The CEOs of America’s major passenger and cargo airlines wrote a letter to key members of the Biden administration on Monday, sounding the alarm if 5G C-band implementation goes forward as planned this Wednesday.In the letter from Airlines for America, the industry’s lobbying group, the CEOs called for a 2-mile buffer zone around airports that are near 5G towers. The current plan calls for buffer zones that would be much smaller, attenuating signals for just the last 20 seconds of flight.“Immediate intervention is needed to avoid significant operational disruption to air passengers, shippers, supply chain and delivery of needed medical supplies,” the CEOs wrote in the letter, which was first reported by Reuters.Want more airline-specific news? Sign up for TPG’s free new biweekly Aviation newsletter!The CEOs said they were sounding the alarm for two reasons: the fact, they said, that 5G C-band could impact more than just the ability to conduct low-visibility landings and the fact that the Federal Aviation Administration’s carve-out, announced on Sunday, was at too few airports.On Sunday, the FAA said that approximately 45% of the U.S. commercial fleet can conduct low-visibility approaches and landings at a little more than half the airports most affected by 5G C-band.Internal control part of the aircraft cockpit including altimeter. (Photo by zhihao/Getty Images)Verizon and AT&T are set to switch on their 5G C-band spectrums this Wednesday following a two-week delay at the behest of the FAA, the airline industry and other aviation interests.“The agency approved two radio altimeter models that are installed in a wide variety of Boeing and Airbus planes,” the FAA said in a statement. “This combination of aircraft and altimeter approval opens up runways at as many as 48 of the 88 airports most directly affected by 5G C-band interference.Sign up for our daily newsletterEmail addressSign upI would like to subscribe to The Points Guy newsletters and special email promotions. The Points Guy will not share or sell your email. See privacy policy.The FAA said that “some” Boeing 737, 747, 757, 767 have the cleared type of radio altimeter, along with the McDonnell Douglas MD-10/-11 and the Airbus A310, A319, A320, A321, A330 and A350.“FAA expects to issue more approvals in the coming days,” the statement added.Notably absent from this list are popular aircraft such as the Boeing 777 and 787 — the cornerstone of American Airlines and United Airlines’ long haul fleet — as well as all regional jets, which make up a significant amount of U.S. airline capacity.More: What you need to know about 5G interfering with aircraftA radio (or radar) altimeter is a type of instrument that is used to precisely measure an aircraft’s height above the ground. This type of instrument is essential during low-visibility conditions because the data from it is essential for pilots to be able to conduct high-precision instrument approaches and even automatic landings, allowing operations to continue in little to no visibility. A 2020 study found that 5G C-band, which operates on an adjacent set of the frequency spectrum, can interfere with this instrument. In addition, the FAA has warned that other flight deck instruments and safety systems that rely on radio altimeters could be also be affected.As part of the deal between the FAA and Verizon and AT&T, the telecom companies will lower 5G signal strength near a number of airports for six months as more data is collected. Even with the lower signal strength, the FAA last week began taking the drastic step of issuing Notices to Air Missions (NOTAMs) which ban these low visibility approaches. So far, 1,757 such NOTAMs have been issued.According to the CEOs, Sunday’s action will provide limited relief for some aircraft at some of these airports that have the NOTAMs in effect, but more needs to be done.