Air India is close to placing landmark orders for as many as 500 jetliners worth tens of billions of dollars from both Airbus and Boeing as it carves out an ambitious renaissance under the Tata Group conglomerate, industry sources said on Sunday.The orders include as many as 400 narrow-body jets and 100 or more wide-bodies, including dozens of Airbus A350s and Boeing 787s and 777s, they said, speaking on condition of anonymity as finishing touches are placed on the mammoth deal in coming days.