http://wikipg.com/images/context/files/matalebe%20elmi/%D8%B5%D9%86%D8%A7%DB%8C%D8%B9%20%D9%88%20%D9%85%D8%AF%DB%8C%D8%B1%DB%8C%D8%AA/%D9%85%D9%82%D8%A7%D9%84%D9%87/Customer%20satisfaction%20using%20low%20cost%20carriers.pdf

http://www.jstor.org/discover/10.2307/20053994?uid=3738328&uid=2&uid=4&sid=21101921390383

http://onlinelibrary.wiley.com/doi/10.1111/j.1468-0106.2010.00537.x/full