You have two different structures there: When NOUN X, then NOUN Y. (X and Y represent verbs) X must be subjunctive. Cuando el avión llegue(X), todos estarán(Y) felices Then the plane comes, everybody will be happy. Cuando tengas(X) tiempo, podrás venir(Y) a visitarme. When you have time, you will be able to come visit me. But in the structure: When NOUN X that NOUN Y, then NOUN Z. (X, Y and Z represent verbs). X must be in subjunctive, but Y cannot be subjunctive. In your sentence: Cuando vean(X) que no llega(Y) el avión, se irá(Z) cada uno a sus asuntos. X is in subjunctive Y is conjugated in third person (the plane is "él" in Spanish) Z is conjugated in future tense. Cuando mi tío vea(X) que tengo(Y) frío, me pasará(Z) su chaqueta. When my uncle see that I am cold, he will give me his jacket. Cuando él sepa(X) que haces(Y) tu trabajo, confiará(Z) en ti. When he knows that you do your job, he will trust you. I hope this helps. (I had to repeat the answer because the letters did not show up in the right position).

You have two different structures there: When NOUN X, then NOUN Y. (X and Y represent verbs) X must be subjunctive. Cuando el avión llegue, todos estarán felices Then the plane comes, everybody will be happy. Cuando tengas tiempo, podrás venir a visitarme. When you have time, you will be able to come visit me. But in the structure: When NOUN X that NOUN Y, then NOUN Z. (X, Y and Z represent verbs). X must be in subjunctive, but Y cannot be subjunctive. In your sentence: Cuando vean que no llega el avión, se irá cada uno a sus asuntos. X Y Z X is in subjunctive Y is conjugated in third person (the plane is "él" in Spanish) Z is conjugated in future tense. Cuando mi tío vea que tengo frío, me pasará su chaqueta. X Y Z When my uncle see that I am cold, he will give me his jacket. Cuando él sepa que haces tu trabajo, confiará en ti. X Y Z When he knows that you do your job, he will trust you. I hope this helps.

If you use llegue it´s correct too. Cuando vean que no llegue el avión a la hora indicada se irá cada uno a sus asuntos.

i think the avion no llega is a fact. equal a ver algo.