Eleven people were killed on Friday when their skydiving plane crashed and burned at a coastal airfield on the island of Oahu, the worst civilian aviation accident in the US since 2011.

Among those who died was Casey Williamson, 29, and his mother Carla Ajaga’s only child, his cousin Natacha Mendenhall said.

“We’re all very upset,” said Mendenhall, speaking from her home in Fort Worth, Texas. “She cannot really talk right now. What she wants everyone to know is how full of life her son was, how loving he was.”

Williamson, who was from Yukon, Oklahoma, worked as an instructor and as a videographer who filmed customers as they completed sky dives. He was trying to earn more jumping hours and learn the trade, Mendenhall said.

Williamson’s family has not been officially notified of his death. But they provided Honolulu police with Williamson’s name and date of birth and police confirmed he was on the flight, Mendenhall said.

No one aboard survived the crash, which left a small pile of wreckage near the chain link fence surrounding Dillingham airfield about an hour north of Honolulu.

Steven Tickemyer said he saw the plane take flight, get 75 to 100ft and turn away from the mountain range nearby. He said the plane then started to nosedive and flip belly forward so that it was upside down. The aircraft then flipped again and hit the ground nose first. There was an explosion when it hit the ground.

This all transpired in about 20 to 30 seconds, said Tickemyer, who watched from a beach across the street where he was attending a friend’s small wedding ceremony. He and his friends hopped in his truck, called 911 and drove over to help. They screamed to see if anyone would respond, but no one did, he said.

The crash appeared to be the worst US civil aviation accident since a 2011 accident at the Reno Air Show in Nevada that killed the pilot and 10 spectators.

Officials in Hawaii initially reported that nine had died and that three were customers of the skydiving company operating the plane and six were employees. But the Hawaii Department of Transportation tweeted later that officials “confirmed there were 11 people on board the plane” and no survivors. They were not identified.

The flight was operated by the Oahu Parachute Center skydiving company. The ratio of employees to customers aboard suggested that tandem jumps may have been planned in which the customers would have jumped while attached to experienced skydivers, Tim Sakahara, a spokesman for the Hawaii Department of Transportation, told reporters.

Witness Wylie Schoonover saw the plane flying over trees while driving from a nearby YMCA camp after picking up a friend. Then she saw smoke billowing from the airfield and drove over. There was an “insane amount of fire”, she said.

“It didn’t even look like a plane. A bunch of people were asking ‘what is this?’ It was completely gone,” Schoonover said.

Two Federal Aviation Administration inspectors went to the crash site and National Transportation Safety Board (NTSB) investigators were expected to arrive on Saturday evening, safety board spokesman Eric Weiss said.

The same plane was involved in a terrifying midair incident three years ago in Northern California that prompted the 14 skydivers aboard to jump earlier than planned to safety.

In that 2016 incident near Byron, California, the twin-engine plane stalled three times and spun repeatedly before the pilot at that time managed to land it safely, the NTSB said in an investigative report. The report blamed pilot error and said that the plane rotated nine times during one of the three spins it experienced.

Investigators found that the plane had lost a piece of horizontal stabilizer and that the elevator had broken off. The plane was also too heavily weighted toward the back, which was also blamed on the pilot.

The plane with two turboprop engines was manufactured in 1967, FAA records said.

No one answered the phone at Oahu Parachute Center, which advertises its services on a web site saying its jumps offer people “a magical experience”. Tandem jumps are featured at prices ranging from $170 to $250.

Videos from the company’s Facebook page show jumps from the plane that crashed, with customers strapped to employee skydivers jumping out the side door of the aircraft from 10,000ft or higher, with the Pacific ocean and the Oahu’s green mountains far below.

Dillingham Airfield is used mostly for skydiving and glider flights. Hawaii shares the airfield with the Army, which uses it for helicopter night-vision training.