What Does It Mean to be "Number One"?

Advertising for Ryanair claiming that the airline was "Europe's number one airline" was recently challenged at the UK's Advertising Standards Authority.  

The ASA determined that consumers were likely to understand that the claim meant that "over a reasonable period before the ads were produced Ryanair had carried more passengers than any other European airline."   Ryanair had based its claim on the International Air Transport Association's ("IATA") World Air Transport Statistics 2017 report for air travel in 2016.  The ASA said that it was reasonable for Ryanair to rely on this data, since it was the most recent data released by the IATA.

The ASA was also not persuaded that the claim was misleading because of the fact that some complainants said that Ryanair had cancelled many of their flights in September and October in 2017.  Even with those cancellations, the ASA found that Ryanair had carried the most passengers.