Four people were killed and three seriously injured Thursday when the Heli USA tour helicopter made a mid-afternoon, clear weather crash landing on grass along the airport runway.

State Department of Transportation spokesman Scott Ishikawa said his agency has been asked to expect the helicopter to be moved today, by flatbed truck, to a secure indoor location for detailed analysis of the wreckage.

"Federal officials have asked us to arrange for hangar space at Lihu'e Airport," Ishikawa said.

In previous helicopter crashes, wreckage was deposited in a fixed-wing aircraft hangar, where investigators would lay out the pieces of the wreckage in rough approximation of how they fit together on the helicopter and try to determine how the accident happened.

Pilot Joe Sulak, who was among those killed in the crash, reported by radio before the crash that he was experiencing a hydraulic failure, so the hydraulic system is expected to get careful attention. Other pilots said the A-Star alarm for a hydraulic failure is the same as for other problems, including low rotor speed, thus the condition of the engine at the time of the crash is also likely to receive critical attention.

One issue that puzzles pilots is why the wrecked helicopter's massive, yellow floats are inflated.

"Very important is whether the floats were deployed before landing or after. This may be a very important key to the puzzle," said Richard Schuman, president of O'ahu's Makani Kai Helicopters.

Schuman and others have said that landing an A-Star helicopter with a loss of hydraulic power is difficult, but is a maneuver pilots practice. Heli USA President Nigel Turner said Friday that Sulak practiced the maneuver successfully on a check ride just a week before the crash.

"The landing without hydraulics is done every day in practice. The pilot did everything he should-could have done up to the last few seconds," said Schuman, who also is a pilot.

But the addition of inflated floats during a landing would make it an exceedingly difficult process, said Mike Danko, a helicopter pilot and aviation attorney in San Mateo, Calif.

"Inflatable floats restrict your ground options. I've never heard of anyone try to land on land with inflatable floats," Danko said.

The standard method for landing a helicopter without hydraulics is what is called a run-on landing, in which the pilot brings the helicopter to the ground while still moving forward, and it can slide to a stop on its metal skids.

"One of the big advantages of the skis is the ability to do a run-on landing," Danko said. The type of inflatable floats used on the crashed helicopter would prevent a successful run-on landing, he said.

Turner said that Heli USA spent $600,000 installing floats on all its Kaua'i A-Star helicopters last year. They are designed to keep a helicopter afloat in case of a water landing.

On Sept. 23, 2005, three Heli USA passengers died when an A-Star helicopter without floats crashed into the water and quickly sank.

In a Feb. 13 press release, Heli USA addressed the issue: "Since this event, Heli USA has installed additional safety equipment including external inflatable floats on its helicopters even though they are still not required (by the FAA). ... The company has done so, so that its helicopters can fly beyond autorotative distance from shore and conduct interisland commercial operations."

Danko said such floats rarely if ever inflate as the result of impact. "I think that's really unlikely. I have never seen that happen. It's certainly possible, but really unlikely," he said.

Others have suggested that Sulak may have initially experienced difficulty over water and deployed his inflatable pontoons. Another theory is that the floats were deployed as a last-minute effort to soften an expected hard landing.

"I would keep an eye on the NTSB/FAA or on the ground witnesses to see if the floats were deployed before landing. ... The industry is waiting to see the expert's opinions," Schuman said.