NavBar not showing up in second and third viewcontroller

Question

I am trying to add Navigation bar to my tabbar view controllers.But, it is showing up in firstViewController but not in the other two views. Any reason why this is not working?

self.firstVC = [[FirstViewController alloc] initWithNibName:@"FirstViewController" bundle:nil fileName:@"firstPlist"];
self.firstVC.tabBarItem.image = [UIImage imageNamed:@"first"];
self.firstNavBarController = [[UINavigationController alloc] initWithRootViewController:self.firstVC];

self.secondVC = [[FirstViewController alloc] initWithNibName:@"SecondViewController" bundle:nil fileName:@"secondPlist"];
self.secondVC.tabBarItem.image = [UIImage imageNamed:@"second"];
self.secondNavBarController = [[UINavigationController alloc] initWithRootViewController:self.secondVC];


self.thirdVC = [[ThirdViewController alloc] initWithNibName:@"thirdView" bundle:nil fileName:@"thirdPlist"];
self.thirdVC.tabBarItem.image = [UIImage imageNamed:@"third"];
self.thirdNavBarController = [[UINavigationController alloc] initWithRootViewController:self.thirdVC];