and higher USM sales. The decrease in Aircraft revenue is primarily attributable to decreased activity in the B757 product line due to lower Flight Equipment sales in the amount of $21.1 million due to softer demand in the freighter market, and lower leasing revenue of $1.9 million, partially offset by higher USM sales activity.
Cost of sales in Asset Management Solutions decreased $8.4 million, or 8.2%, to $94.2 million for the nine months ended September 30, 2024, compared to the prior year period. The decrease in cost of sales was primarily driven by lower costs on Flight Equipment sales. Gross profit in the Asset Management Solutions segment increased $9.3 million to $57.3 million, or 19.5%, for the nine months ended September 30, 2024, compared to the nine months ended September 30, 2023. The gross profit increase is mainly attributable to the higher margin generated on Flight Equipment sales for the nine months ended September 30, 2024, as noted above.
Aircraft gross profit margin increased to 32.8% for the nine months ended September 30, 2024, from 29.2% for the nine months ended September 30, 2023, due to higher margins on Flight Equipment sales. Engine gross profit margin was 39.3% for the nine months ended September 30, 2024, an increase from 33.5% for the nine months ended September 30, 2023, which was primarily due to changes in the USM product mix, along with higher margins on Flight Equipment sales.
TechOps
Our revenue from TechOps increased by $9.3 million, or 10.4%, to $98.9 million for the nine months ended September 30, 2024, compared to the prior year period. The increase was primarily driven by higher MRO product sales.
Cost of sales in TechOps increased $12.5 million, or 18.0%, to $82.0 million for the nine months ended September 30, 2024, compared to the prior year period, driven by the higher revenues discussed above. Gross profit in TechOps decreased $3.2 million, or 15.8% for the nine months ended September 30, 2024, compared to the nine months ended September 30, 2023, driven by lower profit generated on MRO services. Gross profit margin decreased to 17.1% for the nine months ended September 30, 2024 compared to 22.4% for the nine months ended September 30, 2023, and was largely attributable to lower margins on MRO services of 15.1% for the nine months ended September 30, 2024, compared to 21.7% during the nine months ended September 30, 2023.
Selling, General and Administrative Expenses
Selling, general and administrative expenses decreased $8.3 million, or 10.7% to $69.4 million for the nine months ended September 30, 2024, compared to the prior year period. The decrease was primarily related to lower share-based compensation and lower payroll related costs.
Change in Fair Value of Warrant Liability
We account for our private warrants as a liability at their fair value, with changes in fair value recognized in our results from operations for the period. The fair value of our private warrants is determined using a Black Scholes option pricing model. For the nine months ended September 30, 2024, we recorded a change in fair value of the warrant liability income of $2.3 million, compared to a $1.0 million income in the prior year period.
Interest (Expense) Income, Net
Interest expense, net, was $4.2 million for the nine months ended September 30, 2024, compared to $1.2 million interest income, net, for the nine months ended September 30, 2023. This was primarily related to interest expense incurred on higher borrowings under our debt facilities during the current year period compared to the prior period related to feedstock and MRO expansion investments to grow our business.
Income Taxes
The effective tax rate for the nine months ended September 30, 2024, was 5.2% compared to 59.8% for the nine months ended September 30, 2023. The difference between the effective tax rate and the statutory tax rate of 21% for the