Consider the Concorde crash of 25th July, 2000. The aircraft hit metal debris left on the runway by a preceding aircraft, a tyre burst and rubber fragment(s) punctured the wing skin leading to a fuel leak. The fuel was ignited by something, possibly shorted wires in the undercarriage bay, also damaged by flying tyre fragments. On being told by radio of the flames trailing from the port wing, the crew throttled back on the affected engine(s) and at low speed and high weight (depending on sources, suggestions were it was overloaded and also rotated at a speed below the safe rotation speed) control was lost over the aircraft, which fell to the ground on top of a hotel. The large amount of fuel on board led to a large fire.
In addition, the port wheel assembly had been incorrectly put together by maintenance staff, resulting in that wheel not tracking straight. This probably contributed to the way the aircraft tracked on the runway and to the time and distance required to reach the rotation speed.
Concorde underwing skin
Concorde undercarriage bay
This narrative involves two significant (due to the effect that arose from them) energy sources – the Chemical Bonding Energy (CBE) of fuel and the combination of Gravitational Potential Energy (GPE) and Kinetic Energy (KE).
There are other smaller energy sources – the aircraft KE when on the runway and when the metal debris from the preceding aircraft was struck and the Pressure Energy (PE) of the tyre and also the rotational KE of the tyre.
The involvement of so many energy sources is unusual. This case is a good example of chained Occurrences – the Outcome of one Event is the Mechanism of another Event.
What energy led to what damage?
|
KE during take-off run |
Damage to tyre |
|
PE and rotational KE of tyre fragments |
Damage to fuel tank |
|
Fuel CBE |
Development over time of aircraft skin and structure damage due to heat |
|
Aircraft GPE and KE |
Damage to the hotel and to the aircraft structure |
|
Fuel CBE after impact |
Damage to all combustible materials after the impact |
Each line in the table is one Occurrence (accident). Each Occurrence is based on one Event. These can be defined as follows:
|
Energy |
Event definition |
|
KE during take-off run |
The point in time when control was lost over the potentially damaging properties of the KE of the aircraft on the runway – The aircraft tracks towards an unseen piece of metal debris on the runway. |
|
PE and rotational KE of tyre fragments |
The point in time when control was lost over the potentially damaging properties of the Tyre PE and KE of the tyre – Tyre bursts |
|
Fuel CBE |
The point in time when control was lost over the potentially damaging properties of the CBE of the fuel – Fuel leaks |
|
Aircraft GPE and KE |
The point in time when control was lost over the potentially damaging properties of the GPE and KE of the aircraft – Controlled flight no longer possible (due to low speed and thrust) |
|
Fuel CBE after impact |
The point in time when control was lost over the potentially damaging properties of the CBE of the fuel – All fuel tanks rupture on impact |
In my view, the two underlined Events are of most significance in this case. Tyre failures are not uncommon on transport aircraft. If this alone had happened it is unlikely anyone would have heard of it except the operators.
The second Event, involving tyre damage to the underside of the aircraft had been the subject of some discussion and engineering modifications over the years. Only those closely involved in the Concorde operation would have been aware of these efforts.
The third Event is what put Concorde in front of the world’s press due to the spectacular fire that resulted. Tragically, subsequent handling of the aircraft in very difficult circumstances led to a loss of flight control and the subsequent crash. The Fuel leak had the worst possible Outcome and Consequence. To my mind, therefore, the fuel leak Event, is that which is the pivot point of this case.
The associated Occurrences of each are summarised in the following table.
|
Mechanism |
Event |
Outcome |
|
Fuel tank wall (wing skin) punctured by flying tyre fragments |
Fuel Leaks |
Fuel vapour ignited by electrical short circuit in undercarriage bay |
|
Fuel fire flames lead crew to assume an engine fire and one engine shut down, possibly thrust reduced also on the other port engine |
Controlled flight impossible |
Aircraft rolls towards dead engine(s) and aircraft pitch and speed insufficient to maintain flight, so the aircraft falls from the sky onto the hotel. Impact with the ground and hotel, release of total fuel load and ignition of it. |
Why is this analysis worth doing?
-
This analysis can be done before the actual experience. See Chapter 9. In this case it is a significant contribution to understanding how to properly estimate and evaluate the Risk. Each of the early Events may have experience data, which can contribute to a proper estimation of the Risk. There certainly was experience of damage arising from tyre fragments and these were seized on as evidence the Regulator had not done their job with diligence1.
-
Post-hoc, the analysis provides a sensible framework for an investigation into and cataloguing of all the details.
-
Understanding the essential and underlying simplicity of even such a complex string of Events as this contributes to the mental clarity needed to direct and interpret the multitude of facts and assumptions that arise in the investigation of such a case and which contribute to the detailed understanding of Mechanisms and Outcomes.
References
1. http://www.telegraph.co.uk/news/worldnews/europe/france/9710925/French-court-set-to-deliver-Concorde-crash-verdict.html Viewed 8/5/15
2. Bureau Enquêtes-Accidents (n.d) Accident on 25 July 2000 at La Patte d’Oie in Gonesse (95) to the Concorde registered F-BTSC operated by Air France