The Falcon 20 corporate jet departed Helsinki, Finland at 13:28 hours local time on a flight to Tallinn, Estonia. The take-off was normal without any remarks. After the landing gear retraction the green light indicating that the right main gear was in extended position remained lit. The captain reduced speed and made an extension and then a retraction manoeuvre of the landing gear using the normal procedure but the green indicator remained lit. The captain made the decision to continue the flight at reduced speed. During approach to land the landing gear was extended by means of normal procedure. After extension all the three green light indicators for gear down and locked were on and there was no audio warning. All looked normally. The captain decided to land. Touch down took place 50 m beyond the runway 09 threshold and 1 m right of the centre line with a load factor of 2.2 g and with an insignificant start of touch-down on the left main gear. When beginning to brake the crew felt the aircraft starting to list to the right. The captain used ailerons and wheel brakes to hold the aircraft on the runway as far as possible until most speed was lost. Thereafter the aircraft came down smoothly on its right wing-tip while continuing to move turning to the right. At the end of the landing run the aircraft left the runway and stopped about 8 m outside the runway edge. There was no fire. All people on board were evacuated without outside help. No one was injured. CONCLUSIONS The accident was caused by a combination of the following factors: 1) The jamming of the micro switch drive A-23802-102 caused by the corrosion damage to the drive’s mechanism which, in turn, led to the premature disconnection of the hydraulic fluid supply to the power unit A-23722-0. Consequently the right main gear failed to lock in its extended position. 2) The failure of the crew to act in accordance with paragraph 3.10.22 (Procedure A) of the DA-20 aircraft operations instructions as required by the circumstances. 3) The manufacturer’s Service Bulletin 676 regarding modernisation of electrical circuits in the landing gear system was not done because it was only recommendation.