The light propeller plane that crashed into a residential area in Chofu, Tokyo, may have had mechanical trouble and come down less than a minute after takeoff, as people near the accident site heard a sound like an explosion just before the crash, according to investigation sources.
The sound suggests that some problem occurred in the body of the plane just after takeoff.
On Monday morning, the Metropolitan Police Department began investigating the site on suspicion of professional negligence resulting in deaths and injuries.
Three people died and five were hurt in the accident.
The MPD and the government's Transport Safety Board will jointly examine how the plane body was damaged and other factors, to try to determine the cause of the accident.
The crashed plane was a PA-46-350P model manufactured by Piper Aircraft Inc. of the United States. It was 8.7 meters long and 13.1 meters wide.
According to the Tokyo metropolitan government, a branch of the Aerodrome Support and Aeronautical Service at Chofu Airport visually confirmed the plane's takeoff at 10:58 a.m. Sunday.
The MPD said the first emergency call from a nearby resident to police about the accident also came at 10:58 a.m.
A video of the falling plane happened to be filmed at a football field near the runway. The plane enters the camera's sights flying at a very low altitude, and an explosion and flames were recorded about 20 seconds later.
According to eyewitnesses, including residents who were at the football field, the plane's altitude did not rise after taking off.
The plane turned to its left and entered the airspace over the residential area, after which its altitude gradually dropped.
An explosive sound was heard, and the plane crashed into the residential area about 700 meters from the airport.
A man in his 50s who witnessed the accident told the MPD that the plane "was flying at a low altitude like a glider."
Based on these factors, the MPD believes that a serious problem occurred in the body of the plane just after takeoff, and the plane crashed in less than a minute.
The MPD received parts of the video, which was shot by a nearby resident, and is analysing the footage.
The on-site inspections began shortly before 9 a.m. Monday. Investigators from the MPD took photos of things including the burned body of the plane and pieces of the plane body scattered around the site.
The MPD will question Nippon Aerotech Co., the Chofu-based company that managed the light plane, about the details of the plane's maintenance. After the surviving passengers are sufficiently recovered, the MPD also plans to investigate how the four people other than the 36-year-old pilot, Taishi Kawamura, came to be aboard the plane.
The MPD has conducted forensic autopsies on the three people killed, to identify the victims.
Asked about the plane's nearly immediate crash, aviation analyst Kazuki Sugiura said, "I presume a problem occurred in the engine just after takeoff, the pilot noticed the problem and turned to the left to return to the airport, and then the engine's power output fell rapidly."
He pointed out, "Considering the flight conditions, I wonder whether careful checks were made before the flight."