A surge in public interest

After witnesses near London Heathrow saw a British Airways Airbus A319 suffer what looked and sounded like an engine failure soon after take-off in the evening of 6 March, there was, perhaps predictably, a lot of media publicity given to the event.

The airline subsequently confirmed that one of the aircraft’s engines had “surged”, and the crew elected to shut it down and return to Heathrow to land.

No-one was hurt in the incident, but the south runway was closed for about 15min to cope with the precautionary landing and its aftermath. The aircraft had been bound for Lyon, and BA says it put the passengers up in a hotel overnight for departure to their destination the following day.

Now to the event itself. One witness close to the runway described flame emitting from the back of the engine, and hearing a loud banging sound.

With apologies to my knowledgeable aircrew friends who have flown turbine-powered aircraft, here’s a bit of information on engine surges to put the issue in context.

The engines which power BA’s A320-series fleet are International Aero Engines V2500 turbofans. An engine surge is a phenomenon that occurs when something disturbs, and thus destabilises, the flow of air through the engine compressor, resulting in sudden momentary reversals of that flow. The flow reverses can cause some damage in their own right, and when they occur there is a loud banging sound, but the engine doesn’t lose all its power – just some of it. The equivalent event in a car engine would be a “backfire”.

The cause of this particular surge event is not yet known, but BA’s engineering department is investigating. A birdstrike could start it, or unnoticed damage to a compressor blade, but there are many possibilities. The events, however, are pretty rare nowadays.

The usual procedure for pilots when a surge occurs depends on what phase of flight the aircraft is in, although surges normally occur at high power settings, so take-off and climb is surge-risk phase.

Crew action – if it occurs in the early climb – is to leave the surging engine alone if it is still generating power, while the crew ensures they have a safe airspeed and a stable climb with gear up and flaps at an appropriate setting for the speed. Once that is achieved they can throttle the engine back to see if the surging stops, and if it does, they check for any evidence of damage or engine fire risk. If there is no such threat they would normally leave the engine running, but if threats exist they shut it down. The aircraft flies easily on one engine – as do all modern twin-engined aircraft.

A crew faced with a surging engine on take-off at Heathrow would advise ATC, probably with a Pan call rather than a Mayday, and would level off at a height of about 2,000ft (610m) or above, as agreed with the controller.

When cleared by ATC, the crew would aim to carry out a circuit to land back on one of the runways in the same direction that they took off. Finally, fire and rescue crews would meet the aircraft as a precaution and follow it to its parking place.

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