Narrative:

I moved the C172 out of the hangar in order to move my C170 past the C172 and warm up the engine and begin my preflight inspection. I started the franklin engine, set the brakes and placed a set of chocks on the left main gear, and after setting the RPM at 900, I went over to pull the C172 back into the hangar. I had moved the C172 approximately 15 ft when I noticed my C170 had pivoted counterclockwise 90 degrees with the left main gear now parallel to the chocks and beginning to move forward. I dropped the C172 tow bar and ran to the tail of my C170 thinking I could stop the aircraft forward progress, which I did slightly, then realizing that my next best corrective action was to alter the direction of aircraft motion by pushing hard on the tail in a counterclockwise direction. At the point of contact, my C170 had turned approximately 195 degrees counterclockwise with the propeller chewing through the aft portion of the C172 right horizontal stabilizer and elevator. The C170 stopped forward movement with the propeller parallel to the C172 vertical stabilizer and windmilling damaging the right side of the vertical stabilizer and rudder. The C172 left horizontal stabilizer and elevator were undamaged as was the left side of the vertical stabilizer. I then pulled the mixture control on the C170 to stop the engine. Human performance considerations: 1) I was in a hurry, preparing to fly in to fish lake, an idaho wilderness airstrip, to go moose hunting. The franklin 220 hp engine requires an oil temperature 100 degrees or higher before takeoff power can be applied. Therefore, I warmed up the engine. 2) had I physically checked the brakes (by attempting to rotate the tires, which I usually do when I'm not in a hurry) I would have confirmed that the parking brakes were set and functioning. 3) had I chocked both main tires, this incident would not have occurred. (I will obtain another set of chocks before my next flight.) 4) had I straightened the tailwheel before starting the C170, it could not have pivoted as it did. 5) had I moved the C172 back into the hangar before starting the C170, and then stayed with the C170 for the preflight stage, this incident would not have occurred. 6) had I stayed in the aircraft cabin during engine warm up, this would have been a non incident.

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Original NASA ASRS Text

Title: A C170 PLT STARTED HIS ACFT'S ENG WITH THE L TIRE CHOCKED, BUT WITH THE PARKING BRAKE UNINTENTIONALLY NOT FULLY SET. THE PLT THEN EXITED HIS ACFT TO MOVE ANOTHER ACFT WHEREUPON HIS ACFT TAXIED IN TO THE ACFT THE PLT WAS MOVING.

Narrative: I MOVED THE C172 OUT OF THE HANGAR IN ORDER TO MOVE MY C170 PAST THE C172 AND WARM UP THE ENG AND BEGIN MY PREFLT INSPECTION. I STARTED THE FRANKLIN ENG, SET THE BRAKES AND PLACED A SET OF CHOCKS ON THE L MAIN GEAR, AND AFTER SETTING THE RPM AT 900, I WENT OVER TO PULL THE C172 BACK INTO THE HANGAR. I HAD MOVED THE C172 APPROX 15 FT WHEN I NOTICED MY C170 HAD PIVOTED COUNTERCLOCKWISE 90 DEGS WITH THE L MAIN GEAR NOW PARALLEL TO THE CHOCKS AND BEGINNING TO MOVE FORWARD. I DROPPED THE C172 TOW BAR AND RAN TO THE TAIL OF MY C170 THINKING I COULD STOP THE ACFT FORWARD PROGRESS, WHICH I DID SLIGHTLY, THEN REALIZING THAT MY NEXT BEST CORRECTIVE ACTION WAS TO ALTER THE DIRECTION OF ACFT MOTION BY PUSHING HARD ON THE TAIL IN A COUNTERCLOCKWISE DIRECTION. AT THE POINT OF CONTACT, MY C170 HAD TURNED APPROX 195 DEGS COUNTERCLOCKWISE WITH THE PROP CHEWING THROUGH THE AFT PORTION OF THE C172 R HORIZ STABILIZER AND ELEVATOR. THE C170 STOPPED FORWARD MOVEMENT WITH THE PROP PARALLEL TO THE C172 VERT STABILIZER AND WINDMILLING DAMAGING THE R SIDE OF THE VERT STABILIZER AND RUDDER. THE C172 L HORIZ STABILIZER AND ELEVATOR WERE UNDAMAGED AS WAS THE L SIDE OF THE VERT STABILIZER. I THEN PULLED THE MIXTURE CTL ON THE C170 TO STOP THE ENG. HUMAN PERFORMANCE CONSIDERATIONS: 1) I WAS IN A HURRY, PREPARING TO FLY IN TO FISH LAKE, AN IDAHO WILDERNESS AIRSTRIP, TO GO MOOSE HUNTING. THE FRANKLIN 220 HP ENG REQUIRES AN OIL TEMP 100 DEGS OR HIGHER BEFORE TKOF PWR CAN BE APPLIED. THEREFORE, I WARMED UP THE ENG. 2) HAD I PHYSICALLY CHKED THE BRAKES (BY ATTEMPTING TO ROTATE THE TIRES, WHICH I USUALLY DO WHEN I'M NOT IN A HURRY) I WOULD HAVE CONFIRMED THAT THE PARKING BRAKES WERE SET AND FUNCTIONING. 3) HAD I CHOCKED BOTH MAIN TIRES, THIS INCIDENT WOULD NOT HAVE OCCURRED. (I WILL OBTAIN ANOTHER SET OF CHOCKS BEFORE MY NEXT FLT.) 4) HAD I STRAIGHTENED THE TAILWHEEL BEFORE STARTING THE C170, IT COULD NOT HAVE PIVOTED AS IT DID. 5) HAD I MOVED THE C172 BACK INTO THE HANGAR BEFORE STARTING THE C170, AND THEN STAYED WITH THE C170 FOR THE PREFLT STAGE, THIS INCIDENT WOULD NOT HAVE OCCURRED. 6) HAD I STAYED IN THE ACFT CABIN DURING ENG WARM UP, THIS WOULD HAVE BEEN A NON INCIDENT.

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.