Aviation experts confirm grandfather rights provisions for incumbent carriers stifle competition in the US aviation market by allowing historical slot holders to entrench their market position, making it difficult for new entrants to secure access. This mechanism limits market competition, which is critical for driving innovation, keeping fares lower, and ensuring a diverse airline industry. With four carriers controlling roughly 80% of domestic seat capacity, the provision prevents new entrants from effectively challenging the dominance of the top four. The specific articulation by experts that grandfather rights are the primary mechanism limiting competition links historical slot access directly to current market stagnation, directly impacting US airline policy, fare levels, and the ability of new airlines to enter the market.