01
At a glance.
The Aircraft Ledger builds flight histories for business jets from flight data. We then compare each aircraft with others of the same type.
This page explains where the data comes from, how flights are built, how every metric is defined, and where the data falls short.
02
Where the data comes from.
We use a data source for raw flight data. We add reference data on aircraft, airports, runways, weather and maintenance facilities to interpret it.
Flight data
Aircraft broadcast their position, altitude and speed several times a second, and receivers around the world pick these signals up. Where several receivers hear the same aircraft, multilateration (MLAT) can locate aircraft that don’t broadcast a position.
We receive this raw flight data from our data source each day and build every flight from it.
Reference data
| Dataset | What we use it for |
|---|---|
| Aircraft performance data | Takeoff distance, fuel burn and emissions factors by type |
| Global airport database | Airport positions and elevations |
| OurAirports runway data | Longest open runway at each airport |
| Type certificate data sheets and manufacturer specifications | Certified specifications on our aircraft pages |
| Manufacturer service networks and aviation-authority approvals | Which facilities are authorized to maintain each type |
| OpenStreetMap coastlines | Each airport’s distance to the sea |
| Köppen-Geiger climate classification | Each airport’s climate zone |
| ERA5-Land (Copernicus) | Hourly temperature, humidity and pressure on the dates an aircraft was there |
Full credits and licenses are under Sources, licenses and attribution.
03
Which aircraft we track.
We track fixed-wing business jets, from very light jets to ultra-long-range aircraft: our pages benchmark 49 types and about 20,348 individual aircraft. We don’t track turboprops, helicopters or airliners.
Aircraft are selected by ICAO type designator and by our own register of tracked aircraft. Families covered include Cessna Citation, Learjet, Bombardier Challenger and Global, Gulfstream, Dassault Falcon, Embraer Phenom, Praetor and Legacy, Hawker and Beechcraft, Pilatus PC-24, HondaJet and Cirrus Vision Jet. The Embraer Legacy 600/650 is the only airliner-derived type included.
On our free pages we also remove aircraft whose records we can’t trust:
- Flight test and demonstrator aircraft, whose flying isn’t representative.
- Misidentified aircraft, such as a registration matched to an airliner, or one flying far more than is plausible for its type.
- Model mismatches, where the official registry or the serial number shows a different model from the one recorded.
04
Identifying each aircraft.
Every transponder broadcasts a fixed 24-bit ICAO address, often called its hex code. We link each hex code to a registration, type and country of registration. Each flight is then filed under that aircraft.
- Registration and type come from the aircraft database attached to each day’s archive. They are checked against our own register, and only aircraft on it appear on the site.
- History follows the registration. If an aircraft is re-registered, its flights before and after can appear under separate records. If a registration is later reused by a different airframe, our free pages exclude records that show it.
- Aircraft without a stable identity, such as those using a rotating privacy address, can’t be linked to a registration. They don’t appear on the site.
05
How a flight is built.
A flight starts when an aircraft goes from the ground into the air and ends when it is next seen on the ground. Everything else is about what to do when the signal drops out.
Clean the track
We merge each aircraft’s position reports for the day in time order. Points that imply impossible movement, such as a jump of hundreds of miles in seconds, are removed.
Decide ground or air
An aircraft is on the ground when its transponder says so, or when it is slow and close to the ground. Height is judged against the elevation of the nearest airfield, so landings at high fields like Aspen are caught.v2 · coming with our next data update
Find takeoffs and landings
A takeoff is the move from ground to air. A landing is a return to the ground at least a few minutes later, so a bounce on the runway doesn’t split a flight.
Handle gaps in the signal
Low-altitude coverage is patchy, so many landings happen out of view. When the track goes quiet, we decide whether the aircraft landed during the gap or flew on out of coverage. That decision uses how long the gap was, how far the aircraft moved, and what it was doing either side, for example descending near an airfield. An aircraft that disappears at cruise altitude and reappears at cruise further on is treated as one continuing flight.v2 · coming with our next data update
Join flights across midnight
Flights that cross midnight UTC are carried from one day’s archive into the next, so they aren’t cut in two.
Record how each flight was observed
Every flight records whether its takeoff and landing were actually seen or inferred, and why it ended.v2 · coming with our next data update
06
Assigning airports.
Where a takeoff or landing was seen, the airport is the field it happened at. Where it wasn’t, we use the aircraft’s own sequence of flights rather than just picking the nearest airport.
- Seen takeoffs and landings are matched to the airfield they happened on.
- Unseen departures take the airport where the same aircraft last landed, if that’s consistent with where it was first seen.v2 · coming with our next data update
- Unseen arrivals use where the aircraft next took off, or where its track ended, if those point clearly to one airfield.v2 · coming with our next data update
- Only jet-capable fields are candidates for an inferred airport, judged by runway length.v2 · coming with our next data update
- When we can’t tell, we leave it blank rather than guess.v2 · coming with our next data update Flights with an unknown airport still count toward flight totals, but not toward route or distance figures.
Distances are great-circle distances between the two assigned airports, in nautical miles. They are shorter than the distance actually flown.
07
Cleaning and quality checks.
We flag suspect records and leave them out of statistics rather than silently deleting them.
- Duplicates. Each flight has one identity, from its aircraft and takeoff time, so reprocessing a day updates flights instead of adding copies.
- Ground movements and runway hops. Very short records that barely move, such as repositioning between ramps, are excluded.
- Impossible flights. Records implying speeds no business jet can fly, usually two aircraft sharing a code or bad positions, are excluded.
- Over-long records. Implausibly long single flights are excluded.
- Misidentified aircraft. Aircraft whose activity doesn’t fit their type are removed from free pages (see Which aircraft we track).
- Independent cross-checks. Key metrics are calculated twice, in separate code paths, and compared when pages are built. On fleet pages, a mismatch stops the build.
08
Metric definitions.
Every figure on TailCheck reports, Spotlight and our free pages is defined below.
Unless stated, metrics use all flights since 1 January 2025 with both airports known, dated by landing time in UTC.
| Metric | Definition | Shown as |
|---|---|---|
| Flights a month | Flights ÷ months in which the aircraft flew at least once | 1 decimal place |
| Days flown a month | Distinct days with a flight ÷ months in which it flew | 1 decimal place |
| Estimated hours a year | Airborne hours ÷ months in which it flew × 12 | Whole hours, “≈” |
| Hours per landing | Total airborne hours ÷ flights (the flight-hour to cycle ratio) | “x.x : 1” |
| Leg length | Median great-circle distance per flight | Whole nm |
| Short hops | Share of flights under 300 nm | Whole % |
| Domestic share | Share of flights with both airports in the United States | Whole % |
| Days since last move | Days from the latest flight to the end of the data | Whole days |
| Flights in 12 months | Count of flights in the 365 days ending 7 days ago (free tail pages) | Whole number |
| CO₂ | Estimated per flight from aircraft type: a fixed amount for takeoff and landing plus a cruise rate per airborne hour | Tonnes or lbs |
| Operator type | Share of a type’s aircraft flown by fractional, charter, or private and corporate operators, classified from each aircraft’s registration and flying pattern. Shown for whole fleets only, never for one aircraft: individual aircraft pages use only the sourced charter list | Whole % |
In prose, counts are rounded to whole numbers and ratios to one decimal place. Shares under 0.5% show as “<1%”.
09
Peer groups, percentiles and grades.
Every comparison is against aircraft of the same type. We never show a percentile for a group of fewer than 30 aircraft, and the group size is always shown beside it.
Peer groups
An aircraft is compared with its type across all regions, or with its type in its own operating region. Its operating region is where most of its departures are. Aircraft that split their flying evenly between regions are compared across all regions only. Regions follow ICAO airport prefixes, not political borders. Only aircraft with enough flights to measure reliably join a peer group.
Percentiles
A percentile is the share of the peer group with a lower value, from 0 to 100. Tied values share the lower rank. Extremes display as “>99th” or “<1st”.
Grades
TailCheck turns percentiles into plain-language grades:
| Grade | Meaning |
|---|---|
| Typical | Within the middle half of the peer group (25th to 75th percentile) |
| Harsher | Outside the middle half, on the side that means more wear |
| Gentler | Outside the middle half, on the side that means less wear |
For example, more hours per landing is gentler on an airframe, because each pressurization cycle covers more flying. Each report chapter takes the grade of its lead measure. We don’t grade utilization when an aircraft’s tracking coverage is too low to support it.
Spotlight grades each aircraft exactly as its TailCheck report does. It then ranks the aircraft on the board against each other.
10
Coverage and tracking gaps.
We measure how well each aircraft is tracked and show it on every report. The test is simple: an aircraft that lands at one airport should next depart from the same one.
Untracked stretches
When an aircraft lands at one field and next appears departing another, at least one flight was missed in between. Before counting a break, we rule out false alarms: airports in the same city, transits that would be physically impossible, and records whose endpoints weren’t actually seen. Reports show the result as “about 1 flight in N went untracked”.
Coverage grade
Each aircraft gets a coverage grade of High, Medium, Low or Limited, based on its share of untracked flights. A Low or Limited grade means its counts should be read as minimums.
Where coverage is thin
Coverage follows where receivers are:
- Strong: most of North America and Europe.
- Thin: oceans and polar routes, much of Africa, and parts of Asia, South America and the Middle East.
- Low altitude: takeoffs and landings at small fields are often out of view. That’s why we infer so many of them.
Because European receiver coverage is dense, European aircraft often log more tracked hours than North American aircraft of the same type. Comparing within an operating region reduces this effect but doesn’t remove it.
11
Ground periods, home base and service-center visits.
A ground period is the time between two consecutive flights. TailCheck reports pick out extended ones of two weeks or more, because they can point to maintenance, storage or a sale.
- Home or away. An aircraft’s home field is where it spends a clear majority of its flying days, consistently over many months. Each stay is labeled at home or away. Across our data, about 69% of fully tracked stays of two weeks or more are at the aircraft’s own home field.
- Can we vouch for the stay? A stay only counts if the aircraft departed from the field it arrived at. We also check that coverage at that field was good enough to have seen it leave, judged against the field’s own normal traffic rather than a fixed rule. Stays during a tracking break are never credited to either end.
- Likely service-center visits. A long stay at a field with a manufacturer-authorized service center for that type is shown as a likely visit. We never claim what work was done. At airports with several shops, we don’t attribute the visit to any one of them.
12
Environmental exposure.
TailCheck estimates the conditions an aircraft has been exposed to on the ground and at departure. This is exposure, not condition. We can’t see whether an aircraft was hangared, washed or treated.
| Measure | What it captures | Data |
|---|---|---|
| Salt air | Nights spent at airports right by the coast | OpenStreetMap coastlines |
| Near the coast | Nights at airports within a short distance of the sea | OpenStreetMap coastlines |
| Damp air | Hours of high humidity above freezing (time of wetness, as in ISO 9223) | ERA5-Land |
| Freeze–thaw | Days when the temperature crossed 0 °C | ERA5-Land |
| Dust and arid climate | Nights at airports in arid climate zones | Köppen-Geiger |
| Short runways | Departures where the runway was short relative to the type’s takeoff distance | Runway and performance data |
| Hot-and-high | Departures at high density altitude | ERA5-Land, airport elevation |
We only count nights we can place, meaning the aircraft departed from the field it arrived at. Weather is taken for the actual dates the aircraft was there and adjusted from the weather grid to the airport’s elevation. Where too few nights or departures can be placed, we don’t grade the measure.
13
Events and fleet pages.
Event pages show aggregates only, with no individual aircraft named. Fleet pages are mostly aggregates, plus a list of the type’s busiest aircraft.
Events
We count business-jet arrivals and departures at the event’s airports during the event. We compare that with a normal baseline from the two weeks before and after, leaving out days around the event itself and other events. The normal range shown is the middle half of those baseline days. Changes under 3% read as “about as many”. Small categories are grouped into “other” so no individual aircraft can be picked out.
Fleet pages
Figures for a type cover the latest 12 full calendar months. They use only aircraft flown enough to measure, with misidentified and test aircraft removed. Utilization figures use only well-tracked aircraft, and only when doing so doesn’t skew the result toward one kind of operator. Where fewer than 30 aircraft qualify, we don’t show the figure.
Longest flights on fleet pages are checked for hidden stops. A flight is only listed if its speed and distance are possible for that type without refueling.
Fleet pages and tail pages compare against slightly different groups, so a fleet median can differ a little between the two.
14
Privacy and what we publish.
We publish information about aircraft, not people. We never show ownership, and we never show where an individual aircraft is based.
- 7-day delay. Pages about an individual aircraft run 7 days behind, so they can’t be used to follow an aircraft in real time. Aggregate pages, such as events and fleets, are not delayed.
- Small groups are suppressed. No percentile, median or group statistic is shown for fewer than 30 aircraft. Event breakdowns with very few aircraft are grouped together.
- Airport pages name no aircraft. They count arrivals by type and size, so they can’t show where an aircraft is based.
- Opt-outs. Owners and operators can ask us to remove an aircraft from our public pages using the opt-out form. Once a request is verified, we also stop selling the aircraft’s report and refund anyone holding an open one.
- Owners of named aircraft
- Home bases
- Time of day of flights
- Exact dates and locations of maintenance stays
15
Known limitations.
Flight data is good, but it isn’t complete. These are the limits we know about and how they affect what you see.
- Counts are minimums.
Missed flights mean flight counts, hours and cycles are far more likely to be undercounted than overcounted. Check an aircraft’s coverage grade before relying on its totals.
- Coverage varies by place.
Aircraft based where receivers are sparse will look less active than they are. Regional peer groups reduce this but don’t remove it.
- Coverage varies over time.
The receiver network has grown steadily, so early 2025 holds fewer tracked flights than later months. Part of any apparent growth in activity is better coverage.
- Many takeoffs and landings are inferred.
Low-altitude coverage is patchy, so many airports are assigned from the aircraft’s flight sequence rather than seen directly.
- Airborne time, not block time.
Our hours will read lower than logbook block hours.
- Identity follows the registration.
Re-registered aircraft can have split histories.
- Exposure isn’t condition.
Environmental measures describe where an aircraft has been, not its actual condition. A pre-purchase inspection is the only way to know that.
- Estimates are estimates.
CO₂ and annual hours are modeled from tracked data and type averages, not measured.
When something here changes, we log it under Changes to this methodology.
16
Sources, licenses and attribution.
We’re grateful to the open-data projects that make this work possible.
| Source | Used for | License and credit |
|---|---|---|
| OpenStreetMap | Coastlines | ODbL. © OpenStreetMap contributors |
| Köppen-Geiger climate classification, Beck et al. (2023), Scientific Data | Climate zones | CC BY 4.0 |
| ERA5-Land, Copernicus Climate Change Service (C3S) | Hourly weather | Contains modified Copernicus Climate Change Service information. Neither the European Commission nor ECMWF is responsible for any use of this information |
| OurAirports | Runway lengths | Public domain |
| Natural Earth | Land outlines on maps | Public domain. Made with Natural Earth |
17
Changes to this methodology.
Every change that affects a published figure is logged here, newest first.
- UpcomingVersion 2 pipeline. Coming with our next data update. Main and MLAT archives merged; landings judged against airfield elevation; gaps at cruise treated as one continuing flight; inferred airports limited to jet-capable fields and left blank when unclear; each flight records how it was observed. Items marked v2 · coming with our next data update on this page.
- Page published.