SEATTLE — The federal agency investigating the September seaplane crash off Whidbey Island said Monday that its experts have identified a potential cause of the deadly accident and called for similar planes to be grounded until they are inspected. “We’re concerned that another plane could crash as a result of something similar,” said Jennifer Homendy, chair of the National Transportation Safety Board, the agency investigating the Sept. 4 crash that killed 10 people. “Right now, the focus has to be (on) what could contribute to a further tragedy in the future.” However, the NTSB cannot order th…