A Cessna Citation 560 was flying from Brisbane to Townsville (Queensland, Australia), onboard 6 passengers and 2 flight crew.
When climbing through FL320 (~9500 meters) a series of loud bangs were heard and accompanying vibration felt throughout the aircraft.
Upstream view of the low-pressure compressor boost rotor (Source P&W Canada)
Shortly thereafter a slight mist and an acrid smell became apparent in the cockpit. After donning his oxygen mask the pilot monitoring made a "PAN PAN" call to ATC, requesting an immediate return to Brisbane and an emergency descent. The descent was approved and initiated as well as the return to Brisbane. A scan of the engine parameters and other system indications did not reveal an immediate issue. The right-hand engine was not shut down. During the descent, the crew looked at different options for diversion but stuck with their original plan. During the descent, the smoke disappeared, although when thrust was increased when the aircraft was configured for landing, the smell briefly re-occurred. The subsequent approach and landing were uneventful.
An initial examination with a horoscope, of the Pratt & Whitney Canada JT15D-5D engine and the airframe revealed that the cause of the loud bangs was the failure of a blade on the Low-Pressure compressor boost stage rotor. There was no evidence of impact in the area of the fracture, nor was any damage found upstream of the rotor. The blades adjacent to the failed blade displayed various degrees of damage. This indicated that the fracture was not caused by impact.
Boost rotor showing missing aerofoil and surrounding damage (Source P&W Canada)
Extensive damage was found downstream from the failure. The failed compressor blade was found downstream in the compressor, wedged between compressor blades.
The blade fracture surface showed clear signs of high cycle fatigue cracking, a metallurgical section examination of the fracture revealed that there were no signs of an anomaly in the material or a production error.
The detailed report into this engine failure can be found by clicking here.