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After engine 4 failed in Air France Flight 66, the airliner (an Airbus 380) landed at Goose Bay in Canada. I am aware that following that, the failed engine was removed and then something "nonfunctional" was installed in its place "to balance the weight". This looks like a strange story to me:

  • What was this "non-working replacement" and where did they get it? It still needs to have the required weight, shape and mountings. Was it quickly manufactured? The source referenced by Wikipedia even calls it a "spare engine". Did they install the engine intended for a different airliner?
  • In general if the goal was just to have a non-operational engine on the wing, why not leave the failed no. 4 engine where it was? Or was there a risk of it falling to pieces during the ferry flight?
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Here's another article from Oct 15th. They flew out a spare A380 engine. As of the 15th, it wasn't clear yet if this engine will be connected and running during the flight, or if it'll just be there to complete the airframe and act as a counterweight.

Leaving the broken engine in place would do more damage to the engine, complicating the investigation.

Pieces breaking off from the engine may have damaged the wing, the pylon or the connectors on the pylon (power, fuel, electronics etc.), they need to inspect for damage before deciding if the spare engine can be connected and running.

The plane will be empty for the recovery flight, so there's some margin to fly on 3 engines. They have to account for the possibility of an engine failure, leaving 2 operational engines, so the flight is planned to ETOPS rules. There's a procedure to reduce the effects of asymmetric thrust.

If the engine is left off and windmilling, it needs lubrication, this may limit the length of the flight.

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    $\begingroup$ "so there's some margin if they want to fly on 3 engines." In fact, B747s with a failed engine usually take off on recovery flights with only 2 engines running at max thrust and the other at idle, to minimize the issues at the list-off point where the wheels no longer help to control unsymmetric thrust distribution - this is the reverse of a "landing in a very strong cross wind" scenario except that gravity is working against you, not for you! $\endgroup$ – alephzero Nov 5 '17 at 20:09
  • $\begingroup$ The engine/aircraft connectors are often mounted on the fan case (because it's the closest point to the pylon and wing, and also the coolest part of the engine), so it's very likely the aircraft side of them would be damaged when the fan "fell off", irrespective of any other damage to the wing. $\endgroup$ – alephzero Nov 5 '17 at 20:19
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    $\begingroup$ Capt Dave Wallsworth is a British A380 pilot, and has some good info about this in his twitter feed. See mobile.twitter.com/DaveWallsworth/status/917887041278566400 $\endgroup$ – Penguin Nov 5 '17 at 21:31
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    $\begingroup$ @alephzero Your statement that B747s with a failed engine usually take off on recovery flights with only 2 engines running at max thrust and the other at idle" is not quite correct. The procedure, at least on 747-100/200 aircraft, is to start the aircraft rolling with max power on the symmetric engines, idle power on the other. Then as the aircraft gains speed and the rudder gains authority, the third engine is brought to max power. You have full power on all three engines well before rotation. $\endgroup$ – Terry Dec 14 '17 at 18:01
  • $\begingroup$ fixed my answer, thanks $\endgroup$ – Hobbes Dec 14 '17 at 18:26

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