Note 4 - Disaggregation of Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2022	Jan. 31, 2021	Jan. 31, 2022	Jan. 31, 2021
Revenues from customers	$ 18,132	$ 14,612	$ 55,369	$ 43,572
Percentage of Completion Contracts [Member]
Revenues from customers	4,899	4,185	15,877	13,745
Transferred at Point in Time [Member]
Revenues from customers	13,233	10,427	39,492	29,827
Casino [Member]
Revenues from customers	8,255	7,001	25,329	18,571
Casino Non-gaming [Member]
Revenues from customers	1,059	842	3,222	2,135
Professional Services [Member]
Revenues from customers	102	58	266	195
Aircraft Modification [Member]
Revenues from customers	5,394	4,472	17,086	15,206
Aircraft Avionics [Member]
Revenues from customers	485	569	2,025	2,109
Special Mission Electronics [Member]
Revenues from customers	2,837	1,670	7,441	5,356
Professional Services [Member]
Revenues from customers	9,416	7,901	28,817	20,901
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	9,416	7,901	28,817	20,901
Professional Services [Member] | Casino [Member]
Revenues from customers	8,255	7,001	25,329	18,571
Professional Services [Member] | Casino Non-gaming [Member]
Revenues from customers	1,059	842	3,222	2,135
Professional Services [Member] | Professional Services [Member]
Revenues from customers	102	58	266	195
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	8,716	6,711	26,552	22,671
Aerospace Products [Member] | Percentage of Completion Contracts [Member]
Revenues from customers	4,899	4,185	15,877	13,745
Aerospace Products [Member] | Transferred at Point in Time [Member]
Revenues from customers	3,817	2,526	10,675	8,926
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	5,394	4,472	17,086	15,206
Aerospace Products [Member] | Aircraft Avionics [Member]
Revenues from customers	485	569	2,025	2,109
Aerospace Products [Member] | Special Mission Electronics [Member]
Revenues from customers	2,837	1,670	7,441	5,356
North America [Member]
Revenues from customers	17,034	13,221	51,399	39,331
North America [Member] | Professional Services [Member]
Revenues from customers	9,416	7,901	28,817	20,901
North America [Member] | Aerospace Products [Member]
Revenues from customers	7,618	5,320	22,582	18,430
Europe [Member]
Revenues from customers	578	589	2,535	2,417
Europe [Member] | Professional Services [Member]
Revenues from customers	0	0	0	0
Europe [Member] | Aerospace Products [Member]
Revenues from customers	578	589	2,535	2,417
Asia [Member]
Revenues from customers	93	662	856	664
Asia [Member] | Professional Services [Member]
Revenues from customers	0	0	0	0
Asia [Member] | Aerospace Products [Member]
Revenues from customers	93	662	856	664
Australia and Other [Member]
Revenues from customers	427	140	579	1,160
Australia and Other [Member] | Professional Services [Member]
Revenues from customers	0	0	0	0
Australia and Other [Member] | Aerospace Products [Member]
Revenues from customers	$ 427	$ 140	$ 579	$ 1,160