and, therefore, there was no indication that goodwill was impaired.

Identifiable Intangible Assets. Our identifiable intangible assets, which are related to the airline segment, had a net carrying amount of $4.9 billion at December 31, 2015 , of which $4.7 billion related to indefinite-lived intangible assets. Indefinite-lived assets are not amortized and consist primarily of routes, slots, the Delta tradename and assets related to SkyTeam and collaborative arrangements. Definite-lived assets consist primarily of marketing and maintenance service agreements.

In 2015 , we performed quantitative assessments, including applicable factors noted in " Key Assumptions " above, of our indefinite-lived intangible assets (excluding six London-Heathrow slot pairs we acquired for $276 million during the December 2015 quarter) and determined that there was no indication that the assets were impaired as the fair values ranged from approximately 130% to 280% of the carrying values.

We obtained the Pacific routes and slots asset as part of the acquisition of Northwest Airlines in 2008 and is composed of Pacific route authorities and takeoff and landing rights (“slots”) at capacity-constrained airports in Asia, including Tokyo-Narita International Airport ("Narita"). This intangible asset supports Delta’s Narita hub activities and is essential to Delta's entire Pacific network. Changes in key inputs and assumptions, including (1) new or enhanced joint ventures or alliances, (2) foreign currency exchange rates, (3) fuel costs, legislative or regulatory changes, including changes in access to Tokyo-Haneda airport and (4) Pacific region profitability, could impact the value of this asset in the future.

Long-Lived Assets

Our flight equipment and other long-lived assets have a recorded value of $23.0 billion at December 31, 2015 . This value is based on various factors, including the assets' estimated useful lives and salvage values. We record impairment losses on flight equipment and other long-lived assets used in operations when events and circumstances indicate the assets may be impaired and the estimated future cash flows generated by those assets are less than their carrying amounts. Factors which could cause impairment include, but are not limited to, (1) a decision to permanently remove flight equipment or other long-lived assets from operations, (2) significant changes in the estimated useful life, (3) significant changes in projected cash flows, (4) permanent and significant declines in fleet fair values and (5) changes to the regulatory environment. For long-lived assets held for sale, we discontinue depreciation and record impairment losses when the carrying amount of these assets is greater than the fair value less the cost to sell.

To determine whether impairments exist for aircraft used in operations, we group assets at the fleet-type level (the lowest level for which there are identifiable cash flows) and then estimate future cash flows based on projections of capacity, passenger mile yield, fuel costs, labor costs and other relevant factors. If an impairment occurs, the impairment loss recognized is the amount by which the fleet's carrying