C172 ACFT ON TRAINING FLT L GEAR COLLAPSED AFTER LNDG DUE TO FAILED GEAR ACTUATOR AND ACFT VEERED OFF RWY INCURRING DAMAGE.

Narrative

COMING INBOUND FOR LNDG AT MYF 5 MI TO THE E AT 3500 FT MSL; WERE TOLD BY TWR TO EXPECT A STRAIGHT IN LNDG FOR RWY 28L. I DROPPED THE FLAPS 10 DEGS AND DROPPED THE GEAR; GOT A GREEN INDICATION AND SAW A WHEEL MY SIDE. THE CFI SAW A GREEN AND A WHEEL HIS SIDE (L). STILL HIGH I DUMPED IN ALL FLAPS (30 DEGS) PREPARING FOR A SHORT FIELD LNDG ON THE NUMBERS. TWR CLRED US FOR LNDG. WE TOUCHED DOWN ON THE NUMBERS AT 55-60 KTS. AFTER A SHORT ROLL THE PLANE STARTED TO VIBRATE AND THE L GEAR FAILED AND THE PLANE VEERED OFF THE RWY TO THE L. WE STARTED TO SHUT DOWN THE ENG AFTER THE ACFT LEFT THE RWY; THE R GEAR FAILED. THE PROP WAS STOPPED HORIZ; NO DAMAGE. THE NOSE GEAR STAYED DOWN AND LOCKED. THERE WAS DAMAGE TO THE L STABILIZER AND ELEVATOR ONLY. THE MAINT DETERMINED A L GEAR ACTUATOR HAD BROKE (UNDETERMINED WHEN). ONE THEORY OF CHAIN OF EVENTS: WHEN THE GEAR WAS PUT DOWN THE ACTUATOR BROKE AND THE GEAR WAS NOT LOCKED; BUT LOOKED ALMOST AS IF THEY WERE (PERCEIVED TO BE LOCKED). SINCE THE ACTUATOR WAS BROKE THE MAIN GEAR WOULD NOT LOCK SO THEY WERE HELD IN PLACE BY HYD PRESSURE; THE HYD PUMP SHUT OFF AT 1500 PSI AND THEN POPPED THE CIRCUIT (THUS NO WARNING HORN). WHEN THE GEAR HANDLE WAS PUT IN DOWN POS THE KNUCKLE OF THE HAND PRESSED THE GREEN INDICATOR AS IF TESTING AND THEN SHOWED GREEN (BEFORE CIRCUIT POPPED). THUS BOTH MYSELF AND CFI PERCEIVED A GREEN INDICATION AND SAW A WHEEL OUT EACH SIDE (NOT LOCKED BUT HELD IN PLACE BY HYD PRESSURE). ONCE TOUCHED DOWN THE HYD PRESSURE HOLDING WHEELS IN PLACE WAS OVERCOME BY THE ROLLOUT AND THE L GEAR FAILED CAUSING THE VIBRATION AND THE ACFT TO LEAVE THE RWY. IT WAS DETERMINED THAT (BY THE MECHS) THE ONLY WAY TO LOCK THE GEAR WOULD HAVE BEEN TO PHYSICALLY REACH OUTSIDE THE ACFT AND MANUALLY PULL THE GEAR INTO THE LOCKED POS. IT WOULD HAVE BEEN NECESSARY AND HELPFUL TO MEMORIZE WHERE THE GEAR SIT IN THE LOCKED POS SO THAT WHEN WE SAW THE WHEEL ON EACH SIDE WE COULD HAVE DETERMINED THAT THE GEAR WERE NOT LOCKED.