Most systems fail to specifically match the escort tug's ability to apply ... the ship's engine fails as opposed to total system failure including engine, ... suffers a hard over rudder failure before the ship touches the grounding line ...
www.towingsolutionsinc.com/technology-escort_planning.html -

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Note added at 3 minutes (2011-05-06 16:59:07 GMT)
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or steering failure.

MAIN ENGINE OR STEERING FAILURE | Maritime Information
- [ Traduire cette page ]
16 Mar 2008 ... In case of a steering failure: Inform engine room; Engage emergency steering; Take way off the ship; Prepare engines for maneuvering ...
maritimeknowledge.info/main-engine-or-steering-failure

Il me semble que "failure" est trop... définitif ! IMHO, avec une "avarie", le bateau peut continuer à naviguer. Avec une "failure", non !

For "avarie" = "problem", see Web.Ref.

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Note added at 57 mins (2011-05-06 17:52:34 GMT)
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avarie: WordReference English-French Dictionary © 2011

avarie nf damage

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Note added at 58 mins (2011-05-06 17:53:51 GMT)
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Business, Collins, Collaborative Dictionary
avarie n f damage, average

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Note added at 59 mins (2011-05-06 17:55:03 GMT)
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avarie (n.)
average, damage
http://dictionary.sensagent.com/avarie/fr-en/

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Note added at 1 hr (2011-05-06 18:06:00 GMT)
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An attempt to winch it free while jacking over the engine slowly resulted in damage to the rudder post and aft propeller bearing. After the storm, Calypso ....

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Note added at 1 hr (2011-05-06 18:07:32 GMT)
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> avarie
(nom féminin).

Dommage subi par un navire ou son chargement.

Propulsion can be supplied by sail as well as by engine.
Helm or steerage is the ability to steer a craft with or without engine.
The context here is probably a ship but as a matter of interest, rudderless steering of a yacht is possible in an emergency:
"Most boats will sail rudderless with the main half on, and a small jib, in a reasonable line, using the mainsheet control for the steering. To go upwind, bring the mainsheet on, and if necessary the traveller up. To go away, do the opposite."

I'm surprised the moderators haven't pounced on you because you've asked two questions here. Maybe they're having a day off ;-)

Anyway, if we are talking about "emergencies" then I think "failure" or "breakdown" are suitable translations for "avarie". In the case of an event, "damage" may well be the right word.

It's tempting to agree with Dr Manu and his translations "engine" and "rudder" however the terms "propulsion" and "barre" aren't limited to two particular parts but to two whole systems (e.g. propulsion = engine, shaft, propeller, etc.)

DCNS give "steering gear breakdown" for "avaries de barre" in their glossary. They don't mention "avarie de propulsion" although they translate "propulsion" as "propulsion".