What rules must ground crews follow near a moving aircraft?
After a ground worker was fatally struck during a pushback in Montréal, investigators are looking closely at the safety rules ground crews follow around moving aircraft every day. In English, we use modals of obligation — must, have to and should — to talk about rules, duties and strong advice.
Must and have to both express an obligation — something you are required to do. Should is weaker: it gives advice or a recommendation, not a rule. The negative forms work differently too: mustn’t means an action is forbidden, while don’t have to means an action is simply not required — the opposite of a rule, not a ban.
Must, have to, or should?
- Must — the speaker treats the obligation as coming from their own authority, or as a fixed, non-negotiable rule. “Ground crews must wear high-visibility vests on the ramp.”
- Have to — the obligation comes from an outside system or rule (a law, a company policy, an airport requirement). “Marshallers have to complete safety training before working alone near aircraft.”
- Should — advice or a recommendation, not a strict rule. “Airlines should review their pushback procedures regularly.”
In everyday speech, must and have to are often interchangeable in the present tense. The real difference only becomes clear in the negative — and that’s where learners most often go wrong.
Watch out for these mistakes
The most common error with this group of modals is mixing up mustn’t (forbidden) and don’t have to (not required).
- ✗ “You mustn’t finish the safety course today.” (This wrongly suggests finishing today is forbidden.)
- ✓ “You don’t have to finish the safety course today, but you must finish it by Friday.” (Finishing today is optional; finishing by Friday is a rule.)
Before you choose a modal, ask yourself: is this action forbidden (mustn’t), required (must/have to), optional (don’t have to), or just advisable (should)?
Try these
Complete each sentence with the modal of obligation that best fits the meaning.
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Marshallers ______ stand where the pilot can always see their hand signals — it’s a mandatory safety rule, not just good practice.
The sentence describes a strict, non-negotiable safety rule, so it needs the strongest obligation modal, not advice or an optional action.
This is a fixed safety rule, not a personal choice — ‘must’ is the strongest way to state an obligation.
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New ground staff ______ complete ramp-safety training before they can work alone near a moving aircraft.
This obligation comes from an outside rule (the airport’s training requirement), which is exactly where ‘have to’ fits — not ‘should’, which is only advice.
‘Have to’ works just as well as ‘must’ here for an obligation imposed by the airport’s rules, not the speaker’s own authority.
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During a pushback, nobody ______ walk in front of or behind the aircraft — it’s strictly forbidden.
The sentence bans the action completely (‘strictly forbidden’), so it needs the prohibition form ‘mustn’t’ — ‘don’t have to’ would wrongly suggest the action is just optional.
‘Mustn’t’ expresses prohibition — the action is not allowed at all, which is different from simply not being required.
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After any ground incident, airlines ______ review their pushback procedures, even though no regulator forces them to.
The sentence itself says ‘even though no regulator forces them to’ — that rules out ‘must’/’have to’ (external obligation); this is advice, which needs ‘should’.
‘Should’ gives strong advice or a recommendation — the airline isn’t legally required to review its procedures, but it’s clearly the sensible thing to do.
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During a normal pushback, passengers ______ leave their seats — they can simply stay buckled in until the seatbelt sign goes off.
The sentence describes an action that is simply optional (‘they can simply stay seated’), not forbidden — that calls for ‘don’t have to’, not ‘mustn’t’.
‘Don’t have to’ means an action is not required — passengers are free to stay seated, unlike ‘mustn’t’, which would mean they are forbidden to leave.
Now make it real
Think about a job, a course, or flying itself. Write 1–2 true sentences about rules you follow, using at least one modal of obligation (must / have to / should / mustn’t / don’t have to).
Before you check your answer, ask yourself:
- Does the sentence describe a real rule or duty from your own experience?
- Have you picked the right modal — must/have to for a real rule, should for advice, mustn’t for something forbidden, don’t have to for something optional?
- Is the verb after the modal in its base form (no “to” after must/should, but “to” after have to)?
- Does the sentence start with a capital letter and end with a full stop?
“I must complete a safety briefing before every flight I take for work.”
“Cabin crew have to demonstrate the safety equipment before every departure, even on the shortest flights.”
Now rewrite your sentence to make the rule — and the reason for it — clearer.
CEFR Level B1 / ICAO Level 4
For more practice with this modal group in a different context, see our earlier post on the same rules of obligation.
