Taxi-in observed (worst 10%)
arr_continuity_p10
The worst-covered tenth of arrivals.
Taxi-in without gaps (median)
arr_continuity_p50
The same over the taxi-in.
Taxi-in observed (best 10%)
arr_continuity_p90
The best-covered tenth of arrivals.
Whole taxi-in observed (%)
arr_full_capture_pct
The same for taxi-in.
Longest taxi-in gap (min, median)
arr_max_gap_median_s
The same for taxi-in.
Lost at landing (%)
arr_no_ground_pct
The share of arrivals whose track ends at or before landing.
Taxi-in spanned (median)
arr_reach_p50
The same on the arrival side, measured forward from landing to the track’s last report.
Taxi-in received (median)
arr_signal_p50
The same computation over the taxi-in: the interval between landing and in-block, with reports counted against the same 5-second expectation.
One flight, one track (%)
clean_pct_arr
As above, over arrivals.
One flight, one track (%)
clean_pct_dep
The share of movements the track-building algorithm matched to exactly one track that contains no other flight. Position reports arrive as a continuous stream per airframe with no notion of a flight, so they have to be cut into flights first; this says how often that cut was right here.
Coverage index
coverage_index
The share of movements seen at all, multiplied by the share of a typical ground movement received (the average of the taxi-out and taxi-in medians).
Read it as the expected share of one movement the network captures. 1.00 is perfect; 0.00 means the surface is invisible even where the aircraft is tracked once airborne.
Left blank, never zero, where the ground figures are unavailable. Falling back to detection alone would rank an unmeasurable aerodrome as though it were well covered.
Taxi-out observed (worst 10%)
dep_continuity_p10
The worst-covered tenth of departures, by the 30-second-slice measure.
Taxi-out without gaps (median)
dep_continuity_p50
The taxi-out cut into 30-second slices; this counts how many held at least one report, regardless of how many were expected.
Read it against “received”: high here and low there means a thin but unbroken stream, arriving every half-minute but far short of what was expected.
Taxi-out observed (best 10%)
dep_continuity_p90
The best-covered tenth of departures, by the same measure.
Whole taxi-out observed (%)
dep_full_capture_pct
The share of departures where at least 95% of the expected reports arrived during taxi-out — effectively complete coverage of the ground movement.
Longest taxi-out gap (min, median)
dep_max_gap_median_s
The longest unbroken silence during taxi-out, for a typical departure. Measured from the start of the taxi to the first report, between consecutive reports, and from the last report to take-off — so a receiver that stops halfway is counted as having a gap even though no two reports straddle it. A large gap alongside otherwise good reception points at one blind spot rather than weak coverage throughout.
Never seen on the ground (%)
dep_no_ground_pct
The share of departures whose track starts at or after take-off — the aircraft was never heard while it was on the ground at all.
Taxi-out spanned (median)
dep_reach_p50
How far back the track’s first report lies, as a fraction of the taxi: the time between that report and take-off, divided by the taxi duration.
Disagrees with “received” in a revealing way: a single report at the stand and nothing afterwards spans the entire taxi and scores 1.00 here, where “received” scores it near zero.
Taxi-out received (median)
dep_signal_p50
The taxi-out is the interval between two measured times: off-block, and take-off. The feed delivers about one position report every 5 seconds, so a taxi of n seconds should produce about n/5 reports. We count how many arrived and divide by how many were expected, then take the median across this aerodrome’s departures.
1.00 means the aircraft was tracked the whole way out. 0.10 means nine reports in ten never arrived.
Flights seen (%)
detection_pct
Movements seen divided by movements the reference data records. Read it as a floor, not a coverage figure: above 99% at four measured aerodromes in five, it separates “invisible to the network” from “seen, but only partly” and says nothing about how much was tracked.
A flight counts as seen if one position report comes from the same airframe, matched on the ICAO address, and falls between its take-off and landing. That window is the airborne one, which is why this says nothing about ground coverage.
Arrivals seen (%)
detection_pct_arr
As above, over arrivals only.
Departures seen (%)
detection_pct_dep
As above, over departures only.
Split across tracks (%)
fragmented_pct_arr
As above, over arrivals.
Split across tracks (%)
fragmented_pct_dep
The share of movements broken across several tracks. Recoverable — the flight is present, in pieces — but coverage is measured against the largest piece, so a split flight’s coverage is understated. Within the same aerodrome a split departure’s track starts a median 6.5 minutes later than a clean one, which is the size of the understatement.
Track end vs landing (min, earliest 10%)
land_s_p10
The worst tenth, where tracking stops earliest relative to landing.
Track end vs landing (min, median)
land_s_p50
The gap between landing and the end of the track, in minutes, for a typical arrival: the track’s last position report minus the recorded landing time.
Positive is good: the aircraft was still being tracked while it taxied in. Negative means the track ended before the aircraft was down.
Track end vs landing (min, latest 10%)
land_s_p90
The best tenth, where tracking continues longest after it.
Times measured?
measured
Whether this aerodrome’s real stand and runway times are recorded by the operator. Where they are, the taxi phase has exact bounds and how much of it was received can be measured; where they are not, only whether the flight was seen at all.
Milestones measured (%)
measured_pct
The share of this aerodrome’s movements whose stand and runway times come from the airport operator, rather than being estimated. At or above 50% the aerodrome is treated as measured; below it, only whether flights were seen at all.
Arrival milestones measured (%)
measured_pct_arr
As above, over arrivals only.
Departure milestones measured (%)
measured_pct_dep
As above, over departures only.
Merged with another flight (%)
merged_pct_arr
As above, over arrivals.
Merged with another flight (%)
merged_pct_dep
The share of movements sharing a track with another flight. Only one comes out of a merged track; the other does not exist downstream. The survivor’s own coverage shows no consistent shift (median −0.009 against clean flights): a completeness loss, not a coverage one.
Unusable reference rows
n_capture_excluded
Movements whose recorded times are impossible — an off-block after take-off, or an on-stand before landing. They are dropped from the ground-coverage figures and counted here instead. Dropping rather than clamping matters: a movement with a negative taxi duration has no denominator, and forcing it to zero or one would move this aerodrome’s median for a reason that has nothing to do with reception.
Unusable reference rows (arr)
n_capture_excluded_arr
As above, on the arrival side.
Unusable reference rows (dep)
n_capture_excluded_dep
As above, on the departure side.
Movements seen
n_detected
How many of those movements produced any ADS-B position report at all, matched by airframe (24-bit ICAO address) and by time, inside that flight’s own airborne interval. One matching report is enough to count as seen.
Arrivals seen
n_detected_arr
Landings with at least one matching position report.
Departures seen
n_detected_dep
Take-offs with at least one matching position report. See “Movements seen”.
Movements (larger side)
n_gt
The larger of the two sides. The ranking floor and nothing else: 20 movements on one side, a stricter test than 20 across both.
Arrivals
n_gt_arr
Landings the reference data records here, counted against the flight’s destination aerodrome.
Departures
n_gt_dep
Take-offs the reference data records here over the sampled days, counted against the flight’s origin aerodrome.
Movements
n_movements
Take-offs plus landings the reference data records here, one flight contributing a movement at each end. The reference is the Network Manager flight table, independent of ADS-B. Where only one side is known, this counts the side that is.
Track start vs take-off (min, earliest 10%)
off_s_p10
The earliest tenth of departures — how far ahead of take-off tracking begins when this aerodrome is at its best.
Track start vs take-off (min, median)
off_s_p50
The gap between when the track starts and when the aircraft actually left the ground, in minutes, for a typical departure. Computed as the track’s first position report minus the recorded take-off time.
Negative is good: the track began before take-off, so the aircraft was already being followed on the ground. Positive means part of the departure was never seen.
Track start vs take-off (min, latest 10%)
off_s_p90
The latest tenth — how much of the departure is missed in the worst cases here.
Coverage
rating
A band over the coverage index, so a long table can be scanned without reading three decimals on every row: Excellent at 0.90 and above, Good from 0.60, Partial from 0.30, Poor from 0.05, and None below that.
Typical taxi-in (min)
taxi_in_median_s
How long a typical taxi-in takes here, from landing to in-block.
Typical taxi-out (min)
taxi_out_median_s
How long a typical taxi-out takes here, from off-block to take-off. Context rather than a coverage figure: the same three minutes of reception is most of a short taxi and a fraction of a long one, which is why coverage is expressed as a fraction and not as a duration.
Tracking errors (%)
tracking_err_pct
The share of this aerodrome’s movements the track-building step got wrong: split and merged added together.
Split understates coverage, because only the largest piece is scored. A split departure’s track starts a median 6.5 minutes later than a clean one, at 182 of 206 aerodromes.
Merged costs a whole flight: two share a track, one survives, the other is absent downstream. No measurable effect on the survivor (median −0.009, on 0.8% of movements).
So a high figure means coverage understated and movements missing, not poor reception.