What happened
On September 18, 2013, an Embraer EMB-500, registration PR-JAJ, was performing a private passenger flight from Congonhas (SBSP) to Blumenau (SSBL). The flight was operated by AJ Malls Shop. e Merchandising Ltda., carrying two crew members and four passengers.
Upon landing on runway 36 at Blumenau, the pilot applied the brakes, causing the aircraft to veer sharply to the left. Although the commander attempted to correct the path by modulating brake pressure, the left landing gear momentarily exited the paved surface by approximately 0.5 meters. In an attempt to stop the aircraft within the remaining runway length, the pilot applied more braking force, which caused the aircraft to exit the runway again into the paved taxiway area. There were no injuries to the six occupants and no damage to the aircraft.
The investigation
CENIPA investigators examined the aircraft's braking system, specifically focusing on the Brake Control Unit (BCU) and the Right Wheel Speed Transducer (RWST). Initial testing suggested the RWST was functioning correctly after being tested by the manufacturer, Meggitt, in the United States.
Analysis of the Cockpit Voice and Data Recorder (CVDR) and the Central Maintenance Computer (CMC) revealed spurious speed signals. During the flight phase when the landing gear was retracted, the system recorded a speed of approximately 60 knots for the right main wheel. Post-landing, the data showed that while the pilot increased brake pedal deflection, the actual hydraulic pressure applied to the right brake decreased. This discrepancy confused the BCU, which reduced pressure to the right brake to prevent a perceived skid, leading to the loss of directional control.
Findings
- A short circuit was identified in the braking system wiring (W601-00011-24BL) that transmits speed signals between the wheel speed transducer and the BCU.
- Damage was found on the backshell of connector P0404, which may have occurred during manufacturing or during maintenance when wires were potentially crushed against the connector threads.
- The original production inspection seals on the connector were missing, suggesting the component had been handled during a previous maintenance event.
- The investigation could not determine the exact maintenance instance where the seal was broken or if the fault originated during original assembly.
Safety action
CENIPA issued a recommendation to the National Civil Aviation Agency (ANAC) to disseminate the findings of this investigation. The goal is to alert Brazilian civil aviation operators and maintenance organizations to the importance of verifying the integrity of wiring connectors on EMB 500 aircraft during maintenance procedures.