2. (of a competitor in a sports race or match) having a lower score or weaker performance than other competitors.
‘she finished ten meters in arrears’
This use here is spot on, but not common.
I like uses like this one. Gives a bit of texture to the conversation.
The right expression is la porte arrière (not "en arrière"), which usually means the back door of a vehicle. Some will more correctly say la portière arrière. It will rarely endorse the other meaning of "back door". Out of context, absolutely no one would see anything sexual in this expression.
On the other hand, la porte de derrière will point to the door which is on the back side, for instance the back door of a house. In some contexts, it may convey some sexual innuendo.
In modern French, it's used both literally and figuratively. A common folk song goes "3 pas en arrière…" (3 steps backward). Similarly, "arriérés" could mean "people with retrograde mindsets", or "arrears", i.e. rent or taxes that should have already been paid. I suppose the English language merged "arriérés" and "arrière" into a single word.
It comes from "to the rear". So, in a competition (against Airbus), it means you're behind the person in first. On a payment schedule, it means you're behind the schedule.
Every other time someone was behind, they were just "behind" -- never saw that prompt the use of a legalistic French term the way that "being in arrears" did.
Edit: O...kay, getting some pushback on this. Let me try to explain with another analogy.
Let's say I saw a comment that read, "He got involved in human trafficking because he has a mortgage."
I had only ever seen "mortgage" used to referred to a secured loan for a home.
So I'd interpret the statement to mean, "he has a big debt he wants to pay and needs money and that motivated him to do slimy things for it."
But let's further say I had specific knowledge that that guy had paid off his home loan years ago. Then I'd be confused and say so, "uh, what? He doesn't even have a mortgage."
Then a bunch of people respond to say, "oh, duh, 'mortgage' comes from the French 'death pledge'[1] -- here they were talking about how he had pledged his life to serve the cartels on pain of death." "Oh, yeah, man, I use 'mortgage' all the time to refer to a blood oath."
That ... would definitely be news to me. Sure -- I wasn't aware of people who had used it the other way. But do you see why I would never have abstracted "mortgage" to refer to death pledges in general, even with great abstraction skills?
Note: "Mortgage", to my knowledge, is not used in English in this other way -- I'm just conveying the sense of surprise there to learn that, had it actually been true.