What happened
On August 13, 2002, an EMB 120 operated by Rico Linhas Aéreas S/A arrived at Eduardo Gomes Airport (SBEG) in Manaus, Brazil, following a multi-leg flight from Rio Branco. Upon reaching the parking area, the crew attempted to apply the brakes after feathering the propellers, but found the normal braking system to be ineffective.
In an attempt to stop the aircraft, the crew attempted to use reverse thrust; however, because the propellers were already in the feathered position, this maneuver was unsuccessful. To avoid hitting a masonry structure located at the parking stand, the pilot steered the aircraft to the left, exiting the apron limits. The aircraft subsequently struck a concrete building with the left engine and entered a drainage ditch with the right landing gear. The emergency brake was applied too late to prevent the collision. All 25 occupants (three crew members and 2/22 passengers) evacuated the aircraft without injury, but the aircraft sustained severe damage and was deemed a total loss.
The investigation
CENIPA investigators examined the aircraft's braking and anti-skid systems, as well as maintenance records and crew training. Technical analysis by Embraer revealed that the anti-skid system's speed sensor drive clips exhibited excessive play, far exceeding the tolerances specified in the Maintenance Manual.
At low taxi speeds (below 25 knots), this excessive play generated signals that the anti-skid system interpreted as imminent wheel lock-up. Consequently, the system activated its protection mode, which momentarily relieved hydraulic pressure to the brakes, causing the perceived loss of braking effectiveness. The investigation also found that while previous reports of braking issues had been logged, maintenance actions had been limited to bleeding the system and replacing brake assemblies rather than inspecting the anti-skid transducers. Furthermore, the aircraft had not been updated with a specific Service Bulletin designed to assist mechanics in verifying these clip tolerances.
Findings
- Inadequate crew training: The crew failed to follow the aircraft manual's emergency procedures, specifically by attempting to use reverse thrust with feathered propellers instead of applying the emergency brake.
- Maintenance deficiencies: Maintenance personnel failed to adhere to the Maintenance Manual regarding the dimensional adjustment of the anti-skid hub cap drive clips.
- Inadequate oversight: The operator failed to properly supervise maintenance tasks and ensure the implementation of required Service Bulletins.
- Anti-skid system malfunction: Excessive play in the speed sensor clips caused the anti-skid system to erroneously release brake pressure during low-speed taxiing.