Jābir (may Allah be pleased with him) reported: When we ascended (a high land), we used to say Takbīr, and when we descended, we used to say Tasbīh. Ibn ‘Umar (may Allah be pleased with him) reported: When the Prophet (may Allah's peace and blessings be upon him) and his armies, ascended hills, they would say Takbīr, and when they descended, they would say Tasbīh.
The reason for making Takbīr when going up a high place is that people love to be superior and in a higher position due to the feeling of pride and greatness resulted. Therefore, one should belittle oneself by saying "Allah Akbar", meaning Allah is the Greatest. One upon ascending heights needs to remind oneself of Allah's Grandeur and that He is Greater than anything. By doing so, Allah, the Almighty, will appreciate his action and is thankful for his humility and gives him more out of His grace. The reason for making Tasbīh when going down is that low places make one feel constrained, and saying "Subhān Allāh" is a means of relief from constraint and distress. This is what happened in the story of the Prophet Yunus (peace be upon him) who was saved from distress when he made Tasbīh in darkness. Also, going down implies inferiority and humiliation, so the person exalts Allah, Glorified and Exalted, above inferiority and lowness by saying "Subhān Allāh". Indeed, Allah is Above everything. Similarly, one should say Takbīr when the plane takes off and say Tasbīh when it lands. In this case, there will be no difference if ascent and descent occur in the air or on the land. Allah is the Giver of Success!