Intangible assets (Tables)

12 Months Ended

Apr. 30, 2012

Summary of Intangible Assets

	Definite life			Indefinite life						Total
	Embedded equity in lease contracts			Trade names and trademarks			Safety manuals, AOCs and operating licenses
Cost:
Balance, April 30, 2010	$	180,479		$	179,900		$	3,947		$	364,326
Embedded equity in lease contracts realized		(23,384	)		—			—			(23,384	)
Foreign exchange		1,562			—			191			1,753
Balance, April 30, 2011		158,657			179,900			4,138			342,695
Embedded equity in lease contracts realized		(19,840	)		—			—			(19,840	)
Foreign exchange		(1,039	)		—			(197	)		(1,236	)
April 30, 2012	$	137,778		$	179,900		$	3,941		$	321,619
Impairment losses:
Balance, April 30, 2010		(53,903	)		(25,000	)		—			(78,903	)
Impairment loss		(20,608	)		—			—			(20,608	)
Balance, April 30, 2011		(74,511	)		(25,000	)		—			(99,511	)
Impairment loss		(4,218	)		—			—			(4,218	)
April 30, 2012	$	(78,729	)	$	(25,000	)	$	—		$	(103,729	)
Net book value:
April 30, 2012	$	59,049		$	154,900		$	3,941		$	217,890
April 30, 2011		84,146			154,900			4,138			243,184