United Airlines temporarily grounded all of its mainline flights Wednesday evening due to a technical issue, the airline said. Mainline flights are operated directly by United, using its own aircraft and crew. These typically include Boeing 737, 757, 767, 777, and 787 jets, as well as Airbus A319 and A320 models. "Due to a technology issue, we are holding United mainline flights at their departure airports," a spokesperson told FOX Business. "We expect additional flight delays this evening as we work through this issue. Safety is our top priority, and we'll work with our customers to get them to their destinations."