A slip of the tongue by an air traffic controller almost led to a catastrophic plane crash.

According to a report released Tuesday, a miscommunication by an air traffic controller at Paris Charles de Gaulle airport caused two planes to come dangerously close—within 300 feet of each other—in July of last year.

The near-miss occurred on July 20, 2020, between a United Airlines Boeing 787 arriving from Newark, New Jersey, and an EasyJet Airbus A320 preparing for takeoff to Malaga, Spain, as detailed in the French air safety investigation report.

At the time of the incident, planes were landing on runway 09L and taking off from 09R. However, the air traffic controller mistakenly instructed the United Airlines plane to land on 09R instead.

The flight crew sought confirmation of the runway change, using the phrases “understand” and “sidestep for 9 right,” according to the investigation report.

The controller failed to verify the crew's readback and continued to instruct the EasyJet plane to line up for takeoff on runway 09R.

At this moment, the United Airlines plane was still positioned to land on runway 09L. The crew initiated their maneuver, but upon reassessing, they realized the United Airlines plane was about to land on their runway.

Concerned, the EasyJet crew questioned the controller about the United Airlines plane approaching runway 09R and raised an alarm about a possible collision.

At this point, the United Airlines plane was flying at an altitude of 300 feet, just 1,300 meters from the end of the runway. Both the EasyJet crew and the controller instructed the United Airlines crew to climb, and the pilots aborted their landing.

When the two planes crossed paths, they were only 300 feet apart from each other.

The controller lacked direct visibility of the 09 runways due to malfunctioning equipment, and was instead operating from a different screen, as reported.

At the time of the incident, the screen facing the 09 runways had been repaired, and the controller was preparing to switch to it, though she expressed concern about the transition, according to the report.

She also told investigators that she had been confused by a previous landing request from another aircraft for runway 09R, which is longer than 09L, due to technical issues.

The BEA cited several factors contributing to the incident, including the controller's reduced proficiency caused by a drop in air traffic during the Covid-19 pandemic.

Investigators also noted that the United Airlines crew should have used the word 'confirm' rather than the non-standard 'understand' during their communication.

Dinogo has reached out to Paris Charles de Gaulle airport for a statement.