On September 25, 2017, about 1715 local time, a Cessna 172P airplane, N5448K, sustained substantial damage when it impacted terrain following a loss of engine power near Guam International Airport (PGUM), Tamuning, Guam. The commercial pilot and two passengers were not injured. The airplane was registered to and operated by Sky Guam Aviation, Inc. as a Title 14 Code of Federal Regulations Part 91 sightseeing flight. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight that originated from PGUM at 1650. The pilot reported that the accident flight was scheduled as a 20-minute local sightseeing flight, and that it was his last flight of the day. He conducted a normal preflight and reported no issues during the beginning of the flight. While enroute, the pilot noticed fire sparks with smoke on the left side and smoke started to fill the cabin. The pilot opened the left window to disperse the smoke. He did not observe fire, but the smoke continued to accumulate in the cockpit. Shortly after, the engine lost power and the airplane started to shake violently. The pilot decided to return to the airport and made a mayday call to inform the tower of the engine failure. While enroute to the airport, he attempted to restart the engine, but he was unsuccessful. The pilot realized he did not have sufficient altitude to land on the runway and initiated a forced landing to a nearby field. The airplane landed short of the airport perimeter fence. Due to the location of the accident, representatives from the National Transportation Safety Board and Federal Aviation Administration were not available for post-accident examination oversight. A local mechanic and an employee from Sky Guam Aviation, Inc. conducted the post-accident examination of the airplane. They stated that they found evidence of oil around the No.4 engine cylinder and observed that the intake pipes were wet and shiny. They found that the oil dipstick/filler cap was not screwed into the filler neck, and the oil quantity indicated zero. The pilot told them that he checked the oil level before the first flight of the day and had flown the airplane ten more times that day but did not check the oil level prior to those flights. The Pilot's Operating Handbook (POH) required the pilot to check the engine oil quantity and confirm that the oil dipstick/filler cap is secured before each flight.