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Operating Costs and Aging of Air Force Aircraft

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Operating costs for Air Force aircraft are about twice as large as acquisition costs and are thought to depend on age. When researchers have examined the question using data from the 1990s, they have found little or no association (none to 3 percent per year) between airplanes’ age and operating costs, but when they have used data from the 2000s with similar methods, they have found a significant association between the two (3 percent to 8 percent per year).

A current study by CBO reconciles that discrepancy by using the size of the Air Force’s budget as an additional explanatory variable. Estimates that do not account for the Air Force’s budget, according to the study, show that an additional year of age is associated with costs mostly in the range of 3 percent to 6 percent. Estimates that do account for the Air Force’s budget find associations mostly in the 2 to 4 percent range.

Presentation by Derek Trunkey, an analyst with CBO’s National Security Division, at the 93rd Annual Conference of the Western Economic Association International.

Published in: Government & Nonprofit
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Operating Costs and Aging of Air Force Aircraft

  1. 1. Congressional Budget Office 93rd Annual Conference of the Western Economic Association International Vancouver, British Columbia June 29, 2018 Derek Trunkey National Security Division Operating Costs and Aging of Air Force Aircraft
  2. 2. 1 CBO Operating costs are about double acquisition costs and are thought to depend on age.
  3. 3. 2 CBO Source: K.R. Sperry and K.E. Burns, Life Cycle Cost Modeling and Simulation to Determine the Economic Service Life of Aging Aircraft (October 2001). Aircraft Operating Costs Are Expected to Decline in Initial Years of Operation, to Plateau, and Then to Increase During a Final Phase
  4. 4. 3 CBO Estimates of the cost growth associated with age using data from the 1990s found little or no association (0 to 3 percent per year), whereas estimates using data from the 2000s found significant real growth as aircraft age (3 to 8 percent per year). CBO looked to see if there are factors that could explain the higher growth rates in the recent past.
  5. 5. 4 CBO  Studies based on 1990s’ data found little or no growth associated with age – LMI (2003) found no age effect – CBO (2001) found growth of 1 to 3 percent per year  Studies based on 2000s’ data found larger growth – Keating and Arena (2016) found real growth mostly in the 4 to 8 percent per year range – Current study found real growth mostly in the 3 to 6 percent per year range (based on a similar model with age as the only explanatory variable) CBO’s Results Explain Divergent Findings From Previous Studies See Logistics Management Institute, The Relationship Among Cost, Age, and Usage of Weapon Systems (January 2003); Congressional Budget Office, The Effects of Aging on the Costs of Operating and Maintaining Military Equipment (August 2001), Appendix B, www.cbo.gov/publication/13213; and Edward G. Keating and Mark V. Arena, “Defense Inflation: What Has Happened, Why Has It Happened, and What Can Be Done About It?” Defense and Peace Economics, vol. 27, no. 2 (April 2016), pp. 176–183.
  6. 6. 5 CBO CBO’s current study reconciles past studies from different eras by using the size of the Air Force’s budget as an additional explanatory variable.
  7. 7. 6 CBO  CBO used linear regression models to explain the costs per flying hour (semi log form)  The first model used only age of aircraft as an explanatory variable  The second model used both age of aircraft and the size of the Air Force’s budget as explanatory variables  CBO used annual AFTOC data from 1999 to 2016 for B-1B, B-52, C-130, C-17, C-5, F-15 A-D, F-15E, F-16, F-22A, HH-60G, KC-135, RQ-4, and U-2 – Most data are from the midpoint of an aircraft’s life CBO Explored Factors That Could Explain the High Recent Growth in Operating Costs
  8. 8. 7 CBO The model that did not account for the budget found results comparable to those from prior research.
  9. 9. 8 CBO B-1 Costs per Flying Hour Generally Increased as the System Aged 2.9 percent growth in costs per year of age 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000 0 5 10 15 20 25 30 35 Age (Years) Costs per Flying Hour (2016 dollars)
  10. 10. 9 CBO Estimates that did not account for the Air Force’s budget show an additional year of age is associated with costs per flying hour mostly in the range of 3 to 6 percent.
  11. 11. 10 CBO A Number of Air Force Systems Experienced Sizable But Highly Varying Increases in Costs per Flying Hour B-1 B-52 C-130H C-5 F-15 A-D F-16 HH-60 KC-135r F-15E 0 1 2 3 4 5 6 7 8 0 5 10 15 20 25 30 35 40 45 50 Average Age Over Sample (Years) Annual Real Growth in Costs per Flying Hour (Percent)
  12. 12. 11 CBO Some aircraft are still in the immature phase and experienced declining costs.
  13. 13. 12 CBO Some Younger Air Force Fleets (F-22, RQ-4, C-17) Experienced Declining Costs per Flying Hour as They Aged B-1 B-52C-130H C-5 F-15 A-D F-16 HH-60 KC-135rF-15E C-17 U-2 F-22 RQ-4 -60 -50 -40 -30 -20 -10 0 10 0 5 10 15 20 25 30 35 40 45 50 Average Age Over Sample (Years) Annual Real Growth in Costs per Flying Hour (Percent)
  14. 14. 13 CBO The Air Force’s budget increased significantly between 2000 and 2016. Accounting for that budget reduced the association between cost and aircraft age by up to half in the 2000s.
  15. 15. 14 CBO The Air Force’s Total Budget Increased Markedly in Real Terms Between 2000 and 2010 0 50 100 150 200 250 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 Total Air Force Budget, by Fiscal Year (Billions of 2016 dollars) Time period of data for 2001 CBO report Time period of data for 2018 CBO report
  16. 16. 15 CBO The model that accounted for the size of the Air Force’s budget found growth rates that were more consistent with those of models based on 1990s’ data.
  17. 17. 16 CBO The model that accounted for the Air Force’s budget found that the association between aging and cost growth was mostly in the 2 to 4 percent range. Other factors (such as mission capable rates and number of hours flown) had smaller associations or were insignificant.
  18. 18. 17 CBO Including the Air Force’s Total Budget as an Independent Variable Generally Reduced the Association With Age B-1 B-52 C-130H C-5 F-15 A-D F-16 HH-60 KC-135r F-15E B-1 B-52 C-130H C-5F-15 A-D F-16 HH-60 KC-135RF-15E 0 1 2 3 4 5 6 7 8 0 5 10 15 20 25 30 35 40 45 50 Average Age Over Sample (years) Annual Real Growth in Costs per Flying Hour (Percent) Accounting for age Accounting for age and the Air Force's budget
  19. 19. 18 CBO Additional Information on CBO’s Approach
  20. 20. 19 CBO Cost=annual operating cost; age=average age in years; budget=Air Force Total Obligation Authority. 1. Measure simple association: Ln(Cost/FH) = a + b1*age 2. Use an enhanced regression that accounts for the budget: Ln(Cost/FH) = a + b1*age + b2*budget 3. Examine several aircraft types: – B-1B, B-52, C-130, C-17, C-5, F-15 A-D, F-15E, F-16, F-22A, HH-60G, KC-135, RQ-4, U-2 – Use annual AFTOC data from 1999 to 2016 – Most data are from the midpoint of an aircraft’s life How CBO Explored Factors That Could Explain the High Recent Growth
  21. 21. 20 CBO ** indicates that the P value is less than .01. Estimated Coefficient (Standard Error) Aircraft Intercept Age B-1 10.55** 0.0291** (.103) (.005) B-52 8.47** 0.0548** (.329) (.007) C-130H 8.44** 0.0685** (.099) (.005) C-17 18.83** -0.1771** (.082) (.011) C-5 9.88** 0.0400** (.206) (.007) F-15 A-D 8.94** 0.0542** (.143) (.006) F-15E 9.93** 0.0271** (.126) (.008) F-16 9.11** 0.0375** (.176) (.010) F-22 15.05** -0.5610** (.791) (.176) HH-60 9.22** 0.0515** (.155) (.009) KC-135T 8.36** 0.0278** (.248) (.005) RQ-4 12.28** -0.2730** (.681) (.188) U-2 8.36** -0.0412** (.248) (.007) Regression Results for Simple Model, Dependent Variable Is Ln(Cost/FH)
  22. 22. 21 CBO * indicates that the P value is less than .10; ** indicates that the P value is less than .01. Regression Results for Model With Budget, Dependent Variable Is Ln(Cost/FH) Estimated Coefficient (Standard Error) Aircraft Intercept Age AF Budget (Billions 2016$) B-1 10.13** 0.0190** 0.0039** (.131) (.004) 0.0010 B-52 8.25** 0.0406** 0.0055** (.258) (.007) (.0015) C-130H 8.37** 0.0667** 0.0065** (.177) (.006) (.0014) C-17 8.79** -0.0986** -0.0064 (1.094) (.015) (.002) C-5 8.83** 0.0343** 0.0076** (.400) (.006) (.003) F-15 A-D 8.53** 0.0335** 0.0059** (.144) (.006) (.001) F-15E 10.01** 0.0291** 0.0031* (.144) (.010) (.002) F-16 8.21** 0.0153** 0.0084** (.225) (.009) (.002) F-22 29.83** -0.7444** -0.0830 (5.850) (.162) (.006) HH-60 8.58** 0.0370** 0.0056* (.271) (.009) (2.716) KC-135T 8.43** 0.0325** -0.0018 (.249) (.006) (.001) RQ-4 3.35 -0.3491 0.0518 (7.142) (.395) (.037) U-2 11.98** -0.0341** -0.0029 (.240) (.008) (.002)

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