public string TakeOff(AerialVehicle a)
{
string ret;
a.StartEngine();
a.TakeOff();
if (a.IsFlying)
{
ret = $"{a.ToString()} took off successfully.";
Vehicles.Remove(a);
}
else
{
ret = $"{a.ToString()} could not take off.";
}
return(ret);
}
public string Land(AerialVehicle a)
{
a.CurrentAltitude = 0;
a.StopEngine();
a.IsFlying = false;
Vehicles.Add(a);
return($"{a.ToString()} has landed");
}