A small plane crash-landed in a grassy field just off a runway on Martha’s Vineyard on Sunday after the pilot suffered a medical emergency onboard, authorities said. The Massachusetts State Police said in a statement that the 79-year-old pilot “suffered a medical emergency” on his final approach into Martha’s Vineyard Airport, and that a female passenger was forced to take over the controls. Police did not go into details of the medical episode. With the controls, the passenger landed the single-engine 2006 Piper Meridian on its belly without deploying the landing gear; a landing hard enough that it snapped the aircraft’s left wing, according to the West Tisbury Police Department. Both the pilot and the passenger, the only people aboard the flight, were transported to a nearby hospital. The passenger sustained no major injuries, according to authorities, but the pilot was then taken by medical helicopter to a Boston hospital, where he was listed as being in serious condition. An investigation into the incident is being led by the National Transportation Safety Board, with the Federal Aviation Administration and the state police assisting.