History of Flight
On January 9, 2014, at 1515 mountain standard time, a Cirrus Design Corp SR22, N903SR, was in cruise flight near Pocatello, Idaho, when the engine began vibrating severely and lost partial power. The pilot declared an emergency and received vectors from Salt Lake Center for an instrument landing system approach to Pocatello. Despite adjusting mixture and throttle, engine power continued to decrease. After descending through a broken cloud layer, the pilot determined the airplane could not reach the runway, shut down the engine at about 1,000 feet above ground level, and deployed the Cirrus Airframe Parachute System (CAPS). The airplane descended into an open field. The pilot and passenger rapidly exited before the parachute dragged the airplane in a 30-knot wind. The private pilot and single passenger sustained minor injuries; the airplane was substantially damaged.
Pilot Information
The 58-year-old private pilot held ratings for single-engine land, multi-engine land, and instrument airplane, with a third-class medical certificate requiring glasses for near vision. He reported 2,159 total flight hours, with 2,046 hours in the accident airplane make and model and 42 hours in the previous 90 days.
Aircraft Information
The four-seat, low-wing, fixed-gear airplane, serial number 2465, was manufactured in 2007. It was powered by a Continental Motors IO-550-N46B, 310-hp engine modified with a Tornado Alley turbonormalizing system and equipped with a Hartzell 3-bladed composite constant-speed propeller. An annual inspection was performed on December 13, 2013, at a total airframe and engine time of 850.3 hours. On September 2, 2010, at 496.2 engine hours, both magnetos were overhauled and reinstalled.
Engine Examination
On April 15, 2014, the engine was examined at Continental Motors, Inc. under NTSB supervision. When the crankshaft was rotated, both magneto distributor gears did not move. Examination revealed that nylon composite distributor gear teeth had broken off: 10 teeth on the right magneto and 3 teeth on the left. The fractured gear teeth were aligned on an exemplary magneto, showing that the separated teeth would have placed the distributor gear electrode between cylinders' distributor block electrodes, causing improper firing order. New magnetos were installed, and the engine ran successfully to full power in a test cell with no anomalies.
Magneto Distributor Gear Examination
The fractured gears were sent to the NTSB Materials Laboratory. The left gear had three teeth fractured, with fracture surfaces exhibiting crack arrest marks and river patterns consistent with progressive failure. The right gear had ten fractured teeth, also with progressive cracking features. A 0.5-inch radial crack was present on one tooth. Scanning electron microscopy showed no material defects at the crack initiation site. The magnetos had accumulated 860.4 hours at the time of the accident; the last inspection was at 496.2 hours, and the required inspection interval is 500 hours.
Timeline from Flight Data
Data from the Primary Flight Display and Multi-Function Display showed that the descent began at about 14:38:30. RPM started decreasing and fluctuating at 14:41:18. The pilot manipulated mixture and throttle, observed through fuel flow and RPM changes. Cylinder head temperatures for No. 6 and No. 3 cylinders increased above average, and exhaust gas temperatures for several cylinders dropped off while others increased, consistent with ignition issues.