An independent investigative authority on Tuesday released a preliminary report that says one of the engines of a cargo plane involved in last month’s fatal incident at the airport surged to full forward power after touchdown.

An Emirates cargo plane veered off course after landing in the early hours of October 20. It crashed into a patrol vehicle, pushing it into the sea and killing two security workers inside.

According to the preliminary report by the Air Accident Investigation Authority (AAIA) under the Transport and Logistics Bureau, flight data indicated that No. 4 engine on the Boeing 747 freighter suddenly surged to full forward power after landing.

The thrust reverser – a device meant to slow the aircraft – on that engine was found to be inoperative before departure from Dubai, a condition permitted under current aviation regulations.

The other three engines’ thrust reversers functioned normally to slow it down.

The report also says the weather was normal that night, with good visibility, and communication between air traffic control and the crew was smooth right up to touchdown.

Investigators are still looking into why that engine unexpectedly powered up, and they’ll be checking the plane’s maintenance records, the crew’s qualifications, and whether human error played a role.

Authorities plan to release a full report within a year.