On September 28, 2019, about 1035 eastern daylight time, a Robinson R44 helicopter, N21EH, was substantially damaged when it impacted the ground while taxiing at Sanford Seacoast Regional Airport (SFM), Sanford, Maine. The pilot sustained serious injuries. The solo instructional flight was conducted under Title 14 Code of Federal Regulations Part 91. Day, visual meteorological conditions prevailed, and no flight plan was filed. The flight originated at Laconia Municipal Airport (LCI), Laconia, New Hampshire about 1000. A witness reported that the helicopter was taxiing about 15 ft above a taxiway when it began to spin at a high rate of speed. The helicopter then went vertical and crashed nose first in the grass, adjacent to the paved surface. Another witness observed the helicopter enter a spin to the left, then to the right before going vertical into the ground. A third witness reported that the weather was "clear but windy." The witnesses were met by first responders and assisted the pilot at the scene. An inspector with the Federal Aviation Administration responded to the accident site and examined the wreckage. Substantial damage was noted on the main rotor blades, tail rotor assembly, and fuselage. There was no fire. The inspector reported that the pilot was completing a three-leg cross-country flight when the accident occurred. He was receiving instruction on the R44 and was not rated in helicopters. The pilot was asked on two occasions during his recovery about the circumstances of the accident; he had no recollection of the event. The wreckage was recovered to a storage facility for further examination. The nose of the helicopter was crushed in a manner consistent with a nose-low impact with the ground. The tail boom was partially separated from the airframe. The engine was secured to the airframe. The main rotor system remained attached and the blades were impact-damaged along the length of both blades. Flight control continuity was established from the main and tail rotor assemblies to the cockpit. Both tail rotor blades remained attached to the tail rotor system. The engine received minor damage during the accident sequence and test run on the airframe. The engine started immediately and was operated for about 1 minute before it was shut down. No mechanical anomalies were noted that would have precluded normal operation of the airframe or engine. At 1056, the recorded wind at SFM was variable at 4 knots; however, witnesses reported that at the time of the accident, the wind had "picked up" and there were "gusts."