An experienced pilot and a recent high school graduate have been identified as two of three people killed in a plane crash off South Australia’s south coast.

Morphett Vale man Leo Howard, 53, was on board a Cessna with 18-year-old Tristan Scheffers and a 20-year-old from Pasadena, both trainee pilots, when the aircraft spun out of control before nose-diving into waters in the Long Bay area, close to Goolwa South about 4.30pm on Friday.

The plane’s descent was witnessed by several people in the area — a popular sightseeing spot with an airstrip at Goolwa and a number of private runways on nearby Hindmarsh Island.

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“We’ve seen the plane just plummet, just do circles all the way down, bang,” witness Jamie Dicker told 7NEWS.

“We firstly heard the engine noise and then basically looked up, and then we saw the plane doing these spirals,” another witness said.

Goolwa Surf Lifesavers were among the first to respond to the emergency, jumping on jet rescue boats to battle two-metre-high waves.

“Looking for survivors or potential survivors is what’s going through my head,” lifesaver Matt Burrage said.

But the trio onboard the aircraft were found dead.

Howard was an aerobatic pilot and instructor with Goolwa Air, which offers charter flights, flight training and scenic tours.

The company’s social media featured Howard piloting a light aircraft in May last year, describing him as “a highly experienced aerobatic pilot with a passion for precision flying and a strong focus on safety”.

His family shared a heartbreaking statement with 7NEWS.

“Leo was a highly respected and experienced pilot,” his sister Mercedes Howard said.

“He was a loved family man, son, father, and brother.”

Many have paid tribute online to the beloved instructor, with one friend remembering him as “a great pilot and top-notch guy”.

“RIP Leo, took me on my first fixed wing flight all the way through to train me in unlimited aerobatics,” they wrote.

Another said: “I’ll remember all the important lessons you taught me and our aerobatic flight in the decathlon.”

In a longer tribute, Howard was remembered as far more than a skilled aviator.

“He was a friend, a mentor, and someone who made flying better simply by being there,” the post read.

“I’ve spent many hours over the past 6–7 years flying with Leo, both at Adelaide Biplanes and Goolwa Air.

“He was an incredibly experienced pilot — fixed wing, rotary, aerobatics — but more than that, he was a brilliant instructor and a genuinely top bloke.

“I’m grateful for so many great memories flying different planes, in different conditions, with him by my side.

“With a very heavy heart, my thoughts and prayers are with Leo’s family, and with the families of the two young souls who were also lost. May they all rest in peace.”

Scheffers has just finished high school and was on his way to earning his commercial pilot licence.

His dad Bas Scheffers told 7NEWS, “Our beautiful boy who loved flying more than anything else spread his wings one last time on Friday.”

Witnesses described the scene as “gut wrenching”.

“It was gut-wrenching, no-one knew what to say, what to do, it was a very full-on fronting situation,” witness Luke Scafidi said.

The Australian Transport Safety Bureau will next interview witnesses, examine the wreckage, and analyse flight track data, as well as aircraft and maintenance records.

A report will be prepared for the coroner.