Four of the five people killed in a fiery helicopter crash in Tennessee in April died not as a result of the crash, but because of burns sustained in the post-crash fire, according to an autopsy report released to the public Monday.

The revelation adds another case to the growing pile of evidence suggesting the country’s civilian helicopter fleet remains vulnerable to fire after otherwise survivable crashes.

The crash in Pigeon Forge, Tennessee, of a sightseeing helicopter set off a fire near Great Smoky Mountains National Park on April 5. A 911 recording previously made public includes the screams of the pilot who survived the initial impact. When an operator asked a witness if he could help the pilot, the witness – a firefighter himself – said he was worried the pilot’s skin might fall off if he touched him.
All five people onboard subsequently died.

Monday, an autopsy reveled four of the five died as a result of burns. The NTSB is still looking into the cause of the crash.

The news follows a series of reports by 9Wants to Know on the fact that more than 85% of the civilian helicopters in use today do not have fuel systems that would meet the latest crash standards put forth by the FAA in 1994.

Last year, a Flight for Life helicopter erupted into a wall of flames shortly after taking off from St. Anthony Summit Medical Center in Frisco. One of the flight nurses sustained burns over most of his body and remains hospitalized to this day. The pilot, Pat Mahany, died in the crash. While an autopsy showed he died of internal injuries, it also said the fire contributed to his death.

9Wants to Know has tracked 173 fiery helicopter crashes since 1994.