UNITED NEWS INTERNATIONAL (UNI) – An Air China flight dropped over 6,000 meters because its pilots were allegedly smoking in the cockpit.

In a statement released on Wednesday, July 11, Air China said the crew is being investigated by the Civil Aviation Administration of China.

During the Hong Kong to Dalian flight on Tuesday, the plane lost pressure and dropped from above 10,000 meters to below 4,000 within 10 minutes, according to Flight Aware data.

Some of the passengers posted photos of their oxygen masks on social media and one reportedly commented, saying the passengers were told there was a malfunction but not to worry.

However, according to news reports, the pilots accidentally turned the air-recycling fans off while they were smoking in the cockpit, causing the sudden drop in altitude mid-flight.

The pilots reportedly fixed their mistake and landed safely in Dalian.