Structure: ‘Zero conditional’

How do we talk about things that are always true?

Some facts don’t depend on the day, the aircraft, or the weather — they’re just always true. A radio altimeter always works the same way. Pilots always rely on it in poor visibility. English has a special tense pattern for facts and rules like these: the zero conditional.

We form it with if + present simple, + present simple: “If a signal takes longer to return, the aircraft is higher above the ground.” Both halves stay in the present simple — there’s no “will” anywhere, because we’re not predicting a single future event. We’re describing something that happens every time, without exception.

When pilots and engineers use the zero conditional

This week’s FAA news is full of general truths. The FAA’s new rule on radio altimeters exists because of one unchanging fact: if a radio altimeter picks up interference from a nearby 5G signal, the height reading becomes unreliable. That’s not a one-off event — it’s a rule of physics that holds every single time the conditions are met.

We reach for the zero conditional whenever we explain how equipment works, state a safety rule, or describe a routine: “If pilots cannot see the runway clearly, they depend on instruments for an accurate height.” “If the cabin altitude climbs too high, the oxygen masks drop automatically.” “If an engineer finds a fault during a check, the aircraft doesn’t fly until it’s fixed.” None of these describe a single moment — they’re all standing rules.

Watch out for this mistake: learners often slip “will” into the result clause, because it feels like the future. ✘ “If a pilot cannot see the runway clearly, the radio altimeter will give an exact reading.” That sentence describes a general truth, so both verbs stay in the present simple: ✔ “If a pilot cannot see the runway clearly, the radio altimeter gives an exact reading.” Save “will” for the first conditional, where you’re predicting one specific future result, not stating a rule.

Try these

Each item below gives you two separate facts. Join them into one sentence using the zero conditional, without changing the meaning.

1. A pilot cannot see the runway clearly. The radio altimeter gives an exact height reading.
2. Interference reaches an unprotected altimeter. The height reading becomes unreliable.
3. A 5G tower uses the Upper C-band. Its signal sits close to the altimeter’s own frequency.
4. An airline does not upgrade its altimeters by the 2030 deadline. It breaks the FAA’s new rule.
5. An aircraft flies in fog or heavy rain. Pilots depend on the radio altimeter for a safe landing.

Now make it real

Write one or two true sentences about your own flying or work using the zero conditional — a rule or routine that’s always true for you. Use the frame: “If ___, ___.” (both halves present simple).

Before you check your answer, ask yourself:

• Does your sentence describe something that’s always true for you, not just one time it happened?
• Is it about your own real routine or work?
• Are both verbs in the present simple (no “will” anywhere)?
• Does the “if” clause come first, with a comma before the result?
• Capital letter at the start, full stop at the end?

Now rewrite your sentence to make the rule even more specific or clearer.

CEFR Level B1 / ICAO Level 4

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