What happened
On February 25, 2015, a Piper PA-28-140, registration PT-JJM, was conducting a navigation training flight from Aeroclube de Eldorado do Sul, RS, toward Torres, RS. The crew, consisting of an instructor and a student, was cruising at 1,200 feet when the engine experienced a sudden and sharp drop in RPM.
Following the power loss, the crew executed emergency checklists and declared an emergency with Air Traffic Control, expressing their intention to land at Porto Alegre Airport. However, during the glide, the crew determined they would not reach the airport and instead opted for an emergency landing at the Hipódromo do Cristal in Porto Alegre. The landing was completed successfully, and the aircraft sustained no damage. Both occupants were uninjured.
The investigation
CENIPA investigators examined the engine and exhaust system to determine the cause of the power loss. While the engine functioned normally at low and medium power settings—with normal oil pressure, temperature, and fuel pressure—it operated irregularly at high power, characterized by RPM fluctuations and vibrations.
Testing confirmed that the magnetos and spark plugs were in normal working condition, and the carburetor showed no signs of obstruction or ingestion. However, an inspection of the exhaust system revealed that the flame arrester tube (part of the muffler) was loose, deteriorated, and broken. This internal failure partially obstructed the exhaust gas flow, which restricted engine performance specifically during high-power operations.
Investigators also reviewed maintenance records and found that the aircraft's engine had accumulated 8,914 total flight hours, yet there was no record of the flame arrester tube being replaced. While the service manual does not mandate replacement, it recommends a thorough inspection of the exhaust system every 100 hours and a replacement of the muffler at 1,000 hours. Furthermore, the maintenance logs for the airframe, engine, and propeller had not been updated since December 2014.
Findings
- The primary cause of the engine irregularity was a deteriorated and broken flame arrester tube that partially obstructed the exhaust gas exit.
- Inadequate aircraft maintenance practices.
- Deficiencies in management planning and maintenance supervision.