WASHINGTON — The U.S. Air Force has lifted flight restrictions on lightweight F-35A pilots and will not pursue qualifying United Technologies' ACES 5 ejection seat — a major win for Martin-Baker and its US16E pilot escape system, which is used in all variants of the F-35, officials announced Monday.

The service made the decision to remove flight restrictions on May 15 following the development and testing of fixes to the US16E ejection seat — including new settings for lightweight pilots and a head support panel — and changes to the Rockwell Collins-made helmet to reduce its weight, said Brig. Gen. Scott Pleus, director of the Air Force's F-35 integration office.

No pilots under 136 pounds have moved through the F-35A training pipeline since 2015, when testing showed unacceptable levels of risk of head or neck injury for lightweight pilots.

"Combined, these changes reduce the risk to lightweight pilots in both high- and low-speed ejections and make the F-35 ejection safest one of the safest in our entire inventory," Pleus told reporters, adding that the aircraft will now be open to pilots anywhere between 102 and 245 pounds.

"We've done rigorous testing of all the new configurations, and it's clear that the combination of our lighter helmet, the delay in the opening speed of the parachute and the cradling of the pilot's helmet with a head support panel have significantly improved the safety of the seat."

The service is currently modifying its existing fleet of aircraft with a new lightweight seat switch, which modifies the speed of parachute release depending on the pilot’s weight, and a head support panel. It can move 14 aircraft through the modification process per month, Pleus said. At that rate, the service will finish retrofitting its current inventory of about 107 planes in around December or January.

The new lightweight helmets are currently in pre-production and will move into production this fall. To reduce the weight from 5.1 to 4.6 pounds, Rockwell Collins has removed some of the strapping on the inside of the helmet. Also, instead of wearing a clear visor and sun visor at the same time, pilots will switch out their visors depending on the mission.

Both the seat and helmet modifications will need to be in place before a lightweight pilot can begin training in the aircraft. The Air Force intends to place its first lightweight student in training by the end of 2017, and they could begin flying as soon as 2018.

One question hovering around the F-35 program is whether the Air Force will decide to replace the Martin-Baker ejection seat with another option. All variants of the joint strike fighter incorporate the US16E seat, but the Air Force has different airworthiness restrictions than the other services, Pleus pointed out. So while the Air Force imposed flight restrictions on its own pilots, the U.S. Navy and Marine Corps did not raise similar concerns.

The Air Force made its first move away from the Martin-Baker seat last summer, when Lt. Gen. Arnold Bunch, the service’s top uniformed acquisition official, asked the F-35 joint program office to provide details on the cost and schedule implications for qualifying United Technologies’ ACES 5 seat.

The F-35 JPO never produced that information, but the Air Force is satisfied with the current pilot escape solution and will not pursue the ACES 5, Bunch told reporters today.

"I was asked today, am I going to write a letter that will rescind the need to get additional information [on ACES 5], and that currently is my plan," he said.

Martin-Baker applauded the Air Force's decision to lift weight restrictions. The first F-35 with a modified ejection seat flew May 4, the company said in a news release.

"This has been the most scrutinized and intensively tested ejection seat in history. We are extremely pleased that we have successfully met all the specified physiological head and neck load requirements as demonstrated during the ejection seat test program," said James Martin, the company's CEO.

Pleus said he had briefed all F-35A pilots on the changes to the pilot escape system.

"I can assure you that they are confident stepping to their aircraft. I personally have flown in this seat and believe with these modifications this is the safest seat I have ever had a chance to fly in," he said.

In its 2016 report, the Defense Department’s independent testing office criticized the changes to the helmet — specifically that the single visor left pilots having to swap equipment as weather or light conditions changed. The report noted that there was no storage space onboard for the second visor, and Pleus acknowledged that the Air Force was still working on a solution to that particular issue.

"We don’t actually know what the size of that new single visor is going to be — in other words, how big of space it’s going to take up in the cockpit," he said. "As our test pilots continue to fly with these basic pre-production helmets, they will continue to modify the tactics, techniques and procedures for where you’re going to put the external visor … and we’ll create some sort of a storage solution that removes any opportunity for foreign object damage."