What happened
On 18 August 2017, an Airlink flight departing from Cape Town International Airport for Wonderboom Airport experienced a sudden mechanical failure during its ascent. While climbing through 6,000 feet, the crew of the AVRO 146-RJ85A, registration ZS-ASZ, reported a loud bang and a significant yawing motion, immediately followed by a fire warning for engine number four.
In response to the alert, the crew deployed the first fire extinguisher, but the warning persisted after thirty seconds. They subsequently deployed a second extinguisher, yet the indication remained active. The captain requested vectors for a return to runway 19 and proceeded to shut down the fourth engine. As the aircraft approached the runway on final, the fire warning subsided. Upon landing, ground personnel and fire services confirmed there were no visible flames or active fire on the aircraft. There were 0 injuries among the 55 people on board.
The investigation
The SACAA AIID investigation focused on the mechanical failure of the engine's gas producer module. Investigators examined the engine's maintenance history, noting that the engine had accumulated 22,307 cycles since new. The inquiry specifically looked into the condition of the bearing no. 2 package and the associated oil scavenge tube.
Findings
Technical analysis determined that the fire warning was triggered by a leak of hot oil mixed with compressor exit air. This leak originated from a ruptured no. 2 bearing oil scavenge tube. The investigation found that a worn seal within the bearing package allowed excessive compressor air to enter the lubricating system, which aerated the oil and raised its temperature. This heat caused the fire sleeve on the flexible section of the scavenge tube to melt.
The breakdown of the no. 2 bearing pack was attributed to natural fatigue of the component, which had operated for approximately 19,670 cycles.
Safety action
Following the findings, a safety recommendation was directed to the FAA, suggesting that Honeywell Aerospace should establish a maximum allowable service life—specifically at least 15,000 cycles—for the LF507 turbofan engines, as these engines currently operate without a defined periodic inspection schedule or service life limit.