SEATTLE - As fog shrouded Paine Field in Everett on Monday, Alaska Air regional carrier Horizon Air was forced to cancel all commercial flights in and out of the airfield because of limitations on low visibility flying imposed to avoid 5G interference.
Some Tuesday flights were also being canceled.
Horizon is currently the sole airline operating commercial flights out of Paine Field and all those are flown on the Embraer E175, a 76-seat regional jet.
The limitations imposed by the Federal Aviation Administration to prevent interference with cockpit instruments have created a problem specific to that aircraft and certain airports, including Paine Field and Portland International Airport.
A dozen arriving flights and a dozen departing flights were canceled Monday at Paine Field, affecting many hundreds of passengers, said Joe Sprague, president at Horizon Air.
“We tried some accommodations through busing folks down to Sea-Tac,” said Sprague. “Of course, it’s disruptive no matter what, and no guarantee that somebody would be able to get on a similar flight out of Sea-Tac.”
Visibility at Portland’s airport was better Monday and so there were no cancellations there. But Portland could be similarly hit anytime the weather deteriorates, said Sprague.
“We are highly dependent on on what the weather does,” said Sprague. “And obviously in the Pacific Northwest, especially this time of year, that’s quite a wild card.”
The new, more powerful 5G radio signals turned on last week at cell towers around the country can potentially interfere with an instrument called an altimeter that’s used to precisely measure how high a plane is above the ground. That data is fed into other systems and a false reading could endanger the aircraft.
Last week, Verizon and AT&T agreed to temporarily hold off on switching on some cell towers close to major airports. The FAA then conducted an airplane-by-airplane and airport-by-airport analysis and cleared many aircraft to fly in low visibility conditions, including all Boeing and Airbus jets at most airports around the country.
Whether the FAA granted clearance depended on what model of altimeter was installed on each aircraft and also how close the cell towers at each airport were to the runways.
The altimeters on Horizon’s Q400 turboprop planes — supplied by Collins — allowed those aircraft to be cleared everywhere. But Sprague said that the specific Honeywell altimeter on the E175 jet required airport-specific limitations.
“The configuration of the Honeywell radio altimeter in the E175, and how it integrates with the other aircraft systems on the E175, are such that the the likelihood of interference from the 5G signal is greater,” said Sprague.
The FAA therefore cleared the E175 to use only runways further away from the cell towers.
While the E175 was barred from using one runway at Seattle-Tacoma International Airport, it was cleared for the runway there that’s most typically used for low visibility conditions. That “effectively gave us good coverage for Sea-Tac,” said Sprague.
But the E175 was excluded entirely from low-visibility flying at both Paine Field and Portland International.
The limitations apply not just to Horizon, but to regional carriers like SkyWest that operate local regional flights on behalf of all the major airlines. Some airports in California and around the country have similar restrictions on E175 flights.
Flights out of Paine Field fly to larger vacation destinations, such as Phoenix and Palm Springs. But Portland is a hub for Alaska, and Sprague said that if fog closes in on the city in the coming days, the impact will be greater.
“We’re flying to Eugene and Spokane and places in Montana nonstop out of Portland,” he said. “Service to small communities could also be impacted by virtue of a hub like Portland feeling these impacts.”
Horizon operates about 300 flights per day, of which about 135 are on the E175 aircraft.
How this problem will be resolved is unclear, Sprague said.
It’s possible the FAA’s modeling of the potential interference impact could be adjusted based on additional information from the telecom companies about the cell tower placement and the signal strength.
Or the wireless companies might agree to either turn off or reduce power at more cell towers.
As to the likelihood of that happening, Sprague said “I just don’t have any good feel with respect to the telecom company’s willingness to do so.”
In the meantime, passengers scheduled to fly on E175s from those airports need to check their flight status before setting out for the airport.