Note 15 - Segment Reporting and Sales by Major Customer (Details Textual)	6 Months Ended
	Oct. 31, 2021	Oct. 31, 2020
Number of Operating Segments	2
Customer Concentration Risk [Member] | Revenue Benchmark [Member]
Number of Major Customers	2	0
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | The Five Aerospace Customers [Member]
Concentration Risk, Percentage	34.40%
Number of Major Customers	5
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | Top Customer [Member]
Concentration Risk, Percentage	12.40%
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | Next Top Four Customers [Member] | Minimum [Member]
Concentration Risk, Percentage	2.60%
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | Next Top Four Customers [Member] | Maximum [Member]
Concentration Risk, Percentage	10.90%