DENVER, Colo. — The Air Force’s desired adaptations to Boeing’s E-7A battlefield management aircraft are proving to be harder than expected and complicating price negotiations, top service officials said Tuesday.

“We’re having a hard time with [the E-7 program], getting price agreement with Boeing,” Air Force Secretary Frank Kendall told reporters in a roundtable at the Air and Space Force Association’s Air Warfare Symposium here. “We’re still in negotiations with them, and that’s not been finalized yet.”

The Air Force plans to buy 26 E-7s from Boeing by 2032 to replace its aging E-3 Sentry airborne warning and control system aircraft fleet. The service awarded Boeing a $1.2 billion contract in February 2023 to start working on the aircraft.

The service plans to first buy two rapid prototype E-7s, with the first expected to be fielded in 2027, and in 2025 make a production decision on the rest of the fleet.

Australia already flies the E-7, which it refers to as the Wedgetail, and Boeing is also making the aircraft for other nations such as the United Kingdom. The Air Force’s version of the E-7 will have a modified design to meet U.S. satellite communication, military GPS and cybersecurity and program protection requirements.

“We’re partnering with the US Air Force to deliver this critical capability and are working diligently to reach an agreement,” Boeing said in a statement to Defense News.

Andrew Hunter, the Air Force’s assistant secretary for acquisition, technology and logistics, said in another roundtable the sticky negotiations center on the E-7′s first two rapid prototype aircraft.

The level of engineering work needed to adapt the E-7 to the Air Force’s specifications was “above and beyond what we anticipated,” Hunter said.

“The big surprise there was an unexpected amount and degree of non-recurring engineering required to meet the requirement that the Air Force specified, which we thought was very close to what the U.K. is currently procuring from Boeing,” Hunter said. “Those discussions have been challenging.”

Hunter said the Air Force is trying to better understand Boeing’s proposal and determine what elements are essential, and what are unnecessary or could be deferred. The service has narrowed those nagging issues down to a smaller list, Hunter said, but he declined to detail them.

Hunter said he would prefer the process to be going faster. But he acknowledged it’s not surprising that Boeing is being particularly cautious as it negotiates on this program, and that the Air Force and Boeing are working through these challenges together.

“They’ve gotten into some contracts in the past that it’s apparent that as they were bidding those, there was key information they were lacking,” Hunter said. “At some level, it’s not that surprising that they’re trying hard to do their homework and not bid things and not understand the full scope of the work they can be expected to perform when they prepare their proposal.”