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On September 26, 1998, at 1210 hours Pacific daylight time, a Rockwell Commander 114, N114AL, landed hard and severed the right main landing gear after experiencing an engine failure at the Castle Air Force Base in Atwater, California. The aircraft, owned and operated by the pilot under 14 CFR Part 91, sustained substantial damage. The private pilot was not injured. The personal flight originated at the Watsonville, California, airport at 1120, and no flight plan was filed. Visual meteorological conditions prevailed.
The pilot reported that the engine sputtered then quit as he was turning base for runway 31, approximately 400 to 700 feet agl, and about 1/2 mile out. He notified the tower that he was experiencing engine problems and continued toward the runway to land. The pilot reported that he landed hard and the right main landing gear sheared off. The aircraft continued forward on the runway approximately 1,200 feet then impacted a runway light and veered off into a grassy area.
The aircraft maintenance records were reviewed and relevant portions are appended to this file. The accident aircraft was equipped with a Teledyne Continental D-2000 series magneto, which consists of a dual magneto and harness assembly, with two electrically independent ignition circuits in one housing. An annual inspection of the aircraft was performed and signed off on May 28, 1998. The following day, the co-owner of the aircraft conducted a run-up, which resulted in rough idle at lower rpm. The aircraft was left at the maintenance facility until August 14, 1998, during which time the magneto was removed for a 500-hour inspection (June 13, 1998). The mechanic stated that he checked all the points for evidence of arcing and found none. He reported that he ran the magneto on a test bench and it ran normally, with no abnormalities. The records for the 500-hour inspection indicated that all airworthiness directives through AD 82-20-01, and all service bulletins through SB 658 were complied with, including Bendix Mandatory Service Bulletin No. 587, which addresses inspection of the D-2000 series magneto capacitors and capacitor lead crimp terminals. A new magneto cap and harness were installed on September 2, 1998. The pilot flew 19.7 hours in August and September with no noted discrepancies. He reported that on September 19, 1998, while performing a run-up before takeoff, he noted no drop on the right magneto and a full drop on the left magneto. Maintenance was performed on the magneto and the work was signed off on September 25, 1998. The pilot reported that during the run-up before the accident flight he performed two magneto checks on both sides with no noted discrepancies.
A Federal Aviation Administration (FAA) inspector from the Fresno Flight Standards District Office conducted an examination of the engine on October 23, 1998. A copy of his report is attached. He noted no external damage to the engine and reported that the propeller rotated freely. Crankshaft rotation produced thumb compression and accessory gear and valve train continuity. The fuel tanks were approximately 3/4 full. The inspector noted that the left wing's fuel vent line was blocked with an obstruction of mud or wax. He inspected the fuel vent system to check for any blockage from the obstruction. He blew air into both wing fuel access caps and found no blockage that restricted any atmospheric flow. He reported that the alternate hole, which was near the primary opening, provided adequate atmospheric flow. All other vents located under the fuselage were found unrestricted.
The inspector reported that he removed and examined the magneto. He noted no external damage. He verified continuity of the wiring in the cockpit and disconnected the primary "P" leads to establish continuity of the magneto wiring to the engine with the distributor cap still installed. The inspector noted that the right points were not opening and the left points were not closing. The distributor cap was then removed and the distributor gears were checked for movement when the propeller was moved. Continuity was verified for the wires from each condenser and the coils.
The magneto was then checked for proper internal timing of both the neutral and the left points, which are used for starting the engine. The inspector reported that the left breaker points were set properly with a gap of approximately .016 inches. The magneto synchronizer tester indicated that the points would not close completely, thus not allowing the coil to build up voltage to the spark plugs. A piece of paper was placed in between the contact points to check for oil build-up or carbon obstruction. No discrepancies were noted. During the inspection, the points would intermittently close, allowing voltage to build up to the spark plugs. The left points were hooked to a timing indicator and the points didn't fully close after rotating both forward and backward. The points would sometimes touch under a spin of 500 rpm, but would intermittently close momentarily, allowing the magneto to fire. The cam follower would move away from the point arm but the points would not conduct between themselves unless they were pushed harder together. The wiring in the cockpit was checked to ensure that the left magneto had not lost its ground wire. All wires were found to be continuous. Visual inspection of the plastic cam follower for the left side of the magneto revealed that it had melted where it comes in contact with the points assembly.
Examination of the right set of points revealed that the points would not open at all with the rotation of the drive gear and cam. The cam arm would move, but would not move the point arm. All breaker-retaining screws were checked for security to confirm that the points did not move in any way. The screws were found tight; they were checked with a snap-over torque wrench set at 21-inch pounds, and none of the screws shifted position before the wrench registered 21-inch pounds. The cam follower was melted where it met the breaker spring for the right breaker contacts.
TESTS AND RESEARCH
The magneto was sent to Teledyne Continental and was tested under the auspices of the FAA. The Teledyne representative reported that the impulse coupling functioned normally when snapped through by hand, and the spring was in good condition. He stated that electrical continuity was observed through the points for the right breaker contacts at all positions of the breaker cam. Electrical continuity was not established for the left breaker points at all positions of the breaker cam; however, continuity was noted between the housing and the breaker support. The distributor gear timing was correct on the right and left sides.
The Teledyne representative reported that the magneto was mounted on a test stand with a new slave harness and capacitors. The magneto was turned at speeds up to 2,000 rpm, but did not produce sparks. The right side breaker points were reset to .015 inches of clearance, with an 8-degree E-gap. Both sides produced sparks during the second test run.
The original harness and capacitors were visually inspected. The Teledyne representative noted that the capacitors were mounted securely in the cover. The left capacitor rubber boot was found loose. The boot on the right capacitor was firmly attached. Both boots were blackened and cracked. The representative reported that both capacitor's capacitance were within specified tolerances. He further stated that neither capacitor passed the insulation resistance test at 400 VDC.
The magneto was mounted on the test stand again, this time with the original harness and capacitors attached. Both sides of the magneto generated sparks at 500 rpm and 1,000 rpm. A 150-watt lamp was set up next to the magneto to simulate engine heat. The magneto was then run at a speed approximating cruise speed. After 5 minutes, the right magneto ceased to generate sparks. The left magneto generated sparks for the duration of the test.