Ear infections usually occur due to a respiratory tract infection that progresses to affect the ear. This is because the middle ear is connected to the back of the nose through a tube called the Eustachian tube. The Eustachian tubes corrects pressure in the middle ear. When an upper respiratory tract infection occurs, the infection and subsequent inflammation affects the Eustachian tube and blocks the flow of air into the middle ear. This is what causes the pressure imbalance and impaired hearing. It is also common for infections to move from the nose or throat into the middle ear. This is when you get an ear infection.
Earache from flying is a combination of a blocked Eustachian tube and natural changes of pressure. When you are on the ground, there is a pressure that is exerted on you, which is basically that of air acting on you. This effect can be better felt when you dive into a pool. As you go deeper underwater, the effect of pressure is the weight of water on your body. As you ascend, the pressure and weight decreases. In the air, the same effect happens and as you travel up to the mountains, the air pressure decreases and you have to correct the pressure in your ear by swallowing. When you fly, the passenger cabin is artificially pressurized so that humans can survive flying at high altitudes. When the aircraft pressurizes and depressurizes, and if there is a blockage in the Eustachian tube, you will not be able to correct the pressure.
Treating this problem requires that you decongest your ear and nose. The fastest way that you can do this is by a steam inhalation. This requires that you stand over a boiling kettle and inhale the steam. This will cause the steam to condense inside your respiratory tract. Some of this steam condensation will happen on the accumulated mucus making it heavier and more viscous. The mucus will then drain away and your nasal passage and your Eustachian tubes will then come back to normal. Another technique to try out is eating something very spicy. This will have the effect of increasing the amount of mucus secreted and dislodging the existing mucus in the process. For a longer-term measure, consume a lot of ginger in your diet or as a tea. This is a natural anti-inflammatory and can stop the production of mucus and even reduce swelling long enough for accumulated mucus to drain away.