Friends are mourning a pilot who was among those killed during a hot air balloon crash near Eloy, Arizona, early Sunday.

Those who knew him are remembering Cornelius van der Walt in tributes on social media, the Daily Mail reported Monday.

A total of four people died during the incident, and among them was a young nurse. Another person was seriously injured in the crash.

The Mail report detailed the online messages:

One said van der Walt had “mad skills in so many ways” and that those who knew him will remember him as “one h**l of a good man.” Others thanked him for the impact he had on their lives and offered their condolences to his family.

…

Van der Walt was a “character, an adventurer, a friend,” his friend Phil Brandt wrote of the “tragic” incident in an emotional Facebook post.

In a social media post on Sunday, the Eloy Police Department said the hot air balloon crash-landed in the desert near Sunshine Boulevard and Hanna Road.

“We are working closely with federal agencies, including the NTSB and FAA, to investigate the cause of this tragic event. While we continue our efforts, we ask for your thoughts and support for the families and loved ones affected during this difficult time,” the department continued:

Video footage shows the scene of the crash and officials placing the basket on a trailer and assessing the damage to the balloon.

They then appeared to gather the corners of the balloon and fold it up:

The Mail report said the National Transportation Safety Board’s (NTSB) preliminary information about the incident reported that the balloon crashed after something went wrong with its envelope. However, what exactly went wrong has not yet been reported.

The outlet also noted the group of 13, including eight skydivers, four passengers, and the pilot, were in the balloon when the incident occurred.

Eloy Police Chief Byron Gwaltney said, “The skydivers were able to exit the balloon without incident and completed their planned skydiving event, and then shortly thereafter, something catastrophic happened with the balloon, causing it to crash to the ground.”

NTSB and Federal Aviation Administration (FAA) officials are investigating what happened.