The US Air Force has removed a nearly two-year-old restriction in the Lockheed Martin F-35A cockpit that banned pilots lighter than 61.9kg (136lb) over concerns that an ejection could cause a severe neck injury.

The approval means the Martin-Baker Mk16 ejection seat meets the original USAF specification for the F-35A, which requires the manufacturer to accommodate all pilots weighing over 46.7kg.

“I've flown in this seat myself and believe, with these modifications, this is the safest ejection seat I've ever flown,” says Brig Gen Scott Pleus, the F-35 Integration Office director for the air force.

Concerns about neck injuries in fighter cockpits have grown almost in proportion to the size of pilots’ helmets as helmet mounted cueing system technology has proliferated.

A two-year-old report by the Department of Defense’s inspector general found that concerns about how such helmets could injure lightweight pilots were widespread. The US Navy had banned pilots under 61.9kg from flying the Boeing F/A-18E/F Super Hornet due to the same issue.

For the F-35, the solution involved a mixture of modifications to the helmet, the ejection seat and the ejection sequence.

The Vision Systems International helmet was modified to reduce weight. The Rockwell Collins/Elbit Systems joint venture removed internal straps and an external visor.

Martin-Baker added a head support was installed onto the rear risers of the seat as a cushion. The company also added a switch that lighter pilots can activate. If the switch is turned on, the computer inside the seat modifies the ejection sequence in the event the pilot needs to exit the cockpit in flight. The modified sequence delays parachute deployment at high speeds and lowers parachute opening forces.

The modifications will now be retrofitted on 100 F-35As already delivered to the USAF and enter Lockheed’s production system.

As the restriction lifts, Martin-Baker can breathe a sigh of relief. At one point last year, USAF officials contemplated re-opening the ejection seat competition, allowing United Technologies Aerospace Systems a chance to make a pitch for the newly-developed ACES 5 ejection seat.