Yes, airplanes generally fly faster at higher altitudes compared to lower altitudes. There are a few reasons for this:
Reduced air resistance: As an aircraft gains altitude, the air density decreases, which means there is less air resistance or drag acting upon the aircraft. With less resistance, the aircraft can achieve higher speeds more easily. The reduced air density also leads to lower drag on the aircraft's engines, allowing them to operate more efficiently.
Improved aerodynamic performance: At higher altitudes, the thinner air allows for improved aerodynamic performance of the aircraft. The wings generate lift more effectively, and the aircraft experiences less induced drag. These factors contribute to increased speed potential.
Jet stream assistance: Jet streams are high-altitude air currents that flow at high speeds, usually from west to east. They are caused by differences in temperature and pressure. Aircraft can take advantage of these strong tailwinds to increase their groundspeed. When flying in the same direction as the jet stream, an aircraft can benefit from the added speed provided by the wind.
It's important to note that commercial airliners typically have a cruising altitude where they optimize fuel efficiency rather than maximum speed. This altitude can vary depending on the aircraft type and the length of the flight. However, as a general principle, airplanes do have the potential to achieve higher speeds at higher altitudes due to the factors mentioned above.