A loading issue with the refueling boom of the developmental KC-46A tanker has caused the U.S. Air Force to postpone its planned low-rate initial production (LRIP) decision from June to August. The planned delivery date of the first production aircraft has been moved from next March to August 2017, the service said on May 27.

Boeing is working on a solution to address “higher than expected boom axial loads” with the telescoping, fly-by-wire refueling boom, which is derived from the boom used on the KC-10 Extender. The higher loads were recorded during an aerial refueling demonstration with a C-17 Globemaster III transport earlier this year, the service said. In addition, Boeing has been delayed in certifying the KC-46A’s centerline drogue system and wing aerial refueling pods (WARPs).

“Technical challenges with boom design and issues with certification of the centerline drogue system and wing air refueling pods have driven delays to low-rate production approval and initial aircraft deliveries,” said Brig. Gen. Duke Richardson, program executive officer for tankers.

The Air Force now expects to make a “Milestone C” decision to start production in August to allow Boeing additional time to resolve the loads issue and complete required refueling demonstrations on the C-17 and A-10 Thunderbolt II. Once it makes a decision, the service plans to “immediately award” a contract for the first two LRIP lots, followed by Lot 3 in January 2017.

The first KC-46A deliveries to Altus Air Force Base, Okla., where the first training unit will be located; and to McConnell AFB, Kan., the first active-duty operating base, were most recently scheduled for next spring. After conducing a schedule risk assessment, the Air Force now expects those deliveries will take place in the late summer or early fall of 2017.

Under the engineering and manufacturing development (EMD) contract the service awarded in 2011, the expectation was that Boeing would deliver the first 18 production tankers by August 2017. The parties later revised the program schedule to extend the developmental flight-test phase by a year and compress deliveries to six months—from March to August 2017—instead of the original 14 months. As of the latest revision, the 18th aircraft will be delivered in January 2018, according to Boeing.

In a statement, Boeing attributed the schedule stretch to “ongoing complexities associated with qualification and certification of the aircraft’s centerline drogue and wing-aerial refueling pod systems, and the previously announced higher volume of change incorporation to bring the first 18 aircraft up to the certification configuration.”

The manufacturer said “the underlying production system remains on track,” and that 18 tankers will be in various stages of incorporating final changes and certification by August 2017. The first production aircraft will be equipped with the refueling boom and centerline drogue system, but not the wing-mounted refueling pods. “The WARP systems required to complete full contractual RAA (required assets available) will be delivered separately in October 2018,” Boeing said.

Cobham is supplying the KC-46A centerline drogue system and WARPs. In a statement provided to AIN, the company said: “We continue to work closely with Boeing and our suppliers to address qualification and conformity requirements in support of the revised RAA schedule.”