Aviation experts are investigating a Learjet crash in Florida's Palm Beach County. The accident killed nine people, including tech businessman Adam Robinson and his wife Helen Sharp. Their two children, Emma and Charlie, also died in the event. The victims included friends Charmi Fehr and Anita Maria Cetina, as well as a nanny named Rachael Reed. Pilot Jeffrey Gregory and copilot Nathalia Filgueiras were among the deceased. Investigators are reviewing air traffic radio recordings to understand the cause.