The following queries do not:
-- segment_number is in the index, but it's not the first column;
-- there's no logical starting and stopping place
SELECT *
FROM Flights
WHERE segment_number = 2
-- would scan entire table; comparison of first column
-- is not with a constant or column in another table
-- and no covering index applies
SELECT *
FROM Flights
WHERE orig_airport = dest_airport
AND segment_number < 2