The revving engines of an Air Force refueling tanker blew a 25-foot-wide hole in an Alaskan airport last summer, flinging chunks of asphalt 100 feet away during an engine test. The mishap did not damage the Air Force jet, but left Fairbanks International Airport with a $147,044 hole to fix.
While the ill-fated test occurred last July, the service released a formal report on the incident earlier this month.
The president of the investigation board, Air Force Lt. Col Michael Raynor, wrote that the heat and high-speed exhaust from eight hours of engine tests caused the pavement to break free after 10 “high-power engine runs,” which maintenance crews ran to diagnose and fix vibration issues cited by the crew. The plane’s pilots and aircrew were not present during the engine tests, and the report did not cite any errors by the maintenance team running the tests.
The mishap involved a New Hampshire Air National Guard KC-46A tanker from the 133rd Air Refueling Squadron from Pease ANG Base. The plane was returning to New Hampshire from Yokota Air Base, Japan, on July 12 along a route that took it over Alaska. After performing aerial refueling operations, the plane landed at Fairbanks International Airport after the crew reported “abnormal engine vibration indications” in both of the plane’s engines.
The vibrations were severe enough that the jet could not fly, and a special team of maintenance experts was dispatched from McConnell Air Force Base, Kansas, arriving two days later. The crew waited two more days for favorable weather to begin work on the engines.
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In each of the 10 engine tests, the report said, maintenance specialists ran both of the plane’s engines at up to 83% power for between 20 and 30 minutes. Each test evaluated a single engine, the report said, but crews run both during tests to avoid damaging the plane with unequal, or non-symmetric, force from only one side.
The tests ran the engines at the same power levels used during take-offs, according to investigators, during which the engines produce exhaust at “approximately 1,170 degrees Fahrenheit. The high temperature of an operating engine can be felt more than one hundred feet behind the exhaust.”
Eight hours of testing took toll
The repeated tests, investigators found, created “persistent high temperatures in combination with repeated high engine exhaust” that melted the sealant used on the asphalt.
During the tenth test, a slab of concrete approximately 25-feet by 25-feet lifted off from behind the plane’s right engine, tumbling backwards and shattering across an area roughly two-thirds of an acre behind the plane.
“After a comprehensive investigation into this mishap, I find by a preponderance of the evidence the cause of the mishap was persistent high temperatures in combination with repeated high engine exhaust from the [KC-46A’s] right engine,” Raynor wrote. “These conditions severely affected the sealant holding the asphalt together, [which] ultimately failed, allowing the blocks to lift into the air and break apart upon impact with the ground.”
The report also found that the tarmac, though suitable as a parking ramp, was not prepared for an engine test. The asphalt and sealant condition, the report found, was “within inspection standards, [but] unable to endure numerous hours of high temperature and engine exhaust airflow velocity.”
The KC-46A is the Air Force’s newest and most advanced air refueling tanker, with roughly 100 currently in the fleet. The service released three reports earlier this year of KC-46A mid-air mishaps during refueling with other Air Force jets, one of which ripped the tanker’s refueling boom off.
Though Eielson Air Force Base is just outside Fairbanks, the plane landed at the city’s international airport, which has several parking ramps designed for planes as large as the KC-46, a militarized version of the Boeing 767 widebody jetliner. Though remote from the continental U.S., Fairbanks’ northern location has long made it a refueling hub for international flights between North America and Asia, particularly among large cargo jets. The airport even once hosted a summit between then-President Ronald Reagan and Pope John Paul II, who met briefly at the airport as both leaders stopped for fuel on international trips. Though the tarmac remained intact after their meeting.
