Complex sentence: These problems were coupled with even more formidable forms of competition, such as the rapid development of reliable propeller and jet airplane service in the 1950s which began to deprive the NYC of its long-distance passenger trade.
Split into simpler sentences: These problems were coupled with even more formidable forms of competition. The rapid development of reliable propeller and jet airplane service in the 1950s began to deprive the NYC of its long distance passenger trade.