Yes, it's correct.
When you want to express a conditional statement like (if someone does something), one way is to use the (-eba form: ～えば). In the sentence above, we have a conditional statement used in a negative sense. So if you want to express (if someone doesn't do something), you use the negative form of (-eba) which is (-nakereba), constructed by replacing い in ない with ければ.
The original verb is 乗る (to ride). First negate it --> 乗らない. Then ～ければ is added in place of い in ない --> 乗らなければ which literally means (If you don't get on) in this case.
The literal translation of the sentence (If you don't get on an airplane, then you won't be able to go to the trip.)