EMIGRANT GAP, CA, USA
N64AR
Sikorsky CH-54A
While flying upslope with an external load of logs at almost zero airspeed, the pilot (PIC) heard an 'explosion' and noted that the helicopter pitched nose-up and rolled right. He turned to initiate a downslope forced landing, while experiencing control feedback and stiffness. As the crew began an approach, the copilot attempted to jettison the load with the electrical release; however, neither crew member verified the results of the procedure. As the aircraft continued to descend on the approach, the cargo hook struck the ground, opened, and released the logs. At the termination of the approach, the helicopter's main rotor blade struck several trees. After the helicopter touched down, it rolled onto its left side in a shallow stream. The No. 2 engine exhibited evidence indicating that it was producing power at impact; however, the No. 1 engine exhibited evidence indicating that it was not rotating. During subsequent inspections, no preimpact anomaly was found with either of the engines or of associated systems.
On August 26, 1995, about hours 0945 Pacific daylight time, a Sikorsky CH-54A Skycrane, N64AR, collided with trees and terrain while performing aerial logging operations near Emigrant Gap, California. The aircraft sustained substantial damage; however, neither the certificated airline transport pilot nor his certificated airline transport copilot were injured. The aircraft was destroyed during recovery. The aircraft was being operated as an external load operation by Heavy Lift Helicopters, Inc., under 14 CFR Part 133 when the accident occurred. The flight originated in a staging area near Emigrant Gap at approximately 0930 on the morning of the accident. Visual meteorological conditions prevailed at the time and a company VFR flight plan had been filed. The pilot reported that after completing the previous logging cycle the aircraft was refueled and he and the copilot changed seats and duty positions, and he now occupied the right seat. After picking up a sling of logs weighing about 14,000 pounds, they were flying upslope toward the designated landing zone in order to position their load for road transport at an aircraft gross weight of 19,600 pounds. As the flight continued, he heard an explosion and saw the aircraft's nose pitch up and roll right while at almost zero airspeed. The pilot began to experience control feedback and stiffness which he described as similar to a hydraulics off condition. With limited control response available and substantial control feedback, the crew initiated a downslope forced landing from their present position to a point about 1 mile away. At that time the pilot thought the copilot had released the sling load with the electrical hook release, but neither crew member verified the results of the procedure. The copilot told the operator that he thought the pilot had released the sling load. The pilot told investigators that the control feedback they experienced in the cockpit was so violent that any further attempt to reach the mechanical release was impossible to accomplish without losing total control of the aircraft. During the final portion of the approach the cargo hook struck rocky terrain, at which time the hook opened and the logs were released. (The pilot's written statement is appended to this report.) The pilot's operating handbook (POH) (U.S. Army Technical Manual 55-1520-217-10-1) for compressor stalls in flight states the pilot should reduce altitude, if necessary, to aid stall recovery and if the stall condition cannot be controlled to either shut down the engine or land as soon as possible. Abrupt or sudden changes in N1, such as a rapid power application or reduction, can result in compressor stalls, T5 over-temperature, and damage to compressor blades. The POH states that the majority of single engine flameouts are the result of improper fuel flow caused by fuel control malfunctions or improper operating techniques. In the event of a single engine failure, the emergency immediate action procedures direct the pilot to: first, increase both engine trim switches; second, jettison the load as required; and, finally to land as soon as possible. The POH cautions that any external load extending below the landing gear must be jettisoned before landing. (Excerpts from the POH are appended to this report.) The chief pilot for the operator stated that, based on his experience, this aircraft will not maintain flight below effective translational lift (ETL) (approximately 18 to 22 knots) at a gross weight of 19,600 pounds with one engine inoperative. He further stated that attempted flight with insufficient power available can result in low rotor rpm, substantial control feedback, and uncommanded aircraft movements such as rolling or pitching. An engine maintenance technician for the operator stated that an engine relight was possible but only if the ignition switches were turned to the on position prior to N1 on the effected engine dropping below the 40 percent N1 range (the same range the ignition switches are turned to during an engine ground start). After dropping below 40 percent N1 the standard starting procedure is required as prescribed in the POH. Impact marks on the main rotor blades dimensionally correlated with impact marks on the No. 1 engine inlet, the No. 2 oil saddle tank, and the No. 2 engine. There was evidence of fresh breaks and severed trunks and limbs among several trees near the touchdown point. At touchdown, the aircraft rolled about 105 degrees onto its left side and came to rest in a shallow stream at the 2,300-foot level (msl). There was evidence of a limited postcrash fire in the vicinity of the engines. The fire damage revealed a downward flow pattern of molten metal and an upward pattern of soot deposits which were perpendicular to the horizon. Approximately three 55-gallon drums of Jet A were obtained from the aircraft fuel tanks during the defueling operations prior to recovery. During the recovery phase the accident aircraft was being slung from the accident site to a staging area by the accident pilot who was flying another CH-53A aircraft. While in transit he encountered conditions which made it necessary for him to jettison his load. The accident aircraft was destroyed when it was dropped. A postaccident inspection of the aircraft was conducted at the HLM Air Services storage facility in Concord, California, under the supervision of an FAA airworthiness inspector and with the participation an FAA powerplant certification engineer and a Pratt & Whitney representative. The operator previously reported that the compressor section of the No. 2 engine had undergone an overhaul within the previous 50 hours of flight time. The preliminary inspection revealed that, while the compressor section of the No. 2 engine was damaged, both engines would require a more detailed inspection in order to obtain more definitive evidence. There was no evidence indicating any preimpact anomalies with either the main or tail rotor systems. (Preliminary reports from the FAA and Pratt & Whitney are appended to this report.) After being removed and transported to the Sabreliner Corporation in St. Louis, Missouri, both engines were disassembled and inspected under the supervision of an FAA airworthiness inspector, with an FAA powerplant certification engineer and two Pratt & Whitney representatives participating. During disassembly and inspection, no evidence was found which indicated any preimpact malfunctions and/or failures involving the engines or their associated components. A damaged compressor spacer between the third and fourth stages and tie rods from the fifth and sixth stages of the No. 2 engine were submitted to the Safety Board Materials Laboratory for fracture and/or failure analysis. There was no evidence found which was indicative of preimpact defects or progressive failures. The No. 2 engine revealed rotational scoring and uniform bending opposite the direction of rotation. The No. 1 engine revealed random bending and an absence of rotation scoring. (Final reports from the FAA, Pratt & Whitney, Sabreliner and the Safety Board Materials Laboratory are appended to this report.)
a compressor stall in the right engine for an unknown reason, which resulted in a loss of power in that engine; and inadequate crew coordination between the pilot and copilot, which resulted in their failure to ensure that the external load was promptly jettisoned or released.
Source: NTSB Aviation Accident Database
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