Background
Loganair Flight LC423 was a scheduled passenger flight from Glasgow Airport (GLA) to Islay/Port Ellen (ILY). The handling pilot, occupying the first pilot's position, had recently converted to the DHC-6 Twin Otter and was completing supervised route flights required by the airline before award of full command status. A company supervisory captain, the designated commander for this flight, occupied the co-pilot's position.
Flight Sequence
The aircraft's engines were started at 14:38, and at 14:44 Glasgow Airport ATC approved taxi clearance to the holding point of runway 28. The aircraft was operating on a stored Instrument Flight Rules (IFR) flight plan. The requested route was a Standard Instrument Departure (SID) to join Airway Blue 2 for the Skipness VOR beacon, then direct to the Islay/Port Ellen NDB. At 14:46 Glasgow ATC advised LC423 of their flight clearance, cancelling the SID and clearing the aircraft direct to Skipness at cruising level FL55. Takeoff from runway 28 occurred at 14:48. The aircraft reported overhead the Skipness VOR at 15:08. Scottish Airways Control then informed LC423 to clear controlled airspace, contact Port Ellen, and that there was no known traffic to affect their descent.
After passing overhead Skipness VOR, the aircraft did not depart on the 272° magnetic radial but instead turned 15° left and descended on the 257° radial towards the south of Islay. At 15:10, having already begun descent, LC423 contacted Islay/Port Ellen, reported an arrival time of 15:23, and requested weather details. The radio operator reported surface wind 220°/05 knots, visibility 2000 metres in drizzle, cloud 3 oktas at 400 feet, 5 oktas at 700 feet, and 8 oktas at 1400 feet, with sea level pressure 1018 millibars. LC423 acknowledged and was asked to advise when overhead the aerodrome at 3600 feet or when in visual contact. The aircraft continued descending on a track of about 260° magnetic towards the south of the island until it disappeared from radar cover at a height of 1400 feet, 12 nautical miles from Islay/Port Ellen on the 106° radial. From that position, a direct track was estimated towards the southern coast of Islay. The flight continued at very low level parallel to the south coast.
At 15:21, the Islay/Port Ellen radio operator transmitted further weather information recording similar cloud conditions but with heavy drizzle, and changes in barometric pressure. LC423 acknowledged and reported "over Port Ellen," but the aircraft was actually turning inland at very low level over Laphroaig.
Accident
From overhead Laphroaig, the aircraft settled onto a northwesterly heading and very shortly afterwards crashed into rising ground, obscured in hill fog, approximately 1 nautical mile from the coast at a height of 360 feet amsl.