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Pilot And Mechanic Both Miss Aileron Hook-Up Error

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Two Chances Lost: Pilot And Mechanic Both Miss Aileron Hook-Up Error

Apr 27, 2017Richard N. Aarons | Business & Commercial Aviation

This article appears in the May 2017 issue of Business & Commercial Aviation with the title “Two Chances Lost.”

Arguably, among the most challenging and potentially hazardous flights a pilot undertakes are post-maintenance test flights. The NTSB database contains dozens of incidents in which post-maintenance flights ended up tragically, often because the preflight chores were rushed or carelessly executed. This month, we’ll look at an incident that took the lives of two pilots, one of them an experienced U.S. Air Force-trained test pilot.

Piper PA 46-350P, N962DA, crashed into the Spokane River on May 7, 2015, at 1604 PDT following an attempted landing at Felts Field Airport in Spokane, Washington. The commercial pilot and pilot-rated passenger were killed and the airplane was destroyed during the impact sequence. The local flight departed Felts Field at 1553 in VMC.

Both the pilot and passenger were employees of Rocket Engineering, where company personnel had just completed several maintenance tasks including an annual inspection. The accident flight was to be a post-maintenance test flight, and was expected to take about 40 min.

Weather conditions were good at Spokane: winds from 020 deg. at 7 kt., 10-mi. visibility with few clouds at 7,000 ft. The temperature was 71F, the dew point was 26F, and the altimeter pressure was 29.93. 

Felts Field had an operating tower (0600-2000 local) and two runways. The pilot specifically requested to depart from the longer (4,999-ft.) Runway 4L. Eleven minutes after making the initial call to ATC, the airplane began the takeoff roll. Almost immediately after takeoff, the aircraft began a climbing turn, 10 deg. to the right, as recorded by radar. After flying on that heading for about 1.5 mi., the airplane began a more aggressive turn to the right, reaching 1,000 ft. AGL while on a southbound heading.

The tower controller heard labored breathing over the frequency and asked the Piper crew if everything was OK, to which the pilot responded, “That’s negative.”

The airplane’s turn radius then tightened to about 700 ft., and within 45 sec. it completed almost two spiraling turns, while descending about 700 ft. Control tower personnel later told investigators that during this period the airplane was banking about 90 deg. to the right and descending, and they assumed that it was about to crash. However, moments later the bank angle began to reduce, and the airplane appeared to recover.

The airplane then began a meandering climb to the east, and about 2.5 min. later the pilot reported, “We are trying to get under control here, be back with you.”

The Piper eventually overflew the town of Newman Lake, about 11 mi. east of the airport, having climbed to about 5,600 ft. MSL (4,000 ft. AGL), and the pilot reported, “things seem to be stabilizing.” When asked his intentions by the tower controller he replied, “We are going to stay out here for a little while and play with things a little bit, and see if we can get back.”

The airplane began a gradual left turn, and the pilot requested and was approved for a straight-in landing for Runway 22R. The airplane became aligned with the runway about 7 mi. east of the airport, and a short time later the controller asked the pilot the nature of the emergency, to which he responded, “We have a control emergency there, a hard right aileron.” The flight progressed, and a few minutes later the pilot reported that the airplane was on a 3-mi. final. The Piper remained closely aligned with the runway centerline throughout the remaining descent, and control tower personnel observed that it appeared to be flying in a 20-deg., right-wing-low attitude as it neared the runway threshold.

A tower controller later reported that as the still-airborne airplane passed Taxiway D, the engine sound changed, as if the pilot were attempting to perform a go-around. Suddenly, the airplane began a sharp roll to the right and crashed into the river just north of the airport.

 

Rescue operations began immediately; however, they quickly turned into recovery operations. The river was about 25 ft. deep at the accident site, and all major airframe components sank within a few minutes of impact. The airplane was recovered by a dive team from the Spokane County Sheriff’s office over a two-day period during the week following the accident.

The fuselage sustained crush damage and fragmentation from the firewall through to the right-side emergency exit door. The engine remained attached to the firewall, and the propeller hub with all four blades remained attached to the engine gearbox. All blades were bent about 90 deg. aft, 8-12 in. from their roots. Both wings had separated from the airframe at their roots, with the right wing separating into two sections outboard of the main landing gear. The horizontal stabilizer had detached from the tail cone.

The pilot and pilot-rated passenger had died of blunt force trauma. No drugs or persisting conditions were involved.

The Pilot

The 64-year-old pilot-in-command, who was seated in the left front seat, held a commercial certificate with ratings for airplane single-engine land, multiengine land, rotorcraft-helicopter, and instrument airplane and helicopter, along with a flight instructor certificate for airplane single-engine land. He also held a repairman, experimental builder certificate, and was rated in the Bell 212 helicopter and Lockheed L-382 (C-130 Hercules) airplane.

His most recent FAA medical certificate was second class, and dated May 17, 2013, with the limitation that he must have available glasses for near vision. He was a retired Air Force Lieutenant Colonel, with 20 years of active service as a test pilot, instructor, and search and rescue pilot.

The pilot was employed as an engineer for Rocket Engineering, and was the primary liaison with the FAA’s Flight Standards and Certification divisions. He also typically performed post-conversion, post-maintenance and customer familiarization flights for the company. (Rocket Engineering did the turboprop conversion on the accident airplane.)

The pilot had accumulated about 5,800 hr. of total PIC flight time, 950 of which were in the accident make and model. He had flown about 20 hr. in the accident make and model during the 30-day period prior to the accident.

 

Representatives from Rocket Engineering told investigators the pilot had an appointment for his FAA medical examination at 0800 on the morning following the accident, and therefore chose to do the flight test that evening instead of the following day (Friday). The pilot’s wife also stated that he typically did not work on Fridays but would do so if the work schedule required it.

The pilot-rated passenger held a private pilot certificate with an airplane single-engine land rating, issued in 2010. He had accumulated a total of about 122 hr. of pilot-in-command flight experience. He was employed at Rocket Engineering as a customer service and sales representative.

The Airplane

The accident aircraft was originally manufactured by Piper in 1996 as a PA-46-350P equipped with a Lycoming TIO-540-AE2A 350-hp turbocharged piston engine. It was modified by Rocket Engineering in 2007 under a JetProp LLC STC, which included the installation of a 560-hp Pratt & Whitney Canada PT6A-35 turboprop engine.aintenance was performed, along with the replacement of the four aileron cables in the wings and an aft elevator cable. The mechanic who performed the work stated that the aileron and elevator cables were replaced during the three-day period leading up to the accident.

The airplane’s owner also had arranged for another maintenance facility on the field to perform an avionics upgrade concurrent with the inspection being done at the Rocket Engineering facilities. The avionics shop president told investigators the owner made multiple requests to add additional items to the work scope as the upgrade progressed. Due to time constraints, not all of his requests could be accommodated.

The owner reported that he had decided to pick up the airplane on May 5; however as the work progressed, he was informed that the airplane would not be ready in time, and the date was pushed back to May 7 (accident day) and then May 8. He had made plans to travel from Los Angeles the afternoon of May 7, and was en route via a commercial airline when the accident happened.

The airplane’s primary flight controls are conventional, and operated by dual control wheels and rudder pedals through a closed-circuit cable system. The ailerons and rudder are interconnected through a spring system located under the main cabin.

An aileron is mounted on the outboard trailing-edge section of each wing via a series of hinges. Movement of each aileron is controlled through a yoke and pin assembly that interfaces with a sector wheel mounted in each wing forward of each aileron. Each sector wheel is connected to, and driven by, one aileron drive cable and one balance cable. In each wing, both the balance and drive cables are terminated with identical ball swage fittings, and each swage fitting inserts into one of two identically sized receptacles in the sector wheel. Both cables are approximately the same length outboard of the pressure vessel seals, which are located about 1 in. apart vertically at the wing root.

In each wing, both cables are routed to the fuselage along the wing trailing edge, and pass through their respective pressure vessel seals in the wing root. Inboard of the pressure vessel seals, the left and right balance cables connect to one another after passing through a center pulley, while the drive cables are routed forward via pulleys to the control wheel assembly in the cockpit. The balance and drive cables are aligned vertically at the pressure vessel seals and diverge about 3 in. laterally at their respective pulley positions. The sector wheel design is unique within the Piper fleet to the PA-46.

The NTSB said that four aileron cables were replaced during the maintenance operation. “Post-accident examination of the airplane revealed that the aileron balance and drive cables in the right wing had been misrouted and interchanged at the wing root. Under this condition, both the left and right ailerons would have deflected in the same direction rather than differentially. Therefore, once airborne, the pilot was effectively operating with minimal and most likely unpredictable lateral control, which would have been exacerbated by wind gusts and propeller torque and airflow effects.”

The sections of the two interchanged cables within the wing were about equal lengths, used the same style and size of termination swages, and were installed into two same-shape and -size receptacles in the aileron sector wheel. “In combination, this design most likely permitted the inadvertent interchange of the cables, without any obvious visual cues to maintenance personnel to suggest a misrouting. The maintenance manual contained specific and bold warnings concerning the potential for cable reversal,” said the Safety Board.

“Although the misrouting error should have been obvious during the required post-maintenance aileron rigging or function checks,” said the Safety Board, “the error was not detected by the installing mechanic. Although the installing mechanic reported that he had another mechanic verify the aileron functionality, that other mechanic denied that he was asked or that he conducted such a check. The mechanic who performed the work also signed off on the inspection; this is allowed per federal regulations, which do not require an independent inspection by someone who did not perform the maintenance.”

The pilot did perform a preflight check; the preflight checklist included confirmation of “proper operation” of the primary flight controls from within the cockpit. “Although the low-wing airplane did not easily allow for a differential check of the ailerons during the walk-around,” said the Safety Board, “both ailerons could be seen from the pilot’s seat; therefore, the pilot should have been able to recognize
that the ailerons were not operating differentially.”

In analyzing the circumstances of the accident, the Safety Board observed that the accident occurred at the end of the business day, and the airplane had been undergoing maintenance for a longer-than-anticipated period. The airplane’s owner was flying in from another part of the country via a commercial airline to pick up the airplane the following morning. The accident pilot, who was an engineer at the company and typically flew post-maintenance test flights, was assisting with returning the airplane to service. He also had an appointment with an FAA medical examiner the next morning (Friday), and he typically did not work on Fridays. “It is likely that the mechanic and pilot felt some pressure to be finished that day so the owner could depart in the morning and the pilot could attend his appointment.”

The Safety Board determined the probable cause(s) of this accident to be: “The mechanic’s incorrect installation of two aileron cables and the subsequent inadequate functional checks of the aileron system before flight by both the mechanic and the pilot, which prevented proper roll control from the cockpit, resulting in the pilot’s subsequent loss of control during flight. Contributing to the accident was the mechanic’s and the pilot’s self-induced pressure to complete the work that day.”

Unfortunately, the significant causal factors involved in this accident are repeated several times each year. Pressure to get the job done; inspection/installation-unfriendly designs; and rushed preflight inspections are all potential killers. The record shows that post-maintenance flights should never be considered “routine.” They are fraught with hazards that can kill the unwary crew.  

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