The small plane that crashed Sunday morning in western Boulder County, killing four people, was associated with a company that offered sightseeing flights out of Rocky Mountain Metropolitan Airport in Broomfield.
The Cessna 337, a twin-engine propeller plane, was used by Bluebird Aviation, according to online reviews and photos posted by the company. The Colorado Sun matched the plane’s registration number, which was released Monday by the Federal Aviation Administration, with the online reviews and publicly available photos.
It’s not clear if the plane, built in 1972 and registered to a limited liability company that once shared the same address as Bluebird Aviation, was flying for Bluebird at the time of the crash.
Bluebird Aviation’s website was taken down on Monday, as were its social media pages. Phone calls and text messages to representatives for the company from The Sun weren’t immediately returned.
The Federal Aviation Administration says that one pilot and three passengers were aboard the plane when it crashed. The FAA and the Boulder County Sheriff’s Office says all of them died.

The identities of the four people who were aboard the plane have not been released.
First responders couldn’t fully access the crash site Sunday because of the heat from a post-crash fire, which sparked a wildfire that burned about an acre. Carrie Haverfield, a spokeswoman for the sheriff’s office, said a recovery crew was working at the scene on Monday.
Peter Knudson, a spokesman for the National Transportation Safety Board, says the plane entered a descending left turn in the moments before it crashed.
“We do have a number of witnesses,” he said.
An NTSB investigator was at the scene on Monday. Knudson said the NTSB hadn’t determined who was operating the plane at the time of the crash.
Public flight radar records captured by flightaware.com show the plane took off from Rocky Mountain Metropolitan Airport and traveled northwest toward Longs Peak before the crash. The entire flight lasted about 10 minutes.
The plane had made a number of trips into the same area earlier this month, always turning south toward Red Rocks Amphitheatre and landing back at Rocky Mountain Metropolitan Airport. Each of the plane’s recent flights lasted about 40 minutes.
Internet archives reveal that Bluebird Aviation advertised hour-long “date-night tours” and “mountain tours” for several hundred dollars.
This is a developing story that will be updated.