Stop lights installed at Tokyo's Haneda Airport to prevent aircraft from erroneously entering runways were out of service for maintenance when a deadly aircraft collision occurred Tuesday, transport ministry officials said Sunday.

The stop bar lights are installed at the border between the runway and taxiway. The red light will be on until the air traffic controller approves the approach, and if it is approved, the red light will turn off and the green light at the center line of the runway will turn on, according to the ministry.

A stop bar light was installed on the route where a Japan Coast Guard aircraft entered the airport's C runway before colliding with a Japan Airlines passenger jet, but the light was out of service for maintenance at the time, the officials said.

However, the system can only be used when visibility is less than 600 meters due to heavy fog and other conditions and when air traffic controllers deem it necessary.

A ministry official said that at the time of the accident, visibility was more than 5,000 meters, so the stop bar light would not be on if the system was operated.

The airport's C runway has been closed since the accident. It will be reopened Monday, the ministry said.