This should work...
while(true)
{
while (planes.flying)
{
}
MessageBox("ALARM!");
MessageBox("Call the firemen, police and pray for the lives of everyone");
MessageBox("click OK when everything has been solved");
}
Come on! Give us some pointers... I guess this is homework (if not tell us the airport you are working in) and you should definitely tell us what you expect...
PS: we are not giving codes here, we help people solving specific problems...
Work a little bit more your question and probably you will get a better answer...