What happens when both engines in an airplane fail at the same time?

The response of the pilots of a Singapore Airlines A330 that lost power in both engines while near Hong Kong last Saturday 23 May and then dropped some 13,000 feet in altitude before both were restarted has raised some important safety issues.

After having to drop from its cruising altitude of 39,000 feet on its way to Shanghai, to 26,000 feet, the engines of the A330 were restarted and the flight climbed to around 31,000 feet before continuing to its destination rather than landing at the nearest available airport after what was an exceedingly rare event for a twin engined jet.

The decision of the pilots to press on is controversial, and a statement to Reuters by Singapore Airlines says the cause of the incident is unknown, underlining the concern among some pilots that such action under such circumstances in incompatible with the highest and most prudent standards of flight safety.

If the Reuters story is read alongside this Aviation Herald report, written for a more technical rather than general readership, the problems with the statement made by Singapore Airlines become more apparent.

However it is possible that the Singapore Airlines statement to Reuters has somehow been misunderstood, and that the pilots determined they were dealing with something along the lines of a straightforward error in fuel management to both engines at the same moment that once fixed meant the course of action taken was completely justifiable and that no unresolved safety issues stood in the way of it continuing to Shanghai.

The deeper safety issue in that situation would be how the safety standards of Singapore Airlines could have failed to have ensured correct fuel management at the outset, which would be a far from trivial concern.

The references by Singapore Airlines to stormy conditions has caused speculation that rare forms of internal engine icing may explain the simultaneous loss of sufficient power in both engines to sustain its cruising altitude. In 2008 a British Airways 777, operating BA38,  crash landed with enough force to render it irreparable  at London’s Heathrow airport.

The British Airways  jet had made a long minimal thrust descent to the airport but both engines failed to respond adequately when more power was called for to complete the approach and land normally, causing it to pancake, injuring dozens of passengers, one seriously.  The accident was blamed on ice crystals in the fuel clogging the fuel-oil heat exchanger of each engine at the same crucial moment.

In 2013, coincidentally near Hong Kong, an Airbridge Being 747-8 freighter experienced near simultaneous power failures in three of its four engines through internal ice formation causing an emergency landing. This involved GE engines that were much different in key parts of their design to the Rolls-Royce engines used on the British Airways 777 and in a different version on the Singapore Airlines A330.

Aircraft and engine makers have become concerned about engine icing incidents in recent times, and have been funding research studies including some based at Darwin during monsoon conditions to better determine their causes and possible remedies.