Why do planes stall at high altitude?

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Tags

1. #because
2. #lower
3. #altitudes
4. #progressively
5. #density
6. #stall
7. #higher
8. #aircraft
9. #close
10. #angle
11. #speed
12. #increases
13. #greater
14. #level
15. #wings
16. #altitude
17. #reduction
18. #indicated
19. #progressive
20. #attack
21. #airspeed
22. #speeds