As part of our ongoing fleet transformation, during 2019 we committed to accelerating the retirement of our MD-90 fleet. This fleet will now be retired by the end of 2022, which is approximately two years earlier than previously planned. The decision to retire the fleet by 2022, including the permanent retirement of 35 aircraft during 2019, resulted in accelerated depreciation of $79 million during 2019, which is recorded in depreciation and amortization in our income statement.

We have agreed to acquire four A350 aircraft from LATAM, which are included as purchase commitments in the table above. In addition, we plan to assume ten of LATAM's A350 purchase commitments from Airbus, with deliveries through 2025. See Note 4, "Investments," for further information on our investment in LATAM.

Capacity Purchase Agreements. Most of our contract carriers operate for us under capacity purchase agreements. Under these agreements, the contract carriers operate some or all of their aircraft using our flight designator codes, and we control the scheduling, pricing, reservations, ticketing and seat inventories of those aircraft and retain the revenues associated with those flights. We pay those airlines an amount, as defined in the applicable agreement, which is based on a determination of their cost of operating those flights and other factors intended to approximate market rates for those services.

The following table shows our minimum fixed obligations under our existing capacity purchase agreements with third-party regional carriers. The obligations set forth in the table contemplate minimum levels of flying by the contract carriers under the respective agreements and also reflect assumptions regarding certain costs associated with the minimum levels of flying such as the cost of fuel, labor, maintenance, insurance, catering, property tax and landing fees. Accordingly, our actual payments under these agreements could differ materially from the minimum fixed obligations set forth in the table below.

⁽²⁾In January 2020, we agreed not to renew our CRJ-900 contract with GoJet Airlines, LLC and to end those operations by the end of 2020. The table above reflects our commitments under that contract as of December 31, 2019.

Revenue Proration Agreement. As of December 31, 2019, a portion of our contract carrier agreement with SkyWest Airlines, Inc. was structured as a revenue proration agreement. This revenue proration agreement establishes a fixed dollar or percentage division of revenues for tickets sold to passengers traveling on connecting flight itineraries.

We are involved in various legal proceedings related to employment practices, environmental issues, antitrust matters and other matters concerning our business. We record liabilities for losses from legal proceedings when we determine that it is probable that the outcome in a legal proceeding will be unfavorable and the amount of loss can be reasonably estimated. Although the outcome of the legal proceedings in which we are involved cannot be predicted with certainty, we believe that the resolution of current matters will not have a material adverse effect on our Consolidated Financial Statements.

Our VISA/MasterCard and American Express credit card processing agreements provide that no cash reserve ("Reserve") is required, and no withholding of payment related to receivables collected will occur, except in certain circumstances, including when we do not maintain a required level of liquidity as outlined in the merchant processing agreements. In circumstances in which the credit card processor can establish a Reserve or withhold payments, the amount of the Reserve or payments that may be withheld would be equal to the potential liability of the credit card processor for tickets purchased with VISA/MasterCard or American Express credit cards, as applicable, that had not yet been used for travel. We did not have a Reserve or an amount withheld as of December 31, 2019 or 2018.

We are the lessee under many commercial real estate leases. It is common in these transactions for us, as the lessee, to agree to indemnify the lessor and the lessor's related parties for tort, environmental and other liabilities that arise out of or relate to our use or occupancy of the leased premises. This type of indemnity would typically make us responsible to indemnified parties for liabilities arising out of the conduct of, among others, contractors, licensees and invitees at, or in connection with, the use or occupancy of the leased premises. This indemnity often extends to related liabilities arising from the negligence of the indemnified parties, but usually excludes any liabilities caused by either their sole or gross negligence or their willful misconduct.

Our aircraft and other equipment lease and financing agreements typically contain provisions requiring us, as the lessee or obligor, to indemnify the other parties to those agreements, including certain of those parties' related persons, against virtually any liabilities that might arise from the use or operation of the aircraft or other equipment.

We believe that our insurance would cover most of our exposure to liabilities and related indemnities associated with the commercial real estate leases and aircraft and other equipment lease and financing agreements described above. While our insurance does not typically cover environmental liabilities, we have insurance policies in place as required by applicable environmental laws.

Some of our aircraft and other financing transactions include provisions that require us to make payments to preserve an expected economic return to the lenders if that economic return is diminished due to specified changes in law or regulations. In some of these financing transactions, we also bear the risk of changes in tax laws that would subject payments to non-U.S. lenders to withholding taxes.

We cannot reasonably estimate our potential future payments under the indemnities and related provisions described above because we cannot predict (1) when and under what circumstances these provisions may be triggered and (2) the amount that would be payable if the provisions were triggered because the amounts would be based on facts and circumstances existing at such time.

As of December 31, 2019, we had approximately 91,000 full-time equivalent employees, approximately 19% of whom were represented by unions. The following table shows our domestic airline employee groups that are represented by unions.

Employee Group

Approximate Number of Active Employees Represented

Union

Date on which Collective Bargaining Agreement Becomes Amendable

Delta Pilots

13,082

ALPA

December 31, 2019

Delta Flight Superintendents (Dispatchers)

443

PAFCA

November 1, 2024

Endeavor Air Pilots

1,872

ALPA

January 1, 2024

Endeavor Air Flight Attendants

1,492

AFA

December 31, 2018

In addition to the domestic airline employee groups discussed above, 199 refinery employees of Monroe are represented by the United Steel Workers under an agreement that expires on February 28, 2022. This agreement is governed by the National Labor Relations Act, which generally allows either party to engage in self help upon the expiration of the agreement.

We have certain contracts for goods and services that require us to pay a penalty, acquire inventory specific to us or purchase contract-specific equipment, as defined by each respective contract, if we terminate the contract without cause prior to its expiration date. Because these obligations are contingent on our termination of the contract without cause prior to its expiration date, no obligation would exist unless such a termination occurs.