ANALYSIS

KEN FAIRBANK SHOULD airline passengers be worried?

It is, of course, too simple a question to answer in a single word. But if you look at simple odds, then “no”.

The Southwest Airlines Flight 1380 incident appears to have involved an uncontained failure of the left engine that caused debris to strike the aircraft structure. This caused the loss of a window on the left side, which depressurised the aircraft and led to fatal injuries for a passenger.

Photographs taken after landing show clear damage to other parts of the aircraft’s structure, such as the leading edge of the left wing.

The engine was a CFM56-7B, a development of the original CFM56 engine that was first produced in the 1970s.

Developed versions of the original are in widespread use with airlines around the world.

The incident is under investigation by the National Transportation Safety Board, which released a preliminary report that one of the engine’s fan blades may have failed in flight owing to metal fatigue.

It is clear from photographs that the entire forward cowling of the engine separated.

All such engines undergo testing prior to certification, including the simulated failure of a fan blade.

Failure

The intention is that any debris from such a failure should be contained within the engine and its cowlings, since released debris may have very high energy and present a serious threat to the aircraft’s structure and systems.

Uncontained failures are relatively rare, but do occur.

Often the damage is confined to the engine and its casing, but on occasions more widespread damage occurs.

When an uncontained failure does occur, it is classed as a serious incident and subject to independent scrutiny by air accident investigators.

The NTSB will consider whether this incident is linked to a similar incident in 2016, also involving a Southwest Airlines Boeing 737.

In that incident, a fan blade failed and debris punctured the fuselage, although there were no injuries on board.

In this case, the flight crew would have been presented with a serious double failure – that of the engine and also pressurisation.

Both are routinely practised in flight simulators, but not normally together.

Similarly, while cabin crew train for an emergency depressurisation and medical emergencies, the combination would have been particularly demanding.