If your flight is delayed or canceled starting July 1st, blame it on 5G

July 1st is less than a week away and that is important, according to The Wall Street Journal, because U.S. Transportation Secretary Pete Buttigieg said at the end of last week that we could see some airline delays and cancellations starting on the first of the new month. It all comes down to the number of planes that had their altimeters upgraded so they will not face interference from 5G signals.

While the deadline for commercial jets to retrofit the altimeters doesn't come until February 2024, by July 1st planes not certified to fly when near C-band 5G signals will not be allowed to land under certain low-visibility situations. The altimeter measures the distance that an aircraft is off the ground making it an important tool when landing under inclement weather conditions.

After T-Mobile's acquisition of Sprint in 2020 gave the carrier mid-band holdings in the 2.5GHz band, it became apparent that building a mobile 5G network around mid-band, like T-Mobile was doing, was the way to go. That's because high-band signals do not travel far and are easily blocked by trees, signs, and buildings. So Verizon and AT&T together spent $68 billion to obtain mid-band spectrum licenses during an FCC auction, but eventually discovered that some of the C-band frequencies interfere with the altimeters on commercial jets.

Eventually, Verizon and AT&T agreed to hold back on using some of the C-band spectrum near major airports while the airlines agreed to upgrade the altimeters on their planes. Transportation Secretary Buttigieg says that 80% of the planes that fly inside the U.S. and 65% of planes flying to the U.S. from abroad have updated altimeters that are not affected by C-band 5G signals.

Some airlines have complained that issues out of their control, such as supply-chain problems and the inability to certify planes, will force some aircraft to be grounded starting on July 1st. The trade association Airlines for America said in a statement, "Global supply chains continue to lag behind current demand. Carriers have repeatedly communicated this reality to the government." The International Air Transport Association (IATA) says that airlines will do their best to prevent disruptions related to the equipment.

As an example, Delta Airlines said that it was informed by a supplier that it wouldn't have enough radio altimeters to cover its fleet by July 1st. As the owner of over 900 aircraft, Delta still has 190 narrow-body planes (including all of its Airbus A220 jets) using older altimeters. As a result, Delta will keep those planes away from airports that can be affected by adverse weather conditions.

JetBlue has 17 Airbus A220 jets scheduled to have their altimeter replaced in October. Starting on July 1st, the airline could have some delays or cancellations in Boston on days with limited visibility. Southwest Airlines and United Airlines say that the altimeters on their jets are ready to fly through C-band signals starting on July 1st. American Airlines says that its altimeter retrofits will all be completed before next Saturday's deadline.

In case you were wondering, T-Mobile's 2.5GHz mid-band spectrum, the airwaves it acquired when it bought Sprint, do not cause interference. But radio signals in the C-band, which run in the 3.7GHz-4.2GHz range, can interfere with aviation equipment that operates in the 4.2GHz-4.4GHz range. And when you're dealing with one of the instruments that help pilots land when the weather prevents them from seeing clearly, you do not want to take a chance that the readings are off.

While retrofits are easy to install, they are costly and time-consuming, The IATA estimates that airlines will have to spend close to $638 million to replace the altimeters on members' aircraft.