The US Air Force is looking into the possibility of replacing the Martin-Baker ejection seat on the F-35. is reporting that the United Technologies ACES 5 model is under consideration.

Air Force Lt. Gen. Arnold Bunch, the service’s top uniformed acquisition official, confirmed the service’s interest in the ACES 5 design.

“We believe it is prudent to look at what it would take to qualify the ACES 5 seat as a potential risk mitigation step if additional things happen as we go through the testing of the Martin-Baker seat,” Bunch said Friday. “We believe it’s prudent to determine what it would cost, how much [impact on] the schedule, what the timeline would be, if something else happened and we wanted to go a different way.”

Ejection seat issues for the F-35 surfaced last year. Authorities discovered that the ejection seat was not rated for lighter pilots and could cause them injury. Lightweight pilots had a 1 in 50,000 chance of hurting their neck from an ejection, compared with pilots weighing 136 pounds (62 kg) to 165 pounds (75 kg), who had a risk of 1 in 200,000 of a neck injury.

The FY 15 DoD report on the F-35 noted “Testing showed that the ejection seat rotates backwards after ejection. This results in the pilot’s neck becoming extended, as the head moves behind the shoulders in a ‘chin up’ position.”

As every fighter pilot knows, body position is key to a successful ejection. The head and neck must be stable and flush against the seat prior to initiating the ejection sequence. Any deviation from maintaining a stable head and neck position could cause fatal injuries. Having the head rotate in a chin up position would put undue stress on the neck area.

As a result of the current design flaws, US military authorities restricted pilots weighing less than 136 lbs (62 kg) from flying the jets. UK-based Martin Baker Aircraft Corp is conducting further testing to resolve the issues with the seats.

The ejection seat issue is just another set back in the long list of F-35 problems. Delays for the aircraft’s Block 2B software that controls data link and weapons firing, pilot helmet display problems and lightning protection are just some of the recent F-35 issues.