Narrative:

Aircraft was in unheated hangar overnight. Outside air temperature approximately 8 degrees F in fog. We removed aircraft from hangar. Added fuel. Startup and taxi normal. Because of the very cold temperatures, IMC departure (clearance was to pick up IFR at altitude because of truckee's location relative to surrounding high terrain). We performed a very thorough, detailed runup. We did notice what sounded like a small piece of ice hitting the fuselage when checking the magnetos. This raised the question of whether or not the propellers had accumulated ice during taxi, even though the propeller heat had been on since startup. Because we were able to verify (via propeller amps) that propeller deice was operative, we assumed there was no significant ice accumulation on the propellers and taxied onto the runway for departure. Our turn to line up on the runway put sunlight on the copilot side of the aircraft (it was sunrise), and I noticed frost on the wings. The pilot and I discussed this finding and I offered to wipe the frost off. He shut down right engine and I found substantial propeller and air frame ice accumulations. The air frame icing consisted of frost on upper wing surface and mixed rime and clear ice on engine nacelles, vertical stabilizer, horizontal stabilizer. Of particular interest was the ice accumulation on the underside of the horizontal stabilizer -- the side most critical to flight. There was also frost on the upper surface of horizontal stabilizer. There was significant propeller ice, as follows: approximately 1/3 inch on leading edges outboard of propeller boots (clear ice), 1/4-1/3 inches mixed ice on back of propeller blades, some clear ice on front of propeller blades. There are several points to consider about our findings: 1) we assumed the fog was frozen and therefore of no threat as regards air frame or propeller icing. Structural ice on the ground (with exception of during precipitation) had never occurred to me. 2) the aircraft was 200 pounds under maximum gross weight of 6200 pounds. The takeoff performance would have been compromised -- perhaps seriously -- had we attempted to depart carrying that much ice. 3) had we experienced even partial power loss, single engine climb would have been unlikely, particularly considering terrain. 4) not 1 pilot I've asked would have suspected structural ice in those conditions. 5) an small transport had crashed 1 week prior to our incident on takeoff under virtually identical conditions (even time of day). I believe the NTSB should consider our (more fortunate) experience in its investigation, particularly if other causes (power loss, etc) are not conclusive. Callback conversation with reporter revealed the following information: reporter states this was the most shocking and sobering experience of his life. Feels if they had tried a takeoff it would not have worked. They were more than 200 pounds under gross but the ice would probably have prevented lift enough to get airborne. In speaking with many other experienced pilots they all are of the same feeling that they would not have expected air frame icing to occur on the ground in such temperatures. Chipping ice off the air frame in 8 degree WX is not much fun but he is extremely pleased they were able to do that instead of being picked up in pieces. Callback specifically made to suggest to reporter that he contact NTSB with this information since previous accident so similar.

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Original NASA ASRS Text

Title: SMT ACCUMULATES REMARKABLE ICING DURING TAXI WITH LOW TEMP AND FOG.

Narrative: ACFT WAS IN UNHEATED HANGAR OVERNIGHT. OUTSIDE AIR TEMP APPROX 8 DEGS F IN FOG. WE REMOVED ACFT FROM HANGAR. ADDED FUEL. STARTUP AND TAXI NORMAL. BECAUSE OF THE VERY COLD TEMPS, IMC DEP (CLRNC WAS TO PICK UP IFR AT ALT BECAUSE OF TRUCKEE'S LOCATION RELATIVE TO SURROUNDING HIGH TERRAIN). WE PERFORMED A VERY THOROUGH, DETAILED RUNUP. WE DID NOTICE WHAT SOUNDED LIKE A SMALL PIECE OF ICE HITTING THE FUSELAGE WHEN CHKING THE MAGNETOS. THIS RAISED THE QUESTION OF WHETHER OR NOT THE PROPS HAD ACCUMULATED ICE DURING TAXI, EVEN THOUGH THE PROP HEAT HAD BEEN ON SINCE STARTUP. BECAUSE WE WERE ABLE TO VERIFY (VIA PROP AMPS) THAT PROP DEICE WAS OPERATIVE, WE ASSUMED THERE WAS NO SIGNIFICANT ICE ACCUMULATION ON THE PROPS AND TAXIED ONTO THE RWY FOR DEP. OUR TURN TO LINE UP ON THE RWY PUT SUNLIGHT ON THE COPLT SIDE OF THE ACFT (IT WAS SUNRISE), AND I NOTICED FROST ON THE WINGS. THE PLT AND I DISCUSSED THIS FINDING AND I OFFERED TO WIPE THE FROST OFF. HE SHUT DOWN R ENG AND I FOUND SUBSTANTIAL PROP AND AIR FRAME ICE ACCUMULATIONS. THE AIR FRAME ICING CONSISTED OF FROST ON UPPER WING SURFACE AND MIXED RIME AND CLR ICE ON ENG NACELLES, VERT STABILIZER, HORIZ STABILIZER. OF PARTICULAR INTEREST WAS THE ICE ACCUMULATION ON THE UNDERSIDE OF THE HORIZ STABILIZER -- THE SIDE MOST CRITICAL TO FLT. THERE WAS ALSO FROST ON THE UPPER SURFACE OF HORIZ STABILIZER. THERE WAS SIGNIFICANT PROP ICE, AS FOLLOWS: APPROX 1/3 INCH ON LEADING EDGES OUTBOARD OF PROP BOOTS (CLR ICE), 1/4-1/3 INCHES MIXED ICE ON BACK OF PROP BLADES, SOME CLR ICE ON FRONT OF PROP BLADES. THERE ARE SEVERAL POINTS TO CONSIDER ABOUT OUR FINDINGS: 1) WE ASSUMED THE FOG WAS FROZEN AND THEREFORE OF NO THREAT AS REGARDS AIR FRAME OR PROP ICING. STRUCTURAL ICE ON THE GND (WITH EXCEPTION OF DURING PRECIPITATION) HAD NEVER OCCURRED TO ME. 2) THE ACFT WAS 200 LBS UNDER MAX GROSS WT OF 6200 LBS. THE TKOF PERFORMANCE WOULD HAVE BEEN COMPROMISED -- PERHAPS SERIOUSLY -- HAD WE ATTEMPTED TO DEPART CARRYING THAT MUCH ICE. 3) HAD WE EXPERIENCED EVEN PARTIAL PWR LOSS, SINGLE ENG CLB WOULD HAVE BEEN UNLIKELY, PARTICULARLY CONSIDERING TERRAIN. 4) NOT 1 PLT I'VE ASKED WOULD HAVE SUSPECTED STRUCTURAL ICE IN THOSE CONDITIONS. 5) AN SMT HAD CRASHED 1 WK PRIOR TO OUR INCIDENT ON TKOF UNDER VIRTUALLY IDENTICAL CONDITIONS (EVEN TIME OF DAY). I BELIEVE THE NTSB SHOULD CONSIDER OUR (MORE FORTUNATE) EXPERIENCE IN ITS INVESTIGATION, PARTICULARLY IF OTHER CAUSES (PWR LOSS, ETC) ARE NOT CONCLUSIVE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THIS WAS THE MOST SHOCKING AND SOBERING EXPERIENCE OF HIS LIFE. FEELS IF THEY HAD TRIED A TKOF IT WOULD NOT HAVE WORKED. THEY WERE MORE THAN 200 LBS UNDER GROSS BUT THE ICE WOULD PROBABLY HAVE PREVENTED LIFT ENOUGH TO GET AIRBORNE. IN SPEAKING WITH MANY OTHER EXPERIENCED PLTS THEY ALL ARE OF THE SAME FEELING THAT THEY WOULD NOT HAVE EXPECTED AIR FRAME ICING TO OCCUR ON THE GND IN SUCH TEMPS. CHIPPING ICE OFF THE AIR FRAME IN 8 DEG WX IS NOT MUCH FUN BUT HE IS EXTREMELY PLEASED THEY WERE ABLE TO DO THAT INSTEAD OF BEING PICKED UP IN PIECES. CALLBACK SPECIFICALLY MADE TO SUGGEST TO RPTR THAT HE CONTACT NTSB WITH THIS INFO SINCE PREVIOUS ACCIDENT SO SIMILAR.

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.