By Monday the weather is expected to reach 115 degrees in the Tucson area.
Although airline officials say there were no delays because of the heat, they aren't saying there won't be in the coming days.
Officials say flight manuals would be affected if the temperature rose too high. The manuals tell pilots how their aircraft would perform in hot weather.
Since hot air is thinner, one of the problems would potentially be an airplane having to take a longer time to get off the ground.
American Airline officials say passengers with connecting flights into Phoenix could receive waivers in case of delays.
They say this will begin Monday and run through Wednesday from three to six in the evening.