Snow and other winter weather will be testing the effect of 5G cellular services on air travel after a relatively easy first day.

Federal Aviation Administration (FAA) has stated that landings will be restricted in low-visibility areas due to fears that 5G signal’s could disrupt critical equipment. The FAA warned that some flights may be diverted as winter storms made land on Thursday.

The aircraft radio altimeters are at the heart of this issue. They tell pilots the distance the plane has from ground level. Altimeters are used on frequencies similar to the 5G service. This raises concerns that aircraft may receive inaccurate information.

Two delays had occurred since December and the service launched Wednesday. Verizon and AT&T, at the last-minute, agreed to temporarily delay the rollout near airports temporarily after airlines warned federal officials that the signals could cause widespread disruptions and “economic calamity.”

“Due the national expansion of the 5G C-band band and the possibility for interference by radio altimeters, [air traffic control]”The FAA has identified airports in the United States and/or geographical regions which may be adversely affected by severe weather, resulting in a diverted flight,” it said.

According to the report, airports in San Francisco and Philadelphia were worst-affected, as well as San Francisco and Baltimore.

“We do not compromise safety. If FAA says it is unsafe to land, then one, we don’t have any discretion, and two, even though we could, we wouldn’t.” United AirlinesCNBC’s Squawk Box featured Scott Kirby, CEO of the company.

By Wednesday night, the FAA had authorized 62% (up from 45%) of U.S.-based aircraft to land in low visibility. More will be approved by the FAA as soon as possible. All approved altimeters can be found on Boeing717s, 737s 747s 757s 767s 767s 767s 7777s and 777s.

Regional aircraft of smaller size are still awaiting clearance.

We have had favorable weather at most of our destinations since the implementation of 5G, however we are still waiting for updates from FAA to see if there have been any mitigations. SkyWest AirlinesAccording to a Wednesday statement. American, United, Delta are the three major airlines that this carrier serves. The carrier flies for American, United and Delta. It stated that safety will never be compromised.

Because of the clear skies and few cancellations, airlines had little difficulty launching service on their first day. Japan Airlines, Emirates Airline and Japan Airlines had cancelled some U.S. bound flights. However, the FAA allowed the wide-body 777 aircraft to land safely in low visibility. These aircraft are usually used to fly long distances.