WPR17LA180

Maintenance personnel's failure to secure hardware, which resulted in an uncommanded upward deflection of the left elevator and aft movement of the control yoke and inhibited the flight crew from adjusting the airplane's pitch attitude in flight. Contributing to the accident was the lack of maintenance oversight, which should have identified the unsecured hardware before flight.

The company dispatched the accident airplane to a fire as part of an exclusive contract with the United States Forest Service and under the direction of the Bureau of Land Management. During the airplane's climb, the airline transport pilot, who was acting as pilot-in-command, adjusted the trim to reduce nose-down pressure and subsequently observed an uncommanded aft movement of the control yoke and simultaneous increase in the airplane's pitch attitude. The flight crew attempted to regain pitch control by adjusting the trim wheels, but the airplane continued to maintain a pitch-up attitude. Using coordinated inputs, the flight crew was able to land the airplane without incident. A postlanding examination revealed that the variable camber, or varicam, was damaged during the event. This secondary control surface is directly connected to the elevators and provides a primary structural load path for all elevator loads; thus, any damage to the varicam was considered substantial. Postaccident examination revealed that maintenance personnel had failed to secure the drive stop coupling bolts with lockwire and that one of the bolts had backed out of its bolt hole. Because the varicam likely did not display any deformation before takeoff, as it would have been inspected after the previous flight, the bolt likely backed out sometime during the takeoff. When the flight crew adjusted the varicam trim during the initial climb, the absence of this bolt prevented a section of the drive shaft from rotating, allowing only a portion of the varicam to move. This resulted in the deformation of the left side varicam and subsequent upward deflection of the left elevator, which is hinged to the varicam. The resulting feedback in the cockpit was an uncommanded aft movement of the control yoke, which placed the airplane in a pitch-up attitude that could not be corrected by flight control inputs from the cockpit.     The mechanic responsible for installing the lockwire was under stress due to family issues at the time of the varicam was last serviced. The company's task cards indicated that the mechanic failed to lockwire the drive stop coupling bolts to the drive stop, despite noting that the work had been completed by stamping the card with his designation. This omission should have been detected by either the facility's lead mechanic or the quality assurance (QA) inspector through the required inspection item (RII) process. However, the lead mechanic seldom oversaw inspections and most likely did not attempt to review this mechanic's work and others' work, as the investigation revealed 7 additional RII oversights. Further, the QA inspector, whose main duty was to review any work that had been stamped RII by the lead mechanic, failed to notice that the critical flight control areas had not been annotated as RIIs. Although the company retrains its RII staff biennially, the QA inspector did not appear to understand his role in the RII process, as he was reported to have given approvals without verifying if the work qualified as an RII. While the mechanic failed to secure the drive stop coupling with lockwire, the lead mechanic and the QA inspector's lack of oversight contributed to the omission that ultimately resulted in the varicam failure.

On August 5, 2017, about 2000 mountain daylight time, a Lockheed P2V-5 airplane, N410NA, was substantially damaged shortly after departure from Pocatello Regional Airport (PIH), Pocatello, Idaho. The airline transport pilot, commercial pilot and mechanic were not injured. The airplane was registered to and operated by Neptune Aviation Services, Inc., Missoula, Montana, as a public aircraft under contract with the United States Forest Service. Visual meteorological conditions prevailed, and a flight plan was not filed for the local flight. According to the pilot-in-command (PIC), the flight departed on its third mission to disperse fire retardant over a nearby wildfire. During the airplane's climb, the flight crew increased the airplane's nose up pitch by a few more degrees and the PIC subsequently responded with increasing nose down pressure. However, the down pressure control input required additional force, so the PIC used trim inputs to reduce the pressure. Moments later he observed an uncommanded aft movement of the control yoke with a simultaneous increase in the airplane's pitch attitude. He instructed the first officer (FO) to retract the flaps while he re-trimmed the elevator, but they were not able to regain pitch control. The FO attempted to adjust his trim wheel and then re-trim the airplane using the emergency varicam, but the airplane continued to maintain a pitch up attitude. He then deployed 5° of flaps at the PIC's instruction, which reduced the elevator backpressure. The PIC subsequently jettisoned the load of fire retardant over vacant farm land and then asked the FO to declare an emergency with the tower controller while the PIC entered a shallow left turn to intercept the downwind leg for Runway 21. As he made his control inputs he determined that the elevator was bound, as he received little response from the elevator control. As the PIC had previously demonstrated the ability to land without making any adjustments to power or pitch in flight training, he elected to configure the airplane for an approach without trim or elevator control. The flight crew flew a wide traffic pattern and made small adjustments to compensate for altitude. During the final approach leg, the PIC used a combination of wing flaps and engine power for pitch up adjustments, and the crew coordinated application of elevator for trimmed pitch and turns to make their pitch down adjustments. As the airplane reached about 500 feet above ground level, the flight crew deployed the airplane's remaining 5° of flaps to increase the pitch attitude. Both the PIC and FO pulled hard on the yoke while the FO gently retarded the throttles and the PIC trimmed the emergency varicam. Postaccident examination of the airplane revealed damage to the varicam. As this secondary control surface is directly connected to the elevators and provides a primary structural load path for all elevator loads, the damage was classified as substantial. Further examination of the varicam showed that one of the varicam actuator's outboard drive stop bolts had backed out of the drive coupling, and that the two bolts had not been safety wired. The airplane did not sustain any damage during the airplane's landing. The PIC further stated that the airplane was re-trimmed in accordance with the airplane checklist by the FO following the previous landing and is visually inspected after each landing by the FO and the airplane's crew chief. According to Federal Aviation Administration (FAA) records, the airplane was manufactured in 1954, and registered to Neptune Aviation Services on December 16, 2010. The airplane was powered by two outboard Westinghouse J34-WE-36A, axial flow, turbjet, 2,750 shaft horsepower (hp) engines, and two inboard Curtis Wright R-3350-32WA, twin-row, supercharged, air-cooled, 3,250 shaft hp radial engines. The airplane owner reported that its most recent 100-hour airframe and engine inspections were completed on July 10, 2017, at an accumulated flight time of 8,420.2 total flight hours. Its previous annual inspection was completed in October 2016. At the time of the accident the airplane had accrued a total of 8,486.7 total flight hours. The company's website stated that Neptune Aviation operated a fleet of 16 firefighting airtankers, including 9 BAe 146 airplanes, and 7 Lockheed P2V airplanes. Neptune's firefighting airplanes are serviced in-house by the company's two certified repair stations located in Missoula, Montana and Alamogordo, New Mexico. The company has been operating under exclusive use contracts with the United States Forest Service for about 24 years. The airplane was equipped with a variable camber (varicam) horizontal stabilizer in place of an elevator trim tab, mounted on the trailing edge of the fixed horizontal stabilizer. The elevators are hinged to the trailing edge of the varicam, and are kept faired with the varicam by the action of the trim tab installed on the left elevator. The purpose of this type of trim is to provide a wider range of trim movement and to permit the use of a narrow chord elevator, which results in lighter control forces and increased stability. The varicam trim is electrically controlled by switches on both the pilot and co-pilot's yokes, and the travel limitation is controlled by limit switches in the tail section. When an elevator trim adjustment is made in the cockpit, hydraulic pressure from the main hydraulic system flows to the UP or DOWN port of the main system varicam drive motor, which rotates the varicam drive shaft to move the varicam actuators and the secondary control surface's down or up deflection. The varicam actuators are secured to the drive shaft through universal joints located at the outboard ends, comprised of two bolts that are normally threaded and safety wired to the varicam drive coupling, and two bolts with castellated nuts and cotter pins to secure the yoke to the drive stop. Variable Camber Examination An examination of the varicam's LH outboard drive stop and yoke displayed only one bolt that had been secured to the varicam drive stop coupling, which is normally secured to the drive stop using two bolts that are threaded into the coupling and safety wired together at their bolt heads. Photographs provided by Neptune Aviation's Director of Maintenance (DOM) showed that the second bolt was resting against the lower varicam skin, and without any safety wire in the bolt head. Further examination of the varicam did not reveal the presence of safety wire throughout the cavity of the secondary control surface. The DOM reported that an absence of the one of the drive coupling bolts would hinder the torque capabilities of the drive shaft, thereby allowing one side of the varicam to move and the other side to remain stationary or turn incrementally, which would twist and deform part of the varicam. He further added that since the elevator is hinged to the varicam, the twisted varicam can force one of the elevators into an upward deflected position. The DOM stated that the accident airplane's left side part of the varicam was deformed, and that the left elevator was deflected upward. Neptune Aviation uses task cards that are distributed to each mechanic prior to the corresponding work being performed. The service facility's task summary card, dated July 27, 2016, and given the numerical reference 163379-244, stated: "L/H side varicam. Universal joints for outboard drive shaft are worn on both inboard and outboard side. Also lock assembly universal joints are worn on both sides." In the notes section of the entry, a mechanic recorded "26Jul2016. Removed and Replaced three sets of universal joints on L/H varicam, inboard, and outboard sides I.A.W. NAVAIR 01-75EDA-2-3. No defects noted." The entry was stamped "M77," a designation assigned to one of the mechanics who left the company a few days after he completed this service for unrelated reasons. Task card 10-3, line "j" of