After Spirit: which ULCC carries the same balance sheet?

Spirit Airlines ceased operations on May 2, 2026, the day after a federal bailout effort collapsed and a fuel-price spike driven by the Iran war pushed the carrier through what its unrestricted cash position could no longer absorb [1][2]. The company had been twice bankrupt in eighteen months, and although the immediate trigger was the cost of jet fuel, the structural condition that made Spirit fragile was independent of the war: years of margin compression, a fleet partially grounded by Pratt & Whitney's geared turbofan inspection program, slot-constrained airports filling with mainline "basic economy" capacity, and a debt amortisation schedule the operating business could not service. Those pressures are not unique to Spirit. They are visible in the FY 2025 10-K filings of the three remaining publicly listed US ultra-low-cost or low-cost carriers — JetBlue Airways (JBLU), Frontier Group Holdings (ULCC) and Allegiant Travel (ALGT) — and they show up unevenly. The question this piece tries to answer is which of those three sits closest to the same edge, on the data the carriers themselves have filed with the SEC. The answer is not the one with the largest losses.

The structural problem, in margins

The ULCC and low-cost segment was the worst-performing part of US scheduled aviation in FY 2024 and FY 2025. The 10-K disclosures of the three remaining issuers show why.

Source: XBRL facts as filed in each carrier's FY 2023, FY 2024 and FY 2025 10-Ks [3][4][5]. (Revenue for JBLU and ULCC is RevenueFromContractWithCustomerExcludingAssessedTax, which is the total operating revenue line each filer presents; revenue for ALGT is Revenues, which includes Sunseeker Resort and fixed-fee contract revenue alongside scheduled service. Costs are CostsAndExpenses for JBLU and ULCC, and OperatingExpenses for ALGT, matching each company's own income-statement totals.) Spirit's last full-year XBRL submission cannot be retrieved from this dataset — the entity has been delisted and removed — so the comparison set is the three survivors. Two patterns are immediately visible. First, JetBlue has not posted a positive operating margin in the three-year window; its losses are wider in absolute dollars than the other two combined. Second, the carrier whose operating result deteriorated most sharply between FY 2024 and FY 2025 was Frontier — a 554 basis-point swing from +1.54% to -4.00%, and a deepening of operating cash burn from -$82M to -$525M. Allegiant, by contrast, returned to positive operating income in FY 2025 and generated $390M in operating cash. The aggregate FY 2025 picture is that the segment lost money at the operating line at JBLU and ULCC, with only ALGT eking out a small operating profit, and only ALGT generating meaningful cash from operations.

What the filers themselves said

The structural diagnosis is in the documents.

On the Pratt & Whitney geared turbofan groundings, JetBlue is the most exposed of the three. From its 2025 10-K, Item 7:

In July 2023, Pratt & Whitney, a division of RTX Corporation, announced the requirement, mandated by the FAA, for removal of certain engines for inspection due to a rare condition involving powdered metal used in the production of certain engine parts on the PW1100G and PW1500G engine types. These engines power our Airbus A321neo and Airbus A220 fleets... we averaged nine aircraft on the ground in 2025 and as of December 31, 2025, we had four aircraft grounded due to lack of engine availability. The Company currently expects each removed engine to take approximately 200 days for the PW1500G engines and approximately 300 days for the PW1100G engines to complete a shop visit and return to a serviceable condition. [3]

Frontier acknowledges the same exposure but, as of its filing date, less acute disruption:

Since 2022, we have introduced aircraft into our fleet that use the Pratt & Whitney PW1100 Geared Turbo Fan ("GTF") engine, and we have selected this engine for our planned future deliveries... Although our operations have not been impacted as of December 31, 2025, this inspection program may have an adverse impact on our operations, particularly when we are required to temporarily take aircraft out of service. [4]

Allegiant's 2025 10-K contains no Pratt & Whitney disclosure of any kind: the Allegiant fleet is built on second-hand A319/A320ceo aircraft and new Boeing 737 MAX, neither of which uses the affected GTF engines [5]. That is a real differentiator; Allegiant carries different operating risks but does not share Spirit's, JetBlue's or Frontier's GTF exposure.

On fuel cost as a margin variable, all three filers describe it as among their largest expenses and outside management control. Frontier puts it most plainly:

Aircraft fuel prices and availability are subject to market fluctuations, refining capacity, periods of market surplus and shortage and demand for heating oil, gasoline and other petroleum products, as well as meteorological, economic and political factors and events occurring throughout the world, which we can neither control nor accurately predict. [4]

Allegiant adds that it does not hedge: "We have not sought to use financial derivative products to hedge our exposure to fuel price volatility, nor do we have any plans to do so in the future" [5]. Frontier and JetBlue similarly disclose no material fuel-hedging programmes in the MD&A sections of their 2025 10-Ks. The implication is that for all three carriers, the post-Iran-war jet fuel price flows through to the income statement essentially undamped.

On competition from mainline carriers, Frontier is direct:

...some of the legacy network carriers match LCC and ULCC pricing on portions of their network, including through the selective deployment of so-called "basic economy" fares. [4]

This is the brand-fatigue mechanism that hollowed out Spirit's pricing power. Delta's response to Spirit's shutdown was to offer rescue fares to displaced passengers [1] — a reminder that mainline carriers now compete directly for the leisure traveller the ULCC model was originally built to serve.

On liquidity and debt maturities, JetBlue's 2025 disclosure is the most explicit on near-term refinancing pressure:

We had working capital deficit of $1.2 billion as of December 31, 2025 compared to a working capital surplus of $377 million as of December 31, 2024. Our working capital decreased by $1.5 billion primarily due to fewer investment securities and an increase in current maturities of long-term debt, partially offset by an increase in prepaid expenses and other. The increase in current maturities of long-term debt is due to the Company's 0.50% convertible senior notes, with a principal amount of $325 million, becoming current in 2025. [3]

JetBlue states it had $2.5 billion in unrestricted liquidity (cash, equivalents and investment securities) plus a $600 million Citibank revolver at year-end 2025 [3]. Frontier reports $874 million in total available liquidity ($654 million unrestricted cash and $220 million revolver capacity) [4]. Allegiant reports $838.5 million in cash, equivalents and investment securities, plus $250 million of undrawn revolver capacity [5]. Those three numbers are the principal short-run defence against the kind of squeeze that ended Spirit.

The post-war first data point

JetBlue is the only one of the three carriers to have filed a 10-Q reflecting any of the post-Iran-war fuel regime: its Q1 2026 10-Q was filed on April 28, 2026 and covers the three months to March 31, 2026 [6]. (Frontier and Allegiant had not yet filed their Q1 2026 10-Qs as of this writing.) The Q1 disclosure is therefore the cleanest available read on how the early stages of the fuel spike are landing on a ULCC-adjacent income statement.

JetBlue's Q1 2026 aircraft fuel expense was $573 million, against $511 million in Q1 2025: an increase of $62 million, or 12.1%, year over year [6]. The decomposition matters: average fuel price per gallon rose 15.2% to $2.96 from $2.57, while consumption fell 2.7% to 193 million gallons from 199 million, per JetBlue's own MD&A figures [6]. In other words, JetBlue absorbed a 15% input price shock while flying slightly less, and the price effect dominated the volume effect by roughly a 6:1 ratio. Operating loss for the quarter widened to $224 million from $174 million in Q1 2025 [6]. The carrier itself frames the Q1 2026 cost picture in terms management thinks will persist:

...we are focused on preserving liquidity, maintaining cost discipline, and retaining flexibility across our network and fleet amid elevated and volatile fuel prices, which we expect to persist throughout this year, as well as broader macroeconomic uncertainty. [6]

This was Q1 2026 — the war began in earnest in mid-quarter, and the price effect should be larger in Q2.

Who is closest to the same edge, by the numbers

Sources: FY 2025 10-K balance sheets and MD&A liquidity disclosures [3][4][5]. "Net debt incl. op lease" is long-term debt plus finance-lease liability plus operating-lease liability less unrestricted cash; the Frontier figure is dominated by capitalised aircraft operating leases, which is the obverse of Frontier's small disclosed long-term debt balance. "Current portion of LTD" is current maturities as a percentage of total long-term debt.

Reading the table together with the structural disclosures and the Q1 2026 fuel data, the answer is not obvious and depends on which lens is preferred.

JetBlue carries the largest absolute net loss and the largest absolute debt balance, has explicit GTF exposure, has just turned operating-cash-flow negative on a full-year basis, and is the only one to flag a working-capital deficit. But its disclosed liquidity is roughly three times Frontier's and Allegiant's; under the revolver agreement JetBlue placed $100 million of cash into escrow as a covenant — not the full convertible balance, but a meaningful liquidity setaside that should buffer the 2025 maturity wall [3] — and only 9.9% of its long-term debt is current.

Allegiant has the smallest cash buffer in absolute terms ($173M unrestricted), but it generates positive operating cash, is unaffected by GTF, and only 6.6% of its long-term debt is current. Its $250M undrawn revolver is real liquidity, not aspirational.

Frontier sits in the middle on size but is the carrier whose 2025 numbers most resemble the trajectory Spirit ran before its first bankruptcy: a one-year flicker of operating profitability (+1.54% in FY 2024) reverting hard to a -4.00% margin and a $525M operating cash outflow, with $874M of total liquidity against that burn. Critically, 48.5% of Frontier's long-term debt is current — meaning roughly half of the principal balance is scheduled to amortise within the next twelve months, the steepest near-term refinancing requirement in the cohort. Frontier also has explicit PW1100 GTF exposure for its current and planned fleet [4], runs the most negative operating cash position of the three, and disclosed it had to downsize its pre-delivery deposit financing facility from $365M to $135M in 2024 [4]. On the structural diagnosis the filers themselves describe — fuel exposure with no hedging, GTF risk, mainline competition, near-term refinancing requirement, deteriorating cash from operations — Frontier matches the most boxes.

Caveats

This analysis could be wrong in several ways. First, it reads off audited 10-K balance sheets that are four months stale; the carriers' Q1 2026 disclosures (other than JetBlue's) will materially change the picture, and Frontier or Allegiant may pre-announce. Second, ULCC operating leases and ALGT finance leases are treated as debt-equivalent here, which inflates net-debt comparisons against carriers with different fleet ownership models — a Frontier sale-leaseback book is not legally the same instrument as a JetBlue secured term loan. Third, the brief covers the structural pattern, not the optionality: any of these carriers could refinance, sell slots, exit unprofitable routes, find an acquirer or receive ad-hoc government support of the type Spirit was reportedly negotiating before its collapse [1][2]. Fourth, this is an analysis based on what filers disclose; it does not capture private debt covenants, off-balance-sheet aircraft order commitments past the disclosure horizon, or the actual liquidity timing inside the quarter. None of this is investment advice.