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In the event of both the engines failing in a double engine aircraft, does the aircraft a have nickel cadmium battery to provide propulsion to make a successful landing?

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marked as duplicate by mins, SMS von der Tann, Pondlife, fooot, Simon Dec 8 '16 at 20:20

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    $\begingroup$ Are you asking about a battery that would provide propulsion somehow, or just one that would keep instruments running? $\endgroup$ – pericynthion Dec 8 '16 at 6:33
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    $\begingroup$ 787 has Li-ion battery $\endgroup$ – vasin1987 Dec 8 '16 at 6:42
  • $\begingroup$ Also, is there a reason for asking about NiCad specifically rather than batteries in general? Some aircraft use different battery chemistries. For example, the 787 is rather noteworthy (somewhat infamously so) for using Lithium batteries. It should also be noted that the batteries are used for a lot more than just powering things if the engines die. For example, batteries are nice to have around for things like starting the engines in the first place and powering lights and such after the engines have been shut down when external power isn't attached. $\endgroup$ – reirab Dec 8 '16 at 6:42
  • $\begingroup$ Many (all?) commercial airliners have ram air turbines for power in case of all engines failing. Most GA aircraft have magneto ignition, which doesn't require an external power supply. $\endgroup$ – jamesqf Dec 8 '16 at 7:05
  • $\begingroup$ actually i was asking about batteries for propulsion purposes $\endgroup$ – kcihtrak Dec 8 '16 at 7:42
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No, they don't. At least, not for propulsion.

  • Jet engines burn oil and can't be powered by batteries.
  • Even if we forget that, jet engines produce enormous amounts of power and no battery technology can store anything close to that much. Certainly not NiCad, which isn't even suitable for powering your phone or laptop.
  • Airliners are only allowed to operate on routes where, if one engine fails, the plane can still reach an airport with plenty of safety margin. A second engine failing independently is so unlikely that I wouldn't be surprised if it had never happened on a modern plane.
  • Even if the second engine fails, airliners can still glide for tens of miles to find somewhere to land (e.g., the Gimli Glider and Air Transat flight 236).
  • In reality, the only way that all your engines are going to fail is if there's a common cause. Running out of fuel is the most obvious, and is in the news at the moment. The other one that comes up from time to time is flying through volcanic ash clouds. The solution to all of these problems is management, not technology. Airlines are very careful to put enough fuel on board for every flight, and regulations require there to be not just enough fuel to reach the destination but also extra to allow for delays and diversions. Likewise, they're very careful not to fly their planes through conditions that will break them. Another possible common cause is a bird strike, though it's unusual for that to affect more than one engine. However, bird strikes almost always happen close to the ground and it's usually possible to get back to the airport.

So, even if batteries for backup propulsion were possible (which they aren't), they wouldn't be useful. They'd be required on such a minuscule number of flights (surely less than one in a million) that you'd probably kill and injure more people with battery fires than you'd rescue from engine failures.

And that's before you consider the huge amounts of extra weight you'd have to carry around in the form of batteries and electric engines. Extra weight means you need more power, need to burn more fuel and have less space for passengers and cargo.

Note that planes do carry batteries to power some electrical systems. They also have a thing called a ram air turbine (RAT), which is a little windmill that drops down and provides power for the electrical and hydraulic systems in case of engine failure.

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    $\begingroup$ Many information summarized in a short post. Nice to read. $\endgroup$ – mins Dec 8 '16 at 18:36
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    $\begingroup$ One more reason for second engine failure: pilots shut down the good engine. It's happened twice now: BD92 and GE235 $\endgroup$ – TomMcW Dec 8 '16 at 19:51

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