Narrative:

Aircraft was in light rime ice at 9000 ft MSL, the wings and windshield were showing light rime ice accumulation, but not enough to warrant turning the boots on, the pitot static and propeller heat were already on. The aircraft yoke started to flutter and almost immediately the aircraft stalled and pitched over left into a dive. The aircraft would not respond to any elevator input only rudder and aileron input. I turned the pneumatic boots on while in the dive and regained elevator control at approximately 4800 ft MSL. I regained level flight at approximately 4000 ft MSL. I then proceeded to climb up to 7000 ft MSL where I remained for the rest of the flight at a temperature of +2 degrees C. The main reason I wanted to report this is that a similar circumstance occurred to me approximately 14 months ago. It would appear that the tail is accumulating more ice or is unable to carry as much ice as the main wing. Also, there was an ice created fatal accident on mar/fri/02 in wisconsin that also involved a C208B. Do you think this should raise some questions about flight characteristics of caravans (C208B) in icing conditions? Callback conversation with reporter revealed the following information: the reporter stated this was the second incident of loss of elevator control due to rime ice buildup on the horizontal stabilizer. The reporter said at 9000 ft a small amount of rime ice was building up on the lower windshield and wings but not enough to switch on the pneumatic de-icer boots. The reporter stated company procedure is to allow buildup to 1/2 inch before turning on the pneumatic boots. The reporter said the airplane pitched over to the left with complete loss of elevator control until 5000 ft where control was regained after switching on pneumatic boots. The reporter said a company pilot also experienced this same type incident with loss of elevator control in light rime icing. The reporter stated the interesting thing about the 3 events is that all occurred in rime ice and not clear ice conditions. The reporter said the company chief pilot called cessna engineering and related the 3 events and was told by cessna it was an 'upset.'

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Original NASA ASRS Text

Title: A C208B IN CRUISE AT 9000 FT WITH WINDSHIELD SHOWING ONLY LIGHT RIME ICE HAD THE ACFT PITCH OVER L INTO A DIVE WITH NO ELEVATOR CTL.

Narrative: ACFT WAS IN LIGHT RIME ICE AT 9000 FT MSL, THE WINGS AND WINDSHIELD WERE SHOWING LIGHT RIME ICE ACCUMULATION, BUT NOT ENOUGH TO WARRANT TURNING THE BOOTS ON, THE PITOT STATIC AND PROP HEAT WERE ALREADY ON. THE ACFT YOKE STARTED TO FLUTTER AND ALMOST IMMEDIATELY THE ACFT STALLED AND PITCHED OVER L INTO A DIVE. THE ACFT WOULD NOT RESPOND TO ANY ELEVATOR INPUT ONLY RUDDER AND AILERON INPUT. I TURNED THE PNEUMATIC BOOTS ON WHILE IN THE DIVE AND REGAINED ELEVATOR CTL AT APPROX 4800 FT MSL. I REGAINED LEVEL FLT AT APPROX 4000 FT MSL. I THEN PROCEEDED TO CLB UP TO 7000 FT MSL WHERE I REMAINED FOR THE REST OF THE FLT AT A TEMP OF +2 DEGS C. THE MAIN REASON I WANTED TO RPT THIS IS THAT A SIMILAR CIRCUMSTANCE OCCURRED TO ME APPROX 14 MONTHS AGO. IT WOULD APPEAR THAT THE TAIL IS ACCUMULATING MORE ICE OR IS UNABLE TO CARRY AS MUCH ICE AS THE MAIN WING. ALSO, THERE WAS AN ICE CREATED FATAL ACCIDENT ON MAR/FRI/02 IN WISCONSIN THAT ALSO INVOLVED A C208B. DO YOU THINK THIS SHOULD RAISE SOME QUESTIONS ABOUT FLT CHARACTERISTICS OF CARAVANS (C208B) IN ICING CONDITIONS? CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THIS WAS THE SECOND INCIDENT OF LOSS OF ELEVATOR CTL DUE TO RIME ICE BUILDUP ON THE HORIZ STABILIZER. THE RPTR SAID AT 9000 FT A SMALL AMOUNT OF RIME ICE WAS BUILDING UP ON THE LOWER WINDSHIELD AND WINGS BUT NOT ENOUGH TO SWITCH ON THE PNEUMATIC DE-ICER BOOTS. THE RPTR STATED COMPANY PROC IS TO ALLOW BUILDUP TO 1/2 INCH BEFORE TURNING ON THE PNEUMATIC BOOTS. THE RPTR SAID THE AIRPLANE PITCHED OVER TO THE L WITH COMPLETE LOSS OF ELEVATOR CTL UNTIL 5000 FT WHERE CTL WAS REGAINED AFTER SWITCHING ON PNEUMATIC BOOTS. THE RPTR SAID A COMPANY PLT ALSO EXPERIENCED THIS SAME TYPE INCIDENT WITH LOSS OF ELEVATOR CTL IN LIGHT RIME ICING. THE RPTR STATED THE INTERESTING THING ABOUT THE 3 EVENTS IS THAT ALL OCCURRED IN RIME ICE AND NOT CLR ICE CONDITIONS. THE RPTR SAID THE COMPANY CHIEF PLT CALLED CESSNA ENGINEERING AND RELATED THE 3 EVENTS AND WAS TOLD BY CESSNA IT WAS AN 'UPSET.'

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.