rate and (2) the expected long-term rate of return on the assets of our DB Plans. The Pilot Plan and pilot non-qualified defined benefit pension plans were terminated during 2006. For additional information regarding these terminations, see Note 10 of the Notes to the Consolidated Financial Statements.

We determine our weighted average discount rate on our measurement date primarily by reference to annualized rates earned on high quality fixed income investments and yield-to-maturity analysis specific to our estimated future benefit payments. We used a weighted average discount rate of 6.08% and 5.88% at December 31, 2007 and September 30, 2006, respectively. Additionally, our weighted average discount rate for net periodic benefit cost in each of the past three years has varied from the rate selected on our measurement date, ranging from 5.67% to 6.01% between 2005 and 2007, due to remeasurements throughout the year. The impact of a 0.50% change in our weighted average discount rate is shown in the table below.

The expected long-term rate of return on the assets of our DB Plans is based primarily on plan specific investment studies using historical returns on our DB Plans’ assets. The investment strategy for pension plan assets is to utilize a diversified mix of global public and private equity portfolios, public and private fixed income portfolios, and private real estate and natural resource investments to earn a long-term investment return that meets or exceeds a 9% annualized return target. Our historical annualized three, five, 10 and 15 year rate of return on plan assets is approximately 13%, 14%, 8% and 11%, respectively, as of December 31, 2007. The impact of a 0.50% change in our expected long-term rate of return is shown in the table below.

Recently Issued Accounting Pronouncements

In December 2007, the Financial Accounting Standards Board issued SFAS 141R. SFAS 141R provides guidance for recognizing and measuring goodwill acquired in a business combination and requires disclosure of information to enable users of the financial statements to evaluate the nature and financial effects of the business combination. SFAS 141R is effective for fiscal years beginning on January 1, 2009. For additional information regarding SFAS 141R, see Note 9 of the Notes to the Consolidated Financial Statements.

 Market Risks Associated with Financial Instruments

We have significant market risk exposure related to aircraft fuel prices and interest rates. Market risk is the potential negative impact of adverse changes in these prices or rates on our Consolidated Financial Statements. To manage the volatility relating to these exposures, we periodically enter into derivative transactions pursuant to stated policies (see Note 4 of the Notes to the Consolidated Financial Statements). We expect adjustments to the fair value of financial instruments accounted for under SFAS No. 133, “Accounting for Derivative Instruments and Hedging Activities” to result in ongoing volatility in earnings and shareowners’ equity.

The following sensitivity analyses do not consider the effects of a change in demand for air travel, the economy as a whole or actions we