ANNE ARUNDEL COUNTY, Md. (DC News Now) — A Southwest Airlines Boeing 737 was in its takeoff roll at Baltimore-Washington International Thurgood Marshall Airport (BWI) when an ambulance crossed the same runway, coming within 173 feet of the plane.

The distance between the moving plane and the ambulance was less than half the length of a football field.

A Federal Aviation Administration (FAA) analysis of the incident shows that an Aircraft Rescue and Fire Fighting (ARFF) vehicle crossed Runway 15R without authorization from air traffic control (ATC) in January. The Southwest flight had been cleared to take off from the same runway moments earlier.

“The closest estimated horizontal separation occurred at a distance of 173 feet,” the FAA said in its analysis.

Air traffic control recordings obtained by show the moment the Southwest flight was cleared for takeoff at around 1:50 p.m. on Jan. 12, 2023.

Seconds later, the fire and rescue vehicle was cleared to cross Runway 10 and instructed to “hold short” of Runway 15R; however, in reading back to ATC, the driver of the ambulance said “Tower 349, crossing 10 and 15R.”

The incorrect read-back was not caught by the air traffic controller, the FAA said.

Once the issue was spotted, the air traffic controller urgently reminded the ambulance driver of the original instruction only to cross Runway 10. By that point, the ambulance already crossed Runway 15R and was on an adjacent taxiway.

“The plane took off before it reached the point where the vehicle had crossed. The FAA estimates the vehicle was approximately 170 feet past the runway when the airborne plane flew over that intersection,” an FAA spokesperson said.

In a statement sent to DC News Now, BWI spokesperson Jonathan Dean confirmed the incident:

A BWI Marshall Airport Fire and Rescue Department firefighter and medic vehicle crossed a runway without air traffic control authorization. The airport fully cooperated and shared information with the FAA regarding the incident. Based on review of the incident, new procedures were immediately implemented to help ensure safety and to prevent a similar incident in the future. Safety and security remain the highest priorities for BWI Marshall Airport.

Jonathan Dean, Spokesperson for BWI Thurgood Marshall Airport

The FAA categorizes runway incursions based on the level of severity. There are four categories: A, B, C, and D. The BWI incident was ranked in Category B.

“Category B is an incident in which separation decreases and there is a significant potential for collision, which may result in a time critical corrective/evasive response to avoid a collision,” according to the FAA.

A spokesman for Southwest Airlines, Chris Perry, said in a statement: “Southwest adheres to Air Traffic Control directions at all times and our Crew did in this scenario too.”