What happened
On May 24, 2015, a Schweizer 30/0C helicopter was conducting a student navigation training flight at an altitude of 1,500 feet near Węgrowo, Poland. During the flight, the crew experienced a noticeable drop in engine power. Maintaining level flight became difficult, as the engine was operating at its absolute performance limits. In response to the power loss, the instructor decided to perform a precautionary landing in an unprepared field. The landing was executed on a level surface using a short landing roll of approximately five meters, and the aircraft sustained no damage.
Following the landing, the crew notified both the helicopter operator and the aircraft mechanic. Upon arriving at the site, the mechanic inspected the ignition system and discovered contaminated spark plugs. Additionally, the mechanic found oxidation at the contact point between the spark plugs and the high-tension leads. After cleaning the components and performing a ground engine run, the instructor flew the aircraft back to the technical base.
The investigation
The investigation examined the technical condition of the engine and the maintenance history of the aircraft. It was established that several days prior to the incident, the pilot had encountered difficulties starting the engine. During that previous attempt, a drop in RPM of 250 rpm was noted on one of the magnetos, accompanied by irregular engine operation. The investigation also noted that the operator had previously expressed concerns regarding the poor technical maintenance standards and lack of professional care regarding the aircraft's upkeep.
Findings
- The primary cause of the engine power loss was a technical failure of the ignition system.
- Contamination of two spark plugs and oxidation at the spark plug-to-high-tension lead connections contributed to the malfunction.
- Previous engine starting difficulties and irregular engine running had been observed days before the incident.