The phrase "certain airlines" refers to specific airlines or a particular group of airlines that meet a particular characteristic or condition. Full definition
American AAdvantage reserves the right to limit holds on certain special awards and awards with certain airline partners. (travelcodex.com)
However, many people have been able to get credit for various small purchases (generally under $ 100) on certain airlines including gift certificates and the like. (youvebeenowned.org)
I think this is really important for certain airlines, such as American. (uponarriving.com)