Learn Hardcore French: La voiture est en panne, alors nous allons à pied. - The car is broken down, so we are going on foot.

It’s a fixed expression meaning “broken down/out of order.”
You typically use it after être to describe the state of a machine/vehicle: La voiture est en panne. L’ascenseur est en panne.
The noun une panne = “a breakdown.” With en panne de, it can mean “out of”: Je suis en panne d’encre (I’m out of ink).

What’s the difference between être en panne, tomber en panne, and cassé(e)?

être en panne = “to be broken down” (current state).
tomber en panne = “to break down” (the event): La voiture est tombée en panne.
cassé(e) = “broken” (physically damaged). For a car, La voiture est cassée can suggest it’s wrecked; for “not working,” prefer en panne or the colloquial ne marche pas.
Colloquial alternatives: en rade (out of action), HS (hors service).

Why is it à pied, not en pied or par pied?

Rule of thumb for transport:
- à for things you are on/astride or not enclosed: à pied, à vélo, à moto, à cheval.
- en for enclosed vehicles/mass transit: en voiture, en bus, en train, en avion.
par isn’t used to express the means of transport here.
No article is used: say à pied, not à la pied.

Should it be à pied or à pieds?

Standard French is singular: à pied.
You’ll hear à pieds in casual speech, but it’s nonstandard—avoid it in careful writing.

Can I just say Nous marchons instead of Nous allons à pied?

Yes. Marcher = “to walk” (the action).
Aller à pied emphasizes the means of getting somewhere. In many contexts they’re interchangeable.
Note: marcher also means “to function/work” for devices: La voiture ne marche pas (“The car doesn’t work”).

What does alors do here? Could I use donc or du coup?

alors links cause to consequence: “so/then.” Neutral and common.
donc is slightly more formal/logical; perfectly fine: …, donc nous allons à pied.
du coup is very colloquial and frequent in speech: Du coup, on y va à pied. Avoid in formal writing.
Elsewhere alors can also mean “then/at that time.”

What tense is this, and can the present refer to the near future?

Both verbs are present: est, allons.
Context lets the French present imply a near-future plan, so English might render it “so we’ll walk.”
To be explicit, use the future: …, nous irons à pied.
Don’t confuse with aller + infinitif (near future): Nous allons marcher = “We’re going to walk.” Here aller is the main verb “go,” not a future marker.

Why La voiture and not Notre voiture? Does la sometimes mean “our”?

La voiture means “the car,” a specific one known from context. If it’s obvious you’re talking about your own car, French often just says la voiture.
Use Notre voiture est en panne if you want to make ownership explicit.

Any pronunciation tips for this sentence?

Liaison: you’ll often hear a [t] between est and en (… es(t) en …), and a required [z] between nous and allons (… nou(z) allons …).
alors usually ends with a silent final s.
en in en panne is nasal (like “ahn”).
pied ends with a silent d and sounds like “pyeh.”

Is the comma before alors necessary?

A comma is common but not mandatory. Variants:
- La voiture est en panne. Alors, nous allons à pied.
- La voiture est en panne ; alors nous allons à pied.
Starting a new sentence with Alors, … is very natural in writing.

What is the gender of panne, and does anything agree with it?

panne is feminine: une panne.
The phrase en panne itself is invariable: Les voitures sont en panne (no extra endings).
With tomber en panne in the past, the past participle of tomber agrees with the subject (auxiliary être): Les voitures sont tombées en panne.

How else could I say this naturally?