Airport Variable Rate Debt & Interest Rate Risk Management

What Is Variable Rate Debt in Airport Finance?

Variable rate debt refers to bond instruments whose interest rates reset periodically â€" daily, weekly, monthly, or at other intervals â€" rather than remaining fixed for the life of the bond. The most common form in airport finance is the Variable Rate Demand Obligation (VRDO), a long-term bond with a 20â€"30 year maturity and a short-term interest rate that resets weekly based on market conditions. The rate is set by a remarketing agent who seeks to clear the market â€" the rate at which supply of the VRDO meets investor demand.

VRDOs include a "put" or "demand" feature that allows the bondholder to tender the bond back to the issuer at par plus accrued interest on any reset date. Because the issuer cannot guarantee it will have cash on hand to purchase tendered bonds, VRDOs require a liquidity facility â€" either a Letter of Credit (LOC) or a Standby Bond Purchase Agreement (SBPA) â€" provided by a commercial bank. The bank agrees to purchase any bonds tendered and not successfully remarketed.

Other variable rate structures used by airports include:

• Commercial Paper (CP) Notes: Short-term instruments (1â€"270 days) issued on a rolling basis. Dallas Fort Worth International Airport (DFW), for example, refunded approximately $650 million of commercial paper as part of its $1.967 billion revenue bond offering in September 2025.
• Floating Rate Notes (FRNs): Longer-duration instruments with interest rates that reset periodically based on a formula (e.g., SIFMA + spread). FRNs may include "soft put" provisions where a failed remarketing triggers a rate step-up to a maximum rate (9%â€"15% per annum), rather than a mandatory bank purchase.
• Mandatory Tender (Put) Bonds: Fixed-rate bonds with a mandatory tender at a future date, creating a hybrid structure. DFW's September 2025 offering included $300 million of put bonds with mandatory tender dates in 2029 and 2032, producing an estimated $56 million of present value savings over the bond life compared to traditional fixed-rate bonds maturing in 2050.

The SIFMA Municipal Swap Index

The benchmark rate for most tax-exempt variable rate transactions is the SIFMA Municipal Swap Index (formerly the Bond Market Association or "BMA" Index). SIFMA is a 7-day high-grade market index composed of tax-exempt VRDOs meeting specific criteria. The index is calculated and published weekly by Bloomberg and overseen by SIFMA's Municipal Swap Index Committee.

SIFMA serves two functions: (1) as a benchmark against which actual VRDO reset rates are compared, and (2) as the floating-rate leg in most tax-exempt interest rate swap agreements.

Recent SIFMA rate history illustrates the volatility embedded in variable rate exposure:

Between January 1, 2022 and December 14, 2022, the SIFMA Index rose from 0.06% to 3.73% â€" a 367 basis point increase within a single calendar year. For an airport with $200 million of unhedged variable rate bonds, that move equates to approximately $7.3 million of additional annual interest cost â€" a line item that would flow directly through to airline rates and charges under a residual rate-setting methodology.

As of January 21, 2026, the SIFMA Index stood at 1.31%, with taxable SOFR at 3.64%, producing a tax-exempt-to-taxable ratio of 36% â€" compared to 59% on the same date in 2025.

Why Airports Use Variable Rate Debt

Airports have historically incorporated variable rate debt into their capital structures for several reasons:

Lower short-term borrowing costs. Short-term tax-exempt rates have historically been lower than long-term fixed rates. In January 2026, daily-mode tax-exempt VRDNs averaged 0.20%, representing a 5% ratio to SOFR. Fixed-rate airport revenue bonds issued in the same period carried coupons of 5.00%â€"5.75%.

Asset-liability matching. Airports hold substantial cash reserves and investment portfolios whose returns correlate with short-term rates. Maintaining a portion of debt at variable rates can create a natural hedge where investment income rises in tandem with debt service costs during periods of rising rates.

Call flexibility. VRDOs are callable at par on any interest payment date, providing airports with the option to refinance or restructure without paying the call premium (typically 100â€"102% of par) required for fixed-rate bonds with a future optional redemption date.

Interim financing. Commercial paper programs allow airports to fund capital projects on an interim basis while awaiting favorable conditions for long-term fixed-rate bond issuance.

Interest Rate Swap Mechanics

An interest rate swap is a contractual agreement between two parties â€" the airport issuer and a bank counterparty â€" to exchange periodic interest payments based on a notional principal amount. In the most common structure for airports:

• The airport pays the counterparty a fixed rate (negotiated at inception).
• The counterparty pays the airport a floating rate, indexed to SIFMA or a percentage of SOFR.
• Payments are netted: in any given period, only the difference between the two rates is paid.

The combination of variable rate bonds and a pay-fixed/receive-floating swap creates a synthetic fixed rate: the airport pays a fixed swap rate to the counterparty, receives a floating rate from the counterparty that is intended to approximate its variable rate bond interest, and the two floating legs offset â€" leaving the airport with a net fixed cost.

Example:

An airport issues $100 million of weekly-mode VRDOs and simultaneously enters a SIFMA-based interest rate swap with a bank:

• Airport pays bondholders: variable rate (resets weekly, indexed to SIFMA)
• Airport pays swap counterparty: fixed 3.50%
• Airport receives from swap counterparty: SIFMA

If SIFMA resets at 1.31%, the net position is:

• Bond interest paid: 1.31%
• Swap: pays 3.50%, receives 1.31%; net swap payment = 2.19%
• All-in cost: 1.31% + 2.19% = 3.50% (the fixed swap rate)

This works as intended when the actual VRDO rate tracks SIFMA. The risk emerges when it does not â€" a condition known as basis risk.

Risks of Variable Rate Debt

Interest Rate Risk

The most direct risk is that short-term rates rise, increasing debt service costs. Between the start and end of 2022, the SIFMA Index moved from 0.06% to approximately 3.73%. For unhedged variable rate debt, this movement translates directly to higher interest expense.

For airports operating under residual airline use agreements, increased variable rate interest costs pass through to airlines via higher rates and charges. Under compensatory agreements, increased costs reduce net revenue available for debt service coverage.

Basis Risk

Basis risk arises when the floating rate on the airport's bonds does not move in lockstep with the floating rate on its swap. This is particularly relevant for airports that hedged SIFMA-based variable rate bonds with swaps indexed to a percentage of LIBOR (or now SOFR).

The historical SIFMA-to-1-month-LIBOR ratio averaged approximately 70.4% from January 2007 through early 2020. During the March 2020 market disruption, the ratio fluctuated violently â€" the SIFMA Index spiked 390 basis points in a single week (March 18, 2020). During such dislocations, an airport paying its bondholders at the actual VRDO rate while receiving only a percentage-of-LIBOR floating leg from its swap counterparty absorbs the gap as unhedged cost.

The transition from LIBOR to SOFR (completed June 30, 2023, per GASB Statement No. 99) introduced an additional dimension of basis risk, as the historical correlation between SIFMA and SOFR differs from the SIFMA-to-LIBOR relationship that most legacy swap structures were calibrated against.

Remarketing and Put Risk

If the remarketing agent is unable to find buyers for tendered VRDOs, the liquidity bank must purchase the bonds under the LOC or SBPA. This triggers "bank rate" pricing â€" which can reach 12%â€"15% per annum, depending on the LOC agreement â€" and may convert the instrument to a term loan amortizing over a compressed schedule.

The SEC's Fiscal Year 2026 Examination Priorities include the "rates reset process on variable rate demand obligations" as a broker-dealer review area for the first time. This follows ongoing litigation â€" including the class action City of Philadelphia v. Bank of America Corp. (SDNY, Case No. 19-cv-4781), which alleges that major remarketing agents conspired to set artificially high VRDO rates. An Illinois case settled for $70 million in October 2023. In September 2023, Judge Jesse Furman of the Southern District of New York refused to dismiss most claims in the LIBOR manipulation litigation, and in August 2025, the Second Circuit affirmed class certification.

Liquidity Facility Renewal Risk

LOCs and SBPAs are structured with terms of 3–5 years, as documented in official statements and bond indentures of major airports. Upon expiration, the airport must either renew with the existing bank, find a replacement provider, or convert the bonds to a different interest rate mode. If bank credit markets tighten – as occurred during the 2008–2009 financial crisis – renewal costs can increase and availability can decline. LOC fees have ranged from approximately 50 to 200 basis points per annum, depending on credit quality of both the issuer and the bank.

Chicago O'Hare International Airport, as of November 2025, maintained approximately $341 million outstanding in variable rate bonds supported by LOC/SBPA facilities provided by Bank of America, Wells Fargo Bank, and Huntington National Bank.

Swap Termination Risk

An interest rate swap has a mark-to-market value at any point in time. If the airport's fixed swap rate is above current market rates, the swap has a negative fair value â€" meaning the airport would owe a termination payment to exit. Termination can be triggered by:

• Voluntary unwinding by the airport
• A credit rating downgrade that breaches the swap agreement's rating floor
• Counterparty credit events

The City of Chicago held approximately $3 billion of debt tied to interest rate swaps, with annual net swap payments of approximately $60 million. A 2015 Moody's downgrade triggered a potential $58 million termination penalty, and further deterioration to junk status could have triggered an additional $1.2 billion in fees and penalties.

The City of Detroit owed $288 million in swap termination fees in 2013 following a credit downgrade; the final settlement in bankruptcy was $85 million. The Orlando-Orange County Expressway Authority incurred significant swap termination costs when restructuring its variable-rate debt portfolio.

In airport finance, Denver International Airport's Series 2022C-D bond issuance ($1.167 billion, November 2022) included $754,700 for terminating swaps associated with its Series 2007G-1 and Series 2007G-2 variable rate bonds ($46.3 million and $46.5 million principal, respectively). The low termination cost reflected the bonds' approaching maturity and rate environment at the time of execution.

Debt Policy Frameworks

Airport debt policies govern the permissible level of variable rate exposure and the conditions under which derivatives may be used.

San Francisco International Airport (SFO) maintains a formal Debt Policy (revised February 20, 2024) that states: "The Commission shall limit its aggregate unhedged variable rate exposure on long-term Bonds to no more than 20% of the aggregate outstanding principal amount" of bonds. As of November 2025, SFO's variable rate debt constituted less than 3% of its total outstanding debt (approximately $8.9 billion as of July 1, 2024), and SFO reported no outstanding derivative instruments.

SFO's policy also provides that fixed-rate bonds "shall be the primary type of Bonds issued by the Commission" and that variable rate bonds "may be the secondary type." The policy permits interest rate swaps "in accordance with the Commission's Interest Rate Swap Policy" as an attached appendix.

This 20% cap with disclosed actual exposure below 3% reflects a pattern among large-hub airports that entered the post-2008 period with variable rate positions and have since reduced exposure through fixed-rate refundings.

Accounting and Disclosure: GASB 53 and Subsequent Guidance

GASB Statement No. 53, Accounting and Financial Reporting for Derivative Instruments (effective for periods beginning after June 15, 2009), establishes the framework for how airports report interest rate swaps and other derivatives in their Annual Comprehensive Financial Reports (ACFRs).

Key requirements:

• Fair value reporting: Derivatives are reported at fair value on the statement of net position, as either assets or liabilities depending on whether the mark-to-market is positive or negative.
• Hedging vs. investment classification: Derivatives that meet the definition of a hedging instrument (those that "significantly reduce an identified financial risk") report changes in fair value as deferred inflows or outflows. Derivatives classified as investment instruments report fair value changes in the current period as investment income.
• Annual effectiveness testing: Airport issuers are required to assess the effectiveness of hedging derivatives at the end of each reporting period. If a derivative is determined to be ineffective, the accumulated deferred amounts are reclassified to investment income.

Subsequent standards have updated the framework:

• GASB 93 (2020): Addresses the transition from IBOR-based rates to alternative reference rates.
• GASB 99 (2022): Confirms that LIBOR is no longer an appropriate benchmark interest rate for swap effectiveness evaluation as of June 30, 2023, and has been replaced by SOFR.

ACFR note disclosures for airports with outstanding derivatives include the notional amount, fair value, counterparty, reference rate, fixed rate paid, termination date, and a description of the risks (credit risk, basis risk, termination risk, and rollover risk).

The Post-2008 Reduction in Airport Variable Rate Exposure

The 2008â€"2009 financial crisis transformed the municipal variable rate market. Several events converged:

1. Auction rate securities (ARS) market failure (February 2008): The auction mechanism froze when broker-dealers stopped supporting failed auctions, stranding issuers â€" including airports â€" with bonds bearing penalty rates.
2. Bond insurer downgrades: Financial Guaranty Insurance Company (FGIC), Ambac, and others were downgraded, causing VRDOs insured by these entities to lose their money-market eligibility and trade at distressed levels. SFO explicitly cited FGIC's downgrade below triple-A as a driver for its 2008 variable rate refunding program.
3. LOC availability contraction: Banks that had provided liquidity facilities either withdrew from the market or raised fees substantially, creating renewal risk for airports with expiring credit facilities.
4. Swap termination costs: As interest rates fell, airports that had entered pay-fixed swaps at higher rates found themselves with deeply negative mark-to-market values. Terminating these swaps to convert to conventional fixed-rate debt required substantial upfront payments.

The amount of VRDOs outstanding in the municipal market has declined from pre-crisis levels. Airports have been part of this trend. SFO's current variable rate exposure (less than 3% of total debt, with no outstanding swaps) is illustrative of the deleveraging that has occurred at large-hub airports since 2008.

Current Market Context (2025â€"2026)

U.S. airports sold approximately $24 billion of debt in the municipal market in calendar year 2025, an annual record and a 12% increase from the prior year. Total municipal bonds outstanding reached $4.4 trillion as of Q3 2025.

The record borrowing reflects multi-billion-dollar capital programs at airports addressing aging infrastructure and traffic growth. The financing tools available for these programs continue to evolve:

• Mandatory tender bonds: DFW's September 2025 offering ($300 million of put bonds with 4-year and 7-year mandatory tender dates) illustrates an alternative to traditional VRDOs that provides rate savings during the initial period without requiring a bank liquidity facility.
• Direct bank placements: Private placements with commercial banks, structured as variable rate or term-rate loans, avoid the costs of public issuance and remarketing while providing rate flexibility.
• Synthetic fixed-rate structures: For airports that do maintain variable rate exposure, SIFMA-indexed swaps continue to serve as hedging instruments â€" though the LIBOR-to-SOFR transition has required renegotiation of legacy swap terms.

The SEC's inclusion of VRDO rate-resetting practices in its FY2026 examination priorities signals increased regulatory attention to the remarketing process. The ongoing City of Philadelphia v. Bank of America litigation, along with parallel state-level cases in California and New Jersey, may reshape the compliance framework within which remarketing agents operate.

Considerations for Airport Finance Professionals

For airport finance teams evaluating variable rate exposure within their debt portfolios, several areas of analysis may be relevant:

• Quantifying unhedged exposure: Measuring total variable rate bonds outstanding as a percentage of total debt, and comparing to the caps established in the airport's formal debt policy. SFO's framework â€" a 20% policy cap with actual exposure below 3% â€" provides one reference point.
• Stress-testing rate scenarios: Modeling the impact of SIFMA increases on debt service, airline rates and charges, and coverage ratios. The 367-basis-point SIFMA increase observed in calendar year 2022 offers a historical stress scenario.
• Evaluating basis risk in existing swaps: For airports with legacy percentage-of-LIBOR swaps that have transitioned to SOFR-based floating legs, monitoring the SIFMA/SOFR ratio and comparing it to the assumed ratio at swap inception. As of January 2026, the SIFMA/SOFR ratio stood at approximately 36%.
• Tracking LOC/SBPA expiration schedules: Mapping facility expiration dates against anticipated capital market conditions and bank credit availability.
• Reviewing swap termination exposure: Calculating mark-to-market values of outstanding swaps and identifying triggers (rating thresholds, counterparty events) that could force termination.
• Monitoring regulatory developments: The SEC's new focus on VRDO rate-resetting and the outcome of the Philadelphia v. Bank of America litigation may affect the terms, costs, and compliance obligations associated with future variable rate issuance.

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