What happened
On March 8, 2003, at 10:30 local time, a Socata TB-10 Tobago, registration EC-FTG, experienced an engine failure while cruising at 6,500 feet near the Sierra de Peña de Francia in Salamanca, Spain. The aircraft was being operated by Adventia for a solo student pilot training flight.
Upon the loss of engine power, the pilot declared an emergency with the Salamanca Airport tower. After attempting to restart the engine without success, the pilot selected a suitable landing site and performed an emergency landing on unprepared terrain. The pilot sustained no injuries, though the aircraft suffered minor damage to the landing gear fairing due to the rough surface.
The investigation
Investigators examined the engine and ignition systems both at the landing site and at a maintenance center. Initial inspections at the scene showed that while the propeller could rotate freely, the engine would not start because the battery voltage dropped too low during cranking attempts. Subsequent tests at the maintenance facility, using an external power unit, yielded the same failure.
Upon inspecting the Teledyne Continental D4LN3000 magneto, investigators found that the two points (breakers) remained connected even as the cam rotated, preventing the spark from reaching the spark plugs. The cam surface showed signs of roughness, and the points' followers exhibited material wear with a yellowish discoloration. After replacing the points, the engine started normally.
Investigators also examined the lubricant (P/N 10-86527) used to grease the cam and felt assembly. While a visual comparison between the used lubricant and new lubricant showed only a slight difference, it was noted that the lubricant was handled in a secondary container, which could have introduced impurities.
Findings
- The engine failure was caused by a malfunction in the magneto that prevented the generation of a spark.
- The mechanical wear on the points' followers prevented the electrical circuit from breaking during the rotation of the cam.
- The exact cause of the wear could not be definitively established, but the investigation identified two likely contributing factors: contamination of the lubricating oil or an excessive amount of lubricant being applied during maintenance.
- Although the aircraft had implemented Teledyne Continental Service Bulletin No. 651, the investigation noted that the failure of such bulletins to be mandatory in some jurisdictions could pose a risk to other operators.