U.S. AIRLINES (1955–2025) — POWER OF THE GREAT CARRIERS, IN MARKET SHARE

Why they got so powerful. Three structural advantages, compounding for four decades. (1) Born outside the system: flying only inside Texas from 1971, Southwest was exempt from CAB route and fare regulation — it spent the seven years before deregulation learning to run an airline on price while the trunks competed on legroom and carving stations. When the 1978 Act freed everyone, Southwest was the only carrier already built for the new world. (2) One fleet, one mission: a single aircraft type (the 737) from day one, point-to-point flying instead of hubs, 10-minute turnarounds, no meals, no assigned seats. Its cost per seat-mile ran 25–40% below the legacies for decades — the "Southwest Effect" meant fares in any market it entered fell ~30% while traffic doubled. (3) No succession wars: 47 consecutive profitable years (1973–2019) — a streak no other airline on Earth approaches — and not one Chapter 11, while every legacy rival passed through bankruptcy court at least once. Its famous fuel hedges paid out over $3.5B in the 2000s oil spike alone, funding growth exactly when the majors were shrinking in court.

Why they stayed on top while the legacies bled. Strategy: they never marched on the hubs. Southwest let United, American and Delta fight ruinous fortress-hub and transatlantic wars, and spent the difference digesting secondary airports — Love Field, Midway, Oakland, Baltimore. By 2010 the airline the trunks had once dismissed as a Texas commuter was boarding more domestic passengers than any carrier in America.

Why the aura cracked. The same simplicity that made them rich made them rigid. The December 2022 meltdown — 16,900 cancellations from an outdated crew-scheduling system — cost over $1B and its reputation for operational excellence. In 2024 the activist fund Elliott took a stake and forced out the old guard; by 2025 Southwest had abandoned open seating, added bag fees, and started red-eyes — dismantling, one by one, the heresies that had defined it for 50 years.

Handing the airlines their freedom looks like an obvious gift until you count the bodies. For 40 years the Civil Aeronautics Board had fixed every fare and awarded every route — no trunk carrier had gone bankrupt since 1938, and none had been allowed to, either. The 1978 Act was a forced swap, not a gift: carriers traded guaranteed profitability on a frozen map for the right to fly anywhere at any price — against anyone.

From Congress's chair, the logic was consumer surplus: (1) CAB-era fares were set so airlines competed by burning money on service (piano bars on 747s, carved roast beef in coach); (2) intrastate carriers like Southwest in Texas and PSA in California — outside CAB reach — were profitably charging half the regulated fare, proving the system was a cartel; (3) ~150 new airlines entered within seven years; and (4) real average fares fell roughly 45% over the following three decades, and flying went from a luxury (fewer than half of Americans had ever flown in 1971) to a bus with wings.

The carriers paid for all of it. Of the ten trunk airlines that woke up free in 1978, exactly three certificates were still flying under their own name by 2015 — United, American, Delta. Braniff died first (1982), then People Express devoured itself (1987), then the giants: Eastern and Pan Am in a single year (1991), TWA on its third bankruptcy (2001). The industry lost, cumulatively, more money in its first 30 deregulated years than it had made in the previous 40 regulated ones. And the final irony: after ~200 bankruptcies and the great merger wave, the Big Four of 2015 held a larger share of the market than the Big Four of 1978 ever had under regulation. The cartel was dead; long live the oligopoly.

How the share estimates were made (Fermi method): Anchors are CAB traffic statistics (pre-1978) and DOT Form 41 / T-100 data (after), by revenue passenger-miles across all U.S. scheduled carriers, domestic + international. Documented checkpoints keep the bands honest: the Big Four trunks (United, American, TWA, Eastern) carried ≈ 70% of domestic trunk traffic in the mid-1950s; Capital was the 5th-largest U.S. airline when United absorbed it (1961); Delta–Northwest created the world's largest airline (2008), a title American–US Airways took back (2013); the Big Four of today (American, Delta, United, Southwest) hold ≈ 67–74% of domestic traffic depending on the measure; Southwest has boarded the most domestic passengers of any U.S. carrier since ~2010. Between checkpoints, shares are interpolated from fleet counts, enplanement tables, and hub capacity. International-heavy carriers (Pan Am above all) look smaller here than their fame suggests — share of passenger-miles understates a carrier that was banned from the domestic market. Error bars are roughly ±2–3 points.

Two things that look wrong but aren't. (1) The total never shrinks: the stack always sums to 100% — traffic doesn't disappear when an airline dies, it's re-flown. The gray Other carriers band at the bottom is the rest of the industry: local-service airlines of the 1950s–60s (Mohawk, Lake Central, Bonanza…), the ~150 deregulation-era startups (Midway, Air Florida, ValuJet, ATA…), and today's ultra-low-cost and leisure fringe (Allegiant, Sun Country, Breeze, Avelo). Watch it swell after 1978 — that bulge is deregulation — then get squeezed as the startups die or are eaten, then swell again after 2010 as the ULCCs grow in the shadow of the oligopoly. (2) Pan Am at ~10% in 1955 is, if anything, generous. Pan Am was traffic-poor by design: Washington's "Chosen Instrument" for international aviation was barred from carrying a single domestic passenger, so it had no feed for its own overseas flights. Its true asset was legitimacy — routes, treaties, and the most famous brand in world aviation — which is why, once deregulation burned that protection down, there was almost no domestic network underneath to fall back on.