compared to the same quarter in 2021 in which no AerSale 757 P2F conversions were in progress. The decrease in revenue from airport MRO activities was partially offset by revenue from component MRO activities.
Gross margin was 39.4% in the second quarter of 2022 compared to 33.4% in the year ago period mainly due to the sale of higher margin flight equipment.
Selling, general and administrative expenses, excluding Payroll Support Program proceeds, were $23.5 million in the second quarter of 2022 compared to $17.0 million in the second quarter of 2021. AerSale received $8.4 million in Payroll Support Program proceeds during the second quarter of 2021 and did not receive any Payroll Support Program proceeds in the second quarter of 2022. The Company also incurred $3.9 million of stock-based compensation expenses in the second quarter of 2022, which was de minimis in the second quarter of 2021.
Income from operations was $31.5 million in the second quarter of 2022 versus $22.2 million in the second quarter of 2021.
Income tax expense was $6.3 million in the second quarter of 2022 compared to $5.1 million in the second quarter of 2021.
GAAP net income was $26.5 million in the second quarter of 2022, up 59.9% from $16.5 million in the second quarter of 2021. Adjusted for stock-based compensation, mark-to-market adjustment to the private warrant liability, non-cash inventory write-offs, and non-cash impairment of flight equipment, Adjusted Net Income was $31.7 million in the second quarter of 2022 and $21.8 million in the second quarter of 2021. Diluted earnings per share increased to $0.47 for the second quarter of 2022 from $0.38 in the second quarter of 2021. Adjusted for the non-cash items noted above, diluted earnings per share was $0.56 in the second quarter of 2022, compared to $0.50 in the second quarter of 2021.
Adjusted EBITDA in the second quarter of 2022 was $41.1 million, or 29.4% of sales, compared to $30.4 million, or 33.1% of sales in the second quarter of 2021. The improvement in adjusted EBITDA was largely attributable to an uptick in revenues from higher margin businesses. Adjusted EBITDA for the second quarter of 2021 reflected the benefit from $8.4 million in Payroll Support Program proceeds, for which there were no corresponding proceeds in the second quarter of 2022.
Martin Garmendia, AerSale’s Chief Financial Officer, said: “We are excited to report our record results this quarter where our outstanding performance exceeded our own internal projections. We have yet again demonstrated the strength of our purpose built model as well as our excellent execution capabilities. We believe we are well positioned to continue to generate strong returns to all our stakeholders.”
2022 Guidance
AerSale reaffirmed its guidance for revenue of $420 - $450 million and adjusted EBITDA of $80 - $90 million in 2022. In providing this guidance, the Company is mindful that recent geopolitical events related to the Russian invasion of Ukraine may impact the global commercial aerospace industry, but has not specifically adjusted for these factors beyond known impacts that the Company has already identified.
Conference Call Information
The Company will host a conference call today, August 8 2022 at 4:30 pm Eastern Time to discuss these results. A live webcast will also be available at https://ir.aersale.com/news-events/events. Participants may access the call at 1-877-407-3982, international callers may use 1-201-493-6780, and request to join the AerSale Corporation earnings call.
A telephonic replay will be available shortly after the conclusion of the call and until August 23, 2022. Participants may access the replay at 1-844-512-2921, international callers may use 1-412-317-6671, and enter