While in Anchorage, Alaska, airspace on a flight from O’Hare Airport in 2015, the pilot of a Taiwan-based airliner accidentally flew too close to another aircraft.

Though there apparently was no imminent risk of a mid-air collision, the “pilot deviation” by EVA Air Flight 655 should have been investigated by the Federal Aviation Administration.

That didn’t happen until the Chicago Sun-Times asked about the April 12, 2015, incident, according to interviews and recently obtained federal records that show how an FAA mix-up freed the airline from having to face scrutiny by inspectors.

The incident unfolded as the EVA jet “was southwest-bound at 36,000 feet, while a second aircraft was northwest-bound at 32,000 feet,” according to FAA spokesman Ian Gregor.

“An air-traffic controller cleared EVA to descend to and maintain 33,000 feet,” Gregor says. “The EVA pilot correctly read back the instruction but descended below the assigned altitude.”

Though the “two aircraft never got closer than 4.5 miles apart,” they should have remained “at least five miles apart,” according to the FAA.

Records don’t indicate how fast the two planes were going, but 500 miles an hour is a common cruising speed.

Also unclear is whether a “traffic-collision-avoidance system” was triggered in either aircraft. That sounds an alert in a cockpit when planes get too close that can include instructions for maneuvering to safety.

An air-traffic controller noticed the EVA plane “had descended below its assigned altitude and issued the pilot corrective action,” and the planes went on their way, Gregor says.

“Typically, when events like this occur, controllers report them to supervisors, who put them on the facility’s daily log,” he says. “A manager will then forward relevant information to the applicable FAA office for follow-up.”

But someone in the FAA mistakenly forwarded the case to an agency office in Alaska instead of Los Angeles. And no one in Alaska forwarded it to the correct office.

By the time this was discovered in June 2016, the computerized information needed to properly investigate the incident had been destroyed, “purged due to such a large time lapse,” according to FAA records.

Had the right inspectors been alerted, they “would have contacted the airline and/or flight crew,” Gregor says.

He calls such a mistake rare and an “inadvertent oversight” that didn’t warrant discipline for anyone at the federal agency.

The FAA ended up reclassifying the incident — which was one of 50 suspected pilot deviations involving O’Hare departures that strayed from altitudes or routes between 2012 and 2016 — as “insufficient evidence to investigate” and let the matter drop, agency records show.

A spokeswoman for EVA declined to answer questions about the incident, which occurred on a route spanning more than 2,800 miles that takes big jets five to six hours to fly, and whether the pilot faced any disciplinary action or had to undergo additional training.

FAA records show an airline official said last year that an investigation “would not be worth pursuing . . . due to the lack of evidence and the files being purged.”

Earlier this year, the FAA — which regulates U.S. airlines and airspace — ended up initiating an inquiry after all, following questions from the Sun-Times.

“The Los Angeles International Field Office contacted EVA for details about the event,” Gregor says. “EVA provided us with detailed information.”

EVA Air’s office in Franklin Park. | Robert Herguth / Sun-Times

Had the FAA not made a mistake, Gregor says, the agency “would have conducted shortly after the incident . . . the same investigation we conducted [this July.] We would have confirmed with the airline that they had followed up to address the cause of the incident and had taken any action they deemed necessary. When foreign carriers are involved, the decision on how to address the issue from a personnel matter is up to the carrier and the aviation authority in the carrier’s country.

“EVA was aware of this event, and my understanding is EVA addressed the issue.”

The EVA spokeswoman would say only that the FAA “is the authority in charge. EVA Air respects the FAA’s decision.”

With a local office in Franklin Park, the airline offers passenger and cargo service at O’Hare, one of a number of U.S. airports EVA serves.

FAA records show there were another 31 suspected pilot deviations over the past five years with planes from different airlines heading to O’Hare.

An EVA Air cargo flight landing in Anchorage, Alaska. | Frank Kovalchek / Creative Commons

The Federal Aviation Administration said in an initial summary of the EVA Air incident that an official “apparently did not assign the deviation to any inspector” to investigate.