Note 4 - Disaggregation of Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2021	Oct. 31, 2020	Oct. 31, 2021	Oct. 31, 2020
Revenues from customers	$ 19,093	$ 15,972	$ 37,237	$ 28,961
Percentage of Completion Contracts [Member]
Revenues from customers	5,703	5,516	10,978	9,560
Transferred at Point in Time [Member]
Revenues from customers	13,390	10,456	26,259	19,401
Casino [Member]
Revenues from customers	8,486	6,771	17,074	11,570
Casino Non-gaming [Member]
Revenues from customers	1,087	784	2,163	1,293
Professional Services [Member]
Revenues from customers	103	93	164	138
Aircraft Modification [Member]
Revenues from customers	5,910	5,942	11,692	10,735
Aircraft Avionics [Member]
Revenues from customers	665	625	1,540	1,539
Special Mission Electronics [Member]
Revenues from customers	2,842	1,757	4,604	3,686
Professional Services [Member]
Revenues from customers	9,676	7,648	19,401	13,001
Professional Services [Member] | Percentage of Completion Contracts [Member]
Revenues from customers	0	0	0	0
Professional Services [Member] | Transferred at Point in Time [Member]
Revenues from customers	9,676	7,648	19,401	13,001
Professional Services [Member] | Casino [Member]
Revenues from customers	8,486	6,771	17,074	11,570
Professional Services [Member] | Casino Non-gaming [Member]
Revenues from customers	1,087	784	2,163	1,293
Professional Services [Member] | Professional Services [Member]
Revenues from customers	103	93	164	138
Professional Services [Member] | Aircraft Modification [Member]
Revenues from customers	0	0	0	0
Professional Services [Member] | Aircraft Avionics [Member]
Revenues from customers	0	0	0	0
Professional Services [Member] | Special Mission Electronics [Member]
Revenues from customers	0	0	0	0
Aerospace Products [Member]
Revenues from customers	9,417	8,324	17,836	15,960
Aerospace Products [Member] | Percentage of Completion Contracts [Member]
Revenues from customers	5,703	5,516	10,978	9,560
Aerospace Products [Member] | Transferred at Point in Time [Member]
Revenues from customers	3,714	2,808	6,858	6,400
Aerospace Products [Member] | Casino [Member]
Revenues from customers	0	0	0	0
Aerospace Products [Member] | Casino Non-gaming [Member]
Revenues from customers	0	0	0	0
Aerospace Products [Member] | Professional Services [Member]
Revenues from customers	0	0	0	0
Aerospace Products [Member] | Aircraft Modification [Member]
Revenues from customers	5,910	5,942	11,692	10,735
Aerospace Products [Member] | Aircraft Avionics [Member]
Revenues from customers	665	625	1,540	1,539
Aerospace Products [Member] | Special Mission Electronics [Member]
Revenues from customers	2,842	1,757	4,604	3,686
North America [Member]
Revenues from customers	17,198	14,675	34,364	26,086
North America [Member] | Professional Services [Member]
Revenues from customers	9,676	7,648	19,401	13,001
North America [Member] | Aerospace Products [Member]
Revenues from customers	7,522	7,027	14,963	13,085
Europe [Member]
Revenues from customers	1,114	938	1,957	1,828
Europe [Member] | Professional Services [Member]
Revenues from customers	0	0	0	0
Europe [Member] | Aerospace Products [Member]
Revenues from customers	1,114	938	1,957	1,828
Asia [Member]
Revenues from customers	675	2	763	2
Asia [Member] | Professional Services [Member]
Revenues from customers	0	0	0	0
Asia [Member] | Aerospace Products [Member]
Revenues from customers	675	2	763	2
Australia and Other [Member]
Revenues from customers	106	357	153	1,045
Australia and Other [Member] | Professional Services [Member]
Revenues from customers	0	0	0	0
Australia and Other [Member] | Aerospace Products [Member]
Revenues from customers	$ 106	$ 357	$ 153	$ 1,045