Personally I'd bin the 'dangerous dative'! As in 'to or for'. Thus 'Climbing FL280' rather than 'climbing to 280'. Was that 280 or 220? Similarly, was that 'for' or 'four'?
'XXXair passing FL 220 climbing FL 280' or 'XXXair maintaing FL320' or 'XXXair passing FL320 descending FL220, ready for lower when able' seems simple enough.
But we really don't need to get too fussy....