This sentece is a "Direct Object Clause".
Replace "We have to check out soon if we are going to catch our plane" with one word, let's say "the timetable" and you will get " We have to check out soon the timetable".
The timetable is the Direct Object of the verb" To check out".
What do we have to check out? The timetable or, in the case of your sentence, If we are going to catch our plane.
You cannot use "on what condition do we have to check out soon?" it doesn't make sense.
So, your sentence is not a Conditional Sentence.
I have another example for you:
We asked him whether / if he had understood the instructions.
What did we ask him? Whether / if he had understood the instructions.
hope that helps!
Student or Learner