The National Transportation Safety Board has published its preliminary report on the recent midair collision between a United Airlines Boeing 737 MAX and a weather balloon in the skies over Utah.

United Flight 1093 was en route from Denver to Los Angeles on October 16 when the aircraft collided with an object, while in cruise flight at 36,000 ft near Moab, Utah. The object was later identified as a “global sounding balloon” operated by WindBorne Systems. The balloon’s impact shattered the first officer’s windshield, injuring the captain. The flight diverted to Salt Lake City.

According to the NTSB, the 737-8 was in cruise when the captain “noticed an object distant on the horizon.” Within seconds, the aircraft experienced “a significant impact” to the first officer’s forward windshield, “along with a loud bang,” showering both pilots with glass fragments.

The captain suffered “multiple superficial lacerations” to his right arm, but the first officer was uninjured. Despite the violently shattered outer pane, the cabin pressurization remained stable.

After the impact, the captain transferred control to the first officer and began administering first aid to himself while coordinating with dispatch and flight attendants. Shortly afterward, the first officer’s window overheat light illuminated, and the crew requested a diversion. The flight diverted to Salt Lake City International Airport, where it landed without further incident. Emergency medical personnel met the aircraft at the gate.

All 111 passengers and crew, except for the captain, escaped injury, but the aircraft damage was classified as substantial.

Both the cockpit voice recorder and flight data recorder were shipped to the NTSB’s Vehicle Recorder Laboratory. Specialists in meteorology, materials engineering, aircraft performance, and air traffic control have been assigned to the investigation.

WindBorne Systems reported that one of its unmanned research balloons launched the previous day from Spokane, Washington, had stopped transmitting just minutes before the collision. The balloon had reached a pressure altitude of 35,936 ft — within 60 ft of the aircraft’s altitude — and was drifting eastward across Utah at the time of the strike.

The balloon was operating legally as an unmanned free balloon. A Notice to Airmen (NOTAM) had been issued the previous day for launch operations in Spokane, but it expired hours before the incident. It did not apply to the balloon’s later location in Utah.

The balloon’s last known coordinates placed it directly along the aircraft’s ground track. The NTSB’s preliminary review of the flight data recorder showed the 737 was flying nearly along the balloon’s path, at a speed of 395 knots (455 miles per hour).