A FLT INSTRUCTOR IN A C177 RAN OFF THE END OF AN UPHILL RWY. HE THOUGHT THAT IT WAS DOWNHILL. ERROR ADMITTED. ACFT DAMAGE SKIN; PLASTIC ACCESSORIES; AND ANTENNAS.

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MY CHKOUT CANDIDATE HAD COME TO ME ASKING FOR INSTRUCTION IN UNUSUAL ARPTS IN THIS MOUNTAINOUS AREA AND TO GET CHKED OUT IN THE C177. WE WOULD DO A FEW SOFT FIELD LNDGS ON THE DIRT STRIP. THE RWY IS 2600 FT; TEMP WAS 31 DEGS C; DENSITY ALT 4200 FT -- THERE SHOULD BE NO PROB. I HAD LOOKED AT THE FLT GUIDE AS WE WERE INBOUND FOR HIGH DESERT. AS WE WERE TAXIING OUT; OPTED FOR A RWY 24 DEP WITH A 2-3 KT TAILWIND. IT SEEMED LIGHT AND VARIABLE. I THINK UNICOM CALLED IT THAT. I THOUGHT RWY 24 HAD A DOWNGRADE OF 1.4 PERCENT. AS WE ENTERED THE RWY; I NOTICED WHAT COULD HAVE BEEN SMALL STONES ON THE GND. I TOLD THE OTHER PLT WE MAY WANT TO START OUT WITH A SOFT FIELD TECHNIQUE -- ONCE WE GOT SOME SPD ON THE RWY WE WOULD JUST LET THE NOSE DOWN A BIT AND MAKE IT A SHORT FIELD TKOF. FULL PWR APPLIED; ALL WAS GREEN. AIRSPD WAS INDICATING 49 MPH AT 1/2 RWY; WE NEEDED JUST ANOTHER 8-9 MPH TO HAVE LIFTOFF AT 1800 LBS GROSS WT. WE SHOULD HAVE BEEN ACCELERATING; INSTEAD THE NEEDLE WAS JUST CREEPING 50 MPH; 51... X; IN THE L SEAT; STILL HAD FULL THROTTLE. I OPTED TO LET HIM PURSUE THE TKOF SINCE THE RWY WAS UNOBSTRUCTED AND BEYOND WAS ONLY DESERT AND BRUSH. WE WOULD JUST CLB INTO GND EFFECT AND 'WAIT IT OUT' AWHILE. BUT EVEN THAT DID NOT LOOK FEASIBLE AS IT LOOKED LIKE WE HAD 800 FT TO THE END OF THE RWY. I CALLED TO ABORT THE TKOF; BUT X WAS STILL FULL THROTTLE. AS I SAID IT AGAIN AND AGAIN; I REACHED OVER AND PULLED THE PWR TO IDLE; SAID IT WAS MY AIRPLANE AND PULLED UP SLOWLY TO APPLY AERODYNAMIC BRAKING AS WELL AS FOOT BRAKES. THE PLANE TOOK TO THE AIR BUT WAS NOT FLYING; JUST BOUNCING L AND R. WE WERE TAKING SIDE LOADING ON THE GEAR AND THE DESERT WAS COMING UP FAST. I COULD SEE US HITTING THE DUNES SIDEWAYS; OR WORSE; THE MAIN GEAR; L OR R COULD GET CAUGHT IN THICK BRUSH AND SPIN THE PLANE AROUND. I OPTED FOR FULL PWR TO GET CTL AGAIN AND A FULL FORWARD MOMENT. I THINK WE WERE BOTH FLYING THE PLANE AT THIS POINT BECAUSE ALTHOUGH I HAD SAID 'MY AIRPLANE' I STILL CALLED 'FULL PWR; FULL PWR; FULL PWR.' HE ANSWERED; 'WE HAVE IT; WE HAVE IT.' I WAS CONCENTRATED ON MAINTAINING CTL WITH ELEVATOR; AILERON AND RUDDER. HAD I GONE STRAIGHT AHEAD WITH NO PWR; I FEEL I WOULD HAVE HAD TOO LITTLE TO WORK WITH AND LOST CTL. WE BOUNCED OFF THE DUNES UNTIL THE ACFT CAME TO A HALT IN THE SAND; ESTIMATED 1000 FT OR 1200 FT MORE OR LESS STRAIGHT AHEAD. MY MISTAKE WAS TO READ THE INCLINE ARROW IN THE DIRECTORY WRONGLY. I THOUGHT I WAS TAKING OFF DOWNHILL WITH A POSSIBLE TAILWIND. INSTEAD I WAS ROLLING UP 1.4 PERCENT; WORST CASE POSSIBLE. I RAN THE NUMBERS THROUGH THE POH. DESPITE THIS TERRIBLE COMBINATION; IT SHOWED I COULD ADD SOME 60 PERCENT TO MY TKOF ROLL DISTANCE AND STILL HAVE ENOUGH RWY AVAILABLE. I BELIEVE I WAITED TOO LONG BEFORE TAKING POSITIVE CORRECTIVE ACTION; ABORTING THE TKOF SOONER MAY HAVE KEPT US ON THE RWY. DAMAGE TO THE ACFT WAS MINOR; CONSISTING OF SKIN DAMAGE; PLASTIC ACCESSORIES AND ANTENNAS.