Narrative:

The customer had bought a used YAK52 recently. On the day of the incident, I spent around 1 hour reviewing system, preflight, engine start, and normal procedures with the customer. We had all necessary paperwork to include normal and emergency procedures and operations limitations. We did a normal engine start, taxied to the main ramp and shut down in front of the fuel station. After fueling, I stayed on the left wing beside the front cockpit to supervise the engine start which occurred normally. I strapped into the rear seat and we made a 90 degree right turn and taxied approximately 100 yards to the runway midpoint. The runway is narrow and we needed to make a left 90 degree turn to back taxi to the end. About halfway across the runway, I realized that the owner was having difficulty turning the aircraft. I took over control and tried to turn, but we had no brake authority/authorized. In just seconds we nosed over into an approximately 10-12 ft deep ditch. The aircraft flipped over onto its back and rested on its nose and vertical stabilizer. I accompanied the owner to the hospital and both of us were released with only minor cuts and I had a chipped bone in my right thumb. We returned to the airport about 4 or 5 hours after the incident. I had been thinking continuously about the different system components that could have caused the failure. I am familiar with the CJ6, a chinese cousin to the YAK52. They both have extremely similar system. There is one significant difference: the yak air system shows bottle pressure. The cj shows usable system pressure. A valve for the main air system bottle must be opened in order to maintain normal usable system pressure. During the second engine start, I looked over the shoulder of the owner and saw 40 atmospheres (30-50 is normal). Since you wouldn't have that indication in a cj unless the air valve was turned on, I didn't physically check the valve position. When we returned to the airport that afternoon, I checked the main air valve. It was closed. I used the checklist and indications to tell me where something important was, rather than physically checking the position or asking the owner if he had physically checked it. These airplanes are great, affordable and fun to fly. However, they have been engineered to operate with system that are foreign to us here in the united states. A checklist is no good if you don't follow it, and back it up religiously. Plus, a tandem seat arrangement means that you must absolutely ensure that the front seater is thoroughly familiar with the concept and operation of all system. You can't see or know everything from the backseat so you must prepare the student even more diligently.

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Original NASA ASRS Text

Title: INSTRUCTOR PLT AND STUDENT FAIL TO PROPERLY POS PNEUMATIC VALVE FOR BRAKE SYS ON FOREIGN MIL TRAINER. ACFT LOSES STEERING AND BRAKE CAPABILITY, EXITS RWY AND NOSES OVER IN DITCH.

Narrative: THE CUSTOMER HAD BOUGHT A USED YAK52 RECENTLY. ON THE DAY OF THE INCIDENT, I SPENT AROUND 1 HR REVIEWING SYS, PREFLT, ENG START, AND NORMAL PROCS WITH THE CUSTOMER. WE HAD ALL NECESSARY PAPERWORK TO INCLUDE NORMAL AND EMER PROCS AND OPS LIMITATIONS. WE DID A NORMAL ENG START, TAXIED TO THE MAIN RAMP AND SHUT DOWN IN FRONT OF THE FUEL STATION. AFTER FUELING, I STAYED ON THE L WING BESIDE THE FRONT COCKPIT TO SUPERVISE THE ENG START WHICH OCCURRED NORMALLY. I STRAPPED INTO THE REAR SEAT AND WE MADE A 90 DEG R TURN AND TAXIED APPROX 100 YARDS TO THE RWY MIDPOINT. THE RWY IS NARROW AND WE NEEDED TO MAKE A L 90 DEG TURN TO BACK TAXI TO THE END. ABOUT HALFWAY ACROSS THE RWY, I REALIZED THAT THE OWNER WAS HAVING DIFFICULTY TURNING THE ACFT. I TOOK OVER CTL AND TRIED TO TURN, BUT WE HAD NO BRAKE AUTH. IN JUST SECONDS WE NOSED OVER INTO AN APPROX 10-12 FT DEEP DITCH. THE ACFT FLIPPED OVER ONTO ITS BACK AND RESTED ON ITS NOSE AND VERT STABILIZER. I ACCOMPANIED THE OWNER TO THE HOSPITAL AND BOTH OF US WERE RELEASED WITH ONLY MINOR CUTS AND I HAD A CHIPPED BONE IN MY R THUMB. WE RETURNED TO THE ARPT ABOUT 4 OR 5 HRS AFTER THE INCIDENT. I HAD BEEN THINKING CONTINUOUSLY ABOUT THE DIFFERENT SYS COMPONENTS THAT COULD HAVE CAUSED THE FAILURE. I AM FAMILIAR WITH THE CJ6, A CHINESE COUSIN TO THE YAK52. THEY BOTH HAVE EXTREMELY SIMILAR SYS. THERE IS ONE SIGNIFICANT DIFFERENCE: THE YAK AIR SYS SHOWS BOTTLE PRESSURE. THE CJ SHOWS USABLE SYS PRESSURE. A VALVE FOR THE MAIN AIR SYS BOTTLE MUST BE OPENED IN ORDER TO MAINTAIN NORMAL USABLE SYS PRESSURE. DURING THE SECOND ENG START, I LOOKED OVER THE SHOULDER OF THE OWNER AND SAW 40 ATMOSPHERES (30-50 IS NORMAL). SINCE YOU WOULDN'T HAVE THAT INDICATION IN A CJ UNLESS THE AIR VALVE WAS TURNED ON, I DIDN'T PHYSICALLY CHK THE VALVE POS. WHEN WE RETURNED TO THE ARPT THAT AFTERNOON, I CHKED THE MAIN AIR VALVE. IT WAS CLOSED. I USED THE CHKLIST AND INDICATIONS TO TELL ME WHERE SOMETHING IMPORTANT WAS, RATHER THAN PHYSICALLY CHKING THE POS OR ASKING THE OWNER IF HE HAD PHYSICALLY CHKED IT. THESE AIRPLANES ARE GREAT, AFFORDABLE AND FUN TO FLY. HOWEVER, THEY HAVE BEEN ENGINEERED TO OPERATE WITH SYS THAT ARE FOREIGN TO US HERE IN THE UNITED STATES. A CHKLIST IS NO GOOD IF YOU DON'T FOLLOW IT, AND BACK IT UP RELIGIOUSLY. PLUS, A TANDEM SEAT ARRANGEMENT MEANS THAT YOU MUST ABSOLUTELY ENSURE THAT THE FRONT SEATER IS THOROUGHLY FAMILIAR WITH THE CONCEPT AND OP OF ALL SYS. YOU CAN'T SEE OR KNOW EVERYTHING FROM THE BACKSEAT SO YOU MUST PREPARE THE STUDENT EVEN MORE DILIGENTLY.

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.