Aviation investigation glossary

Plain-language definitions of the terms used in aircraft accident and serious incident investigation — recorders, occurrence classes, reconstruction methods and search planning — as SeyAero uses them.

Accident (ICAO Annex 13)

An occurrence associated with the operation of an aircraft in which a person is fatally or seriously injured, the aircraft sustains damage or structural failure, or the aircraft is missing or completely inaccessible. The definition governs when a state must investigate.

Serious incident

An incident involving circumstances indicating that an accident nearly occurred — for example a near collision, a takeoff on a closed runway, or an engine fire contained without damage. Serious incidents carry the same investigative discipline as accidents.

Investigator-in-charge (IIC)

The accredited investigator appointed by the investigating state who directs the investigation, controls the evidence, and owns every finding. Tools such as SeyAero support the IIC but never replace the role.

Flight data recorder (FDR)

A crash-protected recorder that logs hundreds to thousands of aircraft parameters — altitude, airspeed, control positions, engine state — many times per second. The primary factual source for reconstructing what the aircraft did.

Cockpit voice recorder (CVR)

A crash-protected audio recorder capturing crew speech, radio calls and cockpit area sounds. Transcribed verbatim to Annex 13 standards, it evidences what the crew knew, said and heard.

ADS-B

Automatic Dependent Surveillance–Broadcast: the position, altitude and velocity messages an aircraft broadcasts roughly twice per second. Ground receiver networks preserve a track even when radar coverage or recorders are absent.

METAR

A routine aviation weather observation issued by an aerodrome, typically every 30 or 60 minutes: wind, visibility, cloud, temperature, pressure. The baseline weather evidence for any occurrence near an airport.

Reanalysis weather

Modelled historical weather (such as ERA5) reconstructed from assimilated observations. Used for occurrences months or years old where no station record survives; it is an estimate and is labelled with lower certainty than a direct observation.

Event sequence / master timeline

The single chronological ordering of everything known about an occurrence — recorder parameters, radio calls, witness times, weather — aligned onto one clock. Most investigation software failures are clock failures; the timeline is where conflicts surface.

Chain of custody

The tamper-evident record of who handled each piece of evidence, when, and what changed. Without it, an exhibit can be challenged and the finding it supports weakened.

Hypothesis ranking

Testing each candidate explanation against the physics of the airframe and the evidence on file. A hypothesis contradicted by evidence is eliminated and the contradiction named; one the file cannot decide stays open. Ranking is not a finding of cause.

Probable cause

The formal determination of why an accident happened. Under ICAO Annex 13 it is made solely by the investigating state. Decision-support software must refuse to state one; SeyAero does.

Loss of control in flight (LOC-I)

An occurrence in which the aircraft departs from the crew's intended flight path and cannot be recovered — historically the largest single killer in commercial aviation.

Controlled flight into terrain (CFIT)

An airworthy aircraft, under crew control, flown unintentionally into terrain, water or an obstacle, usually without the crew's awareness of the impending collision.

Fuel exhaustion

Engine flameout because no usable fuel remains — distinct from fuel starvation, where fuel exists but cannot reach the engines (blocked lines, mis-selected tanks, contamination).

Fuel contamination

Fuel degraded by water, microbial growth, wrong grade or foreign matter. Suspected when engines lose power together with fuel remaining, and proven only by laboratory analysis of samples.

Hypoxia

Oxygen starvation of the brain following slow or rapid cabin depressurisation. Its danger is that judgement fails before the crew notices — a signature of several ghost-flight accidents.

Crew incapacitation

Partial or total loss of a crew member's ability to perform duties, from medical events, hypoxia, fumes or fatigue. Evidenced by callout patterns, physiological data and medical records.

Centre of gravity (CG) error

Loading that places the aircraft's balance outside certified limits, degrading stability or making rotation impossible. A load-sheet error can be invisible until takeoff.

Wake turbulence

The counter-rotating vortices trailing every wing, strongest behind heavy aircraft at low speed. Encounters can roll a following aircraft beyond its control authority; separation minima exist to prevent them.

Microburst / wind shear

A sudden localised downdraft and outflow that can rob an aircraft of lift and airspeed within seconds, most dangerous on approach and departure.

Wrong-engine shutdown

After an engine failure, the crew identifies and secures the operating engine instead of the failed one. A recurring turboprop accident signature (e.g. TransAsia 235), detectable by comparing parameter loss with crew callouts.

Post-crash fire survivability

The study of whether occupants survived the impact forces and then perished in fire or smoke — which turns a structural question into an evacuation, materials and suppression question.

Surface drift datum

A recovered floating object with a known recovery position and time, used to back-calculate ocean drift and narrow where the aircraft entered the water. Drift modelling powered the MH370 and AF447 search refinements.

Search probability zone

A gridded map where each cell carries the computed probability that wreckage lies within it, built from last-known position, drift, descent physics and search effort already expended. Directs sonar and salvage spend to where it matters.

Sealed prediction

An analysis output timestamped and cryptographically committed before wreckage recovery or official findings, so accuracy on a live case can be checked afterwards instead of claimed. SeyAero publishes its sealed record publicly.

ICAO Annex 13 report

The prescribed structure for accident investigation reports: factual information, analysis, findings, causes and safety recommendations. SeyAero drafts this structure from confirmed facts for the investigator to edit and own.

Safety recommendation

A formal proposal issued during or after an investigation, addressed to a regulator, manufacturer or operator, intended to prevent recurrence. Tracking whether recommendations are acted on is a measure of whether an investigation changed anything.