Five major crashes, some involving cars becoming airborne and flipping over, have raised concerns entering Sunday's 99th running of the Indianapolis 500.

The famed IndyCar oval classic, 200 laps around the 2.5-mile (4km) Indianapolis Motor Speedway, will start with New Zealand's Scott Dixon in pole position followed by Australian Will Power and France's Simon Pagenaud.

But tensions are raised at the "Brickyard" after wrecks that prompted officials to alter qualifying specifications to reduce turbo engine boost and increase downforce to slow cars in hopes of avoiding more spectacular crashes.

Three-time Indy 500 champion Helio Castroneves went airborne and had his car flip end over end in practice.

While Britain's Pippa Mann stayed on the track when she hit the outer wall and outer pit wall entrance, American Josef Newgarden also found the safety fencing in a testing session.

When two-time pole sitter Ed Carpenter went airborne in a crash ahead of Sunday's qualifying, IndyCar officials made last-minute safety changes, somewhat controversially since only Chevrolet-powered cars were having the issue at speed and those powered by Honda engines were not affected.

"We've said all along we want to go faster, but we want to do it safely," IndyCar parent company chief executive Mark Miles said. "Safety for drivers and fans is the top priority."

Officials forced teams to use slower race set-ups for time trials, but there is some uncertainty about what will happen when the full 33-car field takes the green flag even after the qualifying slowdown.

"We don't want to see cars getting in the air and there's only a few tools that you have in the toolbox to use and IndyCar, whether it's the right or wrong situation, for safety, it's kind of all they had," Dixon said.

"If you look at oval racing as some of the most dangerous... it's always in the back of your mind."

On Monday, Canada's James Hinchcliffe suffered pelvic and left thigh injuries that have sidelined him indefinitely in a crash caused by the failure of a suspension component.

Aussie Ryan Briscoe will replace him in the lineup on Sunday.

Although Hinchcliffe was seriously injured, at least his car stayed on the ground.

- Part of the sport -

Reigning IndyCar series champion Power said the earlier airborne crashes were particularly worrying.

"I think that this is the first year we've ever had with this car that you could trim enough to make it quite hard to drive and people were making mistakes and crashing, which when I first started here at Indianapolis in '08, that was happening every day. But the problem was the cars take off," he said.

"So I think it has kind of identified a problem with this car. Until they get that fixed, I'm not sure what they can do," Power added. "It's a pretty tough problem. But I don't think it's just Chevy, either. I think it doesn't matter. It's just the fact that the floor is built for a road course, and we're running it on an oval and it's quite steep. That's maybe one problem. I'm not an engineer. I don't know."

Britain's Justin Wilson said the Castroneves crash put teams on notice.

"Helio's crash got our attention, but that sort of thing has happened in racing for years," Wilson told NBC. "When James' crash happened, that was when people realized we could get hurt doing this."

No racer has been killed at Indy in May since Scott Brayton in 1996, a week after winning the pole.

The IndyCar series has worked hard to improve safety since Briton Dan Wheldon was killed in a 2011 crash at Las Vegas Motor Speedway, in which his car went airborne and struck a catch-fence post.

Despite heightened awareness, drivers are prepared to live with risk.

"Crashing at Indianapolis is not a new thing," Dixon told NBC. "Regarding safety, you kind of take it for granted. You do realize it's part of the sport and the last thing you want to see is what happened to James. You can't do anything when the car fails."
Source: AFP