Which of the following is not an airport by its designator code?

The designator code that is not an airport among the provided options is linked to its specific usage in airport identification. MEX specifically refers to the Mexico City International Airport, which is a very well-known airport in Mexico. Therefore, it is indeed an airport designator code.

In contrast, the codes YYF (Penticton Airport in Canada), YYD (Smithers Regional Airport in Canada), and ZIH (Ixtapa-Zihuatanejo International Airport in Mexico) are all used to identify operational airports. The idea behind airport designator codes is to represent airports with unique identifiers that can be recognized universally in aviation contexts, and in this case, MEX is a valid code and represents an active airport, while the other options reflect other airport codes.

Therefore, the correct knowledge would lead to the understanding that MEX does identify an airport, while the assessment of YYF, YYD, and ZIH confirms they are also associated with operational airports. The distinction arises through familiarity with the codes, and MEX being the recognized international designation.