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:


	June 30,		September 30,
	2020		2019

Raw materials	$	3,681,929	$	3,408,742
Work-in-process		761,060		775,770
Finished goods		266,353		286,182
	$	4,709,342	$	4,470,694

Prepaid expenses and other current assets

Prepaid expenses and other current assets consist of the following:


	June 30,		September 30,
	2020		2019

Prepaid insurance	$	389,078	$	302,376
Income tax receivable		301,519		—
Other		417,126		339,673
	$	1,107,723	$	642,049

Property and equipment

Property and equipment, net consists of the following:


	June 30,		September 30,
	2020		2019

Computer equipment	$	2,297,125	$	2,285,152
Corporate airplanes		5,601,039		5,601,039
Furniture and office equipment		1,031,099		1,033,779
Manufacturing facility		5,733,313		5,733,313
Equipment		5,678,035		5,635,134
Land		1,021,245		1,021,245
		21,361,856		21,309,662
Less: accumulated depreciation and amortization		(13,136,124)		(12,864,970)
	$	8,225,732	$	8,444,692

Depreciation and amortization related to property and equipment was approximately $92,330 and $103,000 for the three months ended June 30, 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.

Depreciation and amortization related to property and equipment was approximately $286,584 and $321,000 for the nine months ended June 30, 2020 and 2019, respectively.

Other assets

Other assets consist of the following:


	June 30,		September 30,
	2020		2019
Intangible assets, net of accumulated amortization of $555,837 and $551,037 at June 30, 2020 and September 30, 2019, respectively	$	44,400	$	49,200
Operating lease right-of-use asset		66,201		—
Other non-current assets		94,675		104,841
	$	205,276	$	154,041

Intangible assets consist of licensing and certification rights which are amortized over a defined number of units. No impairment charges were recorded in the nine months ended June 30, 2020 and 2019.

Intangible asset amortization expense was approximately $0 and $3,000 for the three months ended June 30, 2020 and 2019, respectively. Intangible asset amortization expense was approximately $4,800 and $15,000 for the nine months ended June 30, 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 June 30, 2020 and September 30, 2019 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 June 30, 2020 and September 30, 2019 includes $19,375 and $29,541, 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 $4,067 and $3,000 for the three months ended June 30, 2020 and 2019, respectively. Other non-current assets amortization expense was approximately $10,166 and $7,000 for the nine months ended June 30, 2020 and 2019, respectively.

Accrued expenses

Accrued expenses consist of the following:


	June 30,		September 30,
	2020		2019

Warranty	$	580,049	$	606,680
Salary, benefits and payroll taxes		500,835		212,322
Professional fees		129,997		153,298
Operating lease		63,960		—
Other		231,949		138,618
	$	1,506,790	$	1,110,918

Warranty cost and accrual information for the three- and nine-month periods ended June 30, 2020 is highlighted below:


	Three Months Ending		Nine Months Ending
	June 30, 2020		June 30, 2020

Warranty accrual, beginning of period	$	573,412	$	606,680
Accrued expense		32,023		72,998
Warranty cost		(25,386)		(99,629)
Warranty accrual, end of period	$	580,049	$	580,049