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:


	March 31,		September 30,
	2020		2019

Raw materials	$	3,715,412	$	3,408,742
Work-in-process		831,518		775,770
Finished goods		274,132		286,182
	$	4,821,062	$	4,470,694

Prepaid expenses and other current assets

Prepaid expenses and other current assets consist of the following:


	March 31,		September 30,
	2020		2019

Prepaid insurance	$	466,355	$	302,376
Income tax receivable		310,135		—
Other		281,307		339,673
	$	1,057,797	$	642,049

Property and equipment

Property and equipment, net consists of the following:


	March 31,		September 30,
	2020		2019

Computer equipment	$	2,299,372	$	2,285,152
Corporate airplanes		5,601,039		5,601,039
Furniture and office equipment		1,033,779		1,033,779
Manufacturing facility		5,733,313		5,733,313
Equipment		5,647,371		5,635,134
Land		1,021,245		1,021,245
		21,336,119		21,309,662
Less: accumulated depreciation and amortization		(13,053,261)		(12,864,970)
	$	8,282,858	$	8,444,692

Depreciation and amortization related to property and equipment was approximately $97,610 and $111,000 for the three months ended March 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.

Depreciation and amortization related to property and equipment was approximately $194,254 and $218,000 for the six months ended March 31, 2020 and 2019, respectively.

Other assets

Other assets consist of the following:


	March 31,		September 30,
	2020		2019
Intangible assets, net of accumulated amortization of $555,837 and $551,037 at March 31, 2020 and September 30, 2019, respectively	$	44,400	$	49,200
Operating lease right-of-use asset		87,536		—
Other non-current assets		98,742		104,841
	$	230,678	$	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 six months ended March 31, 2020 and 2019.

Intangible asset amortization expense was approximately $0 and $5,000 for the three months ended March 31, 2020 and 2019, respectively. Intangible asset amortization expense was approximately $4,800 and $12,000 for the six months ended March 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 March 31, 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 March 31, 2020 and September 30, 2019 includes $23,442 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 $3,409 and $2,000 for the three months ended March 31, 2020 and 2019, respectively. Other non-current assets amortization expense was approximately $6,100 and $4,000 for the six months ended March 31, 2020 and 2019, respectively.

Accrued expenses

Accrued expenses consist of the following:


	March 31,		September 30,
	2020		2019

Warranty	$	573,412	$	606,680
Salary, benefits and payroll taxes		272,306		212,322
Professional fees		106,464		153,298
Operating lease		81,899		—
Other		142,984		138,618
	$	1,177,065	$	1,110,918

Warranty cost and accrual information for the three - and six-month periods ended March 31, 2020 is highlighted below:


	Three Months Ended		Six Months Ended
	March 31, 2020		March 31, 2020

Warranty accrual, beginning of period	$	559,180	$	606,680
Accrued expense		63,777		40,975
Warranty cost		(49,545)		(74,243)
Warranty accrual, end of period	$	573,412	$	573,412