MUKILTEO — After two pilots landed a corporate Learjet at Paine Field and started their post-flight routine one summer day in 2017, they were surprised when a man walked up to the aircraft’s open door and asked if he could come inside.

The stranger had strolled onto Everett Hangar’s property without permission. He identified himself as a guest of the Historic Flight Foundation museum next door but wore no identifying badge, the pilots later recalled. One of the pilots asked him to leave.

“The man, however, pressed me several more times to board the aircraft, and I repeatedly and politely told him it was not a public aircraft he could view and that he was trespassing,” the pilot said, in a sworn court statement.

The pilots grew concerned the man might become physically aggressive, though he eventually left.

The encounter from the August before last was part of a running dispute between the private hangar and the neighboring museum. They both lease land from Paine Field. The conflict underscores some of the difficulties vintage airplanes and corporate jets have had co-existing on the west edge of Snohomish County’s airport.

By that point, Everett Hangar, the museum and its affiliates had been clashing in court for years.

The corporate hangar exclusively serves Weidner Property Management, a Kirkland-based company that develops townhomes throughout the western U.S. and Canada. Its facility, just off Mukilteo Speedway, is sandwiched between two lots. One hosts the museum and the other is undeveloped; both neighboring land parcels are leased to a company controlled by Historic Flight founder John Sessions.

In 2014, Everett Hangar sued in Snohomish County Superior Court, claiming that public events at the museum had blocked its access to the property and created unreasonable risks, among other allegations. A later suit in King County Superior Court challenged Everett Hangar over the rules for managing the adjoining properties. Much of the legal back-and-forth deals with the intricacies of airport covenants, conditions and restrictions.

Everett Hangar prevailed in both cases in the state Court of Appeals earlier this year, though not all of its claims were borne out.

The claims that have stood up in court have largely involved patrons wandering over from the museum or an undeveloped lot used for parking, where there was an open gate and no security personnel. Those lapses violated the requirements set out for the museum in a court injunction.

In 2017, a Snohomish County Superior Court judge found the nonprofit museum and a company involved with managing its building in contempt of the injunction. The judge imposed $35,000 in penalties for seven violations.

While the museum had taken steps to prevent violations, the judge said “they are plainly insufficient.”

The contempt order is a tiny fraction of the expense.

Each side has enlisted major Seattle law firms. Legal costs have run into the millions of dollars.

Everett Hangar has been awarded more than $1.6 million in legal fees, including interest, from the two separate court cases and appeals. Davis Wright Tremaine represents Everett Hangar.

The court-awarded fees don’t count what Sessions has paid attorneys from Perkins Coie and Hillis Clark Martin & Peterson.

Opened in 2010, the Historic Flight Foundation houses immaculately restored fighters, passenger planes and other aircraft in flying condition. Together, they showcase aviation history from the late 1920s through the late 1950s, spanning Charles Lindbergh’s solo Atlantic flight to the development of the Boeing 707.

Sessions had been able to fly the planes in the collection, but had a setback last summer while piloting a 1930s biplane at the Abbotsford International Airshow in British Columbia. Sessions crashed shortly after takeoff with four spectators on board. The passengers survived, apparently without grave injuries, but Sessions’ left foot was severed below the knee. He’s learned to walk with a prosthesis and soon hopes to resume jogging.

As the legal fight has worn on, Historic Flight’s activities at Paine Field have shrunk.

The nonprofit last year stopped hosting its Vintage Aircraft Weekend over the Labor Day holiday weekend, an event that attracted 70 airplanes a year earlier.

Political leaders have clipped more ambitious plans as well.

In 2014, Sessions pitched an idea to expand his attraction into a hub of up to a half-dozen buildings for restoring, displaying and studying vintage aircraft. The county would have had to provide the space for free, or at a nominal fee, for the possibility of adding another attraction of global renown. After two years, a majority of the County Council turned down the proposal, reasoning the land could be put to better use at market rate for manufacturing and more contemporary aviation businesses.

Paine Field is a magnet for aviation tourism. It hosts The Future of Flight Aviation Center & Boeing Tour and the late Paul Allen’s Flying Heritage & Combat Armor Museum. The Museum of Flight maintains its Restoration Center and Reserve Collection there.

After the county rejected his expansion plan, Sessions began exploring other alternatives in the region. The Historic Flight Foundation is now working with Felts Field in Spokane on building a second location, an art deco-style hangar expected to be ready later this year.

Noah Haglund: 425-339-3465; nhaglund@heraldnet.com. Twitter: @NWhaglund.