What happened
On 8 October 2006, a Jetstream 4100, registration ZS-OMF, was operating an international flight from Durban International Airport to Maputo International Airport. The aircraft was carrying 3 crew members and 17 passengers. During the climb through 12,000ft, the crew received propeller ice warnings. While the pilot activated propeller de-icing, the engine intake anti-icing remained inactive.
Upon reaching 18,000ft, both engines suffered a flameout. Although the left engine restarted via the auto-ignition system, the right engine failed to relight. This imbalance triggered an uncontrolled rightward roll. The aircraft completed two full rolls, including a steep nose-down attitude of -70 degrees. During this period, the aircraft accelerated to over 400 knots, significantly exceeding its maximum demonstrated diving speed, and lost 13,000ft of altitude within 45 seconds. The pilot eventually regained control at 5,000ft and manually restarted the right engine below 1,000ft before returning to Durban. All 0 fatalities and 0 injuries were reported.
The investigation
SACAA AIID investigators examined flight data recorder information, which revealed that the aircraft had entered icing conditions at 12,000ft, but the engine intake anti-icing was not engaged until 18,000ft. Meteorological analysis confirmed that temperatures between -3°C and -16°C in the area were highly conducive to icing.
Technical examination of the right-hand engine revealed that the Negative Torque Sensing (NTS) valve was operating intermittently, which likely prevented the engine from relighting immediately after the flameout. While the aircraft sustained structural cracks in the wing and fuselage fairing due to the high G-loads and overspeed conditions, no major damage was found elsewhere, and the aircraft was correctly maintained.