Accident Overview
On September 22, 2014, at 1018 Alaska daylight time, a Cessna TU206 (registration N206J) sustained substantial damage during an emergency landing near Deadhorse, Alaska. The aircraft was operated by 70 North LLC under Part 135 as an on-demand air taxi flight. The commercial pilot and three passengers were not injured. Visual meteorological conditions prevailed, and a company flight plan was filed. The flight originated from Badami Airport at 1006, destined for Deadhorse.
Pilot and Passenger Accounts
According to the pilot, approximately 12 minutes after departure, the engine began to vibrate violently during a loss of power. The throttle and propeller controls became unresponsive, and smoke soon filled the cockpit. The pilot executed a forced landing onto the nearest and driest area of tundra. During touchdown, the airplane nosed over, causing substantial damage to the fuselage, wings, and empennage.
Passengers reported hearing a loud bang during cruise flight at about 800 feet above ground level, followed by smoke in the cabin. The engine ran rough and then quit. The pilot called a mayday and initiated a forced landing. One passenger stated that the tail touched down first, and shortly after, the airplane nosed over.
Examination of the Aircraft and Engine
A local mechanic examined the wreckage and found the wings and fuselage buckled, and the vertical stabilizer and rudder crushed near the top. Oil was observed on the lower side of the fuselage. The wreckage was recovered for further examination.
The engine was removed and sent to Continental Motors, Inc. (CMI) in Mobile, Alabama, for detailed inspection on January 14, 2015. The examination revealed a large hole on the top left side of the crankcase near the number 2 cylinder. Visual inspection showed that the number 2 connecting rod had separated from the crankshaft connecting rod journal. The engine was disassembled.
During disassembly, break-away through bolt torque for cylinders 2 and 3 was found to be below CMI specification. The crankcase halves remained secured, but the main bearing support mating surfaces for number 2 bearing exhibited fretting signatures. Cylinder bays 1 through 4 had mechanical damage, while oil galleys were clear of debris.
The number 2 main bearing showed contamination embedded in its surface layer, lubrication distress, and displaced babbit material. It had shed material and shifted to cover the oil port feeding the number 2 connecting rod bearing. The bearing lock tab had moved laterally. Other main bearings had similar contamination but no lock tab movement or slot elongation.
The crankshaft remained intact but displayed thermal distress at the number 2 connecting rod journal. Rear counterweights were mechanically damaged and movable on their hanger blades.
All connecting rods were intact except number 2, which sustained thermal and mechanical damage, separating through the base of the I-beam and both yoke sections. The connecting rod cap was bent with thermal and mechanical damage. Number 1 connecting rod bearing showed normal wear; numbers 3, 4, 5, and 6 had contamination and hard particle damage. Only fragments of number 2 bearing remained, showing evidence of thermal discoloration and heat distress from lack of lubrication.
Maintenance History
According to CMI, the engine was remanufactured on August 3, 2000. It was overhauled and tested on June 9, 2005, and installed on the accident airplane on August 11, 2009. The number 2 cylinder was replaced on August 28, 2012, at 423.3 hours since overhaul. The number 1 cylinder was replaced on September 4, 2013, at 764.1 hours since major overhaul. The most recent maintenance was a 100-hour inspection and oil change on August 19, 2014, at 1,071.8 hours since major overhaul. The tachometer showed 95.5 hours since that oil change; previous intervals were 105.7 and 95.8 hours.