Certain significant amounts included in the Company's consolidated balance sheets as of September 30, 2023 and 2022, consisted of the following (in thousands):


	September 30,			September 30,
	2023			2022
Expendable parts and supplies, net:
Expendable parts and supplies	$	39,630		$	31,913
Less: expendable parts warranty		(6,295	)		(1,373	)
Less: obsolescence		(4,090	)		(3,825	)
	$	29,245		$	26,715
Prepaid expenses and other current assets:
Prepaid aviation insurance	$	3,176		$	2,618
Prepaid vendors		143			1,310
Prepaid other insurance		1,205			1,268
Lease incentives		1,125			352
Prepaid fuel and other		1,645			1,068
	$	7,294		$	6,616
Property and equipment, net:
Aircraft and other flight equipment	$	1,039,782		$	1,260,143
Other equipment		9,421			10,420
Total property and equipment		1,049,203			1,270,563
Less: accumulated depreciation		(351,181	)		(405,309	)
	$	698,022		$	865,254
Other assets:
Investments in equity securities	$	20,320		$	15,178
Lease incentives		954			1,097
Contract asset		8,756			—
Other		516			15
	$	30,546		$	16,290
Other accrued expenses:
Accrued property taxes	$	5,281		$	5,866
Accrued interest		3,447			2,882
Accrued vacation		6,763			4,746
Accrued lodging		3,984			3,795
Accrued maintenance		2,117			1,453
Accrued liability on government payroll program		—			2,967
Accrued simulator costs		1,006			1,045
Accrued employee benefits		1,450			1,679
Accrued fleet operating expense		650			1,606
Short term lease incentive liability		97			97
Other		2,206			2,864
	$	27,001		$	29,000
Other noncurrent liabilities:
Warrant liabilities	$	25,225		$	25,225
Lease incentive obligations		1,050			1,050
Long-term employee benefits		429			1,123
Other		1,818			1,821
	$	28,522		$	29,219

The Company monitors for any indicators of impairment of the long-lived fixed assets. When certain conditions or changes in the economic situation exist, the assets may be impaired and the carrying amount of the assets exceed its fair value. The assets are then tested for recoverability of carrying amount. 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.

We group assets at the CPA and FSA level (i.e., the lowest level for which there are identifiable cash flows). If impairment indicators exist with respect to any of the asset groups, we estimate future cash flows based on projections of capacity purchase or FSA, block hours, maintenance events, labor costs and other relevant factors.

Due to operating losses and the transition of operations from American to United, the Company assessed whether any impairment of its long-lived assets existed for our United fleet as of September 30, 2023. As future cash flows from the operation of our United fleet through the respective remaining useful life exceeded the carrying value of the fleet, the Company determined that no impairment charges were necessary for the United fleet. The asset group associated with the CRJ-900 fleet includes owned aircraft, leased aircraft, intangible assets of customer relationship, and other relevant long-lived assets. The Company recorded impairment losses of zero, $116.6 million, and zero related to its long-lived assets for the years ended September 30, 2023, 2022, and 2021, respectively.

The Company’s assumptions about future conditions important to its assessment of potential impairment of its long-lived assets 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 on property and equipment totaled $60.2 million, $80.5 million, and $81.2 million for the years ended September 30, 2023, 2022, and 2021, 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 a number shares of common stock in Archer Aviation, Inc. (“Archer”), which at the time of our initial investment was a private, venture-backed company. As the initial investment in Archer did not have a readily determinable fair value, we accounted for this investment using the measurement alternative under ASC 321 and measured 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 estimated the initial equity warrant asset value to be $16.4 million based on publicly available information as of the grant date. In September 2021, the merger between Archer and a special purpose acquisition company (“SPAC”) was completed, resulting in a readily determinable fair value of our investments in Archer. Accordingly, gains and losses associated with changes in the fair value of our investments in Archer are measured in earnings, in accordance with ASC 321.

The initial 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.

In connection with closing of the merger between Archer and the SPAC described above, in September 2021, we purchased 500,000 Class A common shares in Archer for $5.0 million, and obtained

an additional warrant to purchase shares of Archer with a total grant date value of $5.6 million. The initial value of the warrants was recognized as a vendor credit liability within other noncurrent liabilities, and 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. Because these investments have readily determinable fair values, gains and losses resulting from changes in fair value of the investments are reflected in earnings, in accordance with ASC 321. All of our vested warrants have been exercised into shares of Archer common stock.

Gains/(losses) on our investments in Archer totaled $5.6 million and ($13.7) million during the fiscal years ended September 30, 2023 and 2022, respectively and are reflected in gain/(loss) on investments, net in our consolidated statement of operations.

The fair values of the Company’s investments in Archer are Level 1 within the fair value hierarchy as the values are determined using quoted prices for the equity securities. The value of the Company's investment in Archer is $11.5 million as of September 30, 2023.

In connection with a negotiated forward purchase contract for fully electric aircraft executed in July 2021, we obtained $5.0 million of preferred stock in Heart Aerospace Incorporated (“Heart”), a privately held company. Our investment in Heart does not have a readily determinable fair value, so we account for the investment using the measurement alternative under ASC 321 and measure the investment at initial 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 change to fair value is warranted. Any changes in fair value from the initial cost of the investment in preferred stock are recognized as increases or decreases on our balance sheet and as net gains or losses on investments in equity securities, in other income (expense), net. The initial investment in preferred stock was measured at cost of $5.0 million. There were no identical or similar transactions during the fiscal year ended September 30, 2023, and as such, no adjustments to the initial cost of the equity investment resulting from observable price changes have been recorded at September 30, 2023.

The fair values of the Company’s investments in Heart are Level 3 within the fair value hierarchy as the values are determined using unobservable inputs in which there is little or no market data, requiring the Company to develop our own assumptions. The value of the Company's investment in Heart is $5.0 million as of September 30, 2023.

In connection with a negotiated forward purchase contract for hybrid-electric vertical takeoff and landing (“VTOL”) aircraft executed in February 2022, we obtained a warrant giving us the right to acquire a number of shares of common stock in the privately-held manufacturer of the VTOL aircraft. These investments 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 value of the warrant assets will be recognized as increases or decreases to the investment on our balance sheet and as net gains or losses on investments equity securities. We estimated the initial warrant asset value to be $3.2 million based on prices of similar investments in the same issuer. The grant date value of the warrants, $3.2 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 VTOL aircraft contemplated in the related forward purchase agreement.

The fair values of the Company’s investments in the privately-held manufacturer noted above are Level 3 within the fair value hierarchy as the values are determined using unobservable inputs in which there is little or no market data, requiring the Company to develop our own assumptions. The value of the Company's investment is $3.5 million as of September 30, 2023.

Total net gains/(losses) on our investments in equity securities totaled $5.4 million and ($13.7) million during the year ended September 30, 2023 and 2022, respectively, and are reflected in gain/(loss) on investments, net in our consolidated statements of operations and comprehensive (loss) income. As of September 30, 2023, the aggregate carrying amount of our investments in equity securities was $20.3 million, and the carrying amount of our investments without readily determinable fair values was $8.8 million.