How can we avoid running out of airport abbreviations? As far as I know, airport name abbreviations are a 3 letter name. For example:


MEL for Melbourne/Australia airport
LAX for Los Angeles/USA airport
YYZ for Toronto/Canada airport


And that means all the options we have for naming are 26 * 26 * 26 = 17,576

Sometimes these match the IATA code, but not always. IATA codes are also 3-letter codes, but are not assigned to every airport as shown in this answer. But what about all of the other airports in the world? Will the world ever run out of "regular" airport codes? 

A simple Google search about the number of the airports worldwide shows there are 17,678 airports. So are they going to extend airport codes to 4 letters or use numbers 0,1,2,...9?

Even by starting to use numbers they may reach a point where they run out of options. What is the approach to fix that ?
Only major airports get all Letters.   Many of the smaller airports also incorporate numbers.

Here are some examples:

Osage City: 53K
Cle Elum: S93
De Vere: 2W1

And many, many, many more...
Once you add in letters and numbers, you'll find plenty of combinations.