Airstream travel trailer windows have rubber seals around the edges which in extreme, heat and dusty conditions can become sticky which makes them more difficult to open. You can help prevent this by regularly cleaning window seals with soapy water and applying a silicone product or Aerospace Protectant 303 to the seals. Cleaning the edge of the window glass also helps prevent this build up over time.
When opening your windows, always lift both handles at the same time with equal pressure to prevent the window from bending. If too much pressure is applied to one side, it is possible the window will crack.