2. Supplemental Balance Sheet Disclosures

Inventories

Inventories are stated at the lower of cost (first-in, first-out) or net realizable value, net of write-downs for excess and obsolete inventory, and consist of the following:


	Decmber 31,		September 30,
	2020		2020

Raw materials	$	3,248,163	$	3,378,246
Work-in-process		663,900		656,382
Finished goods		268,680		256,707
	$	4,180,743	$	4,291,335

Prepaid expenses and other current assets

Prepaid expenses and other current assets consist of the following:


	Decmber 31,		September 30,
	2020		2020

Prepaid insurance	$	576,804	$	336,331
Other		274,057		338,778
	$	850,861	$	675,109

Property and equipment

Property and equipment, net consists of the following:


	Decmber 31,		September 30,
	2020		2020

Computer equipment	$	2,308,218	$	2,302,978
Corporate airplanes		5,601,039		5,601,039
Furniture and office equipment		1,019,891		1,031,099
Manufacturing facility		5,733,313		5,733,313
Equipment		5,776,906		5,723,355
Land		1,021,245		1,021,245
		21,460,612		21,413,029
Less: accumulated depreciation and amortization		(13,304,945)		(13,237,157)
	$	8,155,667	$	8,175,872

Depreciation and amortization related to property and equipment was approximately $93,051 and $96,644 for the three-month periods ended December 31, 2020 and 2019, respectively. The corporate airplanes are utilized primarily in support of product development. The Pilatus PC-12 airplane, one of the Company’s two corporate airplanes, has been depreciated to its estimated salvage value.

Other assets

Other assets consist of the following:


	Decmber 31,		September 30,
	2020		2020
Intangible assets, net of accumulated amortization of $603,569 and $583,655 at December 31, 2020 and September 30, 2020, respectively	$	92,937	$	112,851
Operating lease right-of-use asset		24,307		45,126
Other non-current assets		90,849		91,566
	$	208,093	$	249,543

Intangible assets consist of licensing and certification rights which are amortized over a defined number of units. No impairment charges were recorded in the three months ended December 31, 2020 and 2019.

Intangible asset amortization expense was approximately $19,914 and $4,800 for the three months ended December 31, 2020 and 2019, respectively. The timing of future amortization expense is not determinable because the intangible assets are being amortized over a defined number of units.

Other non-current assets as of December 31, 2020 and September 30, 2020 include the security deposit for an airplane hangar and a deposit for medical claims required under the Company’s medical plan. In addition, other non-current assets as of December 31, 2020 and September 30, 2020 includes $15,548 and $16,266, respectively, of prepaid software licenses that will be earned upon the shipment of a certain product to a customer. Other non-current assets amortization expense was approximately $717 and $2,691 for the three months ended December 31, 2020 and 2019, respectively.

Accrued expenses

Accrued expenses consist of the following:


	Decmber 31,		September 30,
	2020		2020

Warranty	$	578,172	$	547,743
Salary, benefits and payroll taxes		180,218		483,797
Professional fees		235,661		151,956
Operating lease		24,307		45,126
Other		103,460		133,338
	$	1,121,818	$	1,361,960

Warranty cost and accrual information for the three-month period ended December 31, 2020 is highlighted below:


	Three Months Ending
	December 31, 2020

Warranty accrual, beginning of period	$	547,743
Accrued expense		73,866
Warranty cost		(43,437)
Warranty accrual, end of period	$	578,172