Sentence:  It was only because of concerns about how to maintain viability as a regional airline in a <WSD>megacarrier</WSD> environment that both Western's management and its employees responded positively to overtures by Delta, resulting in Western becoming a significant part of Delta's entry into the <WSD>megacarrier</WSD> class. 
Meaning of the word marked with <WSD> tags:  A very large certified airline.