N911JN

HISTORY OF FLIGHT

On March 14, 2000, at 1911 hours Pacific standard time, a Bell OH-58C, N911JN, collided with a trailer and the ground during an autorotation at Compton, California. The autorotation was precipitated by pilot perceived malfunctions in the electrical and hydraulic systems during cruise. The helicopter was owned and operated by the Compton Police Department as a public-use aircraft and was engaged in a routine law enforcement patrol mission. Visual meteorological conditions prevailed at the time and no flight plan was filed. The helicopter was destroyed in the ground collision sequence. The private pilot and an observer, the sole occupants, sustained minor injuries. The local area patrol flight originated from the Compton Municipal Airport at 1730.

According to the statements of the pilot and observer, their shift began at 1600 and they conducted a full preflight inspection of the helicopter prior to the 1730 takeoff. The pilot stated that there were no maintenance items carried forward for this flight. A 1-hour routine patrol mission was flown and they landed at a remote refueling pad and conducted a hot refueling to maximum tank capacity, then took off again about 1840 to continue their patrol. They responded to a traffic accident call about 1900 and orbited the location in left turns. Following release from the call, the pilot exited the orbit. Shortly after that, the pilot and observer noticed that the low rotor rpm warning light flashed on, then back off, then on again. The pilot used the push to test switch and the light returned to normal operation. The pilot checked the tachometer and noted normal rotor and engine rpm. The helicopter was only 3 miles from their base at the Compton airport and the pilot decided to return to base and have maintenance examine the helicopter.

The low rotor warning light then began to flash on and off, with an increasing frequency. Shortly thereafter, the low rotor light came on steady. Suddenly all the cockpit warning and caution lights illuminated, both on the eyebrow panel and center pedestal panel. Concurrent with illumination of the warning and caution lights, the hydraulic system turned off and the pilot had to resort to manual force on the flight controls. The pilot checked the engine and rotor gages and noted that the rotor needle on the tachometer was registering off scale high; however, neither he nor the observer perceived any change in the background engine and rotor sounds. The observer reported that he believed they lost their radios and exterior lights at this time. In his interview, the observer reported that the engine and rotor tachometer needles were married together at 100 percent until the autorotation.

During this period, the pilot had been on an extended final approach to runway 25 left and control of the helicopter was becoming difficult. Suddenly, a fixed wing airplane appeared on base leg to the same runway and the pilot had to maneuver to avoid a collision. According to the pilot, with the control difficulties and uncertainty about what was happening to the helicopter, he decided to autorotate to a clear area in a schoolyard. Both the pilot and the observer stated that during the autorotation the night sun spotlight went out. The pilot cleared a building but could not avoid a tractor-trailer rig that he had not observed before. The helicopter collided with the trailer, then the ground, and rolled over on its back.

In his interview, the pilot stated that he was familiar with the hydraulic system and knew that the solenoid valve was electrically operated and it takes electrical power to close the valve and turn off the hydraulics; he stated that he was aware that the valve fails to the open position when electrical power is lost.

PERSONNEL INFORMATION

The pilot is a patrol officer with the Compton Police Department, assigned as a helicopter pilot with the department's air unit. Review of the Federal Aviation Administration (FAA) airman records database disclosed that he holds a private pilot certificate, with a rotorcraft helicopter rating, which was issued December 6, 1996. In addition, the pilot holds a second-class medical certificate that was issued without limitations on December 23, 1997. The pilot reported that he began flying in 1996 with assignment to the air unit and completed his primary training in the OH-58. The pilot estimated that he has accrued about 3,000 hours in helicopters, all of it in the OH-58, with about 1,500 hours flown in the accident helicopter. His total night experience is about 2,400 hours. The air unit instructor pilot conducted the pilot's most recent biennial flight review on December 13, 1998.

The observer is a patrol officer with the Southgate Police Department and is assigned as an observer with the Compton Police Department air unit. He does not have any aeronautical pilot licenses or ratings. He has been an observer with the Compton Air Unit for 4 months and has flown in the OH-58 about 300 hours.

AIRCRAFT INFORMATION

The helicopter, a Bell OH-58C, serial number 68-16751, was obtained from military surplus by the Compton Police Department in June 1996 and certificated in the Restricted Category. During military service, the US Army operated the helicopter.

Mission specific equipment, including police band radios and a night sun spotlight, were installed by contractors to the Air Unit maintenance department in accordance with FAA Forms 337. Review of the documents and examination of the helicopter revealed that the wiring met the recommendations for gauge standard and circuit protection specified in FAA Advisory Circular 43.13-1A.

The maintenance program utilized by the Air Unit consisted of the inspections and procedures specified in the US Army OH-58C maintenance manual, TM 55-1520 228-23-1 and -2. The most recent 100-hour inspection was accomplished on March 3, 2000, 77 hours prior to the accident. Review of the maintenance records disclosed that all life-limited components were within the specified time limits.

METEOROLOGICAL INFORMATION

The closest aviation meteorological observation station is the Hawthorne, California, airport, which is located 7 miles west of the accident site. At 1953, the station was reporting clear skies with visibilities 4 miles in haze. A Safety Board computer program calculated that the Nautical Twilight ended at 1855. At the time of the accident, the moon was 75 degrees above the horizon on a bearing of 134 degrees; 71 percent of the disk was illuminated.

WRECKAGE AND IMPACT

The accident site is in a side yard of a high school campus about 1/4-mile from the approach end of runways 25L and 25R at the Compton Municipal Airport. All wreckage components were located within the confines of the yard. The helicopter was laying on its right side. Markings consistent with the color and dimensional geometry of the skids were noted on the roof of the trailer.

The right frontal area of the helicopter nose was crushed rearward. The crush line was oriented about 40 degrees to the horizontal axis (nose down), and, 20 degrees to the lateral axis (left yaw). The tail boom remained attached to the fuselage; however, it was buckled downward at a point just aft of the horizontal stabilizer. The tail rotor blades were retained in their grips and undamaged. The upper and lower vertical stabilizers, including the stinger, were intact and undamaged.

The skids and the forward and rear cross tubes were spread and deformed upward. The right skid was separated from the rear cross tube at the skid attach point. The right skid forward cross tube was fractured and separated at the fuselage attach point. The left skid remained attached to the forward and rear cross tubes. The left forward cross tube was fractured and separated from the fuselage attach point. The left rear cross tube remained attached to the left skid and the fuselage.

The white main rotor blade remained attached to the hub grip. The outboard 3 feet of the blade was smoothly curved rearward, with span wise compression wrinkles noted along the trailing edge. The entire blade is bent downward about 15 degrees at a point about 42 inches outboard of the grip. Minor leading edge damage and cord wise scoring is noted on the outboard one third of the blade.

The red main rotor blade was fractured in two places, at 40 inches outboard of the grip pin and 31 inches inboard from the tip. Leading edge damage, chordwise scoring and trailing edge compression wrinkles were noted.

The main rotor hub, grips, and pitch horns were intact. The pitch change links were separated just below the clevis connection to the pitch horns. The links were deformed and the fracture faces angular and shinny. Main rotor drive shaft failed about 2 inches above the center of the droop stop with torsion and bend deformation evident.

The main and tail rotor transmissions rotated freely in both directions. The tail rotor transmission remained attached to the tail boom. The main rotor transmission lower isolation mounts were broken and the entire transmission had rocked forward and contacted the upper deck.

The hydraulic pump was broken from the front of the transmission. A dent matching the dimensional geometry of the pump was noted on the deck directly below the pump. The pumps attach lugs were fractured, with the fracture face angular and shiny. The pump drive coupling shear point was intact.

The engine to transmission drive shaft was connected at both ends; however, rotational scoring was noted where the shaft passes through the transverse bulkhead. The tail rotor drive shaft was separated between the Nos. 5 and 6 hangar bearings, with rotational scoring evident on both sides of the fracture point; the shaft was torsionally deformed at the fracture point.

TESTS AND RESEARCH

The helicopter was recovered from the accident site to the Compton Airport where a detailed examinat...