THE COMET The average air passenger on today’s conventional airliner probably doesn’t take into consideration the safety modifications that are now mandatory on all passenger jets. Unfortunately, these safety modifications have come at a cost of many lives throughout the last half-century. In the aviation business, it is said that the most important lessons are learnt only when lives are lost. Today I am going to speak about one significant incident, which in turn changed air passenger travel forever and was the turning point in aviation safety. The De Havilland Comet was one of the world’s first jet airliners and the world’s first passenger jet. It flew at altitudes of up to 12000m, which was higher than any other civilian aircraft could fly at the time. These altitudes of flight had in the past, only been achieved by military jets. The Comet had been built by De Havilland, a British manufacturer of aircraft in the early 1950s after the war when air travel was becoming ever increasingly popular. It was in early 1954 when a horrific incident involving the Comet shaped the aviation industry forever. As we know, the Comet was able to fly at altitudes of up to 12000m where the air is thinner. To ensure passengers feel comfortable and can breathe easily when flying at speeds of up to 800km/h at this altitude, the air pressure inside the cabin is pressurised to an outside altitude of 2500m, which is easily tolerated by the human body. If there were to be a structural failure in the body of the aircraft whilst it was pressurised, the rapid escape of air would cause a tremendous escape of energy and this is known in the aviation world as an explosive decompression. In January 1954, this happened. A Comet aircraft with 35 people on board took off from Rome, bound for London. 26 minutes into the flight, whilst cruising at an altitude of 11000m, the plane, without warning, disintegrated in mid flight and plummeted into the Mediterranean Sea below. To cut this painstakingly long investigation short. Metal fatigue had developed along the aluminium panels, which join together to make up aircraft’s skin. Metal fatigue is caused when a metal is repeatedly flexed one way, and then the other. After a while, minute cracks start to form and steadily increase in size. The manufacturers of The Comet, De Havilland had done extensive testing on the aircraft for signs of metal fatigue and they had concluded that the life span of the aluminium panelling which makes up the fuselage could last for around 10,000 flights. So why, with only 3,000 flights under its belt had this aircraft crashed? A pressure test was carried out and it was found that the skin of the aircraft became stressed and de-stressed; pressurisation after pressurisation. The square shaped doors and windows on the Comet created weak points in the airframe and this meant that the stress concentrated in these areas when the aircraft was pressurised. It was also found that the rivets or bolts that secure the aluminium panels together to make up the aircraft had been punched rather than drilled into the fuselage. This unwittingly created a manufacturing defect in the skin (a small crack) and after 3,000 flights of pressurisation cycles, the cracks joined together at the weak points (square doors and windows), and this ultimately caused the breakup and explosive decompression of the Comet aircraft on that fateful day. Now, because of these findings, doors and windows on all commercial airliners today are oval shaped and furthermore, the rivets holding the fuselage together are drilled into the airframe, which eliminates the manufacturing defect (small cracks) from developing. It was not only the structural failure of the Comet that changed aviation history; but it was also the landmark investigation of the crash, which fundamentally reshaped aviation safety forever.