Climb and descent
I am working with some people who are developing flight planning software, and an issue came up today that made me want to check against real life experience.
One of them commented that because of wind etc., the optimal route (according to the software) might involve climbing and descending several times during the flight -- so much so, that the calculated flight path might need to be "smoothed" so that the the aircraft wasn't constantly changing altitude during the flight.
However, from my minimal knowledge of aviation, I had the impression that an aircraft would pretty much only climb during a normal flight (as it burned fuel and became light enough for higher flight levels), then descend only at the end of the flight.
In practice, do aircraft tend to both ascend and descend during a flight, or just ascend?
(If there is a more appropriate forum to ask this question, let me know).