Business Segments (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Business segments
Number of business segments | segment	1
FPDS
Geographic Data
Sales percentage	80.00%	90.00%	75.00%
Air data systems and components
Geographic Data
Sales percentage	20.00%	10.00%	25.00%
Engineering development contracts
Geographic Data
Sales percentage	4.00%	8.00%	3.00%
Outside the United States
Geographic Data
Net sales from outside the United States | $	$ 9.4	$ 7.5	$ 4.7