Why is the round trip time of the plane different?

Usually there are two reasons for this situation, one is the influence of the wind, and the other is the different route.

The influence of wind is the main reason. Planes fly in the atmosphere. We control the plane to fly at a speed relative to the air, which is called "airspeed". At the same time, the air is also moving, that is to say, when flying with the wind, the actual speed of the aircraft is airspeed plus wind speed, which is just the opposite when flying against the wind. The time required to fly at the same distance varies greatly. In addition, due to the solar radiation on the ground and the rotation of the earth, the atmospheric circulation phenomenon is caused, and the wind direction and wind speed are different at different latitudes and seasons. The wind direction in the mid-latitude area of China is generally west to east, with high wind speed in winter and spring and low wind speed in summer and autumn. Therefore, when traveling to and from the western and eastern regions in winter, the time difference between round-trip flights on the same route is particularly obvious.

Another reason is that the route is different. Due to the rapid development of contemporary civil aviation industry, there are more and more planes flying in the air with increasing density. In order to maintain a safe interval, apart from altitude difference and time difference, the plane should also increase the gap in the horizontal direction. There are also special weather conditions such as thunderstorms and cumulus clouds when the plane is flying in the air. In this case, the plane will fly around to avoid possible dangers. Therefore, even the time required to fly back and forth on the same route will be different.

Of course, the angular velocity of the earth is the same as the angular velocity of the plane in circular motion under the gravity of the earth (relatively static), and this factor will not affect the above answer.