2 passengers were injured when United Airlines pilots responded to an inflight collision warning

• Two United Airlines passengers were taken to hospital after a plane slowed down during its descent.
• The FAA is investigating the incident and said the plane had responded to a close-collision alert.

The FAA has opened an investigation after two passengers were injured when a United Airlines plane responded to an alert from a midair collision system.

Flight 2428 from Newark was nearing San Francisco International Airport on the afternoon of 19 September when the plane slowed its descent to avoid another aircraft flying at a lower altitude, the airline said in a statement.

"Two customers, including one who was out of their seat at the time, reported possible injuries and were transported to a hospital," United said. The seatbelt sign was on at the time.

"We're grateful to our crew for their efforts to ensure the safety of our employees and customers," United said.

The FAA said in a statement that the flight responded to an onboard alert about another aircraft in the vicinity. It landed safely at San Francisco International Airport and there was "no loss of safe separation.

Data on FlightAware shows a deviation of roughly 30 miles an hour in the Boeing 757's speed shortly after it began its descent.

The Traffic Alert and Collision Avoidance System (TCAS) helps prevent midair collisions by monitoring the surrounding airspace and alerting pilots about nearby aircraft.

The system sounds an alarm in the cockpit, and the pilots notify the air traffic controller that they are responding to a TCAS alarm, Kevin Karpé, a former air traffic controller and air traffic manager, previously told Business Insider.

Cabin crew and passengers are typically not made aware of the situation, and it is standard for the FAA to conduct a performance evaluation and investigation after such an incident, he said.

However, last year, concerns rose about a spike in the number of collision close calls taking place in the US. The New York Times reported that the incidents were happening far more than was known by the public.

In July 2023, human error was the main factor in the majority of 46 near-miss events, The Times reported.

The FAA established a new safety review committee to discuss ways to mitigate risk around the near-miss incidents.

Karpé told BI that close-call collisions are nothing to worry about.

"If you run the percentages of close calls against the total number of completed flights in our national airspace per day, which is roughly 45,000, it's really not that significant," he said.