That flight number on your boarding pass isn't just a random assortment of letters and numbers: it's a code.
Just what that code reveals, however, depends on the airline you're flying with.
The letter component is pretty straightforward: flight numbers usually begin with the two-letter code assigned to the airline by the International Air Transport Association. So that's "NZ" for Air New Zealand, "QF" for Qantas", "JQ" for Jetstar and "EK" for Emirates.
Figuring out what the numbers mean is far trickier. While airlines have different systems for assigning flight numbers, no airline can use more than four numbers.
Patrick Smith, the former pilot author of Cockpit Confidential, told Mental Floss, that flights heading east and north are typically assigned even numbers, while west- and south-bound flights are odd numbered (although there are exceptions). Return flights between destinations are often a number apart. So, if you're on flight NZ6 from Auckland to Los Angeles (northeast-bound), you're likely to be on NZ5 on the way back (southwest-bound).
Often, the lower numbered flights are the most important - or biggest money spinners - for the airline. One or two-digit numbers typically indicate popular-long distance routes. The lowest Air New Zealand flight number, NZ1, is for the London to Auckland route via Los Angeles.
However, some airlines use different systems.
All Jetstar flights in New Zealand, for example, have three numbers. International flights begin with one, domestic jet flights with two and regional flights with three, a spokesman for the airline explained.
Jetstar's "city pair" flights tend to be in sequential order - flight JQ286 from Christchurch to Wellington is followed by flight JQ287 from Wellington to Christchurch.
Qantas assigns odd numbers to outbound international flights and even numbers to inbound flights to Australia. Flights numbered between one and 399 are international flights, while those numbered 400 or more are domestic services. It's not all systematic though - the airline tries to include an eight in routes to Hong Kong as it is considered a lucky number there.
Some airlines deliberately avoid numbers with negative connotations. Qantas, for one, does not have a QF13 or QF666.
Flight numbers often remain in place for many years, even as departure times and aircraft change. It there is a high-profile incident, however, the number will usually be scrapped. American Airlines operated flight AA11 between Boston and Los Angeles for decades, for example, until the September 11, 2001 attacks. In 2014, Brazilian airline TAM took preventative measures, changing one of its flight numbers after a renowned clairvoyant predicted a plane bearing the original number would crash.
Asked how Air New Zealand assigns its flight numbers, a spokesperson said "we have nothing of particular interest to share".
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Written by Lorna Thornber. Republished with permission by Stuff.co.nz.