Four people died in the May 2008 crash in a residential area of Cranbrook, B.C. (Submitted by Larry Belzac)Investigators say they may never know exactly what caused a helicopter to crash into a residential neighbourhood in Cranbrook, B.C., last year, killing four people.

But they say the aircraft should not have been operating at such a low altitude over homes.

Three people on the aircraft and one person on the street died when the aircraft lost power, fell to the ground and burst into flames in the southern Interior town on May 13, 2008.

Investigators with the Transportation Safety Board said in a report issued Thursday in Vancouver that because so much of the helicopter was destroyed in the fire, they have been unable to confirm why the fuel supply to the engine apparently ended.

'There is considerable misunderstanding, misinterpretations in the industry about these regulations,'—TSB chief investigator Damien Lawson

The most likely cause was a problem in the fuel delivery system, said investigators, but there was still work to be done on analyzing other possible mechanical causes.

BC Hydro was using the Bell 206 helicopter to do visual inspections of power lines — a task that requires low-level flight.

The single-engine helicopter was flying at an altitude of about 36 metres when it suddenly lost power over the residential area.

At that height, investigators said, the pilot had virtually no ability to control the craft and barely avoided a house before crashing to the street.

Confusion over low-level flying

The investigators also concluded the pilot did not have the proper clearance to be conducting low-level flights in that area.

Chief investigator Damien Lawson blamed widespread industry confusion over regulations governing low-level flights, and said that if the pilot had applied for permission it would not have been granted.

"We do find that there is considerable misunderstanding, misinterpretations in the industry about these regulations, because they are somewhat complex," said Lawson.

As result of the investigation, Transport Canada plans to issue clearer guidelines on the regulations controlling low-level flights, the investigators said.

BC Hydro has since changed the way it conducts low-level flights, requiring twin-engine helicopters for some work and senior management approval of each helicopter request, they said.