What happened
On February 8, 2007, an EMB 721C operated by Stilus Táxi Aéreo Ltda was performing a cargo transport flight in the state of Pará, Brazil. After departing from Júlio Cesar, the aircraft stopped at Marborges to pick up a passenger and mail. During the subsequent leg toward Chaves, while cruising at 2,000 feet, the pilot experienced intense vibrations and observed significant movement in the engine cowling.
Following the vibration, the engine experienced a drop in RPM, leading to a loss of airspeed and altitude. The pilot attempted to recover engine power, but the aircraft continued to descend. In an attempt to manage the emergency, the pilot instructed the passenger to move to the rear of the cabin to assist with the weight distribution for a forced landing in the jungle. However, this movement increased the aircraft's pitch, further accelerating the loss of airspeed. The aircraft eventually struck trees and the ground, resulting in a post-impact fire that destroyed the aircraft. The pilot sustained serious injuries, while the passenger sustained minor injuries.
The investigation
CENIPA investigators examined the wreckage and the maintenance history of the propeller assembly. The investigation focused on the discrepancy between the part numbers recorded in maintenance logs and the physical components installed on the aircraft. Technical analysis by the CTA revealed that the propeller blade knob had failed due to fatigue.
Investigators discovered that during a previous overhaul, the propeller blades installed were part number 847/75D-4, rather than the required F8475D model mandated by Airworthiness Directive (AD) 2002-09-08. The incorrect blades featured a thinner knob that was susceptible to failure. Furthermore, the investigation found that maintenance records incorrectly listed the parts as the approved version, indicating a failure in part number verification and quality control during the maintenance process.
Findings
- Failure to comply with Airworthiness Directives: The propeller blades installed were not approved for the specific propeller assembly, as they lacked the necessary thickness in the pitch-change knob required by the manufacturer.
- Maintenance and Quality Control failures: Maintenance workshops failed to verify the physical part numbers against the service documentation, allowing the installation of unapproved components.
- Pilot judgment: During the emergency, the pilot prioritized attempting to restore engine power over maintaining a proper glide profile for a forced landing.
- Inaccurate emergency reporting: The pilot transmitted an incorrect position during the emergency call, which complicated search and rescue efforts.