LAS VEGAS (AP) — Authorities say four people who survived when a sightseeing helicopter crashed at the Grand Canyon earlier this month are still hospitalized in critical condition.

Three British tourists were killed on Feb. 10 when the helicopter from Las Vegas went down on tribal land outside Grand Canyon National Park.

The pilot and three other Britons were injured and taken to a Las Vegas trauma center.

A spokesman for University Medical Center of Southern Nevada says the four survivors are still listed in critical condition as of Sunday.

The National Transportation Safety Board is investigating the cause of the crash.

Preliminary findings are expected before the end of the month, though a full report won't be done for more than a year.