Travelers on a recent Air Canada flight from Chile to Montreal received an unwelcome surprise when airline staff enforced a rarely-mentioned TSA rule that applies even when you're not landing in the United States. The incident, shared on Reddit's r/travel forum, left experienced travelers confused and frustrated as they were forced to either check their bags or discard duty-free liquids and water bottles exceeding 100ml—all because the flight path crosses US airspace. The traveler who posted expressed disbelief: "I have never in my life heard this before. I've been flying into, out of, and over the US for decades and never has this ever come up." The rule stems from TSA regulations that technically apply to any flight traversing United States airspace, regardless of whether the aircraft lands on US soil. While this regulation has existed for years, enforcement has historically been inconsistent, leading many seasoned travelers to be unaware of its existence. Aviation security experts note that enforcement can vary significantly between airlines and even individual flights, influenced by security alerts, airline policies, and route changes. For travelers flying routes between Latin America and Canada, or any international route that might cross US airspace, the safest approach is to treat them as if flying directly to the United States: keep liquids to 100ml or less, and don't count on duty-free purchases making it through.