What happened
On December 7, 2021, a Piper PA-36-375, registration PR-TRE, was performing agricultural spraying operations near Fazenda Cachoeira Dourada in Veríssimo, Minas Gerais. During a positioning maneuver, the pilot experienced a sudden drop in engine RPM and a decline in manifold pressure, leading to a total engine failure.
In an attempt to prevent a crash, the pilot jettisoned the agricultural payload and executed a forced landing into a nearby crop field. The aircraft sustained substantial damage, but the pilot emerged uninjured.
The investigation
CENIPA investigators examined the engine, which had been modified with a Special Flight Authorization (AEV) to operate on hydrated ethanol. The investigation focused on the fuel system, specifically a secondary line used for a cold-start system. This system utilized a small reservoir of gasoline inside the cabin to facilitate engine starts in ethanol-fueled operations.
Investigators discovered that a copper tube, connected via an improvised T-adapter to the main pressure line of the fuel metering valve, had ruptured. This modification lacked technical specifications, engineering data, or formal records of incorporation into the aircraft's permanent logs. The investigation also noted that the copper tubing was installed in a misaligned and "forced" manner, creating stress concentrations at the fitting.
Findings
- The primary cause of the engine failure was the rupture of a copper fuel line within an improvised cold-start system, which caused a loss of fuel pressure to the cylinders.
- The use of an improvised, unrecorded modification to inject gasoline into the ethanol fuel stream contributed to the failure.
- The lack of technical parameters or manufacturer-approved procedures for maintaining or recalibrating the fuel system for ethanol use created latent safety risks.
- The installation of the copper tubing was improperly aligned, leading to stress concentrations that facilitated the rupture.
- There was a lack of adequate protection or containment for potential leaks in the modified pressure line.
Safety action
It is recommended that the National Civil Aviation Agency (ANAC) work with the operator to establish supervisory mechanisms capable of identifying unauthorized or undocumented alterations to aircraft components, particularly those related to fuel delivery systems.