Data sources & methodology
Where every figure comes from, how records are matched to an aircraft, and what the scores mean.
Sources
Public records only. Each TailFax prints every source with the date it was last loaded.
- FAA aircraft registry. Registration, serial number, model, year of manufacture and engine of every US-registered aircraft, and its registered owner.
- Weekly FAA registry snapshots. Owner changes, found by comparing one week's registry with the next.
- FAA recorded documents (DOCINDEX). The index of documents filed against an aircraft, such as bills of sale.
- FAA airworthiness directives, via the Federal Register. The published text of each directive, from which the models and serial ranges it covers are read.
- NTSB accident database. Accident and incident records, filed by tail number.
- FAA releasable airmen database. Pilots and mechanics who allow their record to be released.
What the records cannot say
- No maintenance records or logbooks: nothing here shows how an aircraft was maintained, what was repaired, or whether a directive was complied with. A report shows which directives apply, not whether they were done.
- No damage history beyond NTSB records: damage never reported to the NTSB does not appear.
- The records may be incorrect, incomplete or out of date, and they are matched by name, date and serial number, so some links are probable rather than certain.
- It is not an inspection: a summary of public records, a starting point for questions, not a verdict on an aircraft.
Which aircraft an NTSB record belongs to
Tail numbers are reassigned, so the NTSB records filed under a number can belong to earlier aircraft that held it. Each record is matched against the aircraft that holds the number now, in this order:
- The NTSB serial number is present and equals the registration's: this aircraft, matched by serial.
- The NTSB serial number is present and different: not counted, an earlier aircraft.
- No NTSB serial, and the event is in a year before this aircraft was built: not counted.
- No NTSB serial, and the NTSB model is not compatible with the registered model: not counted, a different type.
- No NTSB serial, a compatible model, on or after the year built: this aircraft, matched by model and date.
A record with no serial and no model to compare is not counted and is listed with that reason, never guessed. Who owned the aircraft at the time does not matter: an accident under an earlier owner of the same airframe is its history. Models are compared as upper-case letters and digits, and one matches the other when they are equal or one begins with the other (NTSB “172” and FAA “172S”).
The answer is computed whenever NTSB or registry data is loaded and stored, and each run is checked against the last before anything is written (every record classified exactly once, the share of each outcome, the number attributed to current aircraft, and no event attributed twice to one aircraft); a run that moves too far is refused, not written. Model figures count a record toward a model through the aircraft it belongs to: the current aircraft when the record is attributed to it, otherwise the one deregistered aircraft with the same serial number, if there is exactly one.
Rates
Every rate states what it is divided by: NTSB events in the last ten years per 1,000 active aircraft of the model, and ownership transfers in the last 24 months per 100 active aircraft. The base is the model's active fleet, and it is shown with the rate. Under 20 active aircraft no rate is given; under 100 the base is marked thin.
Scores
Each model is compared only with its peer class: the same aircraft type, engine type, number of engines and seat band. A score is the model's position in that class, from 0 (the worst of the class) to 10 (the best): 10 × (models it beats + half of the models it ties with) ÷ (class size − 1). It is a position among comparable models, not a grade. A category is scored only when at least 8 models of the class have a value; accident and severity are scored only for a model with at least 10 NTSB events in ten years. A missing score is never filled in with a median or a zero.
The overall score
The overall score is the sum of the 5 categories shown that are scored, written “X out of Y”, where Y is 10 for each scored category (50 when all 5 are). It is given only when at least 4 of the 5 are scored. Because each score is a position inside one class, a sum is comparable only between models of the same peer class scored on the same categories; Compare says “not comparable” when they differ, and shows the numbers without ranking them.