The U.S. Air Force has completed modifying the cockpits of its 27 U-2 reconnaissance aircraft so that flying the aircraft is less stressful on the pilots. This became an issue in 2011, when the U.S. Air Force decided to extend the life of its U-2 fleet and cut back on the use of large UAVs for strategic reconnaissance. That meant U-2 pilots would be spending more time in the air. This meant more stress on pilots because of how the air supply in the U-2 operates.
One of the many upgrades U-2s recently received was better cockpit pressurization. This was called CARE (Cabin Altitude Reduction Effort) and involved reinforcing the cockpit so that it could be pressurized to 8 psi (the air pressure felt outdoors at 4,500 meters/15,000 feet) rather than the current 4.4 psi (similar to the air pressure felt at 8,900 meters/29,500 feet, or the top of Mount Everest). This cost about $323,000 per aircraft.
While mountain climbers can handle scrambling to the top of Mount Everest, staying for a few minutes and then heading down, U-2 pilots work under those conditions for over eight hours at a time. This causes a growing number of cases of DCS because all that time in a low pressure environment puts more strain on the pilot's body. That, and the fact that they breathe pure oxygen while up there, means they tend to be completely exhausted after returning from a long mission. So pressurizing the cockpit to the level of a lower altitude eliminates a lot of stressful aspects of each flight (like breathing pure oxygen). U-2 missions can be as long as twelve hours and more is being done to make operating the aircraft and the sensors less of a hassle. Since CARE was implemented there have been no more cases of DCS (decompression sickness) among U-2 pilots.
The increased use of the U-2s means more pilots will be needed, in addition to reducing things like DCS that puts pilots out of action for days or weeks at a time. This is a problem because U-2 pilots are hard to select, train, and retain. Flying the U-2 is very hard on pilots. Because it is a difficult aircraft to fly, only pilots with a lot of previous experience qualify. Even then, most do not last long. Since the 1950s only about three percent of the 900 U-2 pilots have lasted as long as 2,000 hours, and only four pilots have made it to 2,500 hours. The aircraft lasts a lot longer of course. Two of them, both over 40 years old, have been in the air at least 25,000 hours.
With a range of over 11,000 kilometers the 18 ton U-2s typically fly missions 12 hours long. The U-2 flies at an altitude of 21.2 kilometers (70,000 feet). All U-2s have been upgraded to the Block 20 standard and will be receiving more refurbishment and upgrades, so they can be kept in service until the 2020s. The U-2 has been in service since 1955, and only 86 were built.