Delta Air Lines Inc. planes were involved in three wingtip collisions in separate accidents over two days on the ground at New York’s John F. Kennedy airport, injuring one man. The National Transportation Safety Board said Thursday that it is investigating the incidents, indicating that they may be more serious than usual or that there may be a pattern. Low-speed collisions sometimes occur between planes and other aircraft or vehicles on the tarmac and taxiways, and usually don’t cause significant damage or injuries. The first mishap occurred at 7:12 p.m. on Aug. 15, when a Boeing Co. 737 operated by Delta and an American Airlines Group Inc. Boeing 757 each were taxiing out for departure. The Delta plane’s left wing touched the American jet’s tail. No one was injured, according to the Federal Aviation Administration. “The flight returned to the gate and passengers deplaned normally,” Delta spokesman Michael Thomas said. “Customers were accommodated on an alternate aircraft, and we’re sorry for the inconvenience to those customers.” About 4:30 p.m. the next day, a JFK ground crew was directing a Delta Connection regional aircraft operated by Endeavor Air that had arrived from Chicago. As it taxied to the gate, its left wing touched the right wing of a parked Delta Connection plane that was operated by GoJet Airlines. “Each aircraft was returned to service following a maintenance evaluation,” Thomas said. “The safety of Delta’s customers and crew is always our top priority and the incident is being looked into.” An hour later, the left wingtip of a Delta MD-88 jet touched a flatbed truck as it was turning into a ramp area. While the FAA reported no injuries, Joseph Pentangelo, a spokesman for the Port Authority of New York & New Jersey, said the driver of the aircraft tug vehicle was treated at a hospital and released. Close Proximity JFK’s 1950s and ’60s-era layout, which predates the current mix of aircraft, encircles terminals with two tightly spaced taxiways. Their proximity sometimes makes it difficult for planes to enter and exit gates, and can put moving aircraft closer together than at other airports.  In 2011, the NTSB investigated a collision at JFK between an Air France double-decker Airbus SE A380 plane taxiing before takeoff and a Comair Inc. regional jet that was arriving at a gate. A video showed the smaller plane being spun around after the A380 struck its tail. None of the 576 people on the aircraft was injured, according to NTSB.