A Delta Air Lines jet was roughly 300 feet from an American Airlines plane during a close call at Boston’s airport that forced the Delta aircraft to abort a weekend landing attempt, an aviation expert said Sunday.

The Federal Aviation Administration said it was investigating the incident between two commercial flights that happened Saturday at Boston Logan International Airport.

Todd Curtis, a former safety engineer at Boeing, estimated the distance between the two jetliners using Flightradar24, a website that tracks flights. Curtis now coproduces a podcast about flight safety issues.

“This is a significant incident,” Curtis said, adding that it was particularly concerning because it involved two professional airline crews.

He said federal aviation officials have been concerned about such runway incursions for a while now and will scrutinize Saturday’s close call.

Near-misses and runway incursions at U.S. airports will be the subject of a hearing on Capitol Hill on Tuesday. The Senate Commerce Subcommittee on Aviation, Space, and Innovation will seek ways to strengthen safety across the national airspace system.

The Delta flight from Dallas had to execute a go-around, or aborted landing, to avoid the American plane departing from an intersecting runway, according to the FAA and flight logs.

The crew of Delta flight 2351 coordinated with air traffic control to perform the go-around, an airline spokesperson said. The plane, which had 129 passengers and six crew members on board, landed safely and deplaned normally, according to the spokesperson.

Go-arounds are safe, routine procedures performed at the discretion of the pilot or air traffic controllers, according to the FAA.