/ 26 April 2021

From order to chaos in a few seconds

Crash Of Concorde Of Air France In Gonesse, France On July 25th, 2000.
Butterfly effect: Routine systems of maintenance, flight management and training all descended from order into chaos through seemingly inconsequential and unconnected decisions and events, resulting in the crash of Concorde Flight 4590 in 2000. There were no survivors. Photo: Eric Bouvet/Gamma-Rapho/Getty Images

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? 

The “butterfly effect” was first described in the 1960s by Massachusetts Institute of Technology professor of meteorology Edwards Lorenz. It 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, for example, the flap of a butterfly’s wings, would alter the course of previously predicted events. 

Although Lorenz’s focus was weather prediction, the butterfly effect forms the basis of 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 conditions.  

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 in 2000.  

The Concorde was an engineering marvel that has yet to be repeated in the world of passenger aviation. But, because of environmental concerns about sonic booms, the Concorde was required to fly at inefficient subsonic speeds over populated areas. 

As a result, the Concorde burned half its fuel load by the time it was able to fly at its Mach 2 cruising speed over open sea. Fully loaded, the 10 tyres of the Concorde had to support the huge weight of the plane, as well as the higher-than-normal rotational speeds that the Concorde’s swept-back wings required 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. The captain was aware that the flight was almost an hour late and knew his passengers had to meet a cruise ship. Crucially, the captain also decided that the fuel tanks be filled to maximum capacity, rather than the usual standard operating level of about 90%. The extra weight was not a problem if all four engines were working normally and there was sufficient runway. 

For a plane’s take-off, head winds are preferred, because they provide added lift. But the captain, under pressure to get his passengers to their destination on time, chose a runway closer to the gate, with unfavourable winds. The extra weight, together with the lack of a head wind, meant that the aircraft would need most of the length of the chosen runway to reach take-off speed.  

As the 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 a makeshift wear strip from its engine cowling on the same runway. The replacement wear strip had been fabricated by an airline mechanic and riveted to the engine cowling of the DC-10 earlier that July when it had undergone repairs in the US. 

But 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 recommended by the engine manufacturer.

Runway maintenance at Paris’s Charles de Gaulle Airport called for three daily inspections to clean up any foreign-object debris on the runway. On this July afternoon the planned runway inspection, which  may have detected the dropped DC-10 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, hitting the underside of the Concorde’s left wing and the landing-gear compartment, slicing through exposed hydraulic lines and electrical wires. 

The largest tyre fragment struck the underside of the wing, hitting fuel tank number five, which was completely full, as per the captain’s instructions. As a result there was no empty air space in the tank to help to absorb the vibrations from the impact of the tyre fragment.  The resulting pressure wave blew out a panel on the underbelly of the Concorde’s wing, and the sparks from torn electrical wires ignited a fire in the number-one engine.

Adding to the problem was the fact that this Concorde aircraft had been in the hangar at Charles de Gaulle for repairs to its undercarriage. 

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. 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 engine. At the same time the aircraft was veering off the runway in the direction of an oncoming 747, which was carrying the French president.

The aircraft had reached the speed at which aborting the take-off was not an option. The 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 the plane’s nose up and hoping to make an emergency landing at a nearby airport, the plane struggled up into the air with only three working engines and the additional drag of the landing gear, which could not be retracted because of the severed hydraulic lines.

As damaged as the aircraft was, with sufficient power from the three remaining engines, it could still have made it safely into the air. But one final decision sealed the fate of Flight 4590. 

When the plane was just 25 feet off the ground, the flight engineer shut down the now ailing number two engine. This breached all set cockpit procedures for shutting down an engine on take-off. The number two engine itself was not on fire and it would probably have recovered. Robbed of sufficient power from the two remaining engines, Flight 4590 fell out of the sky, crashing into a nearby airport hotel and killing all 109 people on board, as well as four people on the ground.

In the case of Flight 4590, 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 US 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, realising his plane was overweight, had decided to burn off a tonne 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 number two engine? 

What if the National Transport Safety Board in the US  or the British and French aviation safety commissions had paid 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 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 that may end up being detrimental to our long-term wellbeing.

Facts regarding the crash of Flight 4590 were distilled from an article that first appeared in The Guardian newspaper in 2001. Shaun Read is the chief executive and founder of Read Advisory Services