Accident Overview
On March 24, 2015, at approximately 1507 central daylight time, a Cessna 208B (registration N106BZ) collided with terrain and trees during an off-airport forced landing near Verdigris, Oklahoma. The forced landing resulted from a loss of engine power during an en route climb. The airline transport-rated pilot received minor injuries, while the passenger/mechanic was uninjured. The airplane sustained substantial damage.
The aircraft was owned and operated by a private individual under 14 CFR Part 91 as a post-maintenance test flight. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from Tulsa International Airport at 1500.
Pilot Account
The pilot reported that during the climb, the exhaust gas temperature (EGT) indicated 640°F and engine torque was approximately 65% but steady. As the climb continued, both EGT and torque began to decrease. Determining that a return to TUL was not possible, the pilot aimed for a nearby private airstrip. Unable to maintain sufficient altitude, he selected a field for the forced landing. Shortly after touchdown, the airplane impacted trees, completely severing the left wing from the fuselage and partially severing the right wing.
Aircraft and Engine Details
The airplane was equipped with a Honeywell TPE331-12JR engine (serial number P123178). Maintenance records indicated the new engine was installed on March 10, 2015, in accordance with Supplemental Type Certificate SA10841SC. The engine had accumulated approximately 9 flight hours since installation. The Hobbs hour meter showed 9.6 hours.
Post-Accident Examination
Initial on-scene inspection revealed no fuel in the fuel pressure line or filter bowl when removed. The main fuel line at the engine-driven low-pressure pump had no fuel, and very little fuel drained from the line. About 4 gallons of fuel were recovered from the reservoir tank, 40 gallons from the left wing tank, and 20 gallons from the right wing tank. The left and right wing fuel valves were in the ON position. Continuity of the fuel system from the reservoir tank to the engine was verified, with no pre-impact anomalies found.
The airframe and flight controls showed no failure or malfunction precluding control. The flap jackscrew indicated flaps extended between 10 and 15 degrees.
Engine Examination and Testing
The engine was shipped to Honeywell for operational check and teardown. External examination revealed no uncontained failure or fire damage, but evidence of dirt and vegetation ingestion. During a test cell evaluation, initial start attempts failed. Compressor discharge pressure was less than 2 psi during dry motoring, consistent with earthen debris found in the engine core, at the second-stage compressor impeller entrance, and at the combustor entrance.
Fuel Pump and Control Unit Findings
The fuel pump (part number 897390-8, series 3, serial number P1604) was disassembled. The high-pressure drive gear exhibited wear and missing material, while the driven gear showed minimal wear. Metallurgical examination revealed the damaged drive gear was made of 300-series stainless steel instead of the specified M50 steel; the driven gear was of M50 steel. The gear housing showed wear consistent with debris from the worn drive gear.
Honeywell investigated with gear set manufacturer Shimadzu, who reported that three set-up gears made of 300-series stainless steel were used during manufacturing. One was installed in the accident airplane's fuel pump; the other two remain unaccounted for. Honeywell inspected stock, issued Notices of Escape to customers with similarly configured fuel pumps, and released Service Bulletins TPE331-72-A2255, -A2256, and -A2254.
Examination of the fuel control unit (FCU, part number 897801-3/8070-471, serial number 19357690) at Woodward revealed a stub shaft that initially could not be turned by hand. The FCU contained metal contamination. Testing showed most test points out of limits on Accel and Power Lever schedules. Disassembly revealed metal particles on governor assemblies, valve plungers, and sleeves. Scoring was noted on the overspeed governor pilot valve. Metal shavings throughout the FCU were consistent with material from the fuel pump drive gear.