A WestJet spokesperson said flight 662 set to depart from Calgary to Toronto experienced a maintenance issue Friday morning, which caused the air conditioning system to emit smoke into the aircraft. "The smoke quickly dissipated however out of an abundance of caution the crew declared an emergency and returned to Calgary," Lauren Stewart said in an email to Global News. She said the flight landed normally at around 10:40 a.m. After Thursday's incident involving smoke in the aircraft, the plane was removed from service and maintenance was conducted overnight. "The aircraft will again be removed and additional maintenance inspections conducted before a return to service," Stewart said. WestJet expected all passengers would be re-accommodated to Toronto later on Friday. "It is important to remember that just because an emergency is declared does not necessarily mean there is an emergency on board," she wrote. "The declaration is made to ensure priority landing and the presence of emergency vehicles, if required."