Martin-Baker, the British firm that pioneered the ejection seat and is the largest supplier, has another weight problem with its popular Mk16 model used in F-35 fighters. The British RAF (Royal Air Force) found it has a problem with some potential F-35 pilots being too heavy to use the Mk16. The current upper weight limit for the Mk16 is 111.3 kg (245 pounds) but that means some RAF pilots are going to have to lose weight or the Mk16 seat must be modified. Western pilots (the main users of Martin-Baker seats) have been getting heavier over the last half-century and the upper weight limit for pilots has increased 25 percent. This situation is complicated by NATO air forces having a more difficult time recruiting and keeping fighter pilots. Britain plans to obtain 138 F-35s by the mid-2020s, most of them the F-35A used from airbases rather than the F-35B used on the two new aircraft carriers. The British problem is a common one, especially for air forces that recruit female pilots. This has become another solution to the pilot shortage problem but it also complicates the design of ejection seats, which have to be able to handle a range of pilot weights safely. What will Martin-Baker do in this situation? They will do what they have done before but it takes time and money.
For example, in 2017 the U.S. Air Force accepted a modification to the US16E ejection seat used in its F-35A fighters. This mod solved a different weight problem; female pilots who weighed less than the US16E minimum weight. No pilots weighing less than 62 kg (136 pounds) had been allowed in F-35As since 2015 when the problem was discovered. Ejection seats, like cockpits in general, are built to accommodate a limited range (in terms of weight and size) of pilots. The new F-35A ejection seat required some expensive modifications so that it could safely and reliably handle pilots weighing less than 62 kg. Actually, there is some risk for any pilots weighing less than 75 kg (165 pounds). Some female American fighter pilots weigh less than 62 kg and would be subject to injury or death if they used the unmodified US16E. The air force was under a lot of political and media pressure to spend whatever was required to accommodate a handful of (mostly female) pilots. The manufacturer (Martin-Baker) developed a fix but revealed in early 2016 that it would not be in service for about a year. That was good news for the cash strapped air force because if the fix did not work another manufacturer (UTC) had a new seat (Aces 5) that handled the problem and could replace the Martin-Baker seats although that would be even more expensive. Starting in 2017 the hundred or so F-35As with the unmodified ejection seats were upgraded at the rate of about 14 a month. Now all F-35 seats can accommodate pilots weighing from 46.4 kg (102 pounds) to 111.3 kg (245 pounds.) If Martin-Barker has to modify the MK16 seat again the actual engineering changes are not the main problem but the time and expense required to verify that the modified seat works reliably.
Historically aircraft, and other military equipment were designed to handle people of only a certain weight and size. The most obvious example is plate armor and mounted troops, in general, could only serve if they were not too large or too small (or too heavy). In Russia (and a few other countries) this extended to armored vehicles, especially tanks, where only the short of stature (and muscular, especially if you were the gun loader) could serve in tank crews. This enabled the Russians to make smaller tanks. The restrictions were more common in aircraft, especially fighter aircraft. This was never an issue before but now it is. This is more about politics than military necessity.
This is not to say that some items of military equipment are not constantly being updated to handle a wider range of personnel. Modern fighter ejection seats are constantly being upgraded to deal with new pilot equipment and to improve reliability and effectiveness in general. A recent modification has been made to handle the heavier HMDS helmets. Passive arm and leg restraints have been added to greatly reduce arm and leg injuries when limbs are not kept close to the body during ejection. Some seat models have added a new parachute design that descends more slowly thus reducing the number of parachute related ejection seat landing issues. There are also new rocket motors that automatically adjust for pilot weight. This is particularly important for female pilots. The rocket motor controls and stabilization system makes it less likely that the ejection seat will hit the tail of the aircraft or land at a bad (for the pilot) angle. Newer ejection seat designs are also modified so that they are much easier to install and remove from aircraft, saving several man hours per removal or installation.
Since World War II over 10,000 aircrews have successfully used ejection seats (mostly of Western manufacture). Very few have died in ejection seat related accidents but when that does happen it causes consternation among pilots and concern among ejection seat makers. Russian and Chinese made seats have proved to be nearly as reliable as the Western ones. But all ejection seats are vulnerable to poor maintenance, which has been found to be the most common cause of ejection seat use fatalities.
Ejection seats costs between $200,000-300,000. Most ejection seats weigh about half a ton and are complex bits of technology. There's a lot that can go wrong but rarely do you have accidents if the seats are maintained properly. Ejection seats became essential as military aircraft became so fast that a pilot could not safely climb out of the cockpit and jump. With the higher speed, there was the danger of hitting the tail. Also, escaping pilots were often injured or stunned and unable to get out quickly enough.
The first ejection seat design was developed in Germany where the seats were first installed in their He 219 night fighters during 1943. These used compressed air to propel the seat out of the aircraft. A year later rocket-propelled seats were installed in the He-162 jet fighter. By the end of the war, all of Germany's jets were equipped with rocket-propelled ejection seats. While the Swedish firm Saab had also developed a rocket-propelled ejection seat it was British firm Martin-Baker that jumped in after World War II and created a design that quickly filled the needs of most Western air forces, including the RAF.
The U.S. Air Force long insisted on using only American made ejection systems but the U.S. Navy stayed with Martin-Baker because the American ejection seat did not function as well at very low altitudes (where a lot of naval aviators have to eject during carrier operations). Martin-Baker supplies about two-thirds of the ejection seats for Western fighter aircraft including the F-35. The other major supplier of ejection seats was the Soviet Union. Those Soviet era manufacturers continue to produce good ejection seats for Russian aircraft and some foreign customers. China is becoming a major player in this area, usually exporting Chinese made ejection seats in Chinese made aircraft. The Czech Republic and Romania also manufacture lower end ejection seats. Western manufacturers produce about a thousand seats a year, while Russia and China produce less than half as many, almost all of those seats are for locally made aircraft.