19980718044219A

(.19)On July 18, 1998, at 1625 hours pacific daylight time, a Sikorsky CH-54A, N54KL, en route to apple valley California, crashed after experiencing a main rotor blade separation and a subsequent in-flight explosion and fire. The aircraft was destroyed and the three crewmembers sustained fatal injuries. The aircraft was being operated as a repositioning flight by heavy lift helicopters, inc., when the accident occurred. The last leg of the flight originated in blythe, California, about 1543 on the afternoon of the accident. Visual meteorological conditions prevailed at the cruising altitude and a company flight plan was filed. A witness/pilot, who was in the chalk 2 position of the flight of two aircraft, reported that he was in loose trail about .25 to .50 miles behind the accident aircraft when he saw a rectangular shaped object suddenly separate from the 8 o'clock position. The aircraft then made an abrupt right 180-degree rotation with the tailboom subsequently collapsing to the right and downward. This was followed by an explosion and fire that engulfed the aft portion of the aircraft. The aircraft's nose pitched up briefly and it then pitched forward as the aircraft began a roll to the right. The aircraft continued to rotate to the right, about its longitudinal axis, in a nose-down attitude until it collided with terrain. The witness/pilot also reported the the accident aircraft's green blade had failed a blade indicator monitor (bim) test check during the daily inspection that had been conducted the evening before in brownwood, Texas. The aircraft's crew chief subsequently recharged the blade with nitrogen and the aircraft was allowed to remained parked overnight on the ramp. The next morning the bim was checked during the preflight and it was noted that the green blade had retained its charge. The decision was then made to continue to fly the aircraft to its destination. During the next 7.6 hours of flight, the aircraft made four subsequent fuel stops. The crew reportedly checked the bim on each stop and did not note any further discrepancies. According to FAA airworthiness inspectors, the failure of a bim check renders the aircraft non-airworthy until the cause of the bim check failure is positively indentified the the problem has been corrected. If the problem cannot be identified, the aircraft shall not be flown until the blade is replaced. The identification and mode of separation of the blade are pending. (.4) while in cruise flight, a main rotor spar separated. The aircraft exploded in flames and crashed. The green blade had failed an AD directed bim check the evening prior to the accident. The crew chief recharged the blade with nitrogen and allowed the aircraft to remain parked overnight. The next morning he checked the bim and found it had retained its charge. The crew of the accident aircraft, who were accompanied by the company's chief pilot in a second aircraft, made the decision to continue to fly the aircraft to its destination. There were several cellular calls both to and from the operator on the evening before the accident. A new exclusive-use contract for both aircraft was already in effect. The maintenance history of the green blade contained an unspecified minor repair after a reported overhaul. The operator stated that, at no time, had it had performed any maintenance or repair to the blade. After the spar's mating fracture surfaces were examined, it was found that a hole had been drilled from the underside into the spar. The hole terminated at a conical point that is consistent with a drill bit. Fatigue banding could be seen in the immediate vicinity of the hole. Striations near the conical point, typical of fatigue, were seen with a sem. The drill hole was under a blade pocket and had not been visible during previous inspections. There is no prescribed inspection/maintenance procedure short of removing the blade pockets that would have revealed the hole. Blade pockets are condition items. Stop-drilling cracks in blade pockets to prevent crack propagation is an authorized military maintenance procedure. Drilling into the spar as part of the process is not authorized. (-23) a witness stated that on July 17, 1998, while performing the preventive maintenance daily inspection, the aircraft crew chief discovered the blade inspection monitor (bim) on the aircraft's green main rotor blade indicated an unsafe condition. The crew chief subsequently serviced the main rotor blade with nitrogen and the aircraft was allowed to sit statically overnight. The following morning the bim indicator was inspected on preflight which indicated that the blade had retained its charge. The aircraft departed for its home base in apple valley, CA. After approximately 7.6 hours of flight time the green main rotor blade failed in flight and departed the aircraft. Post accident investigation revealed a small drill hole in the green main rotor blade spar.