What happened
On 26 March 2024, a Bombardier CL-600-2B19, registration ZS-CMK, was operating a scheduled commercial flight from O.R. Tambo International Airport to George Airport. While cruising at flight level 300, the starboard cockpit windshield suddenly developed a crack. The incident occurred approximately ten minutes before the aircraft was scheduled to begin its descent.
Following the fracture, the pilot flying immediately donned an oxygen mask and declared an emergency with Cape Town air traffic control. The flight crew subsequently descended to flight level 090. Despite the substantial damage to the windshield, the aircraft remained structurally intact, and the crew completed an unevent and safe landing at George Airport. There were no injuries among the 51 people on board.
The investigation
SACAA AIID investigators examined the windshield assembly to determine the origin of the fracture. The inspection revealed significant cracks in the outer glass layer and extensive delamination between the outer glass and the intermediate layer at the heating element interface. The investigation also noted that the aircraft had been previously stationed in Sudan before being imported to South Africa.
Findings
Technical analysis established that electrical arcing within the heating element was the primary driver of the failure. This arcing, likely triggered by moisture entering the assembly through delaminated zones, created localized high temperatures and electrical stress. The resulting temperature gradient between the layers created enough physical stress to exceed the limits of the tempered glass, leading to the fracture. The investigation also identified that environmental factors, such as UV exposure and moisture ingress, contributed to the delamination of the assembly.
Safety action
To prevent similar occurrences, the investigation highlighted the need for:
- Routine inspections of windshield heating elements to detect discolored interlayers or signs of arcing.
- Enhanced quality control during the maintenance and installation of heating elements to mitigate temperature gradients.
- Specialized training for maintenance personnel to identify early indicators of delamination and electrical malfunctions.