Transportation Safety Board officials say there's no obvious sign of why an air ambulance crashed in Grand Manan, N.B., early Saturday, killing a pilot and paramedic and injuring two others.

Pilot Klaus Sonnenberg and paramedic William Mallock were killed when their Atlantic Charters flight crashed near the airport on Grand Manan Island, in the Bay of Fundy.

A registered nurse and a second pilot were injured. The pilot is in stable condition at the Saint John Regional Hospital. The registered nurse was released from hospital Sunday. 

The small plane had dropped off a patient at the Saint John hospital and was returning to Grand Manan when it crashed.

"Our understanding at this point in time is it was foggy, it was early morning, and right now that's all we really have," said Doug McEwen, a TSB investigator.

"We haven't had a chance to talk to anybody here who was on site at the time."

The cause of the crash remains a mystery.

McEwen said the small plane is destroyed but mostly intact. All major components of the aircraft have been accounted for. There are tire marks on the road several hundred metres before the runway, but no fluid or debris. There was also impact damage to shrubs and brush between the road and the crash site. There was no mayday call.

There is no flight recorder on this type of aircraft, so survivor and witness accounts will be vital to the investigation.

McEwen and another TSB investigator spoke to the survivors on Saturday before heading to the island. They plan to meet with the company on Monday.

They expect to spend most of Sunday photographing the crash site, from the shrubs to the aircraft and the road.

Ambulance New Brunswick has put an additional ambulance and two more crews on the island.​

Meanwhile, condolences continue to pour in from across the country for the families of the victims and the community.

Trent Piercy, a paramedic in New Brunswick who heads the union that represents them, knew Mallock.

"The group, I think, as a whole feels this one ripped the core," Piercy said.

There were no patients on board the small plane when it crashed.