Van Nuys-based Sun Quest Executive Air Charter has suspended flying its Cessna Citation jets in the wake of a crash that killed the company’s founder last week. Frank Kratzer and Fernando “Chris” Fernandez were killed after the twin-engine Citation they were in crashed shortly after takeoff Friday morning into a field a half-mile north of Van Nuys Airport. Kratzer and Fernandez were on their way to Long Beach to pick up passengers and before continuing to Arizona. Shortly after takeoff, Kratzer and Fernandez radioed the control tower of an emergency and said they needed to return and banked right before the plane plummeted to the ground and exploded into flames. The National Transportation Safety Board is investigating the cause of the crash. Kratzer, 72, a former airline pilot, founded Sun Quest in 1992 and operated a flight school at Whiteman Airport in Pacoima. Kratzer was heavily involved with the day-to-day operations of the charter company as its director of operations, trained many of its new pilots and taught at the flight school, said David Burke, a spokesman for Sun Quest. The company will not use its remaining Citation jet while the NTSB investigation is ongoing, Burke said. The Citation has a good safety history in terms of but no one is sure just what happened with the jet when Kratzer and Fernandez were aboard, Burke said. “Until it comes back and is cleared they are not going to risk chartering anyone,” Burke said.