FLAGSTAFF, Ariz. — Three British tourists killed in a fiery helicopter crash at the Grand Canyon earlier this year died of smoke inhalation and burns that covered their entire bodies, according to autopsies released Wednesday.

The reports from the Mohave County Medical Examiner's Office for brothers Stuart Hill, 30, and Jason Hill, 31, and Rebecca Dobson, 27, also confirm all five crash victims died from burn-related injuries.

Newlyweds Jonathan Udall, 31, and, Ellie Milward Udall, 29, died days after the Feb. 10 accident at a Las Vegas hospital. A Nevada medical examiner said both died from complications from burn injuries.

According to the Mohave County medical examiner, the Hill brothers and Dobson were burned beyond recognition. There also was evidence they suffered carbon monoxide poisoning.

Udall's family is suing helicopter owner Papillon Airways and manufacturer Airbus Helicopters. The wrongful-death lawsuit, filed in March in Las Vegas by Udall's parents, says he would have survived if the aircraft had a crash-resistant fuel system.

The Udalls' attorney did not immediately respond Wednesday to a message seeking comment.

The crash-resistant systems have fuel tanks that expand, rather than rupture, on impact and self-sealing components to keep fuel from spreading. They are meant to prevent aircraft from catching fire and lessen the chance that people on board get burned.

Airbus officials said the company now builds helicopters with the new fuel systems and supports operators who chose to retrofit their Airbus aircraft with them.

Papillon Airways CEO Brenda Halvorson has said it is "misguided" for attorneys to make allegations about the accident before the National Transportation Safety Board finishes its investigation.

The crash also critically injured a sixth passenger, 39-year-old Jennifer Barham, and the pilot, 42-year-old Scott Both.

The six friends were in Las Vegas to celebrate Stuart Hill's birthday and were on a sightseeing tour over tribal land in the Grand Canyon.