LAREDO, TX, USA
N6638R
Hughes OH-6A
The engine decelerated and the pilot heard the sound of the engine out audio and observed the red engine out warning light illuminated. When the pilot lowered the collective to enter an autorotation, the engine and rotor RPM increased. The pilot then rolled the throttle off to regain control of the engine RPM. During touchdown, the helicopter landed hard, and the main rotor blades contacted the tailboom. A test run of the engine in a test cell revealed that the engine RPM was not controllable above flight idle, and the engine had a tendency to overspeed and overtemp when the power was advanced. The engine power turbine governor was removed and replaced with an operational unit. The engine operated within normal operational parameters after the governor was replaced. Examination concluded that the failure of the governor's drive shaft bearings resulted in excessive radial and axial play of the drive shaft, which led to a reduced fuel flow to the engine.
On December 27, 1998, at 1158 central standard time, a Hughes OH-6A helicopter, N6638R, was substantially damaged during a forced landing following a loss of engine power while maneuvering near Laredo, Texas. The instrument rated commercial pilot, sole occupant of the helicopter, sustained minor injuries. The helicopter was owned and operated by the U.S. Border Patrol of El Paso, Texas. Visual meteorological conditions prevailed for the Title 14 CFR Part 91 aerial observation flight for which a VFR company flight plan was filed. The local flight originated from the Laredo International Airport at 1030. The operator reported that the helicopter was maneuvering at slow airspeed at an altitude between 75 and 100 feet above the ground, while assisting ground personnel tracking a group of individuals suspected of being illegal aliens, approximately 20 miles northwest of Laredo, Texas. The operator reported that the engine decelerated and the pilot heard the sound of the engine out audio and observed the red engine out warning light illuminated. When the pilot lowered the collective to enter an autorotation, the pilot reported that the engine and rotor RPM increased. The pilot then rolled the throttle off to regain control of the engine RPM. The pilot reported that he initiated the autorotation to a sandy trail. The helicopter touched down hard with forward airspeed, bounced once, and impacted the terrain in a nose low attitude. The main rotor blades made contact with the tailboom. The helicopter came to rest in the upright position on a measured heading of 148 degrees. The 38 year-old pilot had accumulated a total of 2,741 flight hours, of which 285 hours were in helicopters. All of the pilot's helicopter time was in the OH-6A helicopter. Examination of the helicopter by the operator's maintenance personnel revealed that the airframe sustained structural damage. Additionally, the outer halve of the tailboom, the tail rotor gear box and one of the main rotor blades separated from the helicopter. The Allison T-63-A-720 engine, serial number AE405401, was removed from the helicopter for further examination and testing. The engine was run in a test cell at the Dallas Airmotive facilities in Dallas, Texas, on January 19, 1999. The test run revealed that the engine RPM was not controllable above flight idle, and the engine had a tendency to overspeed and overtemp when the power was advanced. The engine power turbine governor was removed and replaced with an operational unit. The engine operated within normal operational parameters after the governor was replaced. See enclosed report from the engine manufacturer for details of the test run and examination. The model AL-AA1 power turbine governor, serial number BR367390, Allied Signal part number 2524912, was examined at the Allied Signal (Bendix) facilities in South Bend, Indiana, on March 10, 1999. The examination concluded that the failure of the governor's drive shaft bearings resulted in excessive radial and axial play of the drive shaft, which led to a reduced fuel flow to the engine. See enclosed report from Allied Signal for details of the examination.
The loss of engine power as result of the failure of the power turbine governor. A factor was the lack of suitable terrain available to the pilot for the forced landing.
Source: NTSB Aviation Accident Database
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