NTSB Factual Report

HISTORY OF FLIGHT

On February 9, 2008, at 1115 central standard time, a Hughes OH-6A single-engine helicopter, N66372, was substantially damaged during a forced landing to a field after a loss of engine power near Valentine, Texas. The commercial pilot sustained serious injuries. The helicopter was registered to the United States Border Patrol Air Operations and operated by Customs and Border Protection (CBP). No flight plan was filed for the flight that departed Marfa Municipal Airport (MRF), near Marfa, Texas, about 1027. Visual meteorological conditions prevailed for the Public Use flight conducted under 14 Code of Federal Regulations Part 91.

The pilot self-dispatched from Marfa for the purpose of providing aerial assistance to ground agents who were pursuing undocumented aliens. Shortly after arriving on-scene, the pilot located the suspects and brought the helicopter into an out-of-ground-effect hover approximately 30-50 feet above ground level (agl). The pilot remained in a hover for approximately 2-3 minutes while directing other ground agents to assist when he simultaneously heard the "engine out" warning horn and felt the helicopter begin to drop and yaw to the right. The pilot stated that he transmitted a distress signal, maintained directional control, and cushioned the impact with the ground using collective.

Authorities from both the CBP and Federal Aviation Administration (FAA) examined the helicopter at the accident site on February 12, 2008, and reported that the helicopter came to rest in a wash-out. It remained upright, but the skids were completely spread, the tail rotor blades were damaged, and the fuselage sustained structural damage. Further examination of the engine revealed that a castellated nut used to secure the governor lever control rod to the idler bell crank had come completely loose, and the cotter pin that secured the nut was missing.

PILOT INFORMATION

The pilot held an commercial pilot certificate for airplane single-engine land, instrument airplane, and rotorcraft-helicopter. His last FAA second class medical was issued on January 11, 2008. The pilot reported a total of 2,014 hours; 379 hours in rotorcraft, of which 255 hours were in the OH-6.

The pilot had been employed by the U.S. Border Patrol since 1996 and became a pilot trainee in 2004. According to the CBP Mishap report, the pilot spent 2006-2007 building flight time and participating in directed aerial actions. In March 2007, he passed his 1,500 hour flight check and then completed training at the National Aviation Training Center (NATC) in El Paso, Texas, where he received his commercial rotorcraft-helicopter and instrument ratings. The pilot was then assigned as an OH-6 pilot-in-command (PIC)/Non-Enforcement Missions with a 200 foot agl limitation. On October 31, 2007, the pilot was given a "Clearance Authority Level 2" designation, which allowed him to clear his own flights. On November 29, 2007, he was designated as an OH-6 PIC/Maintenance Check Pilot/Night Vision Goggle (NVG) second in command (SIC).

HELICOPTER INFORMATION

The accident helicopter was manufactured in 1967 and had been in service with the U.S. Border Patrol since 1992. The airframe had accrued a total of 5,999 hours and the engine had been replaced approximately 5.1 hours prior to the accident on January 31, 2008. A 300-hour inspection was also completed at this time and the helicopter was released on February 6, 2008. The maintenance was conducted by civilian contract vendor in Alpine, TX. The vendor had extensive maintenance experience working on Hughes 500 helicopters, which is the civilian version of the OH-6. The contract mechanic was responsible for conducting the inspection, and the CBP was responsible for overseeing the maintenance inspection.

According to the CBP, there were no mechanics based at Marfa. As a result, the Marfa Supervisor, Air Interdiction Agent (SAIA) and the El Paso DAO elected to contract the maintenance conducted on the accident helicopter. This was the first time this contractor, Alpine Air, had worked on a CBP OH-6 helicopter. The helicopter was maintained using the United States Army OH-6A Technical Manual standards when being maintained at the Marfa base and the contract mechanics used the MD-500 standards during the 300-hour inspection. The owner of Alpine Air hired another certified airframe and power plant (A&P) mechanic to assist him with this inspection. According to the CBP mishap report, the two mechanics split the duties required in a 300-hour inspection and then check/signed off each other's work. The owner stated that during the first engine run-up, he discovered an oil leak on the left side of the engine. As a result, the engine was shut down and the linkages on the left side of the engine were disassembled, including the governor level control rod assembly. During the reassembly, he got "distracted" by a phone call, which delayed him from completing the repair. As a result, when he returned to complete the repair, he got "tunnel vision" and forgot to install the cotter pin during the reassembly process, which would have kept the castellated nut that secured the attachment bolt to the governor level control rod. In a subsequent conversation with an FAA aviation safety inspector, the mechanic also stated that he had disassembled the control idler support bracket for the N2RPM Governor. He removed the bracket, changed the seal, and reinstalled the bracket without checking the governor lever control rod attachment bolt.

On February 6, 2008, the accident pilot performed a maintenance acceptance inspection, which included a thorough preflight, and did not find any maintenance discrepancies. He then performed a maintenance test flight and no anomalies were noted. The following day, the helicopter was flown to Marfa, and tied down overnight. The next day, the pilot and the base Aviation Maintenance Officer (AMO) agreed to perform a main rotor blade track and balance inspection. Again, no anomalies were noted, and the helicopter was returned to service. The third, and fourth flight, was a 2.0 hour mission, and again, no maintenance discrepancies were noted. The fifth flight was the mishap flight. The accident pilot was at the control of the helicopter for all five flights and had performed five separate preflight inspections before each flight.

METEOROLOGICAL INFORMATION

Weather at Marfa Municipal Airport, about 38 miles southeast of the accident site, at 1115, was reported as calm wind, visibility 10 miles, clear skies, temperature 54 degrees Fahrenheit, dewpoint 28 degrees Fahrenheit, and a barometric pressure setting of 30.23 inches of Mercury.

ADDTIONAL INFORMATION

A review of the OH-6A Technical Manuals revealed that only a standard castellated nut and cotter pin was needed to properly install the governor lever control rod, while the more recent Hughes 500 repair manual and an FAA Airworthiness Directive required a castellated nut with fiber inserts to prevent the nut from backing off.

In addition, a review of the helicopter's preflight checklist only indicated that the pilot needed to check the engine compartment before each flight. The checklist did not specifically state that each linkage need to be individually examined.

According to the CBP mishap report, there were no written maintenance policies in effect to ensure quality control in the performance of the contract maintenance. The Marfa Supervisor had established verbal policies regarding oversight only, which included that the AMO would inspect the work, and that he created a Maintenance Check Pilot program with his most qualified pilot, who was the accident pilot.

NTSB Probable Cause

The contract mechanic's failure to properly secure the castellated nut that attached the governor lever control rod to the idler bell crank. Contributing to the accident was the lack of maintenance oversight by the operator.