Field notes
59 field notes, for the charts featured on the question pages. Every chart on the site has a note; these are the featured ones.
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Passenger share by airport hub tier
Large hubs carry a little over two-thirds of US passengers, a share that has stayed roughly flat since the turn of the century. Each year's tiers are set by airports' shares of that year's national passengers.
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Brazilian air travel fell 7.5% from 2015 to 2016 and regained its 2015 level in 2018
On full-year totals the fall took Brazilian air travel back to about where it stood four years earlier. Only part of the loss came back the following year, and a year later the total edged past the one before the fall.
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After COVID, among the models scored on this chart, the seasonal model (SARIMAX) predicts best and the error-correction model (ECM) worst
Before the pandemic the leading models were close together. Afterwards the seasonal model predicts best and the error-correction model worst of those scored here; each sees the quarter's actual economic data.
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Discounted-coach fares dominate the ticket mix
Most flights on US tickets are on discounted-coach fares, though that share has slipped since the pandemic while full-fare coach has grown.
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Longer flights cost more in total but far less per mile
The shortest flights cost roughly six times as much per mile as the longest, even though the longest cost far more in total.
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Fares are higher on longer routes and where more travel is on unrestricted or high-fare ticket codes, and lower where more trips stay on one airline
Each bar is how the fare moves with one route attribute when the others are held constant. Fares in this fit are also lower on busier routes and on more concentrated ones.
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Average fares in nominal dollars now sit above their 2020 Q1 level
Before adjusting for inflation, average US fares sank during COVID, peaked during the reopening and now sit above their level at the start of the pandemic.
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Low-cost carriers spend 3.9 cents less than legacy carriers per seat-mile, but the two margins cannot be told apart
Low-cost carriers spend less per seat-mile but also earn less, and the gap between the two carrier types' pooled unit margins cannot be told apart from zero.
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Within a family, each new generation burns less fuel than its predecessor
Within each family, every newer generation burns less fuel per flying hour than the one before it. The figures are not adjusted for aircraft size, so they do not compare one family with another.
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Southwest, United and JetBlue lead the new-generation fleet share, each near 30%
New-generation aircraft make up about a fifth to a third of the fleets of the large passenger airlines shown. The cargo and regional airlines shown have none.
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In the 3 markets that can be compared, the projection implies flying responds less to income than the estimate from each market's past, and elasticity runs 0.5 to 1.7 lower
The income sensitivity the projection implies sits below the historical estimate in each market that can be compared. Most of that gap is already there in the first year, before income rises any further.
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The economy used less air freight per dollar of GDP in 2024 than in 2003 or at its 2021 peak
Since reporting coverage settled, freight on all-cargo flights per dollar of output has fallen below its level of two decades ago and well below its pandemic peak. Freight in passenger holds is not counted here.
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Air freight swings far harder than the economy it rides on
Growth in freight on all-cargo flights swings about five times wider than the economy's. This compares how much each moves; it is not an estimate of how freight responds to the economy.
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Distance still deters flying: 1% farther means roughly 0.49% fewer passengers
The first bar is the headline estimate: traffic thins as distance grows. The other bars are reference models with known weaknesses, shown for comparison and not as independent confirmation.
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No model saw the COVID trough coming; SARIMAX came closest, and the rest caught almost none of the fall
SARIMAX follows the fall late: its lowest forecast comes two quarters after the actual trough. The other models dip later still or not at all.
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US air travel more than doubled since 1990 and has recovered past its COVID collapse
US passengers each quarter across three and a half decades. The site's US demand models try to explain this series.
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Summer is the peak quarter of US air travel in 31 of 36 years; the widest swings are 2020 and 2021
Each row is a year and each cell one quarter's passengers against that year's average. The first quarter is the lowest in all but three of the years, and the third almost always the highest.
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GDP helps predict air traffic in 10 of 19 markets and air traffic helps predict GDP in 5 markets
Past income helps predict air travel in more markets than air travel helps predict income, and in many markets neither helps predict the other. These are tests of prediction only.
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Route count by type
Point-to-point routes jump in the early two-thousands, when smaller carriers were brought into the data, so part of that rise is coverage. Since then point-to-point counts have thinned while hub-and-spoke counts held up.
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Route entry and exit by year
Airlines open and drop thousands of routes every year, mostly cancelling out. The surge of new routes in the early two-thousands is partly smaller carriers joining the data.
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Within each distance band from 500 to 2,000 miles, routes with more carriers have higher fares per mile
The chart keeps only routes with enough sampled tickets. Among them, more airlines go with higher fares per mile in most distance bands; only distance is held fixed, so this cannot be read as the effect of competition.
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After COVID, the seasonal pattern was out of its pre-COVID range in 2022 and within it in 2023 and 2024
The post-COVID bars average three years. The first, when the winter quarter was unusually weak, fell outside the range expected from the pre-COVID years; the next two fell inside it.
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Airport security counts arrive about three months before the official passenger data
TSA screening counts arrive about three months ahead of the official passenger figures and move with them at a steady ratio. The nowcast applies that ratio to the quarter still being counted and is not a demand model.
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Airport traffic concentration (2024)
A small share of airports carries most US passengers, and the bottom half of airports barely registers. Read the curve from the left: it climbs steeply, then flattens early.
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Domestic capacity fell 7.8% and domestic passengers fell 6.7% from the first two quarters of 2001 to the last two, and all 54 routes on the top-routes list kept service
Australian domestic seats and passengers both fell in the second half of the year Ansett collapsed, against a season that normally lifts them. The September attacks came days earlier, so the two cannot be separated here.
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Brazilian air travel grew 230% from 2000 to 2019 while GDP grew 54%
As a yearly rate over those years, Brazilian air travel grew almost three times as fast as the economy. Its estimated income response is the steepest of any ranked market, though part may reflect new airlines entering.
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Canada: top 15 airports by passenger traffic (2023)
Toronto Pearson alone carries close to twice Vancouver's passengers, and the four busiest airports stand well clear of the rest of the ranking.
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Aviation's share of China's combined air and rail travel rose from 25% to 46% over two decades
Rail still carries the larger part of China's combined air and rail travel. The shares are of distance travelled, so longer air trips raise aviation's share even if people fly no more often.
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China: air cargo volume by market (tonnes)
China's air cargo has nearly tripled, with international shipments growing much faster than domestic. The domestic line steps up partway through, when Hong Kong, Macao and Taiwan routes were moved into it.
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Air travel grows roughly in step with GDP in the US, faster in Australia and far faster in Brazil
The ranked markets are in order of how strongly air travel moves with income. For each one, at least one repeat of the test on pre-COVID years alone disagrees about that long-run link.