The pilot had arrived at the strip the previous day to continue learning to fly the gyrocopter. He flew one circuit during which the craft was observed to porpoise a number of times. After landing, the pilot complained to his adviser that there was something wrong with the aircraft. The adviser then flew the craft and reported that it behaved perfectly. He counselled the pilot that he was overcontrolling in the pitching plane and suggested flying low runs along the strip as practice to overcome the problem. The pilot did this a number of times and showed good pitch control. On the morning of the accident, the pilot flew some further strip runs, again showing good control. He then began flying circuits at about 50 feet above ground level. On the third circuit, as the gyrocopter was turning base with about thirty degrees bank applied, the following sequence occurred in rapid succession - nose pitch-up 15`, nose pitch-down 20`, nose pitch-up 40`, nose pitch-down 50`. The gyrocopter remained in this latter attitude until ground impact. Although the pilot had owned the gyrocopter for some six months, he had flown it only once previously. This was some six weeks before the accident when other instances of pitch control difficulties occurred. There was no evidence of any fault with the gyrocopter. The engine sounded normal up to the time of impact and the shattered propeller blade was evidence of the engine being under power at impact. The gently undulating terrain over which the craft was seen to fly might have given the pilot the illusion that he was descending as he flew the base turn. The porpoising of the gyrocopter as described by witnesses was indicative of the pilot overcontrolling in the pitching plane. When the craft pitched nose down the second time, the airflow through the rotor disk would have been reversed from the normal upwards flow to a downwards flow. Once this condition arises, recovery to normal flight is impossible. It was noted during the investigation that there was no part of the gyrocopter in the pilot's normal forward field of view which could assist him in judging the in-flight attitude of the craft. Such information is particularly important for control in the pitching plane, especially during the learning phase.