The accident took place around 12:40 pm local time, according to police. The aircraft was en route to pick up a patient from a nearby hospital at the time, according to the Navajo Police Department. 

All four people on board the plane died. The cause of the crash is unknown at this time, police said. 

The FAA and the National Transportation Safety Board are investigating. Police said, all access to the airport is currently closed due to the investigation.