After the accident of an A400M in Seville on May 9th, a lot of information was leaked to the media, and many hypotheses were made about what could have happened during the flight that ended with 4 deceased and 2 seriously wounded people. This article tries to reconstruct the how and why from publicly available data. Evidently, this is just a hypothesis made by the author, and it should be read with a critical view. The truth will be known once the investigation is over.

On May 9th, in Seville, at 12:53 local time, an A400M is waiting at the end of the runway 09 for takeoff clearance. This aircraft, serial number MSN023, is doing one of a series of routine test flights before its delivery to the Turkish Air Force. The A400M is already certified, and has had no major incidents during its development. As many other military programs, it has suffered from delays and has been plagued by cost overruns.



This particular aircraft, flying under the call sign CASA423, is now cleared for takeoff by the control tower. Conditions are optimal for flight. It is just another sunny spring day in southern Spain. The A400M takes off and starts climbing normally. At 500 meters altitude, pilots perform a routine check: they reduce engine power to the minimum (idle) and then throttle them back up to climb power.  When they try this, three out of four engines stay at idle power. After trying again, they still don’t react.

The pilots are now in a very complicated situation. Without engine power, airplanes can glide to an airport and land safely. The distance they can cover depends on two factors:

  1. The altitude at which engine failure happens. The higher, the better.
  2. The aircraft’s maximum “glide ratio”. For the A400M, this is probably about 12. This means that for each meter the A400M descends, it can cover 12 meters.

With one engine still operating, the descent can be slowed down, to an estimated ratio of about 19. The engine failure occurred at 500 meters altitude, which is a really low altitude. Pilots have, in the best case-scenario, 9.5 kilometers they can cover before hitting the ground. At their current speed, this means that they have just two minutes of time. They have to react and take a decision, quickly!

The first reaction is to veer off course and head towards the airport. The distance to the end of runway 27 is 6.5 kilometers in a straight line, but the aircraft needs to maneuver to align with the runway. The engines still show no reaction, so the pilots will not have enough margin to land safely on the airport.

If they make a small mistake during the approach, they could crash on the airport and hit some of the buildings, or a civilian airplane. There is also a shopping mall nearby, full with people doing their Saturday shopping. Trying to land at the airport is too risky.

The only option is to try an emergency landing in some of the fields near the airport. It is a reasonable option: the A400M is a military transport airplane, capable of landing on very rough surfaces, so a landing on a wheat field should not be fatal. It would probably be hard and damage the airplane, but the whole crew should survive.

Emergency landings are also a standardized procedure. Normally, fuel tanks are emptied to the necessary minimum before landing, to decrease aircraft weight and avoid the risk of fire after the crash. In this case, the crew did not have time for this, and it probably had tragic consequences.

The A400M touches down softly, and starts rolling on the ground, slowing down in the process. Some aircraft parts start falling apart, but the fuselage is probably still intact. By this point, however, the aircraft is no longer under control. A rupture somewhere in the aircraft causes the fuel tanks to start leaking. And then, it hits a high-power transmission line. This immediately sets the aircraft ablaze. The rest of the story is well-known.

This accident is a tragic example of how systems fail. Like chains, they break at their weakest link. An aircraft is as vulnerable as the most vulnerable of its subsystems. A modern military transporter, with an armored fuselage, state-of-the-art autopilot and exceedingly powerful engines will be helpless if the system that controls these engines does not work properly. And even more so if, during an emergency landing, it crosses its way with something it was not designed for: high voltage transmission lines.

Preventing accidents is a daunting task, because it requires a rare ability: being able to predict the unpredictable: when it will happen, and how.