Sunday, August 11, 2019

Flight Control System Malfunction / Failure: Lockheed P2V-5F Neptune, N410NA; accident occurred August 05, 2017 near Pocatello Regional Airport (KPIH), Bannock County, Idaho

The National Transportation Safety Board did not travel to the scene of this accident.

Additional Participating Entities:

Federal Aviation Administration / Flight Standards District Office; Helena, Montana
Neptune Aviation; Missoula, Montana
Department of the Interior; Boise, Idaho

Aviation Accident Final Report - National Transportation Safety Board:

Investigation Docket - National Transportation Safety Board:

Aviation Accident Data Summary - National Transportation Safety Board:

Location: Pocatello, ID
Accident Number: WPR17LA180
Date & Time: 08/05/2017, 2000 MDT
Registration: N410NA
Aircraft: LOCKHEED P2V 5F
Aircraft Damage: Substantial
Defining Event: Flight control sys malf/fail
Injuries: 3 None
Flight Conducted Under: Public Aircraft 


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. 

Probable Cause and Findings

The National Transportation Safety Board determines the probable cause(s) of this accident to be:
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.


Elevator tab control system - Failure (Cause)

Personnel issues
Repair - Maintenance personnel (Cause)

Organizational issues
Oversight of maintenance - Maintenance provider (Factor)

Factual Information

History of Flight

Enroute-climb to cruise
Flight control sys malf/fail (Defining event)

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 the annual inspection requires the installation of the drive shafts, u-joints and drive shaft stop assembly, secured with lockwire. The entry was verified as completed with the notation of the stamp, "M77." A task card with the numerical reference 163379-17 indicated that card 10-3 was completed on July 28, 2016, at the time of the annual inspection.


A series of interviews were conducted by the Department of Interior, Federal Aviation Administration, and the NTSB Investigator-in-Charge at Neptune Aviation's Missoula, Montana offices. Representatives of Neptune Aviation from the following positions were interviewed:

- Director of Maintenance

- Director of Operations

- Shop Manager

- Quality Assurance

Service Facility History

The DOM stated that the accident airplane was serviced at their facility in Alamogordo, New Mexico, which had been dormant until 2014 when they reactivated the repair station. Neptune's New Mexico facility employs only one daytime shift of mechanics who work from 0700 to 1730, 4 days per week. The facility does not employ any contractors and crews only work on one aircraft at a time. At the time of the annual inspection that took place in July 2016, Neptune had a total of 12 full time employees at their New Mexico location: one shop manager, a lead mechanic, a quality assurance mechanic, and 6 line mechanics, each of whom held an airframe and powerplant certificate. The facility additionally employed 3 people whose function was parts purchasing.

After the facility re-opened full time in 2014, the DOM, Assistant DOM, and Chief Inspector cross-trained the employees separately in one-week rotations. The employee who was responsible for the safety wire work in July 2016, was hired in October 2015, and his lead had been with the company since September 2014.

Required Inspection Item Procedures

Neptune's Standard Operating Procedure (SOP) guide includes criteria to designate certain task cards as required inspection items (RII). The lead mechanic is responsible for annotating "RII required" on the corresponding task cards at the time the cards are generated and assigned. From this notation, the quality assurance (QA) inspector is required to inspect the mechanic's work. Under Table 8.1 of the company's RII guidance, ATA 27, item no. 10 states: "Varicam System Components – Install/Rig/Adjust (P2V)." In the right hand column of the same table, item no. 1 states to "Check proper installation, required torque values, security, and safety." An "RII required" notation was not placed on sub-task card 163379-244, the procedure that required lockwire to secure the drive stop bolts. Although the varicam qualifies as an RII under the company SOP, the QA's oversight never registered with either the mechanic or lead mechanic.

At the request of the NTSB, FAA and DOI, the company subsequently completed an audit of the aircraft's annual inspection package and discovered a total of seven task cards that did not record a mandatory RII.

Workflow and Workday

Neptune's maintenance staff includes a shop manager who oversees the lead mechanic's activities and the operations of the overall facility. The lead mechanic is responsible for organizational planning, and normally sits at a desk located atop a podium on the shop floor, accessible to any employees who need assistance during their shift. At his side is the QA inspector who is responsible for overseeing the inspections, but reports to the Chief Inspector. The QA's main responsibility is to review any RII that are notated on a task card. To prevent any lapse in work continuity, the company trained other mechanics at its Alamogordo, New Mexico location in the company's RII procedures in the event the QA is ill or unable to complete an inspection. Part of the QA's responsibility is to also inspect areas that have not been designated as RII as part of his follow-up work, but at his own discretion.

During a normal workday, the lead mechanic will generate and assign task and sub-task cards to the line mechanics that cover different areas of the aircraft. For example, task card 163379-17 furnished specific instructions under its "Task Description" to "Comply with Card 10-3 of Annual Inspection per Neptune Aviation Services AIP." Additionally, task card 163379-16 included instructions to comply with card "10-2 of Annual Inspection…" In this case, the mechanic notated that the work had been completed with his stamp designation, "M77". This particular mechanic was further issued a sub-task card, 163379-244, part of task card 163379-16. In this entry, he notated that three sets of universal joints on the inboard and outboard sides of the L/H varicam were removed and replaced in response to the task description of the sub-task card, which stated that the universal joints for the outboard drive shaft were worn. Once the mechanic has completed the work, he gives the task cards to the lead mechanic who then sends the records to the QA inspector. In this case, the inspector stamped sub-task card 163379-244 with his designated stamp, "Q03" to indicate that the task had been processed by inspector. He additionally processed annual inspection card 10-4, which includes tasks to verify installation and safety of the varicam universal joints and mechanical stop assembly. Entry no. 2, part "a" was stamped as approved by the QA inspector for proper installation of the varicam universal joints, which could not be accomplished without safety wiring the drive stop bolts together.


The DOM further reported that training for incoming and current staff mechanics for the P2V airplane consists of a one-time course that includes both hands-on and classroom training. Additionally, they send their mechanics through recurrent training when necessary. Although the company does maintain a two-year recurrent requirement on RII training, it does not currently offer recurrent training on its internal procedures for quality assurance, lead mechanics and line mechanics.

Mechanic, Lead Mechanic, and Quality Assurance Inspector

The mechanic who was responsible for safety wiring the drive coupling bolts departed the company on August 2, 2016, a few days after he serviced the varicam. At the time of the inspection he had already submitted his 2 weeks notice due to family issues.

The Director of Operations reported that the lead mechanic's employment had been terminated for poor attitude and for falsifying completed work, as he had inscribed a mechanic's name on a task card when the mechanic was not present for work. Additionally, the lead mechanic had created a stressful work environment by reviling the mechanics to expedite their work efforts. The shop manager and the lead mechanic's manager reported that the lead mechanic worked well in his position and with others until his second year, 2016, when he attempted to create a barrier between the New Mexico facility and the company's Missoula headquarters. During this time, the shop manager received complaints from several employees that the lead mechanic was not involved in the day-to-day work of the company. Additionally, he preferred to remain at his desk instead of conversing with the line mechanics and performing spot inspections.

According to the QA inspector, he had been with Neptune Aviation as a mechanic since 2010, and had been the primary QA since November 2015. He reported that the lead mechanic was too preoccupied with paperwork and spent most of his time sitting at the podium instead of completing inspections. When asked about the RII inspection process, the QA mechanic stated that although an RII requirement is not documented on the task card paperwork, the paperwork will go to the lead and then the QA will review the paperwork and stamp the work as approved despite the company's requirement for him to verify if the item is an RII. The QA then returns the paperwork to the mechanic who closes the corresponding aircraft section. 

Pilot Information

Certificate: Airline Transport; Flight Instructor; Commercial; Flight Engineer
Age: 62, Male
Airplane Rating(s): Multi-engine Land; Single-engine Land
Seat Occupied: Left
Other Aircraft Rating(s): Glider
Restraint Used: 3-point
Instrument Rating(s): Airplane
Second Pilot Present: Yes
Instructor Rating(s): Glider
Toxicology Performed: No
Medical Certification: Class 2 Without Waivers/Limitations
Last FAA Medical Exam: 12/12/2016
Occupational Pilot: Yes
Last Flight Review or Equivalent:
Flight Time:    (Estimated) 18200 hours (Total, all aircraft), 2900 hours (Total, this make and model), 15000 hours (Pilot In Command, all aircraft), 200 hours (Last 90 days, all aircraft), 75 hours (Last 30 days, all aircraft), 5 hours (Last 24 hours, all aircraft) 

Co-Pilot Information

Certificate: Commercial
Age: 45, Male
Airplane Rating(s): Multi-engine Land; Single-engine Land
Seat Occupied: Right
Other Aircraft Rating(s): None
Restraint Used: 3-point
Instrument Rating(s): Airplane
Second Pilot Present: Yes
Instructor Rating(s): None
Toxicology Performed: No
Medical Certification: Class 2 Without Waivers/Limitations
Last FAA Medical Exam: 12/15/2016
Occupational Pilot: Yes
Last Flight Review or Equivalent: 03/28/2017
Flight Time:   (Estimated) 3000 hours (Total, all aircraft), 240 hours (Total, this make and model), 2600 hours (Pilot In Command, all aircraft), 150 hours (Last 90 days, all aircraft), 85 hours (Last 30 days, all aircraft), 5 hours (Last 24 hours, all aircraft)

Aircraft and Owner/Operator Information

Aircraft Make: LOCKHEED
Registration: N410NA
Model/Series: P2V 5F H
Aircraft Category: Airplane
Year of Manufacture: 1954
Amateur Built: No
Airworthiness Certificate: Restricted
Serial Number: 131482
Landing Gear Type: Retractable - Tricycle
Seats: 3
Date/Type of Last Inspection: 07/10/2017, AAIP
Certified Max Gross Wt.: 80000 lbs
Time Since Last Inspection: 34 Hours
Engines: 4 Reciprocating
Airframe Total Time: 8486.7 Hours at time of accident
Engine Manufacturer: Westinghouse
ELT: C91A installed, not activated
Engine Model/Series: J34-WE-36A
Rated Power: 2750 hp
Operating Certificate(s) Held: Agricultural Aircraft (137)

Meteorological Information and Flight Plan

Conditions at Accident Site: Visual Conditions
Condition of Light: Night
Observation Facility, Elevation: PIH, 4451 ft msl
Distance from Accident Site: 1 Nautical Miles
Observation Time: 1953 MDT
Direction from Accident Site: 
Lowest Cloud Condition:
Visibility: 6 Miles
Lowest Ceiling: Overcast / 4200 ft agl
Visibility (RVR):
Wind Speed/Gusts: 10 knots /
Turbulence Type Forecast/Actual: /
Wind Direction: 200°
Turbulence Severity Forecast/Actual: /
Altimeter Setting: 29.92 inches Hg
Temperature/Dew Point: 26°C / -2°C
Precipitation and Obscuration: Moderate - Smoke
Departure Point: POCATELLO, ID (PIH)
Type of Flight Plan Filed: None
Destination: POCATELLO, ID (PIH)
Type of Clearance: VFR
Departure Time: 2000 MDT
Type of Airspace: Class D

Airport Information

Runway Surface Type: Asphalt
Airport Elevation: 4452 ft
Runway Surface Condition: Dry
Runway Used: 21
IFR Approach: None
Runway Length/Width: 9060 ft / 150 ft
VFR Approach/Landing: Traffic Pattern 

Wreckage and Impact Information

Crew Injuries: 3 None
Aircraft Damage: Substantial
Passenger Injuries: N/A
Aircraft Fire: None
Ground Injuries: N/A
Aircraft Explosion: None
Total Injuries: 3 None
Latitude, Longitude:  42.905833, -112.590833


  1. Another reason why I am an LSRM-A and soon an A&P.... my ass is in that airplane. You can triple guarantee that I will triple check any work I do on my airplane. Or anyone else's for that matter as my manic compulsion to recheck everything suits me well naturally to an airplane mechanic as it seems.

  2. How can anything as fundamental as missing wire locking happen and not get checked before releasing the aircraft ? that is sloppy maintenance,what happened to dual inspection on flying controls too ?

  3. I thought the same. This maintenance shop was a disaster looking for a way to happen. SMH. Wondering if their FAA certifications were revoked?