE INSTALLATION OF GOODYEAR P/N 4053-111 FLOATS ON BELL 47 HELICOPTER HELD BY UTILITY HELICOPTERS HAS DISCLOSED NO DEFICIENCY IN THIS APPROVAL AND NO EVIDENCE OF NON COMPLIANCE WITH CAR 6.221, 6.224, AND 6.710.
SERVICE RECORDS AND ACCIDENT REPORTS SHOW THE AD70-10-8 PROVIDES FOR THE SAFE OPERATION OF HELICOPTERS EQUIPPED WITH BELL METAL TAIL ROTOR BLADE P/N 47-742-102. 5/25/71 THE FAA ACKNOWLEDGED THE BOARD'S LETTER OF MAY 10, 1971, AND STATED THEY WERE REVIEWING THE ADDITIONAL EVIDENCE. 9/21/71 - THE FAA RESPONDED STATING THAT THE ADDITIONAL EVIDENCE AND WITNESS STATEMENTS HAD BEEN CONSIDERED EARLIER, AND FROM THEIR ANALYSIS OF THE ACCIDENT THEY FOUND NO REASON TO TAKE FURTHER ACTION. THE UNUSUAL CONTROL PROBLEMS DESCRIBED BY THE EMPLOYEE PILOT WAS TYPICAL WITH INADEQUATELY INFLATED FLOATS.
THEY CONCLUDED FROM THEIR SURVEYS THAT NO UNSAFE CONDITION DEVELOPED IN BELL 47J-2 TAIL ROTORS FROM THE POSSIBLE INSTALLATION OF GOODYEAR FLOAT BAGS IN LIEU OF BELL FLOAT BAGS. ALSO, THE SERVICE RECORD OF BELL 47J-2'S EQUIPPED WITH EITHER FLOATS, SHOWED THAT THE FATIGUE LIFE OF THE TAIL ROTOR TO BE UNAFFECTED EXCEPT WHEN INADVERTENTLY ALLOWED TO CONTACT THE WATER. AD 70-10-8 WAS CONSIDERED ADEQUATE TO PROTECT AGAINST FATIGUE FAILURES OF THE TAIL ROTOR BLADE.