Wreckage localisation methodology

SeyAero is built to be investigation infrastructure: the evidentiary record an authority, operator or insurer runs its cases on, year after year. Infrastructure earns that position differently from software. It cannot ask to be trusted on the strength of a demonstration; it has to publish its method, its assumptions and its failures, and let technical reviewers judge it on those.

This document is part of that obligation. It states, in full, how one of the platform's engines works and where it should not be trusted. The same standard applies across the platform: the validation record publishes back-test results including misses, and the sealed track record publishes predictions before their outcomes are known. An institution should be able to evaluate SeyAero from these public documents before it ever opens an account.

This document describes the model used by SeyAero to estimate the location of an aircraft following a hull loss, and to plan the search for it. It is written so that a technical reviewer in an investigating authority, a search coordinator, or an insurer's engineering assessor can judge the model on its assumptions rather than on its output.

The model produces a probability distribution over position. It does not determine cause, apportion blame, or replace the judgement of the investigator-in-charge. Every output is decision support for search planning under ICAO Annex 12 and Annex 13 processes.

The model consumes only evidence held in the case file:

• Last known flight state — position, altitude, ground speed, track, vertical speed, and a fix confidence in [0,1].
• Full position track where available — radar, ADS-B, ACARS or satellite handshakes — used for the multi-fix trajectory fit.
• Meteorology by altitude band — wind direction and speed, temperature, visibility, phenomena.
• Oceanography — surface current set and drift rate, sea state, and water depth from the GEBCO 2020 grid.
• Ground and witness reports — observer position, bearing, distance, and an investigator-assigned reliability in [0,1].
• Negative search effort — swept areas with an assessed probability of detection.

Meteorological and oceanographic fields can be pulled automatically from historical reanalysis for the occurrence position and time, rather than entered by hand. A recovered-debris backcast can use the recovery date and position, a selected current preset or a dated field, and its chosen drift model as separately recorded inputs.

Where more than two fixes exist, a segment-wise fit derives track angle, turn rate, vertical speed and specific-energy trend across the final portion of the track. Specific energy is computed as altitude plus the kinetic term v²/2g expressed in feet, which exposes energy bleed that a raw altitude trace hides.

The residual scatter of segment bearings about the fitted turn gives a 1σ heading uncertainty. That uncertainty is carried into the Monte Carlo as an additional dispersion term rather than being discarded, so a noisy track widens the answer instead of producing a falsely confident one.

Between 500 and 20,000 particles are released from the last known state. Each particle is advanced through four stages.

• Glide footprint. A lift-to-drag ratio is sampled uniformly: 10–18 for a controlled glide, 0.8–4.5 for an out-of-control descent. Forward travel is (altitude / 6076.12) × L/D nautical miles.
• Departure heading. Dispersion about the last known track scales inversely with the sampled glide ratio: a steep, low-L/D descent has ground travel small relative to height lost, so the departure direction is only weakly constrained by the last recorded track. Dispersion runs from roughly 18° for a controlled glide to 120° for a near-vertical departure.
• Wind transport. Descent duration is altitude divided by the sampled descent rate; mean wind for the release altitude band advects the particle over that duration, with 25% speed variance and 12° directional variance.
• Water-column behaviour. Heavy structure sinks at 1.0–2.2 m/s and is displaced by current only for the sink duration implied by local depth, then scattered by break-up. Buoyant debris is advected by surface current for the full elapsed window, plus leeway at 2–4% of surface wind, plus turbulent diffusion growing as √t.

Impact and floating populations are solved as separate fields. The impact field is the sonar and seabed search zone; the floating field is the aerial and surface search zone. Conflating the two is a common cause of wasted search effort in real campaigns.

Recovered-debris backcasting is a separate indicative calculation. It resolves down-current and cross-current transport over the chosen interval, including persistent jibe, and normalises longitude across the date line. Crossing the date line triggers an explicit reliability warning because the present model is two-dimensional and does not resolve full ocean circulation or vertical mixing.

Ground and witness reports act as soft anchors. Each is converted to an implied position — directly, or by projecting bearing and distance from the observer — with a positional σ of 12–50 km scaled by the investigator's reliability rating. Particle weights are multiplied by a Gaussian likelihood raised to the power of the reliability, floored so that no single report can veto a particle outright. An unreliable report nudges the field; it cannot move it.

Negative search effort is applied with Koopman's law. A particle inside a swept area survives with probability (1 − POD) per pass. The field is then renormalised, so probability flows out of searched water and into unsearched water. This is why each fruitless sweep sharpens the next one rather than merely crossing an area off.

Sweep planning uses the standard maritime SAR random-search law. For an asset of speed V and effective sweep width W spending time t on a sector of area A, coverage is C = V·W·t/A and probability of detection is 1 − e^(−C).

Effort is allocated greedily by marginal probability of success per hour. For exponential detection functions this greedy allocation is the optimal allocation, so the resulting plan is not merely a heuristic ordering — it maximises the chance of finding the wreckage in the hours available.

The engine is a pure function of its inputs and a seed. Re-running a saved solution with its stored parameters and seed reproduces it bit for bit, which is what makes the output admissible as a documented analytical step rather than an opaque assertion.

Every action on a case is written to an append-only activity log. Each entry is hashed together with the hash of the entry before it, forming a chain: altering, deleting or re-ordering any historical entry invalidates every hash after it, and verification reports the exact sequence number where the break occurs. When a report is issued its fingerprint is bound to the chain head at that moment, so a report can be proven to correspond to a specific, unmodified investigative history.

The model is back-tested against real hull losses where the wreckage was subsequently recovered. Each case is re-run using only the information searchers held at the time; the recovery position is withheld from the model and used solely for scoring. Results, including any misses, are published in full and are stable across seeds.

These are the conditions under which the model should be treated with caution:

• Single-fix priors. With one position and no track, heading is unconstrained and the field is correspondingly broad. The result is honest but wide.
• Long unpowered flight after the last fix. Where an aircraft continued for tens of minutes beyond its final fix, the dominant uncertainty is duration, not aerodynamics, and the model's dispersion is optimistic.
• Coarse ocean fields. Reanalysis currents resolve to roughly 0.08°, which under-resolves eddies that matter for day-one debris drift.
• Long drift and date-line crossings. The debris backcast is a two-dimensional surface model. Reliability falls with elapsed time, and any date-line-crossing result is labelled indicative.
• Witness bearing bias. Human bearing estimates are systematically biased and night-time distance estimates are unreliable; reliability ratings should reflect that.
• Seabed relief. High relief creates sonar shadow zones, so an assessed probability of detection over rough terrain should be reduced accordingly.
• No terrain masking on land. Over land the model does not currently account for slope, canopy or terrain channelling of the descent.

This wreckage-localisation model is calibrated for transport-category fixed-wing aircraft. Rotorcraft, light aircraft and unmanned systems descend differently and remain outside its validated envelope. Rotorcraft occurrences are instead analysed by a first-class rotary-wing frame in the occurrence-analysis engines — weight-class rotorcraft envelopes with the fixed-wing stall and V-n tests gated off, autorotation energy and flare budget, height–velocity exposure, vortex-ring onset and rotor-system integrity read from the wreckage — alongside the propeller frame for propeller-driven aeroplanes — feathering drag, minimum control speed corrected for the bank held, overspeed and blade-signature power at impact — and the ditching, in-flight fire and icing frames. Those frames are uncertainty-bounded diagnostic aids and are not part of this back-tested localisation model.

Aircraft envelopes are a finite library. Where a type is not held, the analysis engines solve on a parametric synthetic envelope derived from class and mass, and every result carries that provenance on its face.

Model changes are versioned and re-validated against the full benchmark set before release; a change that improves one case but degrades containment across the set is rejected. Benchmark reference positions are taken from published official reports and cited on the validation page.

SeyAero outputs are advisory. The investigating authority remains the sole determiner of findings and causes under ICAO Annex 13, Chapter 5.