First, let’s determine if a collision between 2 airplanes is possible with all the high-tech equipment operating in the airplane and on the ground. Based on the flight’s direction, planes have specific altitudes to follow. If your direction is east, the altitude is an odd thousand and if you are flying to the west, it is an even thousand.
If you are flying over the ocean, the designated altitude is 2,000 feet separations. Therefore, if 2 planes are intercepted to be on the same altitude, one of the pilots must be on the wrong altitude. It may be possible that one of the 2 pilots has set the wrong altimeter pressure.
If we take the case of an American plane and a Russian plane, there may be a collision because perhaps the Russian plane makes use of Metric gauges and possibly had a conversion error or it could be that one plane was on top of the other which was flying in a sloppy manner.
Another point is that the warning devices on board may be so sensitive to interact with each other. This means that when the 2 planes are close to each other, the warning devices automatically shuts off due to the strength of their devices that overpower each other based on their sensitivity.
It could be that the planes were several miles with each other and heading on the same path. However, the sensors are not that smart to know exactly which direction is the other plane heading to. All they can tell you is that there is a plane coming as shown by bubbles of air in all directions thus, giving a warning signal to the pilot.
When 2 planes are so close with each other, the pilot has the responsibility to avoid collision. But there are times when the problem also lies on the ground controllers. If the air traffic controllers on the ground give a wrong signal due to poor visibility, collision may occur.
Airplanes follow a preset route that many aircrafts do. Since these aircrafts travel in the same spots, the air traffic controllers make sure that they pass along the route at different times. If the system is not perfectly done, an increased possibility of collision will arise. At 33,000 above the ground, collisions are very rare.
Collisions commonly happen near the airports where several aircrafts are taking off and landing in a limited space. Pilots and air traffic controllers are strictly trained regarding their jobs and they have to obey strict rules while operating in airport areas to avoid accidents. But even with the most careful handling of their jobs, still accidents happen caused by the slightest error in maneuvering within the area.
So at this point, you can be relieved that it is only at the most extreme cases that a collision may occur in the sky unless intended. However, you know fully well that there are other causes of plane crash like zero visibility and mechanical troubles. Just be attentive on safety measures then, whatever happens.