History of Flight
On July 5, 2014, at 1513 Pacific daylight time, a Globe Swift GC-1B, N3773K, made a forced landing into a field following a loss of engine power during approach to Pierce County Airport/Thun Field, Puyallup, Washington. The private pilot, the sole occupant, was not injured; the airplane sustained substantial damage. The local flight departed from Vashon Municipal Airport, Vashon, Washington, about 1455 with a planned destination of Puyallup. Visual meteorological conditions prevailed, and no flight plan was filed.
The pilot reported that while on the downwind leg for runway 34, he configured the airplane for landing, including lowering the landing gear. He extended the downwind leg to allow spacing for other traffic and lowered the wing flaps during the turn to base leg. During the turn, the engine made a loud "bang" and experienced a partial loss of power. The JPI engine monitor indicated minimal exhaust gas temperatures (EGTs) on the right side (cylinders 1, 3, and 5). Oil and fuel pressure gauges remained normal. Gray smoke emanated through the right side of the cockpit, but no fire was detected. Activating the fuel boost pump to "low boost" worsened the engine operation; turning it off temporarily restored power, but EGTs on the left side then dropped. The airplane continued to descend and collided with an embankment on airport property before the runway. The airplane bounced and slid to a stop, incurring structural damage to the left wing.
Preliminary engine examination revealed that the no. 3 cylinder's piston was not intact.
Aircraft Information
The Globe GC-1B Swift, serial number 1466, was manufactured in 1946. The engine was a Continental Motors IO-360-KB3B, serial number 288571-R, with 1,393 total hours. The last annual inspection was dated October 20, 2013, at an airframe total time of 3,431.5 hours, noting that the engine would be airworthy upon completion of repair to the no. 3 cylinder for an exhaust leak.
Maintenance in December 2013, about 30 hours before the accident, involved repairs to the no. 3 and 5 cylinders for exhaust anomalies. Records show replacement of intake valves, intake guide seals, one exhaust valve (the second was on back order), exhaust guides, and eight valve keys. Labor paperwork indicated assembly of cylinders with valves, springs, piston, and rings. A logbook entry dated December 12, 2013, stated both cylinders were removed, exhaust guides and valves replaced, intake valves replaced, and new gaskets and seals installed.
On May 27, 2014, the pilot changed the oil and filter at tachometer time 170.8 hours (19.1 hours after the December maintenance). He observed small metal flakes in the oil filter, the largest measuring 0.108 inches, and sent an oil sample for analysis. The laboratory report on May 31, 2014, indicated high copper content, advising corrective action. The pilot consulted an aviation mechanic, who recommended scanning electron microscope (SEM) evaluation of the flakes. Material analysis on June 19, 2014, identified the flakes as carbon steel with a closest match to Aerospace Material Specification (AMS) 5040 and 7225. The pilot decided to fly an additional 10 hours before taking another oil sample; the accident flight was intended to purchase parts for the upcoming oil change.
Engine Examination
Post-recovery examination revealed that all cylinders were secured to the crankcase. The no. 3 spark plug showed significant mechanical damage; spark plugs for cylinders 1 and 4 had thin metallic splatter on the electrode faces. Induction system risers were attached, and metal debris was found in the intake above the no. 4 cylinder. Borescope examination of the no. 3 cylinder disclosed a large rectangular hole in the top of the piston and significant mechanical damage to the cylinder head. The exhaust-valve head was separated from its stem and lodged in the exhaust valve seat perpendicular to its normal position. Rockerbox covers on the no. 3 cylinder contained metal debris. The no. 3 cylinder's exhaust pushrod was bent, and the exhaust valve retainer key (keepers) was destroyed; the rocker toe exhibited light deformation. The cylinder was removed, revealing a fractured piston skirt, but the piston remained secured to the connecting rod by the piston pin. The propeller blades were bent aft with leading edge gouges. The oil sump contained numerous pieces of fractured piston and rings. The oil filter (dated May 27, 2014) contained metallic particles embedded in the pleats.
Metallurgy
Examination by the NTSB Materials Laboratory focused on the no. 3 and 5 cylinders. The top interior surface of the no. 3 cylinder was heavily damaged with batter and impact marks. The exhaust valve head detached from its stem and was wedged in the exhaust port. The damage was consistent with the exhaust valve fracturing at the stem, after which the liberated head was pommeled between the cylinder and piston crown. No remnants of the valve stem were found. The rocker arm exhibited abnormal wear, and the keeper components showed gouging, material loss, and chatter marks. One keeper was missing its entire upper half, with crescent-shaped witness marks on the remaining fragment. These signatures were consistent with keeper misalignment during operation. Debris from the no. 3 cylinder assembly was consistent with material from the keepers, valve, or damaged cylinder; no foreign material or contamination was found.