AN MU2 CARGO PLT HITS HIS NON STANDARD FOLDING BOARDING LADDER WITH THE R PROP WHEN DEPARTING THE RAMP AT ZZZ; US.

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THE ACFT I WAS PLT OF WAS ON A PARKING RAMP OR TXWY AT TIME OF INCIDENT. THERE ARE 2 ENTRANCES TO THE AIRPLANE; A LARGE CARGO DOOR BEHIND L WING AND AN EMER PLT WINDOW ON THE R SIDE OF THE COCKPIT. DUE TO THE CARGO LOAD I USUALLY HAD TO ENTER THROUGH THE EMER; OR PLT WINDOW. I HAD ASKED FOR AND COULD NOT OBTAIN THE LADDER FROM THE COMPANY THAT ATTACHED TO THIS WINDOW FOR ENTRANCE; NOT ALLOWING THE WINDOW TO BE CLOSED UNTIL THE LADDER IS IN THE AIRPLANE. INSTEAD I WAS INSTRUCTED TO BUY A FOLDING LADDER AT THE HARDWARE STORE. THIS TYPE OF LADDER COULD NOT BE SEEN FROM THE COCKPIT WHEN PLACED ON THE GND. ON THE NIGHT OF THE INCIDENT I HAD FORGOTTEN THE LADDER AND DURING TAXI THE R PROP STRUCK THE LADDER. THERE WAS A SLIGHT NOISE THAT SOUNDED LIKE CARGO SHIFTING IN THE REAR OF THE ACFT. THE WIND SURFACES AT THE ARPT WERE GUSTING TO 40 MPH. SO DURING TAXI THERE WAS NO NOTICEABLE VIBRATION OTHER THAN THAT CAUSED BY THE SHIFTING OF THE WIND. DURING THE TKOF RUN I NOTICED THE R TORQUE GAUGE SHOWING HIGHER THAN NORMAL INDICATION AND THERE SEEMED TO BE A LACK OF NORMAL PWR. I DISCONTINUED THIS TKOF AND ASKED ATC TO BE ALLOWED A RUN-UP OFF THE RWY. AS I RAN UP THE ENGS ON THE TXWY THEY BOTH APPEARED TO BE RUNNING NORMAL. I TAXIED TO THE APCH END AND DEPARTED ON COURSE. DURING FLT THE TORQUE GAUGE WENT TO FULL SCALE DEFLECTION (HIGH SIDE). I GENTLY REDUCED THE PWR TO FLT IDLE ON THE R SIDE TO SEE THE RESPONSE OF THE GAUGE. THE TORQUE GAUGE STAYED FULLY DEFLECTED AND I BELIEVED IT TO BE A FAULTY INDICATION. UPON ARR AT THE DEST ARPT I SHUT DOWN THE AIRPLANE. ON INSPECTION OF THE ACFT I FOUND THAT THE TIPS OF THE PROP ON R SIDE HAD ABOUT 1-2 INCHES BROKEN OFF. I INFORMED MY DIRECTOR OF OPS IMMEDIATELY AND GROUNDED THE PLANE. I FAULT MYSELF FOR NOT RELYING ON THE TORQUE GAUGE. THIS IS AN INCIDENT I HAVE LEARNED GREATLY FROM AND WILL STAY WITH ME THE REST OF MY LIFE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT THE SUBJECT 'ACFT' LADDER HAD BEEN PLACED IN THE HANGAR AND SOMEONE WAS SIMPLY TOO LAZY TO FIND IT. THE COMPANY HAS SINCE FOUND THAT LADDER; BUT IT IS A MOOT POINT AS THE COMPANY IS GOING OUT OF BUSINESS SHORTLY. THIS LADDER PROB HAD HAPPENED ONCE BEFORE; WITH THE PLT RUNNING OVER IT RATHER THAN CREATING A PROP STRIKE ON IT. THERE IS NO RAMP GUIDANCE GND CREW ON DUTY AT NIGHT; NO 'TOUR DE FORCE' AT ALL IN FACT.