January 2021 — December 2025

An Almanac of
American Air Travel

Five years of movement, recorded in full

Compiled from the T-100 Segment Database • Bureau of Transportation Statistics • Fiscal Year 2025
Total Carriers
32
domestic operators
Route-Month Records
1.41M
segment observations
All-Time Passengers
4.45B
across five calendar years
Airport Nodes
2,342
served hubs & fields
▴ Carbon Framing: At the FAA-standard approximation of 0.09 kg CO₂ per passenger-mile, the 4.45 billion passengers documented here — assuming an average domestic sector of ~900 miles — represent approximately 360 million metric tons of CO₂ equivalent across the five-year period. Route-level estimates appear throughout this almanac where distance data permits derivation.
Chapter I

Of Carriers & Their Commerce

The twelve leading air carriers, ranked by five-year passenger volume • 2021–2025
Market Distribution Among the Four Majors

Share computed as proportion of four-major combined passengers (Southwest, American, Delta, United) totalling approximately 2.94 billion passengers.

# Carrier Passengers Load Factor Routes Airports

Load factor = passengers ÷ available seats. Records span January 2021 through December 2025 inclusive. Data sourced from BTS T-100 Domestic Segment.

A Note on Southwest

Southwest Airlines, the volume leader with 812.9 million passengers, operates on a single-class, open-seating model that historically yields a load factor slightly below the mainline peers. At 76.9% against Delta's 82.6%, the gap reflects seating policy as much as demand.

The Regional Tier

SkyWest (OO) ranks fifth with 202 million passengers yet operates 6,943 distinct routes — more than any carrier listed, achieved by feeding the hub networks of United, Delta, and American under capacity purchase agreements.

Carbon note: The four legacy majors — Southwest, American, Delta, United — collectively carried 2.94 billion passengers in this period, representing roughly 238 million metric tons of CO₂ equivalent at 0.09 kg/pax-mile × 900 mi average.
Efficiency Spectrum
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Chapter II

The Grand Junctions & Their Gravity

Twelve principal hubs by passenger throughput • All carriers • 2021–2025
# Hub Passengers Load Factor Carriers Destinations

Hub figures represent domestic-only T-100 segment data. "Carriers" counts distinct IATA codes reporting routes through the hub. "Destinations" counts unique city-pair endpoints.

Hub Scale Comparison — Passengers (millions)
Hartsfield-Jackson Atlanta

ATL's 232.2 million passengers over five years gives it a per-day average of roughly 127,000 boardings. Served by 57 carriers reaching 427 destinations, it remains the world's busiest passenger airport by most annual rankings.

Connectivity note: Newark (EWR) achieves the highest load factor in this cohort at 83.1%, outpacing even ATL's 82.2% — evidence of a constrained hub where every seat is dear.
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Chapter IV

The Principal Corridors of Commerce

Fourteen highest-volume city-pair routes, all carriers combined • 2021–2025
# Route Passengers Load Factor Carriers Leader Share

Routes are bidirectional city-pairs. Load factor computed as segment passengers ÷ offered seats. "Carriers" counts distinct operators filing T-100 data on this segment. "Leader" is the single carrier with the highest cumulative passengers on the route; share is their proportion of all-carrier pax.

JFK–LAX: The Flagship Corridor

New York to Los Angeles generated 13.3 million passengers over the period — the busiest domestic city-pair — with an exceptional load factor of 86.8%. Delta leads with 44.2% share; 12 carriers compete.

MCO–SJU: Island Premium

Orlando to San Juan achieves the highest load factor in this table at 89.4%, reflecting strong leisure demand on the Florida–Puerto Rico corridor where capacity is constrained by available slots and aircraft gauges.

▴ JFK–LAX Carbon: At 2,475 mi (one-way), 13.3M pax × 2,475 mi × 0.09 kg/pax-mi ≈ 2.96M metric tons CO₂ equiv. over five years — for this one corridor alone.
Competition note: LAS–LAX has the most competing carriers (28) of any route in this table, yet Southwest's 27.3% share keeps it distinctly pluralistic. DFW–LAX is the most concentrated: American controls 73.5% of that corridor.
Chapter V — Signature Study

The Annual Almanac of Flight

Three-year calendar heatmap • load factor by month • all US carriers combined

Like a botanist's pressed specimen — each month pinned and classified by the fullness of its aircraft. Darker terracotta denotes higher load factors; ochre the shoulder seasons; sage the quiet winter months when planes fly partly empty and the industry breathes.

Lower load factor (<77%)
Mid-season (77–82%)
Peak season (>83%)

Each cell displays month abbreviation, load factor %, and passenger volume in millions. Three years 2023–2025 are displayed side by side to reveal inter-annual consistency and year-over-year trends.

Annual Passenger Totals
Load Factor Range
2023 → 2025 growth: July passengers grew from 88.9M to 93.0M, a +4.6% rise. Available seats grew from 104.1M to 111.9M (+7.5%), suggesting capacity expanded faster than demand in peak season.