By Shaun Read


An edited version of this article was published in the Mail & Guardian on 23 April 2021


Many a crisis has its origins in a series of seemingly unconnected events, a phenomenon known as “the butterfly effect”.  Who would have thought that events in Wuhan, China (laboratory or wet market – take your pick), would result in the worst global health and economic crisis in the past 100 years.  Likewise, who knew that when US banks started issuing NINJA loans to customers with No Income, No Job or Assets this would result in a global financial crisis in 2008.


The “butterfly effect” was first described in the 1960’s by MIT professor of meteorology Edwards Lorenz and has often been confused as describing a series of linear connected events starting with the metaphorical flutter of a butterfly’s wings in one part of the world and ending in a tornado in another.  In fact, Lorenz’s theory sought to prove the exact opposite, namely that predicting the future, using past events, was impossible because any slight change in circumstances e.g. the flap of a butterfly’s wings, would alter the course of previously predicted events.


In the case of weather prediction, Lorenz showed that past weather patterns could not be used to predict future weather conditions as any slight change in barometric pressure would have a major effect on the resulting weather and no 2 weather days on earth were exactly alike.  Although Lorenz’s focus was weather prediction, the butterfly effect forms the basis of the broader chaos theory, which describes the point at which systems move from a point of order to one of chaos or unpredictability based on even the slightest change to the conditions of the system.


An illustration of this point was the doomed flight of Concorde Flight 4590, which crashed shortly after take-off near Charles de Gaulle airport outside Paris.


Developed during 1960’s and entering into operation in the early 1970’s, Concorde was an engineering marvel that has yet to be repeated in the world of passenger aviation.  Concorde’s biggest attraction, its supersonic speed, was also its Achille’s heel.  Because of environmental concerns regarding sonic booms, Concorde was required to fly at inefficient subsonic speeds over populated areas.  As a result, Concorde burned half its fuel load by the time it was able to fly at its Mach 2 cruising speed over oceans and less populated areas.  With its fuel tanks full and a hundred passengers strapped in and their baggage stowed, the 10 tyres of Concorde had to support the huge weight of the plane as well as higher than normal rotational speeds that the Concorde swept back wings required in order to get the aircraft off ground.  As a result tyre vulnerability on the Concorde was higher than other passenger aircraft.


On that fateful day in July 2000 the Air France Concorde Flight 4590 was serving as a chartered flight carrying passengers from Paris to New York where they were to catch a cruise ship destined for the Caribbean.  The Captain was aware that the flight was almost an hour late and knew his passengers had to meet a cruise ship.  Passengers on chartered flights often carry more luggage and the plane was loaded slightly beyond its weight capacity.  Crucially, the Captain also decided that the fuel tanks be filled to maximum capacity, rather than the usual standard operating level of +/- 90%.  The extra weight was not a problem if all 4 engines are working normally and with sufficient runway.


For a plane on take-off, head winds are preferred because they provide added lift and this was particularly important for Flight 4590 because it was overweight.  However, under pressure to get his passengers to their destination on time, the Captain chose a runway closer to the gate with unfavourable winds.  The extra weight along with the lack of a head wind meant that aircraft would need most of the length of the chosen runway to reach take-off speed.


As Concorde prepared to take off, the crew did not know that a few minutes before, a Continental Airlines DC-10 had taken off from the same runway and had dropped makeshift wear strip from its engine cowling on the same runway.  A wear strip is a piece of metal that acts both as a cushion as well as a tight seal for the engine’s thrust reverser cowling.  The replacement wear strip had been fabricated by an airline mechanic and riveted to the engine cowling of the DC 10 earlier that in July when it had undergone repairs in the USA.  However, the DC 10 mechanic did not follow the manufacturer’s recommendations when he fabricated it and decided to use a piece of titanium rather than the softer aluminium material recommended by the engine manufacture, presumably thinking that the much harder and stronger metal would last longer.


Typical runway maintenance at Paris’ Charles de Gaulle Airport called for three daily inspections to clean up any foreign object debris that may have scattered on the runway. On this July afternoon the planned runway inspection, that may have detected the dropped DC10 wear strip, was cancelled in favour of a routine fire drill.


When Flight 4590 sped down the runway its vulnerable tyres encountered the titanium wear strip that had fallen from the DC-10.  The tough metal strip, lying sharp side up, sliced through the tyre on Concorde’s left side. When the tyre burst, large pieces of rubber flew off at more than 450 km per hour, hitting the underside of the Concorde’s left wing and firing like shrapnel into the landing gear compartment, slicing through exposed hydraulic lines and electrical wires. The largest tyre fragment, approximately 1 meter long, struck the underside of the wing hitting fuel tank number 5, which was completely full as per the Captains instructions.  As a result there was no empty air space in the tank to help absorb the vibrations from the impact of the tyre fragment.  The resultant pressure wave blew out a panel on the underbelly of the Concorde’s wing.  As fuel poured out of the ruptured wing tank, the sparks from torn electrical wires, ignited a fire in the No. 1 engine.


Adding to the problem (and what the French investigative report refused to take account of) was the fact that this Concorde aircraft had been in the hangar at Charles de Gaulle for repairs to its under carriage.  To keep the wheels steady and in position, they are separated by a small aluminium spacer. When the plane left the maintenance hangar, the spacer was missing.  After the crash, it was found in the Air France workshop, still attached to the old beam which had been replaced.  Over the course of the previous week, the wheels had gradually moved out of alignment during a series of take offs and landings.  As the plane sped down the runway with a burst tyre, there was nothing to keep the front wheels of the undercarriage in line with the back and it started to veer off the runway.


Meanwhile, inside the cockpit the fire sensors were blaring and the crew shut down the affected No.1 engine.  At the same time the aircraft, owing to the missing wheel spacer, was veering off the runway in the direction of an oncoming 747 on an accompanying taxiway, carrying the French President, who had just returned from a G7 Summit.


The aircraft had reached the speed where aborting the take-off was not an option.  Concorde was also running out of runway, veering left and the Captain had to get airborne to avoid crashing off the end of the runway. With the crew desperately trying to pull her nose up and hoping to make an emergency landing at a nearby airport, the plane struggled up into the air with only 3 working engines and the additional drag of the landing gear, which could not be retracted due to the severed hydraulic lines.


As damaged as the aircraft was, with sufficient power from the 3 remaining engines, the aircraft could still have made it safely into the air.  However, one final decision sealed the fate of Flight 4590 the aircraft.  When the plane was just 25 feet off the ground, the flight engineer, shut down the now ailing No. 2 engine. This was another disastrous mistake, which breached all set cockpit procedures for shutting down an engine on take-off.  The No.2 engine itself was not on fire, and as the blazing fuel tank emptied and the fire burnt itself out, it would probably have recovered.  However, robbed of sufficient power from the 2 remaining engines, Flight 4509 fell out of the sky crashing into a nearby airport hotel killing all 109 onboard and 4 people on the ground.


In the case of Flight 4509, routine systems of aircraft maintenance, flight management and crew training all descended from order into chaos through seemingly inconsequential and unconnected decisions and events.  The decision of a mechanic in the USA to install a titanium wear strip was the easiest to blame for the crash but there were other events and decisions that all contributed to the tragedy. For example, what if the runway inspection had been conducted and the titanium strip found? What if the wear strip had fallen flat on the runway allowing the Concorde tyre to crush it rather than falling and landing upwards, like a knife blade? What if the Captain not filled the tanks or realizing his plane was overweight had decided to burn off a ton or so of fuel while taxiing or, what if he had selected another runway without such a strong headwind? What if the flight engineer had not shut down the No. 2 engine? What if the NTBS or the British and French aviation safety commissions had placed the proper attention to Concorde’s continual tyre problems and forced the airlines to work with manufacturers to develop a more reliable tyre that could handle the speeds and loads?


Too often decision makers focus on achieving an immediate the goal and discount the effect of their decisions on the later course of events.  A better understanding of the butterfly effect may result in fewer actions which may end up being detrimental to our long-term well-being.