F-35’s Heavier Helmet Complicates Ejection Risks
By Lara Seligman
WASHINGTON — In the latest hurdle for the Pentagon’s F-35 joint strike fighter, testers this summer discovered that a lightweight pilot’s neck could snap during a low-speed ejection.
The Joint Program Office has blamed the phenomenon on the jet’s ejection seat, Martin Baker’s US16E. But interviews conducted by Defense News in recent weeks indicate the added weight and bulk of the new F-35 helmet complicates the problem. It is still unclear whether the blame rests squarely with the helmet, or the seat, or somewhere in between.
The JPO is trying to improve safety for lightweight pilots during an ejection by reducing the weight of the new helmet, built by Rockwell Collins and Elbit Systems of America, which is on its third iteration due to repeated technical problems. Rockwell Collins is now on contract to build a Generation III “Light” helmet, David Nieuwsma, company vice president of strategy and business development for government systems, told Defense News on Tuesday.
During testing this summer with the Gen III helmet, testers discovered increased risk of injury when a lighter pilot ejects at low speeds, a spokesman for the Pentagon’s director of operational test and evaluation confirmed to Defense News in a recent email. Testers found the ejection snapped the necks of lighter-weight test manikins, according to a source with knowledge of the program.
The potentially fatal problem did not occur during previous tests with the slightly lighter Gen II helmets, according to the source.
The problem was discovered this summer after two slow-speed sled tests of the F-35 ejection system failed, according to the DOT&E spokesman. A July sled test of a 103-pound manikin in July at 160 knots and an August sled test of a 136-pound manikin at the same speed both failed. The tests were conducted using the Gen III helmet.
Until a permanent fix is found, the US military services have grounded pilots weighing less than 136 pounds, Defense News first reported Oct. 1.
“DOT&E is aware of the two slow-speed sled test failures of the F-35 ejection system in July and August this year with 103lb and 136lb manikins, respectively, equipped with the new Generation III helmet system,” spokesman Adrian J.T. Rankine-Galloway said in an Oct. 9 email. “The F-35 Program Office has determined pilots who weigh less than 136 lbs. are more susceptible to injury than heavier pilots as a result of seat design and the dynamics involved in the ejection sequence, and have restricted any pilots below 136 lbs. from flying the aircraft, regardless of helmet type.”
The main physical difference between the helmets is that the Gen III system weighs 5.1 pounds, about six ounces more than the old Gen II helmet, according to the source. This weight increase is primarily due to improvements to the night-vision camera, including better sensors to fix problems with the system’s resolution and sensitivity.
The Gen III helmet met the JPO’s specifications before testing began, Nieuwsma stressed. The ejection problem was discovered during flight tests earlier this year, he said. Lockheed Martin suggested “system workarounds” that could alleviate the problem, for instance adding chin pads, but the JPO decided the best long-term solution was to remove weight from the helmet, he said.
The program is planning a decision in late 2016 on Gen III “Light,” which aims to reduce the weight of the helmet by about five ounces, the source said.
The JPO is also evaluating whether an ejection seat configuration change can fix the problem, the source noted. One idea is adding a switch that adjusts ejection system sequencing depending on pilot weight.
“Our understanding is that the F-35 Program Office plans additional testing to evaluate risks to pilots in the ejection sequence,” Galloway said.
Although the JPO did not respond to requests for comment by deadline, one top Air Force official indicated the helmet is part of the ejection problem.
“It’s complicated because part of the flight envelope it’s an ejection seat issue. There is a different part of the flight envelope which is a helmet issue, that is being fixed as well,” William LaPlante, assistant secretary of the Air Force for acquisition, told reporters Oct. 6 during an event hosted by Defense One.
But the JPO may not be able to find an easy solution, one expert warned.
The Physics of Ejection
The sequence of an ejection is basically the same across different seat designs, according to a subject matter expert in crew escape systems. After the windscreen canopy is breached, the seat and pilot are launched upward via a rail system at a jarring rate of at least 12-14Gs. The acceleration force is greater for a lightweight person, and can be as much as 18Gs. Back and neck injuries can occur at this point if the pilot is not in the correct position, with his or her head directly centered on the spine.
Once the pilot and seat reach the top of the rails, a rocket under the seat is ignited to lift the pilot-and-seat package free of the plane. At this point, the seat can begin pitching back and forth, a motion much like that of a rocking chair, due to an offset of the rocket thrust with the pilot’s center of gravity. The pilot’s physical build determines the direction and degree of the pitching motion, according to the expert: a tall, heavy person with a high, forward center of gravity tends to pitch forward, while a short, light person with a low, aft center of gravity tends to pitch backwards.
Wind speed and air drag also aggravate the pitching problem, the expert said. Some seats, like the F-35’s, utilize an airbag system stowed in the headrest that deploys on either side of the pilot’s head. This is meant to stabilize the pilot’s head and neck during ejections. However, the inflated air bags add wind resistance near the top of the seat, causing a lightweight pilot and his or her seat to pitch backwards even further.
These two factors combined cause a potentially dangerous position of the pilot when the main recovery parachute deploys at speeds under 250 mph, the expert said. This can cause a “snapping” of the head and neck backwards, leading to serious and potentially fatal neck injuries.
Ejection seat manufacturers have figured out how to correct the pitching phenomenon at high speeds, before the main parachute deploys. In these conditions, most systems deploy a small drogue chute that slows down the seat, the expert said. But during low-speed ejections, 250 mph or lower, the main parachute must deploy immediately to prevent the pilot crashing into the ground. Drogue chute deployment at that speed would slow deployment of the main chute at a critical moment. Even worse, the two chutes could get entangled.
Some companies have developed pitch-control technologies to solve this problem at low speeds. For instance, UTC Aerospace Systems’ ACES II ejection seat – featured in the Air Force A-10s, F-15s, F-16s, F-22s, B-1s and B-2s – and UTC’s new ACES 5 seat use what is called a stability package, or “STAPAC” to control pitch motion, according to Jim Patch, senior program manager for ACES 5. STAPAC is a small vernier rocket motor mounted under the seat, which is controlled by a spinning gyroscope. In addition, ACES II can sense the weight of the pilot, and adjusts the amount of rocket thrust accordingly, Patch said.
Martin Baker does not appear to have any pitch control at low speeds. The UK-based company has not responded publicly since Defense News broke the story about the dangers to lightweight pilots earlier this month.
A bulkier helmet, like the F-35’s Gen III, increases the risk of neck injury during both phases of an ejection, because the forward center of gravity brings the pilot’s head down. However, removing helmet weight will not solve the basic problem of misalignment of the pilot when the main parachute deploys, the expert said.
The Rise of Helmet-Mounted Displays
The advent of modern “helmet-mounted displays,” which are rapidly displacing traditional helmets, contribute to an increased risk of neck injuries during ejections. HMDs project information similar to that of head-up displays (HUDs) on an aircrew’s visor, and are now commonly used in combat aircraft. These devices often incorporate night-vision systems, cuing systems and more. While HMDs greatly enhance pilots’ situational awareness, a March DOD Inspector General report found these systems add weight and bulk compared to a traditional helmet, increasing the risk of neck injury – particularly for lightweight pilots.
The F-35 helmet is large even compared to today’s average HMD. All the information pilots need to complete their missions is projected on the helmet’s visor, rather than on a traditional HUD. The latest iteration of the helmet, Gen III, is wide from side-to-side and front-to-back, meaning that if a pilot’s head is even slightly off center, a significant amount of weight is displaced.
If a pilot’s head is off-center during the first phase of ejection, acceleration of the pilot and seat up the rail, serious neck and spine injuries can occur.
Martin Baker’s F-35 seat, it seems, attempts to fix this problem with airbags on either side of the pilot’s head – the same airbags that aggravate the pitching phenomenon that occurs in the second phase of the ejection.
Congress has recently tried to crack down on ejection seat safety issues due to HMDs. In a report accompanying the fiscal 2015 National Defense Authorization Act, lawmakers wrote that a secretary of the Air Force report on various aspects of the health and safety risks associated with ejection seats “confirmed that, with increased use of helmet-mounted devices, the risks of death or serious injury increases, and increases even more for lighter aircrew.” Lawmakers called on the Air Force to review and update a 2010 analysis of alternatives exploring options for a safer ejection system.
In light of the recent revelations about the danger to lightweight pilots, the chairman of the House Armed Services subcommittee on tactical air and land forces has pledged to hold an oversight hearing on the issue.
“We’re having an F-35 hearing scheduled for Oct. 21. I’m certain it will show up then,” Rep. Mike Turner, R-Ohio, told Defense News earlier this month, noting that he was not previously aware of the ejection seat concern. “I am going to have an oversight hearing on this.”
For the F-35, the low-speed ejection problem is worst with the lightest pilots, from 103 to 135 pounds, and lessens as aircrew weight increases, according to the expert. But the risk does not disappear above 136 pounds, the expert stressed. F-35 pilots above that weight could still experience serious and potentially fatal injury during a low-speed ejection.
The US military services decided to restrict lightweight pilots from flying the plane until a solution is found, but the Pentagon has not yet addressed the risk to pilots just above the 136-pound threshold.
At least one F-35 pilot is grounded by the weight restriction, Defense News previously reported. However, the first and only female F-35 pilot, Lt. Col. Christina Mau, the 33rd Operations Group deputy command, is still flying the plane. The three F-35 pilots at Hill Air Force Base, Utah, are also unaffected.Back to Top