JACKSON, Miss. (AP) _ The pilot of the small plane that crashed and killed Rep. Larkin Smith appeared nervous before the flight, ran the aircraft off the runway before takeoff and flew in the wrong direction, an investigator says.

A second investigator with the National Transportation Safety Board said weather may have been a factor in the crash Sunday night.

The single-engine plane carrying Smith, 45, and pilot Chuck Vierling, 58, traveled east of its planned flight path, slamming into a 70-foot pine tree in a forest. The Mississippi Republican was returning from Hattiesburg to Gulfport, 70 miles south. Both men died in the crash.

Witnesses reported that before takeoff, Vierling ''appeared kind of nervous ... like he was concerned about the flight, Jorge Prellezo, regional director for the National Transportation Safety Board, said in an interview Wednesday in Miami.

William Dowden, an employee of Southeast Aviation, said he observed Vierling's plane during and after takeoff from the Hattiesburg Airport.

''He taxied straight out off the ramp area onto the grass and when he realized what had happened, he made a 180-degree turn, then taxied slowly out to the runway,'' said Dowden. ''The taxiways are lit up with blue lights and what happened struck us as being highly unusual.''

Prellezo said there were other questions about the flight, including why the pilot had indicated to controllers he would follow the established route along a highway but instead flew about nine miles east over the forest.

''After taking off he headed east and when he contacted (air traffic control at) Houston they told him, 'Well, if you want to go to Gulfport, you had better take a southerly heading,''' Prellezo said.

Vierling was a licensed pilot and a friend of Smith's. He had been flying since 1963, said his stepson, Glenn Terrell. The plane belonged to Gulfport's Institute for Marine Mammal Studies, authorities said.

Jeff Kennedy, another NTSB investigator, said at a news conference in Biloxi on Wednesday that although weather reports cited visibility of nearly six miles, darkness and haze may have affected the pilot's vision.

Vierling would have had few ground lights to guide him over the rural area, Kennedy said. He noted that search helicopters were grounded by fog about 4:30 a.m.

''It's hard to determine what kind of flying conditions he was in,'' Kennedy said.

Charles Theologos, a part-time Federal Aviation Administration instructor, said Vierling was not certified to fly by instruments alone. But authorities said the weather was good enough for him to take off Sunday night.

Investigators were also examining the possibility the plane ran out of fuel, following reports there was no smell of gasoline at the crash site, said Prellezo.