I heard that an Austrian airliner dumped some of its fuel over Lake Ontario

I heard that an Austrian airliner dumped some of its fuel over Lake Ontario when a malfunction forced it to return to Pearson. How often does this happen, and should I stick to bottled water?—Mark Mietkiewicz, Thornhill

When an airliner gets into trouble—mechanical problems, passenger illness—near Pearson, air traffic controllers route it toward less busy airspace, so its crew can get a handle on the issue without bumping into other planes. This can mean pointing the aircraft toward farmland north of town or, as with the Austrian airliner last December, flying it over the lake before coming back for a landing. But landing puts a lot of pressure on a plane, so ideally a fully fuelled jetliner sheds some tonnage before touching down. A Boeing 747 that takes off at its maximum weight with a full tank of fuel should drop 102,500 kilos before hitting the tarmac. Usually, that fuel gets burned en route. When a plane with enough gas to get to Vienna does a U-turn over Pickering, something has to go. On the upside, fuel dumping doesn’t happen very often. In 2005, there were only 18 instances across Ontario out of 200,000 takeoffs at Pearson. And the fuel doesn’t splash into the lake; it vaporizes on the way down, joining every other pollutant we pump into the air. So no need to buy bottled water, but gas masks, as always, are at your discretion.