What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
Pilot performed a preflight before first flight of the day and added 1 quart of oil to left engine. Departed with parachute jumpers and just before returning to the airport, pilot noted low oil pressure on left engine. Upon landing, pilot noted engine oil covering the left engine nacell, landing gear and wing. Pilot inspected left engine and found oil cap unsecured. He cleaned up oil and added 5 quarts under the direction of a mechanic. Pilot was instructed to perform a test flight prior to taking another load of parachute jumpers. Pilot departed, retracted gear and flew the pattern with the flaps in the takeoff/approach position while watching the left engine gauges. Proceeded to approach of runway 25, rounded out, reduced power, heard the gear unsafe warning and the props hit the ground. Pilot reduced power full aft and bellied the aircraft down the center of runway 25. .
As the FAA filed it
PILOT PERFORMED A PREFLIGHT BEFORE FIRST FLIGHT OF THE DAY AND ADDED 1 QUART OF OIL TO LEFT ENGINE. DEPARTED WITH PARACHUTE JUMPERS AND JUST BEFORE RETURNING TO THE AIRPORT, PILOT NOTED LOW OIL PRESSURE ON LEFT ENGINE. UPON LANDING, PILOT NOTED ENGINE OIL COVERING THE LEFT ENGINE NACELL, LANDING GEAR AND WING. PILOT INSPECTED LEFT ENGINE AND FOUND OIL CAP UNSECURED. HE CLEANED UP OIL AND ADDED 5 QUARTS UNDER THE DIRECTION OF A MECHANIC. PILOT WAS INSTRUCTED TO PERFORM A TEST FLIGHT PRIOR TO TAKING ANOTHER LOAD OF PARACHUTE JUMPERS. PILOT DEPARTED, RETRACTED GEAR AND FLEW THE PATTERN WITH THE FLAPS IN THE TAKEOFF/APPROACH POSITION WHILE WATCHING THE LEFT ENGINE GAUGES. PROCEEDED TO APPROACH OF RUNWAY 25, ROUNDED OUT, REDUCED POWER, HEARD THE GEAR UNSAFE WARNING AND THE PROPS HIT THE GROUND. PILOT REDUCED POWER FULL AFT AND BELLIED THE AIRCRAFT DOWN THE CENTER OF RUNWAY 25. .