By Andrea Lorenz

HOUSTON (Reuters) - A World War II-era P-51 Mustang plane owned by a Texas museum and once used by the Air Force of El Salvador crashed into Galveston Bay on Wednesday, killing the two people who were on board, the Texas Highway Patrol said.

The cause of the accident has not been determined, but the pilot was not in contact with air traffic control just before the crash at about noon local time, Federal Aviation Administration spokesman Lynn Lunsford said.

The P-51 Mustang was manufactured in 1944, according to FAA records, and owned by the Texas Aviation Hall of Fame, a part of the Lone Star Flight Museum in Galveston.

Police said Keith Hibbett, 51, of Denton, Texas, was flying the plane, and John Stephen Busby, 66, of the United Kingdom, was the plane's only passenger, according to Sampas. Busby had paid the museum to take the flight as part of a program offered by the museum. Busby and his wife had been visiting to celebrate their 41st wedding anniversary, Sampas said.

According to museum officials, Hibbett was an experienced pilot, Sampas said. Witnesses told police the plane went down without warning or any signs of trouble, he said.

According to the museum website, the plane was used by the El Salvadoran Air Force in the 1960s, during which time the one-person plane was modified to allow it to carry two people. It had been painted with the markings of the Galveston Gal, a tribute to the World War II fighter group of a Galveston native.

The museum offered rides in the plane for $1,995 for one passenger, according to its website. Museum officials did not respond to requests for comment.

The National Transportation Safety Board will be in charge of the investigation, authorities said.

(Reporting By Andrea Lorenz in Houston; Editing by Greg McCune and Ken Wills)