non-ticket revenues also include revenues derived from the sale of advertising to third parties on our website and on board our aircraft . substantially all of our revenues are denominated in u.s. dollars . passenger revenues , as well as most non-ticket revenues , are recognized once the related flight departs . accordingly , the value of tickets and portions of non-ticket revenues sold in advance of travel is included under our current liabilities as “ air traffic liability , ” or atl , until the related air travel is provided . some of our non-ticket revenues are recognized at the time the ancillary products are purchased or ancillary services 39 are provided , such as revenues from our subscription-based $ 9 fare club , which we recognize on a straight-line basis over 12 months . revenue generated from the free spirit credit card affinity program are recognized in accordance with the criteria as set forth in accounting standards update asu no . 2009-13. please see “ —critical accounting policies and estimates—frequent flier program . ” we recognize revenues net of certain taxes and airport passenger fees , which are collected by us on behalf of airports and governmental agencies and remitted to the applicable governmental entity or airport on a periodic basis . these taxes and fees include u.s. federal transportation taxes , federal security charges , airport passenger facility charges and foreign arrival and departure taxes . these items are collected from customers at the time they purchase their tickets , but are not included in our revenues . we record a liability upon collection from the customer and relieve the liability when payments are remitted to the applicable governmental agency or airport . operating expenses our operating expenses consist of the following line items . salaries , wages and benefits . salaries , wages and benefits expense includes the salaries , hourly wages , bonuses and equity compensation paid to employees for their services , as well as the related expenses associated with employee benefit plans and employer payroll taxes . aircraft fuel . aircraft fuel expense includes the cost of jet fuel , related federal taxes , fueling into-plane fees and transportation fees . it also includes realized and unrealized gains and losses arising from any activity on our fuel derivatives . our fuel derivatives generally consist of united states gulf coast jet fuel swaps ( jet fuel swaps ) and united states gulf coast jet fuel options ( jet fuel options ) . aircraft rent . aircraft rent expense consists of all minimum lease payments under the terms of the company 's aircraft and spare engine lease agreements recognized on a straight-line basis . aircraft rent expense also includes supplemental rent . supplemental rent is made up of maintenance reserves paid or expected to be paid to aircraft lessors in advance of the performance of major maintenance activities that are not probable of being reimbursed and probable return condition obligations . aircraft rent expense is net of the amortization of gains and losses on sale leaseback transactions on our flight equipment . as of december 31 , 2016 , 59 of our 95 aircraft and 11 of our 12 spare engines are financed under operating leases . landing fees and other rents . landing fees and other rents include both fixed and variable facilities expenses , such as the fees charged by airports for the use or lease of airport facilities , overfly fees paid to other countries and the monthly rent paid for our headquarters facility . depreciation and amortization . depreciation and amortization expense includes the depreciation of fixed assets we own and leasehold improvements . it also includes the amortization of heavy maintenance expenses we defer under the deferral method of accounting for heavy maintenance events and recognize into expense on a straight-line or usage basis until the earlier of the next estimated heavy maintenance event or the remaining lease term . maintenance , materials and repairs . maintenance , materials and repairs expense includes parts , materials , repairs and fees for repairs performed by third-party vendors directly required to maintain our fleet . it excludes direct labor cost related to our own mechanics , which is included under salaries , wages and benefits . it also excludes the amortization of heavy maintenance expenses , which we defer under the deferral method of accounting and amortize as a component of depreciation and amortization expense . distribution . distribution expense includes all of our direct costs , including the cost of web support , our third-party call center , travel agent commissions and related gds fees and credit card transaction fees , associated with the sale of our tickets and other products and services . special charges . special charges include lease termination costs and secondary offering costs . loss on disposal of assets . loss on disposal of assets includes the net losses on the disposal of our fixed assets . other operating expenses . other operating expenses include airport operations expense and fees charged by third-party vendors for ground handling services and food and liquor supply service expenses , passenger re-accommodation expense , the cost of passenger liability and aircraft hull insurance , all other insurance policies except for employee related insurance , travel and training expenses for crews and ground personnel , professional fees , personal property taxes and all other administrative and operational overhead expenses . no individual item included in this category represented more than 5 % of our total operating expenses . 40 other expense ( income ) interest expense . interest expense in 2016 and 2015 was primarily related to the financing of purchased aircraft . for 2014 , interest expense primarily represented interest related to the financing of purchased aircraft , interest related to the underpayment of prior year jet fuel fet and interest charged under the tax receivable agreement ( tra ) which was settled during 2014. capitalized interest . story_separator_special_tag these revenues also include commissions from the 43 sales of hotel rooms , trip insurance and rental cars recognized at the time the service is rendered . non-ticket revenues also include revenues from our subscription-based $ 9 fare club , recognized on a straight-line basis over 12 months . customers may elect to change their itinerary prior to the date of departure . a service charge is assessed and recognized on the date the change is initiated and is deducted from the face value of the original purchase price of the ticket , and the original ticket becomes invalid . the amount remaining after deducting the service charge is called a credit shell which expires 60 days from the date the credit shell is created and can be used towards the purchase of a new ticket and our other service offerings . the amount of credits expected to expire unused is recognized as revenue upon issuance of the credit and is estimated based on historical experience . estimating the amount of credits that will go unused involves some level of subjectivity and judgment . frequent flier program . we accrue for mileage credits earned through travel , including mileage credits for members with an insufficient number of mileage credits to earn an award , under our free spirit program based on the estimated incremental cost of providing free travel for credits that are expected to be redeemed . incremental costs include fuel , insurance , security , ticketing and facility charges reduced by an estimate of amounts required to be paid by the passenger when redeeming the award . under our affinity card program , funds received for the marketing of a co-branded spirit credit card and delivery of award miles are accounted for as a multiple-deliverable arrangement . at the inception of the arrangement , we evaluated all deliverables in the arrangement to determine whether they represent separate units of accounting . we determined the arrangement had three separate units of accounting : ( i ) travel miles to be awarded , ( ii ) licensing of brand and access to member lists and ( iii ) advertising and marketing efforts . at inception of the arrangement , we established the estimated selling price for all deliverables that qualified for separation , as arrangement consideration should be allocated based on relative selling price . the manner in which the selling price was established was based on the applicable hierarchy of evidence . total arrangement consideration was then allocated to each deliverable on the basis of the deliverable 's relative selling price . in considering the hierarchy of evidence , we first determined whether vendor-specific objective evidence of selling price or third-party evidence of selling price existed . we determined that neither vendor-specific objective evidence of selling price nor third-party evidence existed due to the uniqueness of our program . as such , we developed our best estimate of the selling price for all deliverables . for the selling price of travel , we considered a number of entity-specific factors , including the number of miles needed to redeem an award , average fare of comparable segments , breakage , restrictions , fees to redeem miles and other charges . for licensing of brand and access to member lists , we considered both market-specific factors and entity-specific factors , including general profit margins realized in the marketplace/industry , brand power , market royalty rates and size of customer base . for the advertising and marketing element , we considered market-specific factors and entity-specific factors , including our internal costs ( and fluctuations of costs ) of providing services , volume of marketing efforts and overall advertising plan . consideration allocated based on the relative selling price to both brand licensing and advertising elements is recognized as revenue when earned and recorded in non-ticket revenue . consideration allocated to award miles is deferred and recognized ratably as passenger revenue over the estimated period the transportation is expected to be provided which is currently estimated at 17 months . we used entity-specific assumptions coupled with the various judgments necessary to determine the selling price of a deliverable in accordance with the required selling price hierarchy . changes in these assumptions could result in changes in the estimated selling prices . determining the frequency to reassess selling price for individual deliverables requires significant judgment . for additional information , refer to “ notes to financial statements—1 . summary of significant accounting policies—frequent flier program ” . accounting for property and equipment . property and equipment is stated at cost , less accumulated depreciation and amortization . depreciation of operating property and equipment is computed using the straight-line method applied to each unit of property . property under capital leases and related obligations are initially recorded at an amount equal to the present value of future minimum lease payments computed using our incremental borrowing rate or , when known , the interest rate implicit in the lease . amortization of property under capital leases is on a straight-line basis over the lease term and is included in depreciation and amortization expense . in accounting for property and equipment , we must make estimates about the expected useful lives of the assets , the expected residual values of the assets , and the potential for impairment based on the fair value of the assets and their future expected cash flows . the depreciable lives used for the principal depreciable asset classifications are : 44 estimated useful life aircraft 25 years spare rotables and flight assemblies 7 to 15 years other equipment and vehicles 5 to 7 years internal use software 3 to 10 years capital lease lease term leasehold improvements lesser of lease term or estimated useful life of the improvement as of december 31 , 2016 , we had 36 aircraft and 1 spare engine capitalized within flight equipment with depreciable lives of 25 years . as of december 31 , 2016 , we

net cash flows provided by operating activities . operating activities in 2016 provided $ 473.7 million in cash compared to $ 473.0 million provided in 2015 . cash provided by operating activities remained relatively flat , year over year , despite lower net income , primarily due to the non-cash lease termination costs in 2016 of $ 37.2 million recorded within special charges on the statement of operations . other notable differences include $ 65.0 million of federal income tax payments made in 2015 and refunded in 2016 and lower deferral of income taxes , year over year . operating activities in 2015 provided $ 473.0 million in cash compared to $ 261.8 million provided in 2014 . the increase resulted from higher net income , larger cash collections on flights sold but not yet flown , and higher deferrals of income taxes year over year . net cash flows used in investing activities . during 2016 , investing activities used $ 826.3 million , compared to $ 701.3 million used in 2015 . the increase was mainly driven by the purchase of short-term available-for-sale investment securities of 57 $ 103.3 million made during 2016. in addition , there was an increase in paid pdps , net of refunds , driven by timing of future aircraft deliveries .


 Write a concise suspicious activity report of the following text delimited by triple backquotes. Return your response as a formal report which covers the key points highlighting the location,dates,entity names and account holder information in chronological order of the text.
     ```net cash flows provided by operating activities . operating activities in 2016 provided $ 473.7 million in cash compared to $ 473.0 million provided in 2015 . cash provided by operating activities remained relatively flat , year over year , despite lower net income , primarily due to the non-cash lease termination costs in 2016 of $ 37.2 million recorded within special charges on the statement of operations . other notable differences include $ 65.0 million of federal income tax payments made in 2015 and refunded in 2016 and lower deferral of income taxes , year over year . operating activities in 2015 provided $ 473.0 million in cash compared to $ 261.8 million provided in 2014 . the increase resulted from higher net income , larger cash collections on flights sold but not yet flown , and higher deferrals of income taxes year over year . net cash flows used in investing activities . during 2016 , investing activities used $ 826.3 million , compared to $ 701.3 million used in 2015 . the increase was mainly driven by the purchase of short-term available-for-sale investment securities of 57 $ 103.3 million made during 2016. in addition , there was an increase in paid pdps , net of refunds , driven by timing of future aircraft deliveries .
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 Suspicious Activity Report : non-ticket revenues also include revenues derived from the sale of advertising to third parties on our website and on board our aircraft . substantially all of our revenues are denominated in u.s. dollars . passenger revenues , as well as most non-ticket revenues , are recognized once the related flight departs . accordingly , the value of tickets and portions of non-ticket revenues sold in advance of travel is included under our current liabilities as “ air traffic liability , ” or atl , until the related air travel is provided . some of our non-ticket revenues are recognized at the time the ancillary products are purchased or ancillary services 39 are provided , such as revenues from our subscription-based $ 9 fare club , which we recognize on a straight-line basis over 12 months . revenue generated from the free spirit credit card affinity program are recognized in accordance with the criteria as set forth in accounting standards update asu no . 2009-13. please see “ —critical accounting policies and estimates—frequent flier program . ” we recognize revenues net of certain taxes and airport passenger fees , which are collected by us on behalf of airports and governmental agencies and remitted to the applicable governmental entity or airport on a periodic basis . these taxes and fees include u.s. federal transportation taxes , federal security charges , airport passenger facility charges and foreign arrival and departure taxes . these items are collected from customers at the time they purchase their tickets , but are not included in our revenues . we record a liability upon collection from the customer and relieve the liability when payments are remitted to the applicable governmental agency or airport . operating expenses our operating expenses consist of the following line items . salaries , wages and benefits . salaries , wages and benefits expense includes the salaries , hourly wages , bonuses and equity compensation paid to employees for their services , as well as the related expenses associated with employee benefit plans and employer payroll taxes . aircraft fuel . aircraft fuel expense includes the cost of jet fuel , related federal taxes , fueling into-plane fees and transportation fees . it also includes realized and unrealized gains and losses arising from any activity on our fuel derivatives . our fuel derivatives generally consist of united states gulf coast jet fuel swaps ( jet fuel swaps ) and united states gulf coast jet fuel options ( jet fuel options ) . aircraft rent . aircraft rent expense consists of all minimum lease payments under the terms of the company 's aircraft and spare engine lease agreements recognized on a straight-line basis . aircraft rent expense also includes supplemental rent . supplemental rent is made up of maintenance reserves paid or expected to be paid to aircraft lessors in advance of the performance of major maintenance activities that are not probable of being reimbursed and probable return condition obligations . aircraft rent expense is net of the amortization of gains and losses on sale leaseback transactions on our flight equipment . as of december 31 , 2016 , 59 of our 95 aircraft and 11 of our 12 spare engines are financed under operating leases . landing fees and other rents . landing fees and other rents include both fixed and variable facilities expenses , such as the fees charged by airports for the use or lease of airport facilities , overfly fees paid to other countries and the monthly rent paid for our headquarters facility . depreciation and amortization . depreciation and amortization expense includes the depreciation of fixed assets we own and leasehold improvements . it also includes the amortization of heavy maintenance expenses we defer under the deferral method of accounting for heavy maintenance events and recognize into expense on a straight-line or usage basis until the earlier of the next estimated heavy maintenance event or the remaining lease term . maintenance , materials and repairs . maintenance , materials and repairs expense includes parts , materials , repairs and fees for repairs performed by third-party vendors directly required to maintain our fleet . it excludes direct labor cost related to our own mechanics , which is included under salaries , wages and benefits . it also excludes the amortization of heavy maintenance expenses , which we defer under the deferral method of accounting and amortize as a component of depreciation and amortization expense . distribution . distribution expense includes all of our direct costs , including the cost of web support , our third-party call center , travel agent commissions and related gds fees and credit card transaction fees , associated with the sale of our tickets and other products and services . special charges . special charges include lease termination costs and secondary offering costs . loss on disposal of assets . loss on disposal of assets includes the net losses on the disposal of our fixed assets . other operating expenses . other operating expenses include airport operations expense and fees charged by third-party vendors for ground handling services and food and liquor supply service expenses , passenger re-accommodation expense , the cost of passenger liability and aircraft hull insurance , all other insurance policies except for employee related insurance , travel and training expenses for crews and ground personnel , professional fees , personal property taxes and all other administrative and operational overhead expenses . no individual item included in this category represented more than 5 % of our total operating expenses . 40 other expense ( income ) interest expense . interest expense in 2016 and 2015 was primarily related to the financing of purchased aircraft . for 2014 , interest expense primarily represented interest related to the financing of purchased aircraft , interest related to the underpayment of prior year jet fuel fet and interest charged under the tax receivable agreement ( tra ) which was settled during 2014. capitalized interest . story_separator_special_tag these revenues also include commissions from the 43 sales of hotel rooms , trip insurance and rental cars recognized at the time the service is rendered . non-ticket revenues also include revenues from our subscription-based $ 9 fare club , recognized on a straight-line basis over 12 months . customers may elect to change their itinerary prior to the date of departure . a service charge is assessed and recognized on the date the change is initiated and is deducted from the face value of the original purchase price of the ticket , and the original ticket becomes invalid . the amount remaining after deducting the service charge is called a credit shell which expires 60 days from the date the credit shell is created and can be used towards the purchase of a new ticket and our other service offerings . the amount of credits expected to expire unused is recognized as revenue upon issuance of the credit and is estimated based on historical experience . estimating the amount of credits that will go unused involves some level of subjectivity and judgment . frequent flier program . we accrue for mileage credits earned through travel , including mileage credits for members with an insufficient number of mileage credits to earn an award , under our free spirit program based on the estimated incremental cost of providing free travel for credits that are expected to be redeemed . incremental costs include fuel , insurance , security , ticketing and facility charges reduced by an estimate of amounts required to be paid by the passenger when redeeming the award . under our affinity card program , funds received for the marketing of a co-branded spirit credit card and delivery of award miles are accounted for as a multiple-deliverable arrangement . at the inception of the arrangement , we evaluated all deliverables in the arrangement to determine whether they represent separate units of accounting . we determined the arrangement had three separate units of accounting : ( i ) travel miles to be awarded , ( ii ) licensing of brand and access to member lists and ( iii ) advertising and marketing efforts . at inception of the arrangement , we established the estimated selling price for all deliverables that qualified for separation , as arrangement consideration should be allocated based on relative selling price . the manner in which the selling price was established was based on the applicable hierarchy of evidence . total arrangement consideration was then allocated to each deliverable on the basis of the deliverable 's relative selling price . in considering the hierarchy of evidence , we first determined whether vendor-specific objective evidence of selling price or third-party evidence of selling price existed . we determined that neither vendor-specific objective evidence of selling price nor third-party evidence existed due to the uniqueness of our program . as such , we developed our best estimate of the selling price for all deliverables . for the selling price of travel , we considered a number of entity-specific factors , including the number of miles needed to redeem an award , average fare of comparable segments , breakage , restrictions , fees to redeem miles and other charges . for licensing of brand and access to member lists , we considered both market-specific factors and entity-specific factors , including general profit margins realized in the marketplace/industry , brand power , market royalty rates and size of customer base . for the advertising and marketing element , we considered market-specific factors and entity-specific factors , including our internal costs ( and fluctuations of costs ) of providing services , volume of marketing efforts and overall advertising plan . consideration allocated based on the relative selling price to both brand licensing and advertising elements is recognized as revenue when earned and recorded in non-ticket revenue . consideration allocated to award miles is deferred and recognized ratably as passenger revenue over the estimated period the transportation is expected to be provided which is currently estimated at 17 months . we used entity-specific assumptions coupled with the various judgments necessary to determine the selling price of a deliverable in accordance with the required selling price hierarchy . changes in these assumptions could result in changes in the estimated selling prices . determining the frequency to reassess selling price for individual deliverables requires significant judgment . for additional information , refer to “ notes to financial statements—1 . summary of significant accounting policies—frequent flier program ” . accounting for property and equipment . property and equipment is stated at cost , less accumulated depreciation and amortization . depreciation of operating property and equipment is computed using the straight-line method applied to each unit of property . property under capital leases and related obligations are initially recorded at an amount equal to the present value of future minimum lease payments computed using our incremental borrowing rate or , when known , the interest rate implicit in the lease . amortization of property under capital leases is on a straight-line basis over the lease term and is included in depreciation and amortization expense . in accounting for property and equipment , we must make estimates about the expected useful lives of the assets , the expected residual values of the assets , and the potential for impairment based on the fair value of the assets and their future expected cash flows . the depreciable lives used for the principal depreciable asset classifications are : 44 estimated useful life aircraft 25 years spare rotables and flight assemblies 7 to 15 years other equipment and vehicles 5 to 7 years internal use software 3 to 10 years capital lease lease term leasehold improvements lesser of lease term or estimated useful life of the improvement as of december 31 , 2016 , we had 36 aircraft and 1 spare engine capitalized within flight equipment with depreciable lives of 25 years . as of december 31 , 2016 , we

