Nearly 1 in 3 pilots who will fly the F-35, the military’s $159 million fighter jet of the future, runs a heightened risk of fatal whiplash during an emergency ejection, according to defense officials and internal documents obtained by CQ.

What’s more, the Pentagon lacks information to assess the safety of a substantial portion of its remaining pilots.

The Defense Department has acknowledged this risk to its lightest weight pilots. But those who are closer to average weight are also potentially in danger, according to the documents and experts.

This is just the latest of many afflictions to beset the program to acquire 2,457 F-35s for nearly $400 billion, plus about $1 trillion to operate them — the most expensive military initiative in history. Fourteen years into its development, the F-35 program is seven years behind schedule, the cost per plane has roughly doubled and the jets are still plagued by everything from engine fires to structural cracks to software glitches.

But the Pentagon has put virtually all its eggs in the F-35 basket. The jet is the only new manned fighter rolling off U.S. assembly lines. It will be used by the Air Force, Navy and Marine Corps, with a different model for each.

Despite differences among the variants, the services’ planes have much in common with each other — including the same troubled ejection seat, made by Martin-Baker Aircraft Co. Ltd. of the United Kingdom.

Lightweights and Welterweights

An ejection from any fighter jet in flight is a violent, if relatively rare, event. It is also inherently risky. But the ejection seat in the F-35 jet makes it more dangerous than it needs to be, some officials say.

During an ejection from the F-35, the canopy over the pilot is deliberately shattered by an explosive charge. Then the entire seat is blasted skyward with tremendous force. Mannequin tests this summer showed that the lightest F-35 pilots, in particular, face a lethal risk when the F-35 is taking off or landing. The pilots are rotated backward into a position where they face all but certain death from the rocketing parachute’s force snapping their heads.

This is “potentially fatal whiplash,” said Air Force Lt. Gen. Christopher Bogdan, the manager of the F-35 program, in a previously undisclosed summary of the problem written last month.

According to the September documents from the jet program, for F-35 pilots weighing 135 pounds or less, there is a 98 percent “probability of fatal injury” during ejections from the jet at 160 knots, a typical speed at take-off or landing.

Those lightweight pilots are currently not allowed to fly the F-35 because they are at “high risk,” the documents say. Historical data indicate, according to the documents, that more than 7 percent of Air Force officers fall into this weight category, which is equivalent to that of a lightweight boxer.

The Pentagon has acknowledged that much. However, of far greater concern is data that has not previously been made public about the possible effects of ejection from the F-35 at relatively slow speeds for pilots of more normal size — the welterweights and middleweights of U.S. military aviation, to use the boxing analogy.

Indeed, a large percentage of F-35 pilots could find themselves at risk, some in the Pentagon worry. Female pilots, who tend to weigh less than their male counterparts, would be disproportionately affected, experts say.

First, in relatively low-and-slow flight, the probability of fatal injury to pilots weighing up to 165 pounds is 23 percent — a degree of peril that the documents officially term a “serious risk” — and fully 27 percent of male and female officers weigh that much, the program documents indicate.

“The at-risk population is pilots weighing between 103 and 165 pounds for all F-35 variants,” wrote Gregg D. Costabile, the F-35 program’s director of engineering.

An Aug. 27 document, “F-35 System Safety Risk Assessment,” put it this way: “The Serious risk for pilots between 136 and 165 pounds will require acceptance of the Serious risk or further weight restrictions.” That document was signed by Mike Nennmann, a safety executive with Lockheed Martin Corp., the main contractor on the F-35, and Jack Landreth, a safety official with Naval Air Systems Command.

Bogdan, the program manager, signed a document on Sept. 14 indicating he is willing to accept the “serious risk” for pilots between 136 and 165 pounds. In the document, he recommends that U.S. armed services and U.S. allies do the same.

So roughly 7 percent of pilots could be at “high risk” and 27 percent at “serious risk”  during ejections near take off or landing — or about a third of personnel — if historical data about Air Force officer weights provide any clue.

However, some senior Air Force officials are concerned there is even more to the story.

The brass are worried that pilots weighing as much as 199 pounds — if they are wearing the latest F-35 pilot’s helmet, which is heavier than its predecessor — may have a risk of severe neck injury that has yet to be quantified due to a lack of test data, according to a knowledgeable official who requested anonymity.

That’s because no tests have been done to gauge the pressures of ejection on mannequins weighing more than 136 pounds, the officials say.

The program office assumes that tests on a 136-pound mannequin can be used to determine the effects on pilots weighing up to 165 pounds. If so, then tests on mannequins heavier than 136 pounds would be needed to gauge the effect on pilots who weigh up to 200 pounds. But those tests have apparently not been done.

What’s more, the only mannequins whose necks were broken in tests were mannequins that wore the latest, heavy helmets, according to officials and documents. That begs the question of what role the heavier helmets played in the testing failures.

Until these questions are settled by additional tests, senior Air Force and Pentagon officials say they will not rest easy about any F-35 pilots.

Hard Questions Ahead

Martin-Baker, the ejection seat manufacturer, was not the Air Force’s first choice to build the ejection seat, Defense Department and industry officials said. The service wanted to stay with the same “ACES” model that had worked on most other warplanes.  But after a cost-benefit review, the Pentagon decided to go with Martin-Baker.

Martin-Baker did not return emails requesting comment. A Lockheed Martin spokesman said the F-35 program office is answering queries about the ejection seat.

The F-35 office did not reply to a series of detailed questions but provided a statement. In it, they did not acknowledge even potential problems for pilots weighing more than 136 pounds.

“The safety of our pilots is paramount and the F-35 Joint Program Office, Lockheed Martin and Martin-Baker continue to work this issue with the US Services and International Partners to reach a solution as quickly as possible,” said Joe DellaVedova, the F-35 program spokesman. “There are no flying restrictions with higher weight pilots.  The escape system restrictions only affect pilots weighing less than 136 lbs. because lightweight individuals are assessed to have lower neck strength to absorb force.”

Efforts are underway to improve the odds of survival for the lightest pilots, including reducing the weight of the new helmet, according to DellaVedova.

“The potential for an increased risk of neck injury will be reduced with three fixes: installing a switch on the seat for lightweight pilots that will slightly delay parachute deployment and lessen parachute opening forces; designing a lighter helmet; and mounting a head support panel, which is a fabric panel sewn between the parachute risers which will protect the pilot’s head from moving backwards during the parachute opening,” he said.

The congressional defense committees are keeping a keen eye on the ejection seat issue.

A House Armed Services subcommittee will hold a hearing Oct. 21 on the F-35 at which the ejection seat and helmet issues are likely to come up, aides say.

“It’s extremely serious any time a weapons system could pose a danger to its own pilot,” said Jackie Speier, a California Democrat on the committee and one of those most concerned about the ejection seats. “I will be looking into this issue very carefully to make sure that F-35 cockpits are made safe and that the Pentagon is taking appropriate measures in light of the risk. We need to put safety first above the desire to field an untested aircraft.”