HARRISBURG, Pa. (WHTM) — More than three out of every four airline seats landing in Philadelphia are now on aircraft types completely cleared by the FAA to land near 5G towers, following the FAA’s clearance Thursday of more aircraft types.

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That’s based on an abc27 News analysis of seats scheduled to land at the four Pennsylvania airports on the FAA’s list of 88 airports where airlines worried new AT&T and Verizon 5G cell phone towers could interfere with cockpit equipment.

Here are the percentages of seats unaffected by current precautions at the airports:

AirportPercentage of seats on fully-cleared aircraft types
Philadelphia (PHL)77%
Pittsburgh (PIT)62%
Harrisburg (MDT)40%
Allentown/Lehigh Valley (ABE)38%
Source: abc27 News analysis of January 2022 Cirium schedule data; fully-cleared aircraft types are 717, 737, 747, 757, 767, 777, 787, MD-10/-11, A300, A310, A319/320, A330/340, A350 and A380

In other words, 77 percent of seats landing at Philadelphia are on aircraft that could not potentially be required to divert to another airport for safe landing when visibility is low — the higher the number, the less chance of a diversion; in Allentown, the figure is just 38 percent.

That’s because the FAA is testing and subsequently approving different altimeters for aircraft landing near 5G towers. Altimeters measure aircraft height. Airlines and the FAA worried 5G towers near runways could cause altimeters to provide inaccurate readings, which could be dangerous when visibility is low and pilots rely more on equipment like altimeters, rather than their eyes, to land planes. The FAA has now approved 13 altimeter models, up from five Wednesday and just two on the eve of Wednesday’s AT&T and Verizon 5G debut.

So why, based on the figures above, are the largest airports least affected by the threat of a flight having to divert to a different airport when visibility is low?

“The FAA has made the decision, and the right one, to look at the biggest aircraft first because they have the most impact on the most people,” said Scott Miller, Harrisburg International Airport’s spokesman.

In turn, the biggest aircraft tend to serve the biggest airports.

But just because a particular aircraft could be forced to land elsewhere for now — if visibility is low and if a working 5G tower is near a runway — doesn’t mean it will. In fact, at Harrisburg, Miller said exactly zero flights have diverted since Wednesday’s 5G debut; the most recent diversions (to Philadelphia and Hartford) were during bad weather early in the week.

“We haven’t tested this yet,” said Miller. “The weather conditions this morning got close to conditions called ‘Cat 2’ conditions” — lower visibility than clear-skies “Category 1” — but “we never quite got there with the snow, the low cloud ceilings this morning.”

Nationally, evidence was that a non-zero but likely small number of flights had diverted because of the 5G precautions. American Airlines, in a memo to employees Wednesday, noted “some delays and four cancellations” on Airbus planes — which were cleared Wednesday by the FAA to land near possible functioning 5G towers — and a higher number on smaller regional jets, which the FAA began clearing Thursday.

SkyWest — which American, Delta, and United pay to fly Embraer 175 jets on their behalf — described a “small number” of cancellations and diversions. Embraer 175s are among the jets the FAA began clearing Wednesday, based on the altimeter models in their cockpits.

Republic, the second largest regional airline — as the contracted carriers are called — behind SkyWest described “a meaningful impact to our schedule because of this situation.” It implored the FAA and FCC — regulators, respectively, of the aviation and telecommunications industries — to work together on a resolution.

A source at a major airline, who asked not to be named, noted that the relatively small number of issues Wednesday and Thursday were partly due to luck: The relatively benign weather in most parts of the country, which didn’t force pilots to make earlier and more conservative decisions about diverting to other airports when they would normally attempt to land.

But airline and airport leaders were generally confident that any issues would be short-lived.

AT&T and Verizon — which turned on the vast majority of their 5G towers, as planned, and which have invested billions of dollars in network upgrades — have expressed frustration that airlines and the FAA seemed (in the view of the mobile phone providers) seemed caught off-guard by the long-anticipated rollout of 5G.

America’s third major mobile phone provider, T-Mobile — which uses different 5G radio frequencies — is unaffected by aviation-related issues.