A Provincetown-Boston Airline (PBA) commuter plane crashed shortly after taking off from Jacksonville International Airport Thursday night, killing all 13 persons on board, after vital controls and other parts of the tail section fell off, investigators said yesterday.

The airline had been returned to service only 11 days earlier, after the Federal Aviation Administration had grounded it on Nov. 10 for violations of federal safety rules.

National Transportation Safety Board Vice Chairman Patricia Goldman said yesterday that it was unknown why the separation of the tail section occurred.

One question for the safety board and the FAA will be whether there is a potential problem with the 130 other aircraft of the same type that are being flown in the United States. A related question is certain to be whether the FAA was too hasty in returning PBA to service after 15 days on the ground.

A potential side question stems from the hiring by PBA, immediately after it was grounded, of Michael J. Fenello as its new operations director. Fenello left the FAA as deputy chief in April. He has talked to some FAA employes since PBA was returned to the air, officials said yesterday.

It is illegal under the Ethics in Government Act for a former senior federal employe to represent anyone in an attempt to influence his former agency.

Federal safety officials have ordered a metallurgical examination of the tail section of the Brazilian-made plane and said that they are expediting their search of its maintenance history.

Metal fatigue -- the exhaustion of metal through constant stress, as happens to a paper clip when it is bent back and forth repeatedly -- is an early suspect in the crash, according to aviation sources.

There are a number of other possibilities, however ranging from a maintenance error to collision with a large bird.

The plane was a twin-engine Embraer 110, known as the Bandeirante or Bandit. About 450 of the planes are in service worldwide, including 130 in the United States.

The plane has two turbine-driven propeller engines and carries up to 19 passengers. It was certified as airworthy in the United States in 1979, and is highly regarded as a relatively low-cost workhorse by many of the commuter airlines that have grown rapidly with airline deregulation.

PBA, before it was grounded, carried more passengers than any other commuter airline in the United States. The airline started in New England, serving Cape Cod resorts in the summer, then expanded to Florida for year-round balance.

PBA Flight 1039 from Jacksonville to Tampa landed upside down in a field about 1 1/2 miles from the end of the runway. The parts of the tail were located about one-third of a mile from the end of the runway.

"There was an in-flight breakup," Goldman said, adding that the pilot "was not trying to land. He was out of control."

This was because he had lost his horizontal stabilizer -- the shorter wing-like structure in the rear of the tail -- and the elevators, which are the moving horizontal parts of the stabilizer. The assembly gives a plane stability in level flight and enables the plane to go up or down.

"With the stabilizer and the elevators missing, there was nothing the pilot could do; he had no possible input," Goldman said.

She said that safety board investigators are checking all recent airworthiness directives, as the FAA safety orders are called, that concern themselves with the tail section of the airplane.

Sabotage or an explosion have been all but ruled out, Goldman said.

Because PBA so recently was grounded by the FAA and then quickly returned to the air, the safety board's investigation "will obviously emphasize" the question of the FAA's maintenance surveillance, she said.

The FAA grounded PBA on Nov. 10, charging it with "fraudulent or intentionally false statements" concerning the training and required recurrent testing of its flight crews.

The FAA also revoked the pilot's license of the airline's chairman, J.C. Van Arsdale Jr., for personally operating a flight "in a reckless manner endangering the lives" of passengers and crews. Van Arsdale resigned and a new chairman was named.

The pilot of the crashed plane was identified by PBA as Thomas M. Ashby of Punta Gorda, Fla. He was the second most senior PBA pilot, the airline said. The copilot was identified as Louis Fernandez of Miami. He had been with the airline for seven years.

Names of the passengers were being withheld.

Both crew members and the aircraft itself had been recertified by the FAA in the days following the grounding of the airline, officials said yesterday.

PBA was returned to service in phases, with its smallest aircraft restored Nov. 25, after the FAA supervised rewriting the company's manuals and rechecked its equipment records and the training of its crew members. Some of PBA's larger planes are still grounded.

Fenello, who had several years' experience as an executive at Eastern Air Lines before he went to the FAA as an appointee of the Reagan administration, was hired by PBA about Nov. 15.

Jonathan Howe, administrator of the FAA's Southern Region in Atlanta and the former deputy chief counsel at FAA headquarters, said yesterday that he had talked by telephone with Fenello on Monday.

"The only discussion Mike and I had on the subject of recertification of the airline was that he and I were in agreement that it was in PBA's interest that they jump through every one of the recertification hoops," Howe said in an interview.

"We had a discussion about what he was allowed to do and not allowed to do under the Ethics in Government Act. I recommended that he discuss it with his lawyer."

Chief FAA spokesman Edmund Pinto said that Acting Deputy Administrator J.E. Murdock III placed a call to Fenello about a week ago after hearing that there had been some calls from Fenello to other FAA employes, and reminded him of the law.

Fenello had been seeking factual information about steps to take, Pinto said. He added that the calls all came after PBA had been recertified for operations.