Eagle Aircraft Services Ltd, based at Leavesden, in the United Kingdom was the UK distributor for Beechcraft. It sold Beech aircraft and in some cases provided crew training for customers; it also operated transport flights on request. At the time of the accident in 1979, the company was negotiating a contract for the sale of a Beech 200 to the Angolan Diamond Company. It had been agreed that it would train three pilots of that company on the Beech 200. The pilots had already had ground instruction on this type of aircraft from Beechcraft in Wichita, and had reached the flight training stage. On 25 September, after a flight from Leavesden to Stansted, the instructor had filed an IFR flight plan for Stansted-Exeter, at FL 310, the planned departure from Stansted being at 14:00 hrs. Take-off from Stansted was at 13:03 hrs, and during the following 40 minutes the aircraft flew locally in the Stansted zone where it conducted two ILS approaches followed by an overshoot. At 13:45 hrs it was authorised to change from the Stansted frequency and contact the London Centre. The climb to FL 310 was normal. At 14:21 hrs the pilot asked ATC whether it would be possible to perform an emergency descent exercise before reaching Exeter, his intention being to begin the descent after passing Dawlish. The controller agreed and asked the pilot to call back when he was ready to begin the manoeuvre. At 14:35 hrs the Beech was almost over Dawlish and the crew announced they were ready to begin the exercise. They stated that they would keep a listening watch on the frequency during the descent, but would not be able to transmit while they were donning their masks. At 14:36 hrs, the flight was authorised to begin the descent, initially to FL 120. At 14:38 hrs the controller gave the Beech a right-hand turn heading for Exeter. At 14:39 hrs he repeated the heading. At 14:43 hrs, noting that the aircraft had commenced a turn to the left, he authorised it to turn left to head for Exeter. At 14:44 hrs he asked for the pilot to give an identifying ‘squawk’ on the transponder. He did not receive a reply to any of these communications. Since 14:38 hrs Beech G-BGHR had been describing large circles to the left at FL 310. The wind at that altitude made the aircraft drift towards the south, and it was to pass successively over Guernsey, Jersey, Dinard and Rennes. At the end of its endurance at 20:20 hrs the aircraft crashed near Nantes, 20 km to the east/south east of the town. An RAF Nimrod escorted the Beechcraft during its progress to the vicinity of Nantes. G-BGHR was also followed by two Dassault Mirage III and three Mirage F1 of the French Air Force from 18:10 hrs until 20:10 hrs. The pilots of these aircrafts checked the external condition of the Beech, which appeared normal, the doors and emergency exits were in their normal position, the cabin and cockpit were illuminated and the navigation lights were operating. However, they were unable to make any contact but they all noted the presence of warning lights on the control panel. PROBABLE CAUSES: “The immediate cause of the accident was the aircraft striking the ground at a steep angle. The cause of the accident was depressurization of the cabin at high altitude by the pilot. This exercise is too dangerous to be carried out on an aircraft in this class, in view of the useful consciousness time available to the pilots in the case of any failure of the oxygen circuit. In this particular case, the oxygen masks were not connected and the crew died in flight due to hypoxia.”