ORLANDO, Florida—The U.S. Air Force expects to take delivery of its first Boeing MH-139 test aircraft in May as it moves toward receiving its last required FAA certification, after a yearlong production delay due to airworthiness concerns.

The MH-139 needs one more supplemental type certification (STC) from the FAA, said Darlene Costello, the Air Force’s acting head of acquisition. The aircraft needed three. One was issued on Feb. 18. Another, which was dependent on the one recently completed, is scheduled for May 2022. The first was issued in 2021.

With this progress, the Air Force is expecting military flight release in May. Costello said the Air Force would then be in “conditional DD-250,” referring to the Defense Department’s form for the acceptance of the aircraft. This would cover four aircraft for developmental test, she said.

The production delay stemmed from an FAA concern about a fairing for the aircraft’s defensive aids that disturbed airflow to a pitot tube. The European Union Aviation Safety Agency (EASA) had approved  an STC for the Leonardo AW139, the helicopter from which the MH-139 is derived, but the FAA had rejected the application. Boeing redesigned the fairing.

The Air Force awarded Boeing the development contract for the MH-139 in September 2018 and received approval to buy eight of the helicopters in 2021. The certification delay forced the Air Force to cut a planned buy of eight more in the 2022 budget. The service wants to eventually buy 84 of the helicopters to replace aging UH-1Ns that are used to patrol nuclear missile bases, ferry VIPs, and for survival, evasion, resistance and escape training.