This is taken from: Invalid Link Removed
But there are plenty of comments I have heard both ways. As it is quite a major flight (24 hours) would rather not chance it on the wrong info. ?
Air Travel
String Tension: You may be advised by airline personnel to be sure to detune your bass before air travel. Do not take this advice, leave your bass in tune. Your bass was designed to handle string tension at all times. Guitar manufacturers ship their guitars fully tuned to music stores and they arrive just fine.
Airline companies fly airplanes, they don't build guitars. If an airline worker at the airport asks you if you've already detuned your guitar, just say yes to avoid the ridiculous lecture. If you intend to do any air travel with your bass, be sure to buy it a flight case. The chances of carrying your bass onboard an airplane are extremely small unless you have purchased an extra seat for it. Even if you were allowed to take it onboard as personal luggage one time, you might not be able to take it onboard the next time, even if it is the same airline. The case for air travel should be an ATA approved fight case. Baggage handlers are moving baggage in and out of planes quickly, so they are unlikely to always be gentle with your case. The right case will hold up to rough handling and other cargo that it rides with.