COMMITMENTS AND CONTINGENCIES Aircraft orders and options (Details) - aircraft	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircrafts purchased without orders	0	1	1
Commitments
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft - beginning balance	32	36	45
Number of aircraft delivered	(5)	(9)	(8)
Number of aircraft ordered	0	5	0
New options	0	0	0
Number of exercised options	0	0	(1)
Number of expired options	0	0	0
Number of aircraft - ending balance	27	32	36
Options
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft - beginning balance	4	14	30
Number of aircraft delivered	0	0	0
Number of aircraft ordered	0	0	0
New options	0	0	4
Number of exercised options	0	0	0
Number of expired options	0	(10)	(20)
Number of aircraft - ending balance	4	4	14