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What happens when an airliner loses engine power?

Every nervous flyer has probably gazed out of the window and wondered what would happen if those enormous engines stopped working. The reality is less worrying than you might think.


Flying in a modern commercial jet has become an unremarkable experience. Routine. Extremely rarely, though, circumstances might just conspire to make all that training and safety backup equipment worthwhile.

The overwhelming majority of pilots go through their entire careers without experiencing a dual flameout: both engines cutting out at the same time and leaving the aircraft gliding – still flying forward at great speed but no longer propelled by jet power. John Denker’s comprehensive flying manual See How It Flies is clear on what the cockpit crew should do: “The first step in dealing with any in-flight emergency is always the same: fly the airplane.” 1

No matter what, the pilot must stay calm and in control. A flameout like this might be rare but it has been anticipated and planned for and a skilled pilot can take an aeroplane without engines and land it safely with minimal injury to the passengers.


Miracle on the Hudson: a great pilot and ground support

In 2009, Chesley Sullenberger was able to land his Airbus A320 on the Hudson river on the east side of Manhattan after birdstrike caused both engines to fail shortly after takeoff from LaGuardia airport, New York.2

Having lost all engine power and losing what little altitude he had, Captain Sullenberger stayed in constant contact with air traffic controllers in an attempt to find somewhere safe to land. He knew he wouldn’t get back to LaGuardia and considered using the smaller runway at Teterboro in New Jersey before ruling that out and opting to ditch in the river.3

US Airways Flight 1549 had not reached sufficient airspeed to attempt a restart of the engines and one of them was on fire, so ditching was the only option. Roughly four minutes elapsed between the engine failure and the plane landing in the river. All 155 passengers and crew were saved by a combination of Captain Sullenberger’s skill and composure and the prompt action of the emergency services, who rescued them from the wings of the floating plane.

Captain Sullenberger, interviewed shortly afterwards, said that realizing he had lost power from both engines was “... the worst, sickening, pit-of-your-stomach, falling-through-the-floor feeling I've ever felt in my life. I knew immediately it was very bad. My initial reaction was one of disbelief: ‘I can't believe this is happening. This doesn't happen to me.”4

He knew he had to overcome that feeling to stay in control: “The physiological reaction I had to this was strong, and I had to force myself to use my training and force calm on the situation.”


Batteries step in when jets fail

Many of the systems required to land safely an airplane, including in an emergency condition, rely on electrical power. This was exactly the case experienced by Flight 1549’s Captain Sullenberger, after the dual engine loss.

All large aircraft use 28-volt batteries, either nickel-based or lithium-ion batteries, to accomplish tasks from starting the airplane engines to powering backup functions. In normal flight, the battery is recharged by the aircraft engines. In an emergency, the battery is the primary power source for radio communication with air traffic control, the instruments that give guidance and orientation information and the systems that control the airplane.

However, the battery does not fill this emergency role alone. The airplane may eventually rely on the auxiliary power unit (APU), which has to be started by the batteries and then ensures power generation, engine re-starting and cabin pressurization.

In its report on Flight 1549, the US National Transportation Safety Board said that Captain Sullenberger’s decision to start the APU was “critical because it improved the outcome of the ditching by ensuring that electrical power was available to the plane.”5

Without a powerful and reliable battery to start the APU, the risk to the plane would be much greater - and this is where Saft plays a vital role. In fact, eighty percent of commercial airliners rely on Saft batteries.

Thanks to a plane’s electrical systems, losing engine power doesn’t mean losing control, and a calm presence behind the controls can result in a safe glide to the ground. Whether jet powered or while gliding and powered by emergency batteries, as pilot Karlene Petitt said after another dual flameout that landed safely, this time over Singapore: “Pilots never stop flying the plane, no matter what.6



1. Dealing with emergencies – See How It Flies: www.av8n.com/how/htm/emerge.html

2. US Airways pilot rejected emergency landings at two airports, The Guardian, 16 January 2009: www.theguardian.com/world/2009/jan/16/new-york-plane-crash-hudson-river-sullenberger-pilot

3. FAA transcript of Hudson river plane landing, The Guardian, 5 February 2009: www.theguardian.com/world/2009/feb/05/us-airways-crash-transcript

4. Miracle on the Hudson, CBS 60 Minutes: www.cbsnews.com/news/sully-miracle-on-the-hudson-60-minutes/

5. US Airways Flight 1549 Accident Report, National Transportation Safety Board: www.ntsb.gov/investigations/AccidentReports/Reports/AAR1003.pdf

6. We asked pilots what happens when a jet loses both its engines, Business Insider, 27 May 2015: http://uk.businessinsider.com/a-singapore-airlines-flight-836-lost-engine-mid-flight-2015-5