Narrative:

I was 10 mi from the ZZZ1 airport at 2500 ft when I heard a pop in the engine. A quick scan of the instruments had me doing a double take of the oil pressure gauge. The oil pressure was reading zero. I headed straight for the airport (ZZZ1), called the tower, and declared an emergency. 1 min later, the ammeter showed a 10 amp discharge. More noise from the engine. Tower asked, 'do you want emergency equipment standing by?' I replied 'yes.' I aimed the airplane 1/2 way between the beach and the airport. I called the tower and told them we may land on the beach. At 2000 ft of altitude, with 4 mi of glide range, I turned away from the beach and directly towards the airport. The engine started with a steady grinding noise telling me it was time to shut it down. I reached for the mixture control and shut down the engine. I doublechked the gear down, airspeed, altitude and energy level. All were good and the short approach was stable. The landing was uneventful, not my best, but far from my worst. On the ground, I tried to turn the propeller -- it was nearly frozen. I checked the oil. It had 5 quarts and it should have 6 1/2. No oil leaks. Looks like something on, or near, the oil pump broke and froze the alternator as well. I believe there was a successful outcome due to the fact that I made an immediate decision to treat the zero oil pressure reading as a real emergency. Callback conversation with reporter revealed the following information: reporter stated that the cause of the engine failure was determined to be a sheared magneto impulse coupler pin which dropped down into the accessory case jamming the oil pump and alternator drives.

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Original NASA ASRS Text

Title: M20K PLT RETURN LAND AFTER EXPERIENCING MECHANICAL ENG FAILURE.

Narrative: I WAS 10 MI FROM THE ZZZ1 ARPT AT 2500 FT WHEN I HEARD A POP IN THE ENG. A QUICK SCAN OF THE INSTS HAD ME DOING A DOUBLE TAKE OF THE OIL PRESSURE GAUGE. THE OIL PRESSURE WAS READING ZERO. I HEADED STRAIGHT FOR THE ARPT (ZZZ1), CALLED THE TWR, AND DECLARED AN EMER. 1 MIN LATER, THE AMMETER SHOWED A 10 AMP DISCHARGE. MORE NOISE FROM THE ENG. TWR ASKED, 'DO YOU WANT EMER EQUIP STANDING BY?' I REPLIED 'YES.' I AIMED THE AIRPLANE 1/2 WAY BTWN THE BEACH AND THE ARPT. I CALLED THE TWR AND TOLD THEM WE MAY LAND ON THE BEACH. AT 2000 FT OF ALT, WITH 4 MI OF GLIDE RANGE, I TURNED AWAY FROM THE BEACH AND DIRECTLY TOWARDS THE ARPT. THE ENG STARTED WITH A STEADY GRINDING NOISE TELLING ME IT WAS TIME TO SHUT IT DOWN. I REACHED FOR THE MIXTURE CTL AND SHUT DOWN THE ENG. I DOUBLECHKED THE GEAR DOWN, AIRSPD, ALT AND ENERGY LEVEL. ALL WERE GOOD AND THE SHORT APCH WAS STABLE. THE LNDG WAS UNEVENTFUL, NOT MY BEST, BUT FAR FROM MY WORST. ON THE GND, I TRIED TO TURN THE PROP -- IT WAS NEARLY FROZEN. I CHKED THE OIL. IT HAD 5 QUARTS AND IT SHOULD HAVE 6 1/2. NO OIL LEAKS. LOOKS LIKE SOMETHING ON, OR NEAR, THE OIL PUMP BROKE AND FROZE THE ALTERNATOR AS WELL. I BELIEVE THERE WAS A SUCCESSFUL OUTCOME DUE TO THE FACT THAT I MADE AN IMMEDIATE DECISION TO TREAT THE ZERO OIL PRESSURE READING AS A REAL EMER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE CAUSE OF THE ENG FAILURE WAS DETERMINED TO BE A SHEARED MAGNETO IMPULSE COUPLER PIN WHICH DROPPED DOWN INTO THE ACCESSORY CASE JAMMING THE OIL PUMP AND ALTERNATOR DRIVES.

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.