Certain significant amounts included in the Company's condensed consolidated balance sheet as of June 30, 2021 and September 30, 2020, consisted of the following (in thousands):

	June 30,			September 30,
	2021			2020
Expendable parts and supplies, net:
Expendable parts and supplies	$	29,135		$	27,431
Less: obsolescence and other		(4,428	)		(4,460	)
	$	24,707		$	22,971
Prepaid expenses and other current assets:
Deferred offering and reimbursed costs	$	—		$	1,261
Prepaid aviation insurance		4,662			2,396
Other		4,294			12,410
	$	8,956		$	16,067
Property and equipment, net:
Aircraft and other flight equipment substantially pledged	$	1,606,276		$	1,596,174
Other equipment		5,116			5,147
Leasehold improvements		2,790			2,763
Vehicles		1,115			1,032
Building		699			699
Furniture and fixtures		302			302
Total property and equipment		1,616,298			1,606,117
Less: accumulated depreciation		(452,105	)		(393,702	)
	$	1,164,193		$	1,212,415
Other assets:
Warrants	$	16,374		$	—
Other		8,941			742
	$	25,315		$	742
Other accrued expenses:
Accrued property taxes	$	7,479		$	11,354
Accrued interest		4,814			3,268
Accrued vacation		5,967			5,975
Deferred PSP payments		26,100			11,311
Other		15,092			13,570
	$	59,452		$	45,478

The Company records impairment charges on long-lived assets used in operations when events and circumstances indicate that the assets may be impaired, the undiscounted net cash flows estimated to be generated by those assets are less than the carrying amount of those assets, and the net book value of the assets exceeds their estimated fair value. The Company has assessed whether any impairment of its long-lived assets existed and has determined that no charges were deemed necessary under applicable accounting standards as of June 30, 2021. The Company’s assumptions about future conditions important to its assessment of potential impairment of its long-lived assets, including the impact of the COVID-19 pandemic to its business, are subject to uncertainty, and the Company will continue to monitor these conditions in future periods as new information becomes available, and will update its analyses accordingly.

Depreciation expense totaled approximately $20.6 million and $20.2 million for the three months ended June 30, 2021 and 2020, respectively, and $61.2 million and $60.5 million for the nine months ended June 30, 2021 and 2020, respectively.

In connection with a negotiated forward purchase contract for electrically-powered vertical takeoff and landing aircraft (“eVTOL aircraft”) executed in February 2021, we obtained equity warrant assets giving us the right to acquire 1,171,649

shares of common stock in Archer Aviation, Inc. (Archer), a private, venture-backed company. Our investments in Archer do not have a readily determinable fair value, so we account for them using the measurement alternative under ASC 321 and measure the investments at cost less impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for identical or similar investments from the same issuer. We consider a range of factors when adjusting the fair value of these investments, including, but not limited to, the term and nature of the investment, local market conditions, values for comparable securities, current and projected operating performance, financing transactions subsequent to the acquisition of the investment or other features that indicate a discount to fair value is warranted. Any changes in fair value from the grant date fair value of the equity warrant assets will be recognized as increases or decreases on our balance sheet and as net gains or losses on equity warrant assets, in other (expense) income, net. We estimated the initial equity warrant asset value to be $16.4 million based on publicly available information as of the grant date. There were no observable price changes or transactions as of June 30, 2021 and as such, no adjustments to the recorded grant date fair value of the equity warrant assets were recorded.

The grant date value of the warrants, $16.4 million, was recognized as a vendor credit liability within other noncurrent liabilities. The liability related to the warrant assets will be settled in the future, as a reduction of the acquisition date value of the eVTOL aircraft contemplated in the related aircraft purchase agreement.