A supersonic Concorde jet en route to New York with 69 passengers returned to Paris after cracks appeared above a porthole as the plane was about halfway across the Atlantic, Air France said today.Monday. Air France Flight 001 was at 59,000 feet and had just reached supersonic speed on Sunday when the cracks were noticed in the first of four glass plates in one porthole, said Air France spokesman Laurent Kressman. He did not know who first noticed the crack about 90 minutes into the 3 hour and 45 minute flight. The pilot slowed the jet, dropped to 32,000 feet and returned to Charles de Gaulle airport, Kressman said.