Investigators Seek Clues in Fatal N. Carolina Jet Crash : Accident: Experts look for evidence that wind shears caused DC-9 to sink, killing 37. Crew’s action in aborted landing questioned.

A powerful thunderstorm--and the violent, shearing wind that it may have spawned--were prime suspects Monday as several investigators probed the charred wreckage for clues on why a USAir jetliner crashed Saturday night, killing 37 of the 57 people aboard.

It was typically hot, muggy weather here on the Fourth of July, and the going was slow and tedious for the two dozen specialists brought in by the National Transportation Safety Board to study the crash.

Their work required patience and precision--noting the exact position and condition of each of the thousands of pieces of twisted, shattered debris that once made up a massive DC-9 jetliner.

Officials say co-pilot James Hayes, 41, apparently was at the controls Saturday night as USAir’s Flight 1016 from Columbia, S.C., prepared to land at the Charlotte-Douglas International Airport.

Encountering the heavy rain and dwindling visibility of a rapidly intensifying thunderstorm, the cockpit crew decided to abort the landing attempt and climb to the right, according to transcripts of conversations between the airport tower and the crew.

But after climbing briefly, the plane suddenly sank, slamming into the ground.

About a minute before the crash, the tower had warned that there might be wind shears. Wind shears are sudden shifts in the direction and velocity of localized gusts, which occur at dangerously low levels and can deprive a plane of the airspeed needed to keep it aloft.

Investigators are studying data from cockpit recording devices and from wind-shear monitoring systems on the ground, but there has been no definitive word yet on whether there were wind shears.

There has been no mention of engine failure, and the plane’s abrupt drop could be explained by wind shear. In addition, two witnesses on the ground said Monday that gusts at the time of the crash had been strong enough to shake their truck.

On the other hand, preliminary readings from monitoring systems on the ground show none of the wind-direction shifts normally associated with wind shear.

And John Hammerschmidt, the NTSB member heading the accident probe, said other pilots landing about the time of the crash reported heavy rain but none said he encountered wind shear.

Another issue is whether Hayes and his pilot, Capt. Michael Greenlee, handled the plane properly after they made the decision to abort the landing and told the tower they were “on the go” and circling to the right for another landing attempt.

So-called go-arounds are not uncommon, and USAir officials said Hayes and Greenlee were thoroughly trained on handling a DC-9 in wind-shear conditions.

Hayes and Greenlee survived in relatively good condition.

The NTSB positioned investigators the length of the straight, 1,100-foot swath the plane carved after first striking the ground about 2,200 feet west of the north-south runway.

The landing gear on the right side of the plane hit first, followed by the left landing gear about 18 feet later.

The right wingtip struck the ground a few feet after that, literally mowing the grass as the plane continued to hurtle forward.

The DC-9 sawed through a grove of small trees, scattering tree limbs and debris before colliding into two large oaks.

The impact with the oaks tore the fuselage into three pieces.

All that was left of the mid-section of the fuselage, which burned furiously after the crash, was a five-foot pile of charred debris wrapped around one of the oaks.

Still scattered around it Monday were personal possessions of the living and dead--torn magazines, a baby’s clothing, videocassettes and a stained T-shirt.

The mutilated aft section of the fuselage had hacked its way into a house like an ax into a soft log.

The occupants of the house, Walter and Martha Dunn, were in South Carolina when the accident occurred. The smashed remains of two of the Dunns’ cars were still in their driveway Monday, a few yards from a blue plastic tarp on which rescuers had placed human remains.