The U.S. Air Force is in trouble again over problems with the new F-35 fighter. This latest issue is unique as in the past it was not an issue. It has to do with the restrictions on pilots who do not weigh enough to use the ejection seat safely. Ejection seats, like cockpits in general, are built to accommodate a limited range (in terms of weight and size) of pilots. The new F-35 ejection seat would require some expensive modifications to handle pilots weighing less than 62 kg (136 pounds). Some female American fighter pilots weigh less than that and would be subject to injury or death of they used the current ejection seat. The air force is under a lot of political and media pressure to spend whatever it takes to accommodate a handful of female pilots. It is unclear if there are currently any air force fighter pilots (who are female and eligible to fly the F-35) that would need these expensive mods.
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. 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 (because of aiming and night vision devices) helmets pilots use. 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 aircrew have successfully used ejection seats (mostly of Western manufacture). Very few have died in ejection seat related accidents but when that does happen is 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. This resulted in a least two recent fatal ejection seat failures recently. In 2014 a Russian made Indian ejection seat failed because of, as an investigation revealed, poor maintenance. Another example occurred in 2007. In this accident a navigator in the rear seat of a British Tornado jet fighter died when he fell out of the aircraft. Details of the accident took three years to be made public. It all began with the troublesome ejection seat that had just undergone some updates and was undergoing a flight check. Some of the maintenance work involved the ejection seats. But the work on the rear ejection seat left a small (5 cm/two inch) metal part installed incorrectly. This allowed the ejection seat to come lose when the aircraft was momentarily upside down. When that happened during the test flight the rest of the ejection system did work and the canopy came off. But the rockets in the ejection seat did not ignite and the navigator hit his head on the tail of the aircraft. Worse, the parachute did not deploy from the seat and the navigator still strapped in fell nearly 2,000 meters (6,400 feet) to his death. Several people were involved in checking out the ejection seat during and after this maintenance, and it took a while to sort out who was responsible for what. It turned out to be a maintenance problem, not one involving design or manufacture.
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 (British Royal Air Force).
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.