The Bermuda Triangle is a patch of ocean between Miami, San Juan Puerto Rico and namesake Bermuda where many planes and ships have crashed, sunk or otherwise disappeared. In GTA, this phenomena is not bound to any particular region, instead being a general term for the failure of vehicles and death of protagonists when venturing into the ocean.
Vice City
Rumors of a Bermuda Triangle type anomaly first began in Vice City when several players alleged that they had lost control of their boats and aircraft and crashed into the sea after flying far out into the ocean. With Vice City being based on real life Miami, one of the three vertices that makes up the Bermuda Triangle, players were quick to investigate if the infamous zone was represented in the new release. Initial reports go back as far as 2003 on online forums, with several players claiming to have experienced the phenomena.[1] The city is frequently hit by hurricanes and thunderstorms, most notably with Hurricane Hermione being responsible for the city's bridge closure at the beginning of the game. Some have suggested that the presence of Green Clouds, Ghost Ships, and Sunken Ships may be related to the Bermuda Triangle phenomena.
While several incidents have been reported over the years, there is no compelling evidence of any kind of Bermuda Triangle in Vice City and it is thought that aircraft failures may be the result of reaching the world's Invisible Barriers, which cause the loss of control of aircraft resulting in crashes into the ocean. However, this does not explain reports of water craft failures.
San Andreas
San Andreas saw further reports of strange oceanic phenomena. Many allege that flying an aircraft far out into the ocean will result in losing control of the craft, causing it to crash into the water. No compelling evidence has ever been produced of this phenomena and, being a relatively easy claim to debunk in practice, are regarded as false claims.
Interestingly, some proclaimed that venturing into the deep sea can result in teleportation. These claims were quickly proven when the Ocean Portal was discovered to be capable of teleporting CJ in unique circumstances. The ocean floor of the deep sea happens to lack collision, meaning it is possible for sunken aircraft to completely fall through. While on the surface this appears as unexplainable phenomena, this is merely an intended game mechanic that is designed prevent the player from getting stuck in places outside the game world that they cannot escape from. It is likely that the developers never expected many people to venture into the vastness of the deep sea and become a victim of the lack of collision on the sea floor, and it wouldn't have been an efficient use of their time to fix the issue.
GTA IV
A user named Bermuda Triangle from Vice City comments on the forums at liesdamnlies.net on Liberty City's internet. This may be a subtle acknowledgement by the developers of the obsession with the Bermuda Triangle myth in Vice City. However this could also just be a coincidence and is more likely to be a general stab at conspiracy theorists in general.
GTA V
In GTA V and GTA Online, a mechanic was introduced to limit exploring player's within the game world. Flying too far from the state of San Andreas will cause a aircraft's engines to fail before the entire craft is forced to crash into the ocean. Other events can include the planes engines exploding or one of the plane's wings being sheared from the aircraft. In addition, if the player tries to use a parachute after abandoning their aircraft, it will immediately disappear and the player will continue to fall towards the ocean and die upon impact with the water. If the player manages to survive their aircraft crashing, or them hitting the water, they will more then likely be attacked by a shark not long afterwards.
This event is a predictable occurrence when venturing into the deep sea and is clearly an intended game mechanic to prevent players from straying too far where game breaking issues may arise.