What happened
On September 19, 2015, at 15:55 UTC, a SkyRanger ultralight aircraft, registration CS-ULK, was en route from Figueira dos Cavaleiros to Alqueidão UL. Approximately 12 minutes into the flight, the pilot experienced unusual engine noise, vibrations, and a subsequent loss of power.
Following the onset of intense vibrations, the pilot shut down the engine and executed an emergency landing in a rice field south of Alcácer do Sal. Upon contact with the ground, the nose landing gear became embedded in the wet, clay-heavy soil, causing the aircraft to pivot and come to rest in an inverted position. While the pilot and passenger escaped without injury, the aircraft sustained substantial damage to the engine, propeller, nose gear, and windshield.
The investigation
The GPIAAF investigation focused on the mechanical condition of the power plant and the maintenance history of the aircraft. Investigators examined the engine, a Rotax 912 UL, and found evidence of internal failure. The investigation also reviewed the maintenance logs, noting that while the engine had been maintained since its installation on this specific airframe in 2005, the intervals between maintenance actions were irregular, ranging from one to three years. There were no maintenance records available for the aircraft airframe itself.
Findings
Technical analysis of the engine revealed that the rod-crank system at position #3 had seized, showing wear and damage from extreme temperatures. This failure led to a rupture in the crankcase. The investigation identified the engine lubrication system failure as the primary driver of the event, specifically noting a disconnection of the oil suction line at the oil radiator outlet. The damage to the crankshaft journals suggested that insufficient lubrication had caused the components to overheat and melt.
Safety action
The investigation concluded that no new safety recommendations were necessary, as a previous recommendation (SR2018-09) had already been issued to the National Civil Aviation Authority (ANAC) regarding the need to update regulatory frameworks for ultralight aircraft certification and maintenance procedures.