RAF FAIRFORD, England — The F-35 joint program office (JPO) is at odds with a US Air Force decision to consider a new ejection seat for the aircraft but will reluctantly study the cost and schedule implications of integrating another seat, the program's top official said Saturday.

At issue is the Martin-Baker US16E ejection seat, which was found last year to cause severe and sometimes fatal neck injuries to lightweight pilots upon ejection. Although Martin-Baker is implementing a number of fixes to their seat, the Air Force also wants the JPO to evaluate how certifying and integrating the United Technologies ACES 5 seat would impact the program.

"I think the Air Force is doing it to mitigate a perceived risk that ultimately the seat may not be as good as they need it to be for the entire envelope of the airplane and the entire envelope of body sizes," Lt. Gen. Christopher Bogdan, F-35 program executive officer, said at the Royal International Air Tattoo. "We don't necessarily feel that way in the JPO from a technical standpoint.

"We think that the testing we've seen so far in the last few months with the fixes we have in place are going to work," he continued. "But the Air Force has the right to ask for a new requirement like that on the program, and they have, so we'll walk through that."

Air Force Lt. Gen. Arnold Bunch, the service's top uniformed procurement officer, told Defense News last month that he had sent the program office a letter in June requesting information on how integrating the United Technologies seat could impact cost, schedule and other factors such as the aircraft's sustainment or lifecycle.

The JPO has not yet replied but will soon tell the Air Force that it plans to start a new study to assess those potential challenges in detail, Bogdan said. The study would likely conclude around the same time that testing for the Martin-Baker ejection seat wraps up, in November or December.

Even though the modified Martin-Baker seat should be able to meet requirements, it's reasonable for the Air Force to weigh other options, Pentagon acquisition chief Frank Kendall said Sunday. In fact, this is not the first time the service has looked to replace one program-of-record F-35 technology with another.

"We had a situation with the helmet a few years ago where we did put a fair amount of money to develop an alternative helmet, because at that point we thought there was a very significant risk. We thought we would not mature the baseline design," he said. "I don't feel the same way about the ejection seat. I've been following that and with some design tweaks, modifications, we should be able to solve that problem."

× Fear of missing out? Sign up for the Early Bird Brief, the defense industry's most comprehensive news and information, straight to your inbox. Thanks for signing up. By giving us your email, you are opting in to the Early Bird Brief.

On the industry side, F-35 manufacturer Lockheed Martin has not yet been told by the program office to begin assessing the new seat, its program manager, Jeff Babione, said last week.

Bogdan stressed that the service has not made a final decision on whether to proceed with integrating the ACES model.

"We personally think that the Martin-Baker seat is going to meet all of the specs. We think it's going to open up the envelope down to the 103-pound pilot as we talked about. When it does that, it will have the greatest range of any seat out there for fighter airplanes, so we think it's probably the right seat for the airplane right now," he said.

Until those issues are solved, the Air Force has prohibited pilots weighing less than 136 pounds from flying the aircraft — a decree that has sidelined one pilot.

Replacing the Martin-Baker seat could have wide-ranging impact on the F-35 industrial base, which is made up of companies from the nine international partners who have committed to buying the aircraft.

About 15 percent of the F-35 is manufactured by UK firms, Babione reiterated last week. Of that, BAE Systems is responsible for components comprising 10 percent of the plane, while Martin-Baker and other companies make up the other 5 percent of work.

Should Connecticut-based United Technologies replace Martin-Baker as the ejection seat manufacturer, UK firms could clamor for more work.

It's too early in the evaluation process to speculate on the exact impact on schedule and cost, Bogdan said. However, even if the Air Force decides to integrate the ACES 5 model, Martin-Baker will retain a portion of its work on the F-35 because no other US or international customer wants to replace the US16E seat.

"Clearly if you went down this path you would do it as a parallel effort," he said. "None of the other partners and none of the other services want to delay any portion of the program for this. So if the Air Force were to embark on it, we'd have to figure out a strategy where this could be done in parallel because we do not want to impact the bigger program at all."

Even then, buying fewer Martin-Baker ejection seats overall could raise the price of the plane for other customers. The Air Force's planned purchase amounts to 1,763 planes, more than any other buyer.