Incident
On October 4, 2014, at approximately 0837 eastern daylight time, a Cessna S550, registration N550AJ, experienced a pitch trim malfunction shortly after departing from Tampa International Airport (TPA), Tampa, Florida. The flight, operated by Gulf Atlantic Airways, Inc., dba University Air Center, was a positioning flight under 14 CFR Part 91. Visual meteorological conditions prevailed, and an instrument flight rules flight plan had been filed. The airplane departed TPA at about 0836, destined for Gainesville Regional Airport (GNV), Gainesville, Florida. Both the airline transport pilot and commercial-rated co-pilot were uninjured, and the airplane was not damaged.
According to the captain, the airplane had flown three previous legs that day without any pitch trim issues. After the third landing at TPA, passengers were offloaded and preparations began for the flight to GNV. The co-pilot, serving as pilot flying from the right seat, conducted the pre-takeoff briefing.
Flight and Emergency
After takeoff, at 400 feet and V2 plus 10 knots, the flaps were retracted and a right turn was initiated for the published departure procedure. At that moment, the co-pilot reported stiff controls and pushback. The captain advised him twice to trim the forces away and observed the co-pilot's arms fully extended pushing on the control yoke. The captain also assisted and attempted to use the electric pitch trim, which did not work. Manual pitch trim was also ineffective. The captain then pressed the trim disconnect to address a potential trim runaway and pulled the pitch trim circuit breaker, but the secondary pitch trim remained frozen. Further attempts with manual pitch trim yielded no movement. The captain concluded it was not a runaway trim issue.
The captain declared an emergency with air traffic control. Aggressive power reduction caused a slight pitch-up (normal behavior). He then added power and gradually reduced it. When airspeed dropped below 200 knots, flaps were extended to the approach setting. Once below 172 knots, landing gear was extended, and flaps were set to the landing position. The captain noted that at slower speeds, the airplane became more controllable pitch-wise, as the trim was set to the takeoff range. The controller offered an ILS approach to runway 19L, but the crew advised they were visual flight rules (VFR) and requested a visual approach. They flew a downwind, base, and final approach, landing uneventfully at 0844.
Post-Incident Examination
Examination of the airplane was conducted by the Assistant Director of Maintenance of the operator, with oversight by an FAA operations inspector. With no electrical power, manual elevator pitch trim could only be moved about an inch with normal hand pressure; upon release, the trim returned to its original position. Manual trim felt like it was binding in the nose-down direction, while nose-up trim appeared normal. With electrical power, the electric pitch trim moved but was very sluggish.
Troubleshooting focused on the left elevator trim tab actuator assembly. The left screw of the actuator was removed, cleaned, inspected, relubricated, and reinstalled. Further inspection revealed that the primary and secondary sprockets were separated from the left internal screw (part number 5565450-45). The left elevator trim tab actuator assembly (P/N 5565450-79, serial number 0378-80) with the fractured left internal screw was retained for examination by the NTSB Materials Laboratory.
NTSB Materials Laboratory Findings
The NTSB Materials Laboratory Factual Report noted that the 1-sprocket assembly shaft rotated freely within the actuator, while the 2-sprocket assembly shaft was jammed and could not be manually rotated. The shaft and internal components were disassembled. Both assemblies were missing flat roller bearings that should have been adjacent to flanges on the shaft side opposite the sprockets. Fresh pale pink grease overlay black-colored grease on internal components; some black grease was dry and caked, particularly around shaft flanges. After grease removal, corrosion was visible on the flanges and ends of both shafts, as well as on mating bearings. The 2-sprocket assembly was disassembled, revealing the separated end of the mating shaft in two pieces between the sprockets. Microscopic examination showed fractures through the shaft end of the internal screw at the stake pin holes. Fracture surfaces exhibited dimpled features consistent with overstress in areas without mechanical damage. Circumferential scoring was noted on the outer diameter of the left internal screw between the flanges.
Maintenance Records
Review of the airplane's maintenance records indicated it was maintained per the manufacturer's program. The left elevator trim tab actuator assembly is an on-condition item. It was last installed new on August 8, 1990, at an airplane total time of 1,545.1 hours. No record existed of removal, overhaul, or replacement since installation. A Phase 2 inspection, which includes inspection and lubrication of each elevator trim tab actuator assembly every 300 hours or 24 calendar months, was last performed on March 7, 2014, at an airplane total time of 7,908 hours. At the time of the incident, the airplane total time was 8,105 hours.
Service Difficulty Reports
Review of FAA Service Difficulty Report data for the elevator trim tab actuator assembly part number from 1995 to present revealed 10 reports. Three were associated with pitch trim: one indicated sprocket separation from the internal screw due to pin separation; another reported water inside actuator housings following inoperative manual and electric pitch trim; a third described a jammed elevator trim with worn actuator and loose, binding chain. None mentioned a fractured internal screw. For reports prior to 1995, 14 were found, with two indicating a fractured internal screw.