As many as four major private airports in the country will require an investment of Rs.27,000 crore to expand their existing capacity, which has reached near optimum level. The airports included New Delhi, Mumbai, Hyderabad, and Bengaluru, which are currently catering to nearly 55% of the country's total air traffic. These airports are operating at near-full capacity and will need to spend heavily on expansion through 2021, said the report by ratings firm Crisil. "Because of surging footfalls and high capacity utilisation of over 90%, we estimate the four airports would need huge investment for expansion," President, Crisil Ratings, Gurpreet Chhatwal said, adding that their credit quality will remain healthy because of business model strength backed by robust traffic growth and predictable cash flows under a regulated tariff framework. He further informed that air passenger traffic in the country grew 20% in the last fiscal which was a big leap over the sedate 9 per cent average seen since 2011. Bengaluru and Hyderabad airports have clocked even faster growth of over 24% and to add to this, rising private consumption and healthy economic growth would continue to provide tailwind to traffic growth across airports in the country.