Getting the timing of ihram and niyyah right is one of the more practical worries first-time pilgrims raise with us, and it's simpler than it first appears once you know the shape of it.
For men, ihram is worn either at home before leaving the UK, or at the airport before boarding — there's no facility to change on the plane itself, so this needs to be sorted before departure. If your route takes you to Madinah first, ihram isn't required yet at that point. Women travel in their normal clothing throughout, with no separate ihram garment required.
Niyyah — the intention — is typically made around 40 minutes before landing, timed to coincide with reaching the Meeqat boundary (for example, Al Johfa on certain routes). In practice, this is usually cued by an announcement from the cabin crew or pilot rather than something you need to time yourself using a watch or app.
It's worth being deliberate about this: don't make your niyyah early unless your group leader has specifically instructed you to, since timing it to the Meeqat is part of what makes it valid. If you're travelling and it affects your prayer times, prayers can generally be combined according to your madhab — your group leader can advise on the specifics for your journey.
None of this is complicated once you've done it once, but it's exactly the kind of small logistical detail that's reassuring to have clear before you're mid-flight and wondering whether now is the moment. Ask your group leader to talk you through it before departure if you're ever unsure.