U.S. officials are investigating two more incidents at San Francisco International Airport where planes could have wound up on the same runway, the National Transportation Safety Board said Monday.
The incidents include an event in December 2016 when a SkyWest plane crossed a painted runway line it was supposed to stay behind while another plane was taking off, according to a safety board preliminary report.
The safety board report also revealed that a Compass Airlines plane in February was forced to abort a landing because a Virgin America jet was lined up and waiting to take off on the same runway.
Air traffic controllers received a warning about the potential conflict from an automated system and were able to redirect the Compass plane in time.
Both incidents happened at night, and there were no injuries in either case.
News of the investigations emerged a month after an Air Canada jet ignored or did not receive instructions to abort a landing.
In the fiscal year that ended Sept. 30, there were 1,704 so-called runway incursions nationwide, according to the Federal Aviation Administration.
Two-thirds were blamed on pilots, such as a pilot taking a plane across a runway without approval from the control tower. Most of the rest were blamed either on errors by air traffic controllers or pedestrians or vehicles being on a runway without permission.
The safety board is still investigating a San Francisco airport incident in July, when an Air Canada jet that was landing mistakenly headed toward a taxiway where four other planes were on the ground. The Air Canada pilots pulled up just in time to avoid a collision.
That led to changes in control tower staffing at night and procedures pilots must follow when landing at the airport during certain nighttime hours.
Preliminary reports issued by the safety board indicated that the Air Canada plane dipped as low as 59 feet above the ground, barely high enough to avoid the tops of the jets on the ground.
Separately, the FAA is investigating an incident last month in which another Air Canada crew ignored or did not receive instructions from the tower to abort a landing.
The controller feared another plane that had just landed might still be on the runway, but the Air Canada jet landed safely.
Officials for the safety board and the FAA declined Monday to provide updates about those investigations.