ZURICH, Switzerland -- Swiss investigators said an Alitalia DC-9 that crashed into a mountainside, killing all 46 people on board, approached a Zurich airport nearly 1,000 feet lower than it should have been.
'The plane was 300 meters (990 feet) too low on its approach, and was slightly off course,' the official investigating Civil Air Authority team said Thursday in a statement.
'(The captain) was not following the radio beacon signals,' the statement added. The statement did not say why the plane was too low.
The airliner, on a 50-minute flight from Milan to Zurich, crashed and burned on a thickly wooded 2,000 foot hill 5 miles north of Zurich's Kloten airport at 8:13 p.m. Wednesday.
It was raining at the time, but Milan airport traffic controllers said visibility was 6 miles and there was almost no wind at the time of the crash.
The commandant of the plane, Raffaele Liberti, 47, was a former Italian Air Force pilot with more than 10,000 flying hours to his credit.
The DC-9 was 16 years old, but underwent its latest technical inspections on Oct. 21 and Nov. 4, Alitalia said in a statement. It said the pilot did not report problems of any kind to Zurich air controllers and 'the causes of the crash are not known.'
Zurich airport officials said the pilot was clearly flying too low as he approached the airport from the north after circling it.
Eugen Thomann, chief of police rescue operations for the Zurich Canton, said several witnesses reported that there appeared to be an explosion aboard the DC-9 before it hit the hill. But Italian press commentators said these reports were doubtful, although the possibility of a terrorist bomb was not entirely ruled out by investigators.
Another possible cause of the crash suggested in Italian media was a phenomenon known as 'wind shear' -- a sudden gust of wind -- or the formation of ice on the wings, which several pilots were reported to have complained of on landing at the Zurich airport.
Swiss authorities said 80 people were investigating the crash and that one of the two flight recorders on board, the one that recorded technical details of the flight, had been found. No other details were immediately available.
Italy sent teams of aviation experts and police to Switzerland Thursday to help Swiss authorities solve the mystery of what caused the crash.
Alitalia, Italy's state airline, said the passengers included six Italians, six Americans, and two Japanese officials of the OKI electric company. The others apparently were Swiss. The crew, which included two pilots and four cabin attendants, were Italian.
Alitalia identified the six U.S. citizens as William Briggs, Karol Forman, John Stuckey, Paul Vaughan, Stephen Ritter and a passenger named Bass. It did not say whether Bass was a man or a woman nor did it release towns of origin of those who died.
Both Swiss police and Alitalia confirmed around midnight that all 46 aboard the plane were killed when the DC-9 broke into small pieces and burned.
The crash was the most serious for Italian aviation since June 27, 1980, when a DC-9 of the Italian Itavia company crashed into the Mediterranean near the island of Ustica, north of Sicily, killing all 81 people aboard, while on a domestic flight from Bologna to Palermo.
Investigation into the Ustica crash continues after 10 years, with controversy raging over whether the airliner was shot down by a missile or whether a terrorist bomb exploded aboard it.