What happened
On April 23, 2013, at approximately 17:45 UTC, an Aero Boero AB-115, registration PP-GBC, was conducting a flight instruction mission near Maringá, Paraná. The aircraft, operated by Aeroclube Regional de Maringá, departed from the Maringá Aerodrome under VFR flight rules with an instructor and a student pilot on board. After 45 minutes of flight, while the crew was beginning their return to the airfield at a level altitude, the engine experienced a sharp decrease in RPM. To prevent a more critical situation, the instructor took control and executed an emergency landing on a rural road known as Estrada Romeira.
There were no injuries to the two occupants, and the aircraft sustained no damage during the landing.
The investigation
CENIPA investigators conducted ground tests on the engine, which revealed that the RPM could not exceed 1900, significantly lower than the required 2700 RPM. While the magneto system was found to be operating according to maintenance manuals, an inspection of the spark plugs revealed that the four lower plugs contained lead deposits inside. This buildup was identified as a potential cause for spark leakage, which would result in a reduction of the maximum available engine power. Additionally, investigators noted that while flight hour tracking was being maintained in the aircraft logbook, the specific airframe, engine, and propeller logbooks were not up to date regarding flight hour records.
Findings
- The primary cause of the power loss was lead accumulation within the lower spark plugs, which likely caused spark leakage and reduced engine performance.
- The instructor successfully managed the emergency by selecting a suitable landing site.
- The crew members held valid medical and technical certifications.
- The aircraft was within weight and balance limits and possessed a valid Certificate of Airworthiness.
- Maintenance record-keeping for the airframe, engine, and propeller components was incomplete regarding flight hour updates.