Combat aircraft spend about a quarter of their down time just being examined and checked for problems. But in the last decade, more and more aircraft have been equipped with the same kind of diagnostic circuitry and software found in most new automobiles. Aircraft maintenance crews connect a laptop computer to a dataport on the aircraft and instantly find out what's not working. Usually, the diagnostic software is upgradeable, something that is also done through the dataport. While the diagnostic software doesn't precisely identify all problems, it narrows them down in most cases. Moreover, when problems the software couldn't catch are encountered, details are downloaded and the diagnostic software is upgraded to accurately, or more accurately, detect the problem next time. The software diagnostics system is often used in flight as well, giving pilots more accurate information on current, or impending, failures. The diagnostic software systems, plus easier access to aircraft components, and more reliable components, is actually reducing the amount of aircraft maintenance required for each hour in the air. The number of man hours of maintenance required per hour of flight is now getting down to five. In the 1950s is was 30-40 hours, although that was about cut in half by the 1970s. The F-16 requires about 19 hours of maintenance per flight hour, and the F-22 will be under ten hours.