The pilot, Adriano Jimenez, had his license revoked in 2006 in part because he had organized other unauthorized charters for immigrant workers, according to Jose Tomas Perez, director of the Dominican Civil Aviation Institute.

Authorities said passengers on the missing plane were carrying work permits for the nearby Turks and Caicos.

Three aviation officials were suspended Thursday and two pilots were detained as authorities investigated why Jimenez was allowed to take off Monday with only a U.S. student pilot's license and without declaring the flight as a charter.

"There really was some negligence on behalf of authorities," said Col. Cesar Cotes, the institute's security supervisor.

Jimenez sent out an emergency signal about 35 minutes after taking off from Santiago, Dominican Republic, and the plane disappeared from radar. The U.S. Coast Guard called off its search for the twin-engine BN2A MK III Trislander on Wednesday night.

The suspended officials included an inspector, a fee collector and the operations director for the aviation institute, Cotes said.

One of the detained pilots allegedly helped Jimenez load and balance the plane. The other had been hired by the airplane's owner to fly the plane from Puerto Rico to the Dominican Republic for an inspection by Jimenez, a potential buyer, Cotes said.

The flight plan filed by Jimenez called for him to land in Mayaguana Island in the Bahamas.

But Perez said workers often pay for charters because they cannot find direct flights to their destination on commercial airliners.

It is not illegal to take documented migrants to another country, but Perez said pilots are prohibited from using a private plane for that purpose without declaring it as a charter flight. Penalties for organizing such trips include fines and suspension of a pilot's license.

It is unclear how many unauthorized charter trips Jimenez allegedly made previously.