Incident at near London, Ontario (20 NE) (TCAS alert)

1996-03-29: Initial information from T.S.B. Initial Notification (#A96O0058): The aircraft (a Learjet 35A) departed Acapulco, Mexico (MMAA) on a flight to Toronto (LBPIA) (CYYZ) with a planned fuel stop in New Orleans, LA (U.S.A.) (KMSY). Once airborne, the flight crew re-calculated the aircraft's fuel state and amended the flight plan to go direct to Toronto (LBPIA). The aircraft was at FL330 with a clearance to descend to FL290 when the aircraft was passed from Cleveland Center to Toronto Centre. The Toronto controller cleared the aircraft to descend to FL240 and when passing through on its present heading FL270 cleared to go direct to Waterloo. The restriction was intended to maintain adequate spacing between the Learjet and a United Airlines B737 at FL280. The Learjet's crew turned the aircraft to head direct to Waterloo as they began the descent. This brought the two aircraft within the required five mile spacing at the same altitude. The crew of the United Airlines B737 reported a TCAS advisory. The controller issued new heading vectors to the Learjet pilot to regain adequate spacing.