The Beechcraft 200 Super King Air aircraft suffered a runway excursion after landing with a tailwind at Union Island Airport (UNI), Saint Vincent and the Grenadines. The intended destination of the flight was Canouan (TVSC) in the Grenadine Islands but the pilot landed instead at Union Island (TVSU), some eight miles to the south of Canouan Island. In his report, the pilot stated that the ADF (Automatic Direction Finder) on board the aircraft was unserviceable and that they were navigating using the GPS and visual reference. On seeing Union Island, he assumed that it was Canouan and did not confirm this with the GPS distance. On seeing the high terrain to the west of the airport in Union Island the pilot decided to land from the east; hence his request to the Canouan ATC (STSC) to land on Runway 31. It was not until the aircraft was on short final approach that the pilots observed that the runway was 26 (the runway heading in Union Island (TVSU)) and not Runway 31 (the runway heading in Canouan TVSC)). The captain stated in his report that at this point, he did not believe that it was possible to execute a go-around due to the hills in his flight path. As a result of landing on the reduced runway length available at Union Island (TVSU), in addition to the tailwind component of approximately 10 kts, the aircraft was unable to stop and having veered off to the left, came to rest on the southern side of the end of Runway 26 striking the perimeter fence. CONCLUSIONS: Although the incorrect call sign (YV-192T instead of YV-196T) was consistently used by all of the Air Traffic Controllers, it does not appear to have contributed to the aircraft landing at the incorrect airport. The captain of the aircraft was not fluent in English and did not have an endorsement for English Language Proficiency on his licence. The Co-pilot had a level 4 endorsement. This lack of English Language Proficiency by the crew, particularly by the captain was, in the opinion of the investigators, a significant contributing factor in the aircraft landing at the wrong destination and therefore a major contributor to the accident. The Air Traffic Controller at Canouan (TVSC) issued landing clearance to the aircraft in spite of the fact that he did not observe the aircraft on when the pilot reported on final approach. The controller, in his report, stated that he found it strange that the pilot was requesting Runway 31 although the wind was favouring Runway 13. This coupled with the poor English Language Proficiency of the pilot should have caused him to be more vigilant prior to issuing landing clearance. The captain stated in his report that he did not observe the numbers on Runway 26 in Union Island until he was on short final. At that point, he decided that it was possible to execute a go- around due to the high terrain to the west of the runway and landed. The investigation revealed that the aircraft’s performance was such that it could have executed a go-around up to the point of the threshold of Runway 26 in Union Island, by executing a turn to the south.