Most international flights operated by Star Alliance carriers, including all United international flights and select United domestic flights, are assigned to Boarding Area G's 14 gates (G1-G14). Most international flights operated by SkyTeam, Oneworld, and non-aligned international carriers board and deplane at Boarding Area A's 15 gates (gates A1–A15). However, Star Alliance carrier Avianca El Salvador operates out of Boarding Area A, and non-aligned carriers Aer Lingus, Fiji Airways, and WestJet typically park at Boarding Area G. Boarding Area A is also used by domestic carriers Frontier Airlines, Sun Country Airlines, and Hawaiian Airlines. When all gates in an airline's designated international boarding area are full, the passengers will board or deplane from the opposite international boarding area. Air Canada, Aer Lingus, and WestJet operate from airports with United States border preclearance, allowing arriving passengers to skip the wait at customs and immigration when they arrive at SFO, and exit the airport from the departure level.