What happened
On June 23, 2000, at approximately 08:15Z, a Boeing B747-244, registered as ZS-SAL, was preparing for a domestic scheduled flight from Cape Town International Airport to Johannesburg International Airport. During the taxi phase of the operation, the aircraft experienced a sudden failure in its braking systems, specifically involving the loss of pressure in the number 4 primary hydraulic system and the number 1 secondary hydraulic system.
Despite the loss of these systems, the pilot was able to maintain control of the aircraft's movement by immediately engaging the number 2 reserve hydraulic brake system to bring the plane to a halt. There were no fatalities or injuries reported during the incident, though 2 individuals sustained injuries.
The investigation
SACAA AIID investigators examined the mechanical failure of the braking assembly to determine why the hydraulic pressure dropped across multiple systems. The investigation focused on the integrity of the anti-skid module assembly and its associated components.
Findings
Technical analysis revealed that the failure originated within the anti-skid module assembly. Specifically, the investigation established that a crack developed in the body of the cartridge check valve at the threaded section. This structural failure in the valve was the direct cause of the pressure depletion in both the number 4 primary and number 1 secondary hydraulic brake systems.