Where aircraft reported degraded navigation

Ninety days over the Baltic, from publicly broadcast aircraft data. A measurement, openly derived and open to challenge.

Loading…

Point at the map for cell detail.

Day by day, across the region

Pooled across every well-observed cell, so each point rests on millions of reports rather than the handful any single cell contributes. The dashed line is the 6.02% regional background. Ticks below the axis mark days the detector produced at least one candidate — candidates for review, not findings, and 98% of them fall in control airspace where a firing is a false positive by construction.

There is no per-cell time slider, and that is a data limit rather than a missing feature. Across the backfill only 4.9% of cell-weeks carry the thousand integrity reports a rate needs. At any position of such a slider 95% of the map would be blank, and the rest would move mostly on sampling noise. Animating that would look like information and be nothing of the kind. Pooled region-wide the same days are measurable many times over, so the time axis is regional.

A dark cell has two very different explanations, and this map does not separate them.

At 54.74°N 9.39°E, one of the best-observed cells in the region, 51.5% of integrity reports are degraded — but split by aircraft type, fifteen Cessna 172s report 68.8% and two gliders report 100%, while 264 Boeing 737s, 159 A320neos and 105 Boeing 787s in the same cell report between 0.0% and 0.5%. That cell is measuring the avionics fitted to light aircraft, not the sky above them.

The darkest cell is the other kind. At 59.78°N 29.79°E, on 1,404 reports across ninety days, 63 Airbus A350s report 100% degraded, as do the Boeing 737s, the A319 and the Tupolev 204s recorded there. Interference does not politely skip airliners, and neither does that cell. It is also thinly observed, which is why it is drawn faint and why no finding is claimed from it.

Telling those two apart is what the rest of the method is for, and it is not finished. Read a dark cell as a question, not an answer.

What has been measured

Ninety days are loaded and continuous — 10 May to 7 August 2026, 141 million position reports and 35 million navigation integrity reports from 12,734 aircraft, with no gaps. Across the region, 6.02% of integrity reports are degraded. That is the background any real finding has to rise above, and it is measured rather than assumed.

The primary detector has been measured against control airspace: over a 31-day window across 106 cells where nothing was reported, it fires on 0.66% of the cell-hours it evaluates. Most of that came from a rule rather than a threshold — light general-aviation avionics report poor integrity constantly, so a firing requires several different aircraft types to show it, not merely several aircraft.

How much it would catch is not known. The one effect in this region large enough to serve as a reference sits in airspace too thinly flown to meet the coverage bar — around two aircraft per cell against the five required — so the detector declines to evaluate it, and no sensitivity figure has been measured under the same rules the false-positive figure was. An earlier estimate of 81% was taken without that restriction and does not describe the detector as it runs; it has been withdrawn rather than restated. Knowing what a method misses matters as much as knowing when it is wrong, and that half is open.

No findings are published here. Half of the bar has been cleared — the control-airspace test — and half has not: no independently documented, dated event has yet been found in airspace this method can actually see. Until one is, what appears on this site is measurement, and it is labelled as such.

Region: Baltic — 53.5°N to 66.0°N, 9.0°E to 30.0°E
Cell size: Hexagons roughly 20 km across, on 15-minute windows
Cadence: Daily batch processing of published archives. Nothing is real-time
Expansion: Further regions only after the method is validated in this one

About

What this is, how it works, and the rules it is built to.

Satellite navigation signals reach an aircraft receiver extremely weak — roughly the power of a car headlight seen from twenty thousand kilometres away. They are correspondingly easy to disrupt.

Episodes of degraded satellite navigation affecting commercial aviation over parts of Europe have been reported publicly by airlines, aviation authorities and the trade press. Individual accounts exist. What does not is a continuous, independent, reproducible record of where and when aircraft reported degraded navigation integrity — one built to survive being challenged, and held by someone with no stake in the answer.

GNSS Observatory is being built to be that record.

How it works

Aircraft broadcast their position continuously over ADS-B, derived from onboard GNSS receivers. Those broadcasts also carry navigation integrity fields — the receiver's own assessment of how far its reported position can be trusted.

When reception degrades, that self-assessment falls, and the aircraft broadcasts the degradation to anyone listening. The effect publishes its own evidence. We read those public broadcasts and look for populations of aircraft whose navigation integrity falls together, in the same airspace, at the same time — then record the result in a form that can be re-derived and audited later.

What this is

A project, not a service. It is built in the open, one region at a time, and it publishes what it can defend. There is no product, no subscription and no customer. Where the method is uncertain the site says so, and the uncertain parts are currently the interesting ones.

The public map is the whole of it today. Everything drawn there is derived from archives anyone can download, using code whose parameters travel with every number it produces, so a disagreement can be settled by rerunning it rather than by argument.

Method and principles

These are design rules rather than aspirations. They exist because the failure modes are worse than the missed detections — and because they are what allows a finding to survive being challenged.

No conclusion is drawn from a single aircraft. One malfunctioning receiver is indistinguishable from localised interference. Any finding requires a population of independent aircraft, across more than one aircraft type and operator.
Effects are observed; transmitters are not located. Measuring the effect on aviation is data analysis. Locating a transmitter is radio direction finding, which carries an entirely different legal and regulatory posture. GNSS Observatory does not do it, and operates no radio receiving equipment.
No attribution of cause or actor. The data can show that navigation performance degraded over an area. It cannot show who or what caused it, and no such claim will be made.
Every record carries the software version that produced it, with its full parameter set, so any published statement can be reproduced, re-derived or challenged afterwards.
Findings are superseded, not silently revised. When the method improves, earlier findings are marked superseded rather than quietly rewritten — the audit trail is part of the work. Where an aircraft is excluded on request, its identifiers are removed regardless.
The method is measured against quiet airspace, not only against known events. Any detector can be tuned until it finds the incidents you already know about. What matters is how often it fires over control airspace where nothing was reported, and that rate is measured and published alongside the method rather than left unstated.
Human review before publication. Nothing reaches the public automatically.

Data and licensing

Source: Publicly released daily archives of aircraft transponder broadcasts, from the adsb.lol community project
Licence: Used under the upstream project's published terms (ODbL 1.0 and CC0), with attribution
Coastline: Natural Earth, public domain — clipped and served by this site, not fetched from anyone
Collection: No radio equipment is operated. Only archives already published by others are processed

Get in touch

Corrections and challenges are the most useful thing anyone can send. If you work in aviation, avionics or air traffic management and something here looks wrong, please say so — especially about the map.

contact@gnssobservatory.com

Privacy

The data processed consists of transponder broadcasts made openly by aircraft: position, altitude, velocity, and navigation integrity values, together with the transponder's assigned address. It contains no passenger or crew information, and none is derived.

Analysis is carried out at the level of airspace and populations of aircraft, not individual flights, and individual aircraft are not identified in the public map or in public findings.

A transponder address can, in some cases, relate to an identifiable person — for example where an aircraft is privately owned. Where it does, processing is carried out on the basis of legitimate interests under Article 6(1)(f) GDPR: the independent documentation of navigation interference affecting aviation safety, using data already broadcast openly and published by others.

You may object to that processing at any time. An owner or operator may request exclusion, and the aircraft will be removed from processing and from any published output. Requests go to the contact address above. A full privacy notice will be published before any findings are.

This site sets no cookies, loads no third-party resources, and performs no tracking.

Important limitations

GNSS Observatory is not an aviation information service. Nothing published here is certified, validated for operational use, or suitable for navigation, flight planning, dispatch, or any safety-of-flight decision. Authoritative information about GNSS availability is issued by the relevant national aviation authorities and air navigation service providers, through NOTAMs and equivalent channels. Always use those.

GNSS Observatory is independent and is not affiliated with, endorsed by, or acting on behalf of any government, aviation authority, air navigation service provider, or aircraft operator.