A planeload is as many people, or as much stuff, as one aircraft can hold — or a full load of that size, even if you are speaking roughly. News and everyday English both use it: a planeload of tourists, a planeload of aid, a planeload of passengers stuck on the tarmac. It measures an amount by the plane, the way a busload measures by the bus. You almost always say “a planeload of …” It is informal-to-neutral, at home in headlines and talk; a shipping form would more likely give kilograms. Though actually writers sometimes use it for a large group that arrived by air, even if the plane was not packed to the last seat.