PHOENIX - Temperatures are expected to come close to 120 degrees Tuesday, which could cause problems across the Valley.

The hottest temperature ever recorded in Phoenix was 122 in 1990. That temperature famously caused Sky Harbor International Airport to shut down, because flight manuals didn't include information about how planes would operate and what settings to use in such high temperatures.

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What could happen at Sky Harbor

The main concern now is for airline employees on the ground, where the temperature can be 15-20 degrees hotter.

"It's coming off the concrete," American Airlines' Kevin McCarthy said. "It's coming off the equipment -- obviously, the aircraft (are) coming in from a long flight, (so) the engines are hot.

"American is setting up cooling stations and employees get a break between flights anyway," McCarthy said.

In addition, while most of the larger planes that fly in and out of Phoenix can handle higher temperatures, some of the smaller commuter planes cannot.

American Airlines recently announced that some of their regional planes have a limit of around 118 degrees, so some flights may be cancelled between 3 and 6 p.m. Monday through Wednesday.

What could happen to city streets

The City of Phoenix says streets won't melt or soften, but at 122 degrees, the streets might start leaking oil.

"Some newly paved roads might be a little more sticky," Peter Rupal with the City of Phoenix materials lab said. "Other roads you might see a little bleeding of that tar."

The city tests the asphalt it lays down by cooking it in ovens to make sure it holds up. Rupal said different types of asphalt are rated to higher temperatures. Phoenix uses asphalt rated to around 200 degrees.

What could happen to the power grid

Power companies are also bracing for a huge demand in power consumption on Monday and Tuesday as most air conditioners may not shut off at all.

SRP officials said the most common impact of that high demand is on power transformers, which could fail under the load.

Crews will be out in the heat and SRP officials said they're reminding their employees to stay hydrated.