Airport Debt Portfolio Management and Refunding Strategies

The Debt Portfolio as a Managed Asset

An airport's outstanding debt portfolio—the aggregate of all bond series, notes, and credit facilities—is not a static obligation. It is an asset that can be actively managed through refunding transactions, lien management, amortization design, and capital planning to reduce borrowing costs, reshape debt service profiles, and preserve financial flexibility.

At the largest U.S. airports, the outstanding portfolio can exceed $10 billion in par amount. Los Angeles World Airports (LAWA) had $10.8 billion in outstanding airport revenue bond debt as of its 2024 authorization request, with $3 billion in additional issuance authorized through FY2028 (May 22, 2024). Phoenix Sky Harbor International Airport (PHX) carried $1.86 billion across senior-lien ($610 million) and junior-lien ($1,253 million) obligations as of May 2025. San Francisco International Airport (SFO) issued $924.7 million in Second Series Revenue Refunding Bonds in 2024 alone (May 2024).

Managing a portfolio of this scale requires analyzing every outstanding series against current and projected interest rates, evaluating optional redemption dates, assessing the interaction between lien tiers, and timing new money and refunding issuances to optimize the airport's aggregate debt service profile. Failure to conduct this analysis leaves refunding opportunities unexploited and increases aggregate interest costs.

Core Portfolio Metrics

Airport finance teams and municipal advisors track several metrics to evaluate portfolio health and identify refunding opportunities:

Metric	What It Measures
Weighted Average Coupon Rate	Average stated coupon across all outstanding par, weighted by par amount per maturity
True Interest Cost (TIC)	Discount rate equating present value of all future principal and interest payments to the purchase price paid by the underwriter; accounts for time value of money
Net Interest Cost (NIC)	Total future interest payments less any premium, divided by bond dollar-years; does not account for time value
All-In Cost (AIC)	TIC including issuance costs (underwriter discount, bond counsel, financial advisor, rating agency fees, trustee fees)
Maximum Annual Debt Service (MADS)	Highest single-year debt service on all outstanding obligations; used for DSRF sizing and additional bonds test calculations
Debt Service Coverage Ratio (DSCR)	Net Revenues ÷ Annual Debt Service; measures the margin of revenue above debt service obligations
Days Cash on Hand	Unrestricted cash and investments ÷ (annual operating expenses / 365)
Fixed / Variable Rate Mix	Percentage of portfolio at fixed vs. variable rates; variable-rate exposure introduces interest rate risk
AMT / Non-AMT Mix	Percentage of par outstanding subject to the Alternative Minimum Tax; AMT bonds carry wider spreads due to a narrower investor base

TIC has replaced NIC as the standard measure for awarding competitively bid bond sales because it accounts for the time value of money—a $1 million payment in Year 1 is more costly than the same payment in Year 20.

The Refunding Decision

Current Refunding vs. Advance Refunding

The Internal Revenue Code draws a bright line at 90 days. Under IRC § 149(d)(5), a refunding is "advance" if the refunding bonds are issued more than 90 days before the redemption of the refunded bonds. A refunding where the refunded bonds are redeemed within 90 days is a "current" refunding.

This distinction became the defining constraint on airport refunding strategy after December 31, 2017.

The TCJA Elimination of Tax-Exempt Advance Refunding

Section 13532 of the Tax Cuts and Jobs Act of 2017 (P.L. 115-97) repealed the exclusion from gross income for interest on bonds issued to advance refund another tax-exempt bond after December 31, 2017. Prior to the TCJA:

• A bond issued after 1985 could be advance refunded once on a tax-exempt basis (IRC § 149(d)(3)(A)(i)).
• Issuers used advance refundings to lock in lower interest rates years before the refunded bonds' call date, eliminating the risk that rates would rise before the call date arrived.

After December 31, 2017, tax-exempt advance refunding is no longer available. An airport issuer with callable bonds carrying a 5.00% coupon and a call date three years away cannot issue tax-exempt refunding bonds today; it must wait until 90 days before the call date (current refunding) or pursue one of several alternative structures.

Multiple legislative proposals have sought to restore tax-exempt advance refunding since 2018, including the LOCAL Act (S. 479, 2021), the LIFT Act (H.R. 8396, 2024), and the Investing in Our Communities Act. As of March 2026, none have been enacted.

NPV Savings Threshold

The primary financial objective of a refunding is to reduce the net present value (NPV) of debt service payments on the refunded bonds. Airport debt policies and governing body resolutions set minimum NPV savings thresholds that a proposed refunding must meet before management will proceed.

Two published examples:

• San Francisco International Airport (SFO): SFO's debt policy requires that refunding bonds issued solely for debt service savings produce estimated NPV savings of at least 3% of the par amount of the refunded bonds — or at least 1% if, in the judgment of the airport's municipal advisors, a future refunding is unlikely to realize greater savings (February 20, 2024).
• City of Austin — Austin-Bergstrom International Airport (AUS): Austin's bond ordinance applies a 4.25% NPV savings target. Austin's Series 2025 (AMT) refunding of $244.5 million of Series 2014 (AMT) bonds produced estimated NPV savings of 7.16%, or $17.5 million (March 6, 2025).

These thresholds serve as a discipline: they prevent the issuer from incurring issuance costs for marginal savings that could be exceeded by waiting for a more favorable rate environment.

Post-TCJA Refunding Alternatives

The elimination of tax-exempt advance refunding created demand for substitute structures. Four primary alternatives have emerged since 2018:

1. Taxable Advance Refunding

The most common post-TCJA alternative. The issuer issues taxable advance refunding bonds, places the proceeds in escrow, and redeems the refunded bonds on their call date. Because the refunding bonds are taxable (not tax-exempt), they are not subject to the IRC § 149(d) limitation.

The tradeoff: taxable bonds carry higher yields than tax-exempt bonds, which reduces—and in some rate environments eliminates—the savings from the refunding. In periods where taxable rates are still below the coupon on the refunded bonds, this approach can produce positive NPV savings.

2. Forward Delivery Bonds

The issuer sells tax-exempt refunding bonds to an underwriter pursuant to a bond purchase agreement with a delayed settlement date. The bonds are priced and the interest rate is locked in at the sale date, but delivery and closing occur within 90 days of the refunded bonds' call date—qualifying the transaction as a current refunding under IRC § 149(d)(5).

Forward periods can extend up to approximately 24 months. This structure carries risks that a conventional current refunding does not:

• Change-in-law risk: An adverse change in federal tax law between sale and settlement could prevent closing.
• Market risk to the underwriter: The underwriter bears the risk that rates move between pricing and delivery; this risk is priced into the forward delivery spread.
• Credit risk: A rating downgrade or covenant default during the forward period could trigger termination events.
• Regulatory risk: MSRB considers forward delivery transactions "complex municipal securities financings" subject to enhanced fair dealing obligations.

3. Cinderella Bonds

A hybrid structure in which bonds are initially issued as taxable obligations and later convert to tax-exempt status on or near the refunded bonds' call date. The issuer redeems the refunded bonds with the converted (now tax-exempt) refunding bonds in a current refunding. The structure is named for the conversion event—the bonds "transform" at a defined point.

Cinderella bonds involve greater structural complexity and require careful tax counsel analysis. They have been used selectively but have not become a standard tool.

4. Tender Offers and Exchange Offers

The issuer offers to purchase its own outstanding bonds from current holders at a specified tender price, or offers to exchange outstanding bonds for newly issued bonds at different terms. This approach does not rely on optional redemption at all—it bypasses the call date entirely by negotiating directly with bondholders.

Tender offers are funded either from new bond proceeds or from the issuer's available cash. Exchange offers swap old bonds for new bonds at par or at a premium/discount. Both approaches can be combined with a concurrent new money issuance.

Bond Indenture Mechanics That Affect Portfolio Management

Flow of Funds

The bond indenture's flow of funds determines the priority in which airport revenues are applied. A standard flow of funds follows this sequence:

1. Operating and Maintenance Expenses — paid first from gross revenues
2. Debt Service Fund — principal and interest deposits (typically monthly at 1/12 of annual debt service or 1/6 of semiannual debt service)
3. Debt Service Reserve Fund — topped up if below required balance
4. Coverage / Surplus Fund — amounts required by rate covenant in excess of 1.00x debt service
5. Renewal and Replacement Fund
6. Improvement Fund
7. Discretionary / Unrestricted Fund

The position of refunding savings within this waterfall depends on whether the refunding reduces annual debt service (lowering Step 2 deposits) or restructures it (shifting principal to later years). A refunding that reduces aggregate debt service frees revenue at Step 2, which flows down to Steps 4–7, improving coverage ratios, building reserves, or reducing airline rate requirements under a compensatory methodology.

Multi-Lien Structures

Large airports issue debt across multiple lien tiers, each with its own rate covenant, additional bonds test, and debt service reserve requirement:

Lien Position	Description	Rate Covenant (PHX example)
Senior Lien	First claim on net revenues	1.25x (PHX management target: 1.75x–2.00x)
Junior / Subordinate Lien	Paid from "designated revenues" (net revenues after senior debt service)	1.10x at PHX
Special Facility / Conduit	Paid solely by tenant; does not touch airport net revenues	N/A (tenant credit)

Refunding decisions interact with lien structure. An airport may choose to refund junior-lien bonds rather than senior-lien bonds if the junior-lien series carries higher coupons or if the refunding will improve the aggregate debt service profile without affecting senior-lien covenants. Phoenix's Series 2025 transaction refunded junior-lien Series 2015A and 2015B bonds ($85.2 million par), leaving its senior-lien debt unchanged (May 2025).

Rate Covenant

The rate covenant is the airport's promise to charge fees sufficient to generate net revenues equal to a specified multiple of annual debt service. The most common ratio is 1.25x. A refunding that reduces annual debt service directly lowers the minimum revenue requirement under the rate covenant, which translates to lower required airline fees under a compensatory methodology.

The arithmetic: if annual debt service drops by $5 million through a refunding, the minimum net revenue requirement under a 1.25x covenant drops by $6.25 million ($5M × 1.25). Under a compensatory rate structure where the airport passes through airfield and terminal costs to airlines, this reduction flows directly to landing fees and terminal rentals.

Additional Bonds Test

Before issuing refunding bonds (or any new bonds), the airport must satisfy its additional bonds test (ABT). Two standard approaches:

• Historical test: Net revenues in the most recently completed fiscal year ≥ 1.25x MADS on all outstanding bonds plus the proposed bonds.
• Prospective test: An airport consultant certifies that projected net revenues for three consecutive fiscal years following project completion ≥ 1.25x MADS on all outstanding plus proposed bonds.

A pure refunding that reduces debt service will always pass the ABT because MADS either stays the same or decreases. A refunding combined with new money issuance (a "combo" deal) requires ABT analysis on the combined impact.

Refunding Timing: The Market Dimension

Interest Rate Sensitivity

Airport bonds are long-dated fixed-income instruments. A portfolio of outstanding 5.00% coupon bonds is a refunding candidate when current tax-exempt yields fall below 5.00% by enough to cover issuance costs (typically 50–150 basis points depending on transaction size) and meet the airport's NPV savings threshold. The refunding "window" is time-sensitive: windows that opened in 2021–2022 (when rates were historically low) closed by mid-2023 and remained closed through late 2024.

Austin's Series 2025 refunding was originally scheduled for April 2, 2025. On that date, the federal administration announced a broad package of import tariffs. Municipal bond yields rose from approximately 3.9% to 4.3% within 48 hours, increasing the cost to refund Austin's 2014 series (4.00% coupon) from an estimated 4.8% NPV savings to 2.1%—below Austin's 4.25% threshold. The transaction was postponed for seven months. On November 6, 2025, when comparable yields had declined to 3.65%, Austin issued its Series 2025 (AMT) refunding at 5.3% NPV savings—producing $12.9 million in present-value benefits (November 2025).

Call Schedule Management

Every airport debt portfolio contains a schedule of optional redemption dates—the dates on which each outstanding series becomes callable. For bonds issued with a 10-year call protection period, a series issued in 2020 becomes callable in 2030. A series issued in 2015 may already be callable.

Managing this call schedule is a core portfolio management function. Options include:

• Current refunding at the call date if rates are favorable
• Forward delivery sale 12–24 months before the call date to lock in rates
• Waiting if the municipal advisor projects that rates may decline further before the call date
• Partial refunding of only the maturities that produce savings above the threshold, leaving below-threshold maturities outstanding

Debt Service Restructuring

Refundings are not limited to achieving interest rate savings. Airports also refund to reshape the debt service profile:

• Level to ascending: Extend maturities or shift principal to later years to accommodate near-term capital needs. This increases total interest cost but reduces near-term rate pressure.
• Back-loaded to level: Accelerate principal repayment in earlier years to reduce total interest cost. SFO's debt policy allows back-loaded amortization when the overall plan of finance contemplates future series that will level aggregate debt service across all issuances.
• Covenant modification: Refunding to a new indenture with more favorable covenants (wider additional bonds test, broader revenue definition, lower DSRF requirement). SFO's debt policy lists changing "covenants otherwise binding upon the Commission" as a permissible refunding purpose.
• Variable-to-fixed conversion: Replacing variable-rate demand obligations (VRDOs) or swapped variable-rate bonds with fixed-rate bonds to eliminate interest rate and remarketing risk.

Analytical Framework for Portfolio Evaluation

Step 1: Inventory Outstanding Debt

Compile every outstanding series: par amount, coupon rates by maturity, call dates, call prices, lien position, AMT/non-AMT designation, variable/fixed rate, swap obligations, and DSRF requirement.

Step 2: Identify Callable Maturities

For each outstanding series, determine which maturities are currently callable and which will become callable within the next 24 months (the practical window for forward delivery transactions).

Step 3: Run Refunding Scenarios

For each callable series or maturity block, calculate NPV savings at current market rates and at rates +/- 25 basis points. Compare to the airport's minimum savings threshold. Identify which series produce savings above the threshold and which are below.

Step 4: Evaluate Aggregate Impact

Model the aggregate debt service profile under a refunding scenario: what does the combined debt service schedule look like after the refunding? Does it improve DSCR? Does it reduce MADS? Does it create room for new money issuance?

Step 5: Consider Timing

Assess whether current market conditions are optimal or whether waiting (for the next call date, for expected rate movements, or for a new money issuance that could be combined with the refunding) would produce better results. Austin's seven-month delay from April to November 2025 resulted in a transaction that met its savings threshold; proceeding on the original date would not have.

Step 6: Coordinate with Capital Plan

Refunding transactions can be combined with new money issuances in a single offering, reducing aggregate issuance costs. Airports with near-term capital needs may wish to evaluate whether a combined refunding/new money deal—using one set of offering documents, one rating agency review, and one underwriter engagement—is more cost-effective than two separate transactions.

Debt Policy as a Governance Tool

SFO's debt policy, adopted February 20, 2024, addresses:

• Authorized purposes for debt issuance (capital projects, refunding, cash flow management)
• NPV savings thresholds for refundings (3% general; 1% if future refunding unlikely to produce more)
• Advance refunding evaluation criteria (escrow efficiency analysis; comparison of advance refunding savings vs. waiting for call date)
• Amortization policy (serial vs. term bonds; level debt service as default; back-loaded permitted within an aggregate leveling plan)
• Variable-rate exposure limits
• Debt service reserve fund sizing
• Method of sale (competitive vs. negotiated; criteria for choosing each)

PHX publishes financial management targets that go beyond minimum covenant requirements: a senior-lien DSCR target of 1.75x–2.00x (vs. a covenant minimum of 1.25x), a days-cash-on-hand target of 475 days, and a PFC leveraging target of 65%–75% of annual collections (May 2025). These internal targets, disclosed to investors, serve as credit-positive signals and provide management with operational guidelines that are more conservative than the legal minimums.

Interaction with Airline Rate-Setting

Under a compensatory rate structure, debt service is a direct pass-through cost to airlines in the applicable cost center (airfield, terminal). A refunding that reduces annual debt service by $5 million reduces the cost base allocated to airlines by $5 million, which in turn reduces the cost per enplanement (CPE)—all else equal.

At PHX, where CPE was $7.84 in FY2024 on 25.5 million enplanements, a $5 million reduction in annual debt service would reduce CPE by approximately $0.20 per enplanement ($5M ÷ 25.5M), assuming the full debt service reduction flows through the compensatory rate calculation (May 2025).

Under a residual rate structure, the effect is similar but flows through a different mechanism: reduced debt service reduces the total revenue requirement, which reduces the airline residual obligation.

In either case, refunding savings translate to lower airline costs—a factor that connects debt portfolio management directly to the airport's competitive position in attracting and retaining air service.