You can technically use the airplane toilet during the boarding process, but it is highly discouraged by cabin crew and should be reserved for emergencies only. During boarding, the narrow aisles are already congested with passengers stowing luggage, and heading against the flow of traffic to reach a lavatory can cause significant delays. Furthermore, ground crew may still be servicing the aircraft's waste tanks or loading catering near the lavatories. If you must go, it is essential to ask a flight attendant first, as the lavatory may be temporarily locked for pre-flight inspections. Once the "Fasten Seatbelt" sign is illuminated and the aircraft begins its pushback or taxi, you are legally required to be in your seat; if you are in the lavatory during this time, the pilots must halt the aircraft until you have returned to your seat and buckled up, which can cause the flight to miss its departure slot. For the best experience in 2026, travelers are advised to use the terminal's facilities just before the boarding call.