title: NSMutableArray keeps multiplying/resetting
body: <p>So I am making a simple app in Objective-C with a single tableview that will display airports and their associated airport codes, as well as allow the user to add new airports.</p>
  
  <p>I have created a class of known airports and their codes in an NSArray to set the initial tableview data with the known airports. In viewDidLoad, I set a local NSMutableArray equal to the known airports array</p>
  
  <pre><code>- (void)viewDidLoad {
      [super viewDidLoad];
  
      self.allAirports = [[GGAirportData knownAirports] mutableCopy];
  
  }
  </code></pre>
  
  <p>In a separate ViewController, an airport and its data can be added to this array through delegate methods, but as you can probably guess, every time the app boots up, having this code in viewDidLoad not only resets my NSMutableArray *allAirports to only the *knownAirports array, but once I implement NSUserDefaults to retain the added airports, it doubles the amount of airports in the original self.allAirports array....so the third airport I add, it triples it and so on....</p>
  
  <p>So my question is, how can I bring the knownAirports data into this application without it multiplying every time? Where else can I declare and set these values other than viewDidLoad where it will only evaluate one time and never look back at the knownAirports array ever again? I have been on this bug for 3 days now and have tried every workaround I can think of. Thanks in advance</p>