LAX00TA318

The probable loss of the main rotor tip weight on the red blade for undetermined reasons resulting in main rotor vibration and oscillation. Sideward movement during the ensuing emergency landing resulted in a dynamic rollover.

During takeoff from a heliport atop a 10-story parking structure, the pilot heard a 'loud pop or snapping sound' as the helicopter transitioned to forward flight and then sensed a main rotor imbalance and vibration. The pilot returned to the heliport and landed on the skids, however, the helicopter subsequently rolled over and came to rest on its left side. Subsequent examination of the helicopter showed the skid cross tubes were displaced approximately 2 inches to the right in their fuselage attachment bushings and the main rotor transmission was inclined approximately 20 degrees to the right and 10 degrees forward. Examination and testing of the hydraulic pump, three flight control servos and two hydraulic filters revealed no anomalies. The tip of one main rotor blade and part of one pitch change link were not located after the accident. The mating end of the pitch change link exhibited bending along its length and crippling at the separation point consistent with overload failure.

On August 29, 2000, at 1535 hours Pacific daylight time, a Bell 206L-1, N5758H, was substantially damaged when the helicopter landed hard and rolled over on the rooftop heliport and came to rest on its left side. The hard landing and rollover were preceded by a main rotor system imbalance during the transition from hover to forward flight at Los Angeles, California. The certificated airline transport pilot, the sole occupant, received minor injuries. The helicopter was operated by the Los Angeles County Sheriff's Department as a public-use aircraft under 14 CFR Part 91. Visual meteorological conditions prevailed and no flight plan was filed. The repositioning flight was destined for Long Beach, California. The heliport is located atop a 10-story parking structure serving the Sheriff's Department's Men's Central Jail. The street address is 441 Bauchet Street, Los Angeles. The heliport is elevated one additional story above the top parking level, and is about 150 feet square with the sides oriented facing northeast, southeast, southwest, and northwest. The pilot was a reserve pilot for the department who was regularly employed as an airline pilot. About 1 week prior to the accident he completed a sheriff's department training program of about 10 flight hours duration. The training included landings at all of the area helipads including the accident site. The pilot reported he also regularly flew a Sikorsky S-76 helicopter to confined landing sites on offshore oil platforms. According to the pilot, he completed a roundtrip flight from the sheriff's department operations base at Long Beach to Catalina Island in the morning, and was then assigned to conduct an aerial photo mission from the Central Jail heliport. He departed Long Beach about 1455 and landed at the helipad (where the accident later occurred) about 1505. After picking up two photographers, he departed from the helipad, accomplished the photo mission, and returned to the helipad at 1525. After deplaning the two passengers, he was departing, alone in the helicopter, to return to Long Beach when the accident occurred. He reported there were no discrepancies with the helicopter during the photo mission flight. He recalled that the surface winds, reported at the nearby Hoover Heliport, were from the southwest at 6 knots. The pilot reported he departed from the center of the heliport, and headed southwest into the wind. After he lifted to a 3-foot hover height and was transitioning to forward flight he heard "a loud snap or popping sound," and experienced the "main rotor system was oscillating and out of balance." He later recalled he could see that the two main rotor blades were no longer tracking in the same plane. He was able to return the helicopter to the helipad and landed on both skids, however, the helicopter subsequently rolled onto its left side. After the accident the helicopter was lying on its left side, pointed northwest, and located about 10 feet from the northeast edge of the heliport. The helicopter was examined by the Safety Board investigator at the facilities of the Los Angeles County Sheriff's Department Aero Bureau in Long Beach on September 7, 2000. The entire helicopter was present except for about 1 foot of the tip of the red-dot main rotor blade and half of the white-dot blade pitch change link. There was no fire. An early responder confirmed turning off switches and circuit breakers, and specifically confirmed moving the flight control hydraulic switch to the "off" position. The fuselage was upright on its landing skids and exhibited modest crushing damage to the left side. The skid cross tubes were displaced approximately 2 inches to the right in their fuselage attachment bushings. The main rotor system had been previously removed to facilitate recovery. The blades were unbolted from the hub; the hub was unbolted from the mast; and the mast was unbolted from the transmission. The tail boom sheet metal structure was separated about 1 foot aft of the juncture with the fuselage; however, the tail rotor drive shaft, the anti-torque push-pull tube, and the stabilizer trim push-pull tube had been unbolted during the recovery. The ceiling structure of the cabin exhibited a downward deformation of about 6 inches in proximity of the transmission and the engine. The transmission was inclined approximately 20 degrees to the right and 10 degrees forward with respect to the fuselage. The tail boom sheet metal separation exhibited a torn or shredded appearance circumferentially over about 12 inches. When the battery was connected and the battery switch turned on, the fuel quantity indicated 360 pounds, the fuel shutoff valve functioned audibly, both fuel pumps functioned audibly, and the fuel pressure indicated in the green arc of the indicator. The transmission chip annunciator light was illuminated, however, when the detector plug was removed from the transmission there was no contamination visible and, when the plug was reinstalled, the transmission chip annunciator was extinguished. The left-hand side of the cyclic control system was intact from the cyclic control to the swash plate. The right-hand side of the cyclic control system was intact within the cabin; however, the frame of the servo actuator was broken with associated bending and the longitudinal push-pull tube was separated at the bellcrank forward of the transmission. The collective control system was similarly intact within the cabin but was separated with associated bending at the servo frame. The anti-torque control system was intact except for two separations in the area where the fuselage ceiling was deformed beneath the engine and transmission. All of the control system fracture surfaces exhibited a uniform, shiny, gray appearance. The engine N1 and N2 stages and associated accessory gearing turned freely when rotated by hand. An irregular shaped section of the swirl tube array about 6 inches across was broken out and there was visible minor damage to the leading edges of the first stage compressor blades. The pneumatic system was pressure tested and no leaks were detected. The fuel and oil filters were clear and the fuel filter bowl was full of clear liquid resembling jet fuel. The engine sump and freewheeling unit chip detectors were free of matter. When rotated by hand, the portion of the tail rotor drive shaft running forward in the aft fuselage to the engine accessory section engaged the overrunning clutch and turned the N2 section of the engine freely and smoothly. The overrunning clutch released when rotated in the opposite direction. The "short shaft" was disconnected but was lying in place between the engine and the transmission. The fingers of the k-flex couplings were separated, however, the surfaces of the separated fingers exhibited a uniform, shiny, appearance. The main transmission turned freely and smoothly when rotated by hand. The main transmission oil was clear and amber brown in appearance. The transmission oil quantity was depleted, however, early responders reported a substantial amount of oil leaked out onto the helipad before the helicopter was righted. The tail boom was intact aft of the separation point from the forward fuselage except for the right-hand vertical fin, which was separated from the horizontal stabilizer. The inboard surface of the fin exhibited an impact mark from upper front to lower rear. The radius of the dent resembled that of the main rotor blade leading edge. The anti-torque control system was intact and operated smoothly through the tail rotor blade pitch change mechanism. The tail rotor drive shaft, which had been unbolted at the coupling to the forward fuselage, was intact and the shaft, gearbox, and tail rotor turned freely by hand. Approximately 1 inch of each tail rotor blade tip was worn off irregularly and the remainder of the blades exhibited a very slight bend inboa