example:
flight 172 SFO 8:45AM - BOS 5:20 PM = about 5 hour flight eastbound
flight 173 BOS 7:35AM - SFO 11:15AM = about 6 hour flight westbound

flight 224 OAK 7:15AM - IAD 3:20PM = about 5 hour flight eastbound
flight 235 IAD 4:35PM - OAK 7:36PM = about 6 hour flight westbound


why westbound always takes longer than eastbound?