Home The Club Trips & Information Members Interests Business Minutes Guest Speakers

Speaker – Alan Clements ‘The Sound of Impact’

Alan Clements studied electronics at Sussex and Loughborough before joining the School of Computing at the University of Teesside, where he became Professor of Computing. He became a National Teaching Fellow and worked with the EU, Hitachi, the UK Government and Sega. He was editor in chief of the Computer Society Press. After retiring from full time teaching in 2010, he developed his interest in photography. He is also a qualified pilot. He gave a very interesting if sobering talk on the use of computers in aircraft.

‘The Sound of Impact’ is the phrase used in the transcription of the end of the Cockpit Voice Recording when an aircraft crashes. Alan looked at disasters as far back as the 1950s. Some were caused by pilot error and some by technical faults. Controlled flight into terrain (CFIT) is when an airworthy plane under pilot control is flown into the ground. Examples are the crash of an Air New Zealand flight into Mount Erebus in 1979 when wrong coordinates entered into a computer, a Polish Airforce crash in 2010 which killed the President, when the pilot landed in bad weather when ordered to do so and the German Wings disaster when a suicidal co-pilot deliberately crashed the aircraft. Examples of non-CFIT accidents were the BOAC Comet crashes caused by metal fatigue, the Turkish Airlines DC10 crashing after losing a door and the Concorde disaster when fire broke out after a fuel tank was ruptured.

A question which he posed at the was ‘Do we trust computers more than people?’ He noted that computers have replaced people in the execution of many routine tasks. They are fast, reliable and accurate. They are cheap, ideal control devices and can be made as accurate as one wants. However there are well documented examples of computer errors. The Therac 25 was a therapeutic X ray machine designed to fight cancer. It was possible for the computer controlled machine to be used without a metal shield being in place, resulting in patients receiving fatal doses of radiation. This was a design fault – no check had been included. The Patriot missile intended to intercept Scud missiles in the first Iraq war needed to be rebooted to avoid a cumulative error. Not doing so for a 100 hour period resulted in a delay of 0.34 seconds and a failure to intercept a missile with the deaths of 28 US soldiers.

Flying is very safe and getting safer. The number of accidents has fallen as the number of miles flown has vastly increased. Every generation of plane has been safer than its predecessor. However in 1982, a pilot on an Air Florida plane failed to turn on the instrumentation heating in icy weather. He was unaware of the ice on the wings which caused the plane to crash immediately after take-off into the Potomac river. Human ingenuity, however, enabled the pilot of a New Zealand 747 to find a lost Cessna over the Pacific and guide it to Auckland Airport. No computer could have done this. In 1988 an Air France A320 crashed at the Habsheim Air Show. The crew had disabled the automatic go around, had carried out aerobatics and overestimated the capability of the computer. In 1982, the crew set descent of an aircraft what they thought was 3 degrees. In fact they had set it at 3000ft/min leading to disaster. At Warsaw in 1993, when a Lufthansa plane landed initially on one wheel and then aquaplaned, the computer did not recognise that the aircraft had landed leading to a runway overshoot. In 1995 in Columbia, predictive text resulted in Romeo rather than Rozo being entered by an overworked crew member. The plane crashed into a mountain. The Air France disaster on a Rio to Paris flight in 2009 happened when the captain was resting. In dreadful weather, supercooled water froze in the pitot tubes. Without instruments, the pilots panicked, raised the nose, ignored audible warnings and the plane stalled. Pilots are now sometimes so deskilled that they cannot react to problems.

Replying to questions, Alan confirmed that computers now do most of the flying of the aircraft. On a flight to Hong Kong, the pilot’s ‘work’ might last for only 2 minutes. Commercial pressures may result in risks being taken. Of course not all pilots are first class. Alan’s final quetion was ‘What do we call the student who passes his medical exams with the lowest mark? – Answer: Doctor’