What happened
A McDonnell Douglas MD-8I3 operating as a scheduled passenger flight was cruising at 31,000 feet when the crew heard a thud and observed the left engine surging. White smoke subsequently filled both the cockpit and the cabin. In response, the flightcrew donned oxygen masks, declared an emergency, and began an emergency descent toward Kansas City International Airport (MCI) in Kansas City, Missouri.
When the aircraft was approximately 18 miles north of Whiteman Air Force Base (SZL) in Knob Noster, Missouri, the crew diverted their landing destination from MCI to SZL. Because the operator does not issue approach charts for SZL to its flight crews, the crew requested the runway 19 instrument landing system (ILS) frequency and the inbound course from air traffic control (ATC). ATC provided an incorrect ILS frequency. Consequently, the crew remained without the correct ILS frequency for the duration of the flight and performed a radar approach instead.
During this radar approach, ATC instructed the crew to maintain a minimum vectoring altitude of 2,500 feet mean sea level (MSL). To descend below a cloud layer located 1,400 feet above ground level, the crew descended to 1,800 feet MSL, which was below the instructed minimum vectoring altitude.
The investigation
A metallurgical examination of the left engine identified a fatigue fracture of one fan blade. Further inspection of the engine revealed a 360-degree fracture of the fan exit case.
Investigation into the engine components noted that several service bulletins (SBs) exist for this fan exit case. These bulletins recommend replacing the older aluminum case with a newer steel version and installing stops to prevent axial separation of the case during a fracture. The engine involved in this incident was equipped with an aluminum fan exit case and lacked the installed stops.