6. Discussion and contributions
Though punctuality is considered a core airline service, this factor does not strongly influence customer loyalty. Punctuality is a minimum required condition; therefore, it is true that consumers' evaluation of customer loyalty is decreased if an airplane has delays. Nevertheless, consumers' evaluation of customer loyalty might not increase drastically if service related to punctuality improves. The reason for this is that, as described in 3.2, there is no difference in punctuality between economy class and premium class, so customers do not select premium class out of high expectations relating to this factor. Because this is not expected service, even when customers perceive that the level of this service is sufficient, they might not evaluate it