During the Second World War, countries rushed to develop fighter aircraft for war, which greatly improved the structure and engine performance of the aircraft. And at that time, civil aircraft manufacturing technology that could carry a lot of passengers and cargo also made great progress, and civil aircraft pilots appeared.
During this period, the aviation maintenance industry has formed a relatively independent and complete systems engineering. In order to ensure aircraft attendance during the war, various countries adopted organizational management systems to manage aircraft maintenance work.
majority o of military transport aircraft were changed to civilian needs. Many airlines have been established. The huge demand for air transportation has promoted the improvement of aviation technology. At the same time, civil aviation transportation has also put forward higher requirements for the safety and economy of aircraft. Important changes have taken place in the maintenance work.
During World War II, aircraft engines, radios, airspeed meters, and other systems adopted redundant designs, while calculating the failure rate for single failure.
Because the aircraft was not safe enough, it still has problems in flighting control, propellers, engine misfires, and harmful environmental conditions. The aircraft in this period has not yet gained public trust.
Well-known aircraft are transport aircraft before World War II, such as Douglas DC-3, DC-4, and Bizi 18 aircraft.
During this period, people began to count the breakdown and accident rates of assembled aircraft based on long-term actual operations and observations. Although some work does not get the failure rate of the components, considering the aircraft as a system, the obtained failure rate value still has certain guiding significance in how to improve the product and certain goals.
Industry and the US government met together in 1945 and developed the 'single failure concept', which assumes that at least one failure occurs during each flight, regardless of its probability. This concept has a significant impact on reducing single-fault accidents. Increased public trust in flight safety has led to a huge increase in air travel. Representative aircraft: Lockheed's 'Constellation' and Douglas' DC-6.
Although safety improved significantly and public confidence increased during this period, flight accidents still occur, often as a result of more than one failure combination. For example, in 1955, an American Airlines Convair 240 crashed near Fort Leonard Wood. The combination of engine misfire and potential malfunction of the fuel shut-off valve caused the wing to break, causing the aircraft to crash.
For multiple-fault type accidents, government departments replaced the single-fault concept with a 'fail-safe concept.'
In 1955, the following concepts were introduced for turbine-powered aircraft in the form of certification rules for new transport aircraft: the combination of any single failure plus any predictable failure must be considered. At this time, the basic principle of fail-safe design is: during any flight, a single failure or a predictable combination failure will not prevent the aircraft from continuing to safely fly and land.
On the first commercial jets designed using this concept, the safety design and verification were carried out by means of safety tests. The result is a significant reduction in accident rates and therefore a further increase in public information. However, the accident rate is still much higher than expected.
In the second-generation commercial jet aircraft designed with this concept in mind, the official use of the fault Model and its impact analysis (FMEA) method for security design and verification. These practices have further significantly reduced the rate of accidents, but related hardware still has accidents, such as disproportionate combinations of failures in automated flight systems.
On the third-generation commercial jet aircraft designed by applying this concept, Formal use of functional hazard analysis (FHA), FMEA, and fault tree analysis (FTA). The accident rate of related systems has decreased substantially, and the main cause of these types of accidents lies in other areas, not the failure of airborne systems. For example, operator errors, maintenance errors, unexpected driver responses to expected failure conditions