CHARLOTTE, N.C. (AP) _ Investigators seeking the cause of a commuter plane crash said Thursday that the aircraft was near its maximum weight and a tail assembly adjusted two days earlier was moving unusually during the 37 seconds the doomed flight was in the air.

The up-and-down motion began after the plane underwent routine maintenance Monday night and showed up during all eight flights before Wednesday's crash, said John Goglia, a National Transportation Safety Board member.

The flight data recorder pulled out of the smoldering wreckage confirmed the unusual movement was also present just before the crash that killed 21 people.

A team of NTSB investigators was sent to the Raytheon Aerospace facility in Ceredo, W.Va., where the maintenance was done.

``We need to know which procedures were followed,'' Goglia said.

Goglia said the plane was about 100 pounds below its maximum weight at takeoff. He said pilots, mechanics, gate agents and baggage handlers interviewed by investigators said they thought the plane ``looked heavy.''

``We have enough concern that we're going to follow that to its conclusion,'' Goglia said. ``Heavy is not a quantifiable word. We're going to quantify it.''

Goglia said there was confusion among workers loading the plane over whether too many bags had been put in the luggage compartment near the tail of the plane. After consulting with the captain, however, it was agreed that the plane could handle the extra load.

The Federal Aviation Administration also told Air Midwest officials to check more than 40 planes that may have been serviced at the West Virginia facility. Air Midwest, a commuter airline of the Mesa Group, operates as US Airways Express in some areas.

``It's pretty clear that Air Midwest needs to take immediate action,'' FAA spokesman Greg Martin said.

In a statement, Air Midwest said it had begun immediate inspection of the elevator controls on three aircraft that have undergone similar maintenance in West Virginia.

The airline also said it would inspect elevator controls on its entire fleet of 43 Beech 1900 Aircraft over the next three days.

US Airways Express Flight 5481 crashed in flames moments after leaving the Charlotte airport, killing the 19 passengers and two crew members aboard. Capt. Katie Leslie reported an emergency to the tower, but the FAA said the transmission was cut off before she could identify the problem.

Information from the flight data recorder shows the flight took off with its nose up 7 degrees, which is normal. But the pitch increased sharply, to 52 degrees, by the time the plane reached 1,200 feet, Goglia said. The plane soon rolled to the right and headed toward the ground.

``Something occurred to drive that pitch angle to 52 degrees,'' Goglia said. ``That is abnormal.''

The data recorder also shows the elevator control on the tail of the Beech 1900 ``moving up and down a lot'' on all nine flights it took following the maintenance work, Goglia said.

Elevators are flaps that swing up and down from the rear of a plane's horizontal tail stabilizer, increasing or decreasing lift. In the case of Flight 5481, Goglia said, the maintenance workers did work on the assembly that controls movement of the elevator.

Earlier Thursday, Goglia said he had been told by Air Midwest that a tab that controls movement of the elevator had been replaced Monday night. But Thursday night, Goglia said the airline had changed its story, saying no tab was replaced.

Asked whether the change in story was cause for suspicion, he said it was simply confusion.

The unusual motion may not have affected earlier flights if the plane was not loaded to capacity, Goglia said. But the twin-engine turboprop was at nearly full weight when it took off from Charlotte for Greer, S.C.

Officials at the Raytheon facility in West Virginia referred calls for comment to company headquarters in Madison, Miss. There, spokesman Chris Blount said only that Raytheon works under contract to Mesa for maintenance on its Beech 1900 fleet.

Frank Graham, an aviation investigator and former pilot, said the fact the pitch of the plane's nose reached 52 degrees hints at an extreme problem.

``This is a very unusual, significant, catastrophic failure that would allow the nose of the aircraft to pitch up to 52 degrees,'' he said. ``It sounds a little bit like the reverse of the Alaska Airlines 261 crash, where a component in the tail failed and aircraft pitched down and no matter what the pilots did they couldn't regain control.''

In that January 2000 crash, the NTSB concluded shoddy maintenance of the MD-80 jetliner led to the failure of a tail component that helps move the stabilizer. The crash killed 88 people.

The FAA has issued nearly two dozen airworthiness directives on the Beech 1900-D since 1994, warning problems that must be repaired if found in an aircraft. A directive issued in November warned that screws in the elevator balance weight attachment could come loose and interfere with the horizontal stabilizer.

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