Management Solutions segment increased $26.9 million or 119.3%, to $49.5 million for the nine months ended September 30, 2021, from $22.6 million for the nine months ended September 30, 2020. The increase is mainly attributable to higher margins generated on flight equipment sales in the amount of $33.7 million and lower obsolescence reserves on inventory of $8.1 million for the nine months ended September 30, 2021.
Aircraft gross profit margins increased to 32.8% for the nine months ended September 30, 2021, from a gross profit reported of 19.9% for the nine months ended September 30, 2020 due to higher margin generated by flight equipment sales as noted above and lower inventory obsolescence reserves. Engines gross profit margins was 37.4% for the nine months ended September 30, 2021, a slight decrease from 37.9% for the nine months ended September 30, 2020, primarily due to fluctuations in the product mix.
Tech Ops
Our revenue from Tech Ops increased by $7.0 million or 9.0%, to $85.2 million for the nine months ended September 30, 2021, compared to $78.2 million for the nine months ended September 30, 2020. The increase was primarily driven by maintenance and storage programs, including preservation work, resulting from the increase in fleet groundings related to COVID-19. This work took place during the nine months ended September 30, 2021, but had a partial impact during the same period in 2020.
Cost of sales in Tech Ops decreased $1.6 million or 2.6%, to $59.5 million for the nine months ended September 30, 2021, from $61.1 million for the nine months ended September 30, 2020, which is directly related to improved margins on the heavy MRO business. Gross profit in Tech Ops increased $8.6 million or 50.4%, to $25.7 million for the nine months ended September 30, 2021, compared to $17.1 million for the nine months ended September 30, 2020. The increase in gross profit was primarily attributable to increased contributions from maintenance and storage programs. Gross profit margin increased to 30.2% for the nine months ended September 30, 2021 compared to 21.8% for the nine months ended September 30, 2020, and was largely attributable to an overall change in the product mix towards higher margin storage related maintenance.
Selling, General and Administrative Expenses
Selling, general and administrative expenses increased $12.5 million, or 30.7% to $53.1 million for the nine months ended September 30, 2021, as compared to $40.6 million for the nine months ended September 30, 2020. The increase was mostly related to stock compensation of $8.9 million based on the probability of meeting performance targets. The remaining increase relates to higher support costs associated with becoming publicly traded.
Payroll Support Program Proceeds
As part of the CARES Act, we received and recognized payroll support program proceeds of $3.7 million during the nine months ended September 30, 2021.
As part of the Payroll Support Program Extension Law, we received and recognized payroll support program proceeds of $5.5 million during the nine months ended September 30, 2021.
As part of the American Rescue Plan Act of 2021, we received and recognized payroll support program proceeds of $5.5 million during the nine months ended September 30, 2021.
As part of the CARES Act, we received and recognized payroll support program proceeds of $12.7 million during the nine months ended September 30, 2020.