Around the state, airplanes can be regularly seen crashing into tall objects. These airplanes seem to be oblivious to their surroundings, and may crash head-on into objects, even though there may be enough time for them to maneuver out of the way. Other times, the airplanes may crash head-on into the ground near the player, often resulting in death of the player or destruction of their vehicle.
The strange thing about these crashes is, that upon inspection of the wrecked airplanes, there does not seem to be any pilot. It is noted that the airplane has no pilot, even when it is in mid flight. This can be proven by looking into the handling files of the game. All of the aircraft are set to spawn without a pilot. Developers did this due to game's limitations, because spawning a pilot could take more memory.
The airplanes crashing into objects can be explained by their artificial intelligence. Airplanes are programmed to fly above the player in a straight line, regardless of whether or not there are any tall objects in their path. When the planes spawn, they end up crashing head-on into these objects, because they are not programmed to avoid them. This random factor may be annoying to some players.
The airplanes that crash are:
Only these airplanes crash, because they are the only ones that are programmed to spawn flying. Even though the AT-400 and the Andromada also spawn flying, these airplanes fly at a much higher altitude, therefore it is nearly impossible for them to crash into anything in the game.
Plane crashes occur wherever there are very tall objects. There are frequent crashes on Mount Chiliad, or around the large rock formations in El Castillo del Diablo and Arco del Oeste. Airplanes also commonly crash into The Big Ear. There are also frequent crashes into the skyscrapers in downtown Los Santos and San Fierro.
The only other games that include NPC airplanes that fly through the sky, are GTA III, GTA Vice City, and Grand Theft Auto V. However, in GTA III and GTA Vice City, the only airplane to be seen flying is the DeadDodo, an unsolid and unobtainable variant of the Dodo airplane. This one, however, follows a predetermined path around the city, and as such, it never comes close to hitting any structures. The player cannot interact with it in any way in both games. It can be seen pulling the Zombie Elvis Found! banner behind it in both games.
In the enhanced versions (Xbox One, PlayStation 4 and PC) of GTA V, due to the addition of Jets flying in the skies of San Andreas, jets may randomly be heard (and seen, albeit aftermath only) exploding. This usually occurs when either loading the game, switching character, or starting a mission. Note that it only occurs in Rockford Hills, presumably because of the high land mass and high rise buildings, such as Weazel Plaza and Richards Majestic. It is possibly a coding error that incorrectly scripts the planes to spawn at a lower point of their Y axis, resulting in them crashing into buildings.
In GTA V, solid NPC-controlled airplanes return. However, their AI is much more intelligent, and airplanes always follow a predetermined path when flying. If the player disrupts their path in any way, however, the airplanes may simply re-adjust their flight path and continue flying like normal.
In GTA V, the planes crash very rarely. They are often found near Michael's house, usually because of the odd height of both the area, and the house, making the plane think it is safe to fly very low, yet this is only a theory.