FTW93FA163

Factual narrative

HISTORY OF FLIGHT: On May 25, 1993, at approximately 0914 central daylight time, a Messerschmidt Boelkow Blohm BK 117 A-4 helicopter, N401PH, sustained substantial damage at Lafayette, Louisiana, during final approach for landing. The airline transport rated pilot and passenger (mechanic) did not sustain injury. Visual meteorological conditions prevailed throughout the area for the maintenance test flight. During personal interviews conducted by the investigator in charge and Federal Aviation Administration inspectors, with the pilot, witnesses, and company management personnel, the following information was revealed. The helicopter was being operated in the experimental category for the purpose of research and development modification. A series of ground runs had been completed within 72 hours prior to this first maintenance operational test flight. During the flight, a series of maneuvers had been completed and the pilot was returning to the ramp area. As the helicopter approached the hover mode, during final approach to the grass area adjacent to runway 11, the helicopter started to roll to the right. Application of left cyclic had no effect on the roll. The main rotor blades struck the runway as the helicopter continued to roll, entered an approximate 90 degree bank angle and then skidded to a stop on runway 11. The pilot revealed the information in this paragraph, during a personal interview conducted by the investigator in charge. He and the mechanic were going to check the helicopter systems and blade tracking. The maneuvers included takeoff, slow flight, pattern work, pedal turns, control movements, climb, descent, and the final approach to hover. During the hover flare at approximately 20 feet above ground level, the collective control was positioned approximately 3/4 up and the lateral cyclic control was placed slightly left of center and forward. The helicopter did not respond to the left cyclic input. As the pilot attempted to input more lateral cyclic, movement to the left was restricted. PERSONNEL INFORMATION: The pilot had received initial and recurrent company training in the BK 117 helicopter. He had satisfactorily completed a Title 49 Code of Federal Regulation Part 135 flight check on August 8, 1992, in the BK 117 helicopter. Training and flight checks included system control functions and limitations. AIRCRAFT INFORMATION: The helicopter was approved on February 19, 1991, for transport from Canada to the United States of America. Exportation records indicated that helicopter model BK 117 A-3 had been converted to model BK 117 A-3D. The owner and operator revealed the information in this paragraph during personal interviews conducted by the investigator in charge. The helicopter, registered as N501AL, was transported disassembled via ground vehicle to the operator in December, 1992. Assembly, modification to an A-4, and an annual inspection of the helicopter, was originally planned. Subsequently, the operator leased the helicopter and made plans for developing and modifying the helicopter for air ambulance operations. On May 4, 1993, the owner received a research and development experimental airworthiness certificate from the Federal Aviation Administration for the modification project. The operator air ambulance contract required the helicopter to be operational by June 1, 1993. With numerous supplemental type certificate modifications planned, the operator implemented a 24 hour maintenance work schedule for the project in order to meet the operational date. A review of the maintenance records and interviews with the mechanics by the investigator in charge, the Federal Aviation Administration inspectors, and company management personnel revealed the information in this paragraph. The helicopter flight controls were rigged on the night shift of May 7, 1993; however, they were not safety wired as the day crew shifts on May 8, 1993, were going to go over the rigging procedure. Following the review of the rigging procedures, without supervision, on May 8, 1993, the mechanics remembered the vertical control tubes being placed on a parts rack. The procedures of May 8, 1993, were not recorded on work orders. On May 9, 1993, work orders indicated the flight control system approved for return to service. The company maintains the flight controls as a compulsory check item for an aircraft to be returned to service. All mechanics who had returned the aircraft to service missed the color coding of the main rotor vertical control tubes. On May 17, 1993, after the helicopter came out of the paint shop, mechanics noted that two cannon plugs, for the stability augmentation system, were color coded incorrectly. The cannon plugs were located on top of the cabin roof on the right side of the hydraulic packs forward of the vertical control rods. Mechanics recolor coding the cannon plugs noted the color coding on the vertical collective and lateral control rods did not match the coding on the remaining control rods. The mechanics noted that the control rods were safety wired and sealed. After checking the work order, which indicated the system as rigged and returned to service, the mechanics, without supervision, color coded the control rods, painting red over white, and white over red. On the morning of May 25, 1993, a mechanic released the aircraft for the flight evaluation. WRECKAGE AND IMPACT INFORMATION: The helicopter impacted approximately 1,000 feet from the approach end of runway 11 at Lafayette Regional Airport, Lafayette, Louisiana. Gouges and striations were observed in the asphalt runway surface approximately 150 feet beyond the helicopter. The helicopter came to rest on its right side on a measured magnetic heading of 195 degrees. Numerous pieces of main rotor blades were located in the area surrounding the helicopter. TEST AND RESEARCH: Swash plate pitch change links, control rods, bearings, bushings, and sleeve components were forwarded to the NTSB metallurgical laboratory for examination. All component fractures were overstress separations. All bearings were free to rotate. During an examination of the flight controls on May 26, 1993, by the investigator in charge, the manufacturer, and the operator, the following was revealed. The vertical collective control rod, adjusted to a 360 millimeter length, color coded red, was installed in the lateral control rod position. The red paint was over white paint. The lateral control rod, adjusted to a 371 millimeter length, color coded white, was installed in the collective rod position. The white paint was over red paint. A rigging check indicated the rod was out of rig approximately 10 millimeters. When the control rods were correctly connected in their respective positions, the rigging was within specifications. Test and calculations (enclosed report) by the manufacturer indicated severe lateral control problems during the flare maneuver with the movement of the left lateral cyclic restricted approximately 50 percent. ADDITIONAL INFORMATION: The helicopter was released to the operator following the investigation. AFTER EXPORTATION FROM CANADA, MBB BK 117 HELICOPTER WAS BEING RE-ASSEMBLED & MODIFIED FROM MODEL A-3 TO MODEL A-4; 24 HOUR/DAY SCHEDULE WAS USED TO EXPEDITE MODIFICATION FOR USE AS AIR AMBULANCE. SHIFT CHANGE OCCURRED DURING MAINTENANCE ON VERTICAL CONTROL TUBES; WHEN COMPLETED, HELICOPTER WAS FLOWN ON TEST FLIGHT. NO ANOMALIES OF FLIGHT CONTROLS WERE NOTED UNTIL FLARING TO HOVER BEFORE LANDING. PILOT SAID THAT WHILE POWER WAS BEING APPLIED, CYCLIC & PEDALS WERE MANIP- ULATED ACCORDINGLY. LEFT MOVEMENT OF CYCLIC WAS REQUIRED TO OVERCOME (ROLL &) DRIFT TO RIGHT. AT THAT TIME, THE PILOT NOTED INSUFFICIENT CYCLIC CONTROL & THE HELICOPTER CONTINUED TO ROLL RIGHT UNTIL THE MAIN ROTOR BLADES STRUCK THE GROUND. THE HELICOPTER THEN IMPACTED ON ITS RIGHT SIDE & SLID TO A STOP. AN INVESTIGATION REVEALED THE LATERAL & COLLECTIVE UPPER ADJUSTABLE CONTROL RODS HAD BEEN INTERCHANGED & COLOR CODING REPAINTED. THE INTERCHANGE OF CONTROL RODS RESULTED IN A MISRIGGED SWASHPLATE WITH A HIGHER PRESET COLLECTIVE PITCH & A RIGHT TILT OF THE SWASHPLATE. Source: NTSB Aviation Accident Database (Pre-2008 Archive) Retrieved: 2026-02-12