An airline pilot came close to crashing his plane near Denver, Colorado this week after encountering a mysterious object in the sky thought to be an unmanned drone aircraft.

A tape recording made available this week confirms that the pilot of a Cessna Citation 525 CJ1 radioed air traffic controllers outside of Denver on Monday after nearly colliding with an unidentified flying object. Several factors have suggested that the aircraft was most likely a robotic drone aircraft.

According to the record, the pilot came close to hitting what he described as “a large remote-controlled aircraft.”

The Cessna’s pilot says that the craft was encountered at around 8,000 feet above sea level, or 2,800 feet above the ground in near the highly elevated city of Denver.

Speaking to reporters at 9News, a spokesman for the Federal Aviation Administration confirmed that the agency is attempting to make sense of the unusual encounter.