UA 901 is not always UAL901
Aviation runs on two numbering systems. A ticket carries the airline’s two-character sales code and a number, say UA 901. In its flight plan and its transponder the aircraft goes by a callsign built on a three-letter code, for United UAL901. That one lines up.
But a large part of Europe flies under callsigns that have nothing to do with the ticket: Ryanair as RYR10AM, easyJet as EZY16NE. It is deliberate. When two aircraft with similar-sounding numbers are on the same frequency, a pilot can answer an instruction meant for the other one, so busy airlines give their flights letter-and-number callsigns that sound nothing alike.
And one flight is often sold under several numbers. On the departure board in Doha, about seven in ten flights also carry the number of another airline. In the United States, a ticket with a big airline’s code is often flown by a regional company under its own callsign: United’s UA 5327 flies as GJS4475.
In North America and East Asia a straight conversion of the number works for the vast majority of flights. In Europe it fails more often than it works.
What the departure boards know
The link between the two numbers is held by airports. Swedish airports even print the callsign on their boards. Elsewhere we pair a board row with the flight we actually saw leave that airport for that destination at that time, and only when there is no doubt. Against the Swedish boards, which give the answer away, this matched correctly in 99.89 percent of rows.
Even the clocks don’t agree. A board shows when the aircraft pushed back from the gate, our network sees when its wheels left the runway. At big hubs like Chicago, Dubai or Hong Kong the typical gap is over twenty minutes of taxiing and queuing, and the pairing has to allow for that.
From the pairs that repeat day after day the search learns the airline’s regular service. But a learned pair goes out only if a flight confirmed it today. A pair nobody has seen fly today turned out to be wrong in one case in three, because airlines reshuffle callsigns. Confirmed by today’s flight, it was wrong in nine cases out of ten thousand.
When we’re not sure, you choose
Where we are not sure of a pairing, we show the options and let you decide. When two sources link the same number to two different callsigns, we don’t pick the likelier one. A conflict means we show you nothing as fact.
On the flight page the ticket number sits next to the callsign, and a small ‘i’ says where the link comes from: a board that confirmed this very flight today, or a regular service that only usually flies at this time. Codeshare numbers are marked as such.
Prague–Split, and the grammar of Prague
Search also learned from people around us. Someone typed ‘praha - split’ and got an empty page. Today the site understands city names in thirteen languages, including Czech declension, and shows the connection between two places across all airlines, with history and local time at both ends.
The share of the world’s flights you can find by the ticket number rose from 68 to 72 percent with the change of 26 September alone. In Europe it went from under a fifth to almost a third, in the Middle East from 59 to 72 percent. North America was at 94.
In Europe a straight conversion of the ticket number works for under a third of flights. You still find your flight.