the consolidated maintenance expense for the nine months ended September 30, 2021, as compared to $2,111 for the prior year nine-month period since Cargo segment service did not begin until May 2020. The Cargo segment expense primarily relates to line maintenance, since heavy maintenance is reimbursed under the ATSA.
Sales and Marketing. Sales and marketing expense increased $3,279, or 25%, to $16,402 for the nine months ended September 30, 2021, as compared to $13,123 for the nine months ended September 30, 2020. The passenger revenue increase between these two periods was 38%, which drove a $1,441 increase in credit card processing fees and a $1,909 increase in global distribution system fees.
Depreciation and Amortization. Depreciation and amortization expense increased $4,472, or 13%, to $40,103 for the nine months ended September 30, 2021, as compared to $35,631 for the nine months ended September 30, 2020. The increase was primarily due to the impact of a change in the composition of our aircraft fleet from operating leases (for which expense is recorded within aircraft rent) to an increased number of owned aircraft and aircraft under finance leases (for which expense is recorded within depreciation, amortization and interest expense). For the nine months ended September 30, 2021 and 2020, there was an average of 18 and 10 owned aircraft, respectively. For the same periods, the average number of finance lease aircraft declined to six in 2021 from eight in 2020.
Ground Handling. Ground handling expense increased $3,868, or 25%, to $19,654 for the nine months ended September 30, 2021, as compared to $15,786 for the nine months ended September 30, 2020. There was an increase of $5,708, primarily due to the 40% increase in scheduled departures during the same time periods. However, we insourced our MSP operations in April 2020, contributing to a reduction of approximately $1,839 in ground handling expenses for the nine months ended September 30, 2021, compared to September 30, 2020, but resulted in higher salaries, wages, and benefits.
Landing Fees and Airport Rent. Landing fees and airport rent increased $7,229, or 32%, to $29,606 for the nine months ended September 30, 2021, as compared to $22,377 for the nine months ended September 30, 2020. There was a $7,532 increase driven by the 40% increase in scheduled departures for the nine months ended September 30, 2021, as compared to the same period in 2020. There was also a rate increase of approximately $891 for the nine months of 2021 versus nine months of 2020. During the nine months ended September 30, 2021, we also received a $1,416 MSP terminal user fee airline relief credit, which partially offset these increases.
Special Items, net. Special items, net was a contra-expense of $65,456 for the nine months ended September 30, 2021 and $64,333 for the nine months ended September 30, 2020. For the nine months ended September 30, 2021, Special items, net included $71,587 of contra-expense related to funds received under PSP2 and PSP3 of the CARES Act, to be used exclusively for the continuation of payments for salaries, wages, and benefits, and $848 in refundable tax credits related to employee retention under the CARES Act. This was partially offset by a $6,963 net charge relating to the purchase of six aircraft that were previously under operating leases. For the nine months ended September 30, 2020, Special items, net included $62,312 of contra-expense related to funds received under the CARES Act, to be used exclusively for the continuation of payments for salaries, wages, and benefits, and $2,069 in refundable tax credits related to employee retention under the CARES Act. Our Cargo segment was responsible for $18,401 of the consolidated income from Special items, net for the nine months ended September 30, 2021, and $10,687 for the nine months ended September 30, 2020. The segment allocation of these credits is based on the respective segment salaries, wages, and benefits.