A newly released preliminary NTSB report has revealed how two commercial airliners narrowly avoided a catastrophic collision at Boston Logan International Airport on June 20 after a chain of errors involving a false cockpit warning and air traffic control confusion.
According to investigators, Delta Air Lines Flight 2351, a Boeing 737, had been cleared to land on Runway 33L while following a small aircraft. Just over a minute later, American Airlines Flight 3161, an Airbus A319, was cleared for takeoff from the intersecting Runway 27.
The American Airlines jet initially began its takeoff roll but stopped after the crew received an erroneous cockpit warning. After confirming it was a false alarm, the pilots resumed the takeoff 23 seconds later. By then, the Delta aircraft was approaching the runway intersection, creating a dangerous conflict.
Seeing the developing situation, the Delta pilots immediately executed a go-around, climbing away from the runway and later landing safely. The American Airlines crew continued their takeoff after observing the Delta aircraft pulling away. At the closest point, the two aircraft, carrying a combined total of 318 people, came within just 670 feet of each other.
The NTSB said the air traffic controller became confused after the unexpected stop in the American jet’s takeoff. Investigators found the controller shifted attention to a small aircraft clearing the runway and did not realize the American flight had resumed its departure. When a tower conflict alarm sounded, the Delta crew had already initiated evasive action. During the incident, the controller was heard asking, “American 3161, where are you going?” to which the pilots replied, “You cleared us to take off.”
Investigators also found that runway stop-bar lights, which could have warned the departing aircraft of the conflict, turned off after the small aircraft landed and did not illuminate again until the Delta jet was already on final approach. Neither flight crew received an onboard collision warning.
The investigation faces another challenge because the cockpit voice recorders retain only the last two hours of audio. By the time the NTSB obtained the recorders, the recordings from the incident had already been overwritten. However, flight data recorders were preserved and are still being analyzed.
The NTSB’s investigation remains ongoing, and a final report determining the probable cause of the serious runway incursion is expected in one to two years.
