You need 2 queues, and a random time delay, etc.
This assignment is a bit vague. Either you will have to assume (make-up your own) details, or they will be provided as the next part of the assignment.
Flight frequency (i.e average time between flights)?
Is there any takeoff schedule?
How long do planes remain on the ground?
I'd suggest that you start-out by writing the program without the randomness, and without worrying about the "busy runway" issue... just get the queue-sequencing working first... Into the first queue... out of the first... into the second... out of the second.
When you get that working, add the "busy runway" delay, then some randomness.
Simulation implies randomness within some paramaters/limits or known probability. A simulation generally runs automatically... like a game that plays itself. :)
OK. You need 2 queues. A landing queue, and a takeoff queue.
The planes should probably be identified as a number or letter sequence (1, 2, 3, or A, B C). That way, its easy to demonstrate that plane A is the first to enter the landing queue, and the first to take-off, etc.
You may need a "runway clear" or a "runway busy" status variable.
1- As planes arrive, they enter the landing queue at random intervals. They can enter the queue at eny time, even during takeoff and landing.
2- As planes land, they exit the landing-queue. They can only land if if no other planes are landing or taking off. (time delay?)
The runway becomes busy during a landing. No other planes can land or takeoff.
3- Planes enter the takeoff queue after landing. (After a time-on-ground delay?)
4- As planes takeoff, they exit the takeoff queue They can only takeoff if no other planes are landing or taking off.
The runway becomes busy during a takeoff. No other planes can land or takeoff.