How to Read an Air Accident Final Report and Probable Cause

An air accident final report is the official account of what happened and why, written by the independent investigating body. Almost every final report follows the same order, set by the international rules in ICAO Annex 13: factual information, analysis, conclusions and safety recommendations. Once you know that order, you can find the answer you need in a 200-page report in a few minutes.

Where to find final reports, by country

Final reports are published by the investigating body of the country where the accident happened. Most are free to download.

Country	Body	Where to search
United States	National Transportation Safety Board (NTSB)	NTSB CAROL
France	Bureau d’Enquêtes et d’Analyses (BEA)	BEA safety investigations
United Kingdom	Air Accidents Investigation Branch (AAIB)	AAIB reports
Canada	Transportation Safety Board (TSB)	TSB air transportation reports
Australia	Australian Transport Safety Bureau (ATSB)	atsb.gov.au
Greece	AAIASB (archive; now succeeded by ΕΟΔΑΣΑΑΜ)	AAIASB report archive
Papua New Guinea	Accident Investigation Commission (AIC)	AIC final reports

NTSB reports are identified by a number such as NTSB/AAR-04/04: “AAR” means Aircraft Accident Report, “04” is the year of publication and the last number is its order in that year. You can usually find the PDF by searching for the airline and flight number together with the investigating body’s name.

Our guide Who Investigates Plane Crashes? lists more bodies, including those that investigated older accidents on this site.

The standard structure

Most final reports follow the format in Annex 13, with ICAO’s investigation manual (Doc 9756, Part IV, Reporting) giving the detailed guidance. The NTSB’s report on American Airlines Flight 587, which crashed in Belle Harbor, Queens, on 12 November 2001, is a good example. It runs to more than 160 pages before the appendixes.

1. Cover and summary. The title page gives the flight, aircraft type and registration, place, date and report number, and the date the Board adopted it. The executive summary, a page or two long, states what happened and the probable cause. If you read only one page, read this.
2. Factual information (section 1). Everything the investigators established, with no interpretation: the history of the flight, injuries, damage, the crew, the aircraft, weather, navigation, communications, the airport, flight recorders, wreckage, medical information, fire, survival aspects, tests and research, and organisational information. For Flight 587 this section runs to 132 pages, including wake turbulence studies, simulator tests and laboratory examinations of the composite tail.
3. Analysis (section 2). Where investigators reason from the facts. They rule out what did not happen, then explain what did. This is where you see why one explanation was accepted and another rejected.
4. Conclusions (section 3). Numbered findings, then the probable cause.
5. Recommendations (section 4). New safety recommendations, each with its own number, addressed to a named organisation, followed by earlier recommendations the investigation reaffirmed.
6. Appendixes. How the investigation was run, the parties, any public hearing, and often the full cockpit voice recorder transcript.

Not every body uses exactly the same headings. Canada’s TSB, for example, sorts its conclusions into findings as to causes and contributing factors, findings as to risk and other findings, and does not use the phrase “probable cause”.

Probable cause, contributing factors and findings

These terms are easy to mix up.

• Findings are the numbered conclusions the investigators reached. Some explain the accident; others are simply facts that were established, such as “the crew were properly certificated”.
• Probable cause is the NTSB’s one-paragraph statement of the main reason the accident happened. “Probable” does not mean “probably right”. It is the board’s formal determination after weighing all the evidence.
• Contributing factors are conditions that made the accident more likely or more severe, without being the main cause. In the NTSB’s wording they often follow “Contributing to the accident were…”.
• Findings as to risk (TSB) are problems the investigation uncovered that did not cause this accident but could cause another.

For Flight 587, the NTSB determined that the probable cause was “the in-flight separation of the vertical stabilizer as a result of the loads beyond ultimate design that were created by the first officer’s unnecessary and excessive rudder pedal inputs”. It named two contributing factors: characteristics of the Airbus A300-600 rudder system design, and elements of American Airlines’ Advanced Aircraft Maneuvering Program, a pilot training course.

Watch the qualifiers. On TWA Flight 800, the NTSB found the probable cause was an explosion of the centre wing fuel tank, but wrote that the source of the ignition energy “could not be determined with certainty”. Of the sources examined, the most likely was a short circuit outside the tank that let excessive voltage into it through the fuel quantity wiring. A careful reader keeps “most likely” as “most likely”.

Reading the factual section: what each part tells you

A few parts of the factual section answer most readers’ questions.

• Injuries to persons is a small table: crew, passengers and others, against fatal, serious, minor and none. It is the authoritative source for the death toll. Use this figure rather than the one in a news report.
• Personnel information gives each pilot’s age, licences, total flying hours and hours on the type, and recent rest. It shows whether experience or fatigue was an issue.
• Aircraft information gives the registration, age, hours and cycles (take-offs and landings), and the maintenance history.
• Meteorological information gives the actual weather reports at the time, in coded form with a plain explanation.
• Flight recorders describes what was recovered and how much data was usable.
• Tests and research is where the laboratory, simulator and structural work is reported.

Times in reports are often in UTC, or “Zulu” time. Swissair Flight 111’s report uses UTC, which was three hours ahead of local time in Nova Scotia. If a timeline seems wrong by whole hours, check the time zone first.

Safety recommendations, and how to see if they were adopted

The recommendations section is where a report changes things. Each NTSB recommendation has a number such as A-04-56 (“A” for aviation, then the year and a sequence number) and is addressed to one organisation. Flight 587’s report made eight new recommendations, A-04-56 to A-04-63. All eight were addressed to the Federal Aviation Administration. The first asked it to add a certification standard for safe handling in the yaw axis, including limits on rudder pedal sensitivity.

A recommendation is not an order. To see what happened to it, look it up in the NTSB’s CAROL system, which records the response and a status such as “Open—Acceptable Response” or “Closed—Acceptable Action”. Other bodies publish their own recommendation status lists or responses alongside their reports.

A walk-through: American Airlines Flight 587

If you open NTSB/AAR-04/04 for the first time, here is a quick path through it.

1. Executive summary. The Airbus A300-605R crashed shortly after take-off from New York’s JFK airport bound for Santo Domingo. On board were 2 pilots, 7 flight attendants and 251 passengers. The vertical stabilizer and rudder separated in flight and were found in Jamaica Bay.
2. Section 1.1, History of Flight. The minute-by-minute account, including the two encounters with the wake of a Japan Airlines Boeing 747 that had departed ahead.
3. Section 1.16, Tests and Research. The heart of the evidence: the wake study, the simulation of the flight, the loads on the tail and the materials examination of the composite attachment lugs.
4. Section 2, Analysis. How the board concluded that the rudder inputs, not a pre-existing flaw, overloaded the tail, and why the first officer may have used the rudder that way.
5. Section 3.2, Probable Cause, and section 4, Recommendations.
6. Board member statement. At the end, Members Carol Carmody and Richard Healing explain why they voted against a change to the probable cause wording. The staff draft listed the training programme as the first contributing factor; the adopted version put the rudder system design first. Carmody wrote that reversing the order would “diminish the role of the AAMP in the accident”.

That last page is a reminder that probable cause statements are written and voted on by people, and that the order of the words can matter to them.

Common traps

• Preliminary reports are not conclusions. A preliminary report, due within 30 days under Annex 13, gives early facts. It rarely states a cause, and later findings can change the picture.
• Media summaries simplify. Headlines tend to reduce a probable cause to one phrase, such as “pilot error”, and drop the contributing factors. Read the probable cause paragraph itself.
• Dissents and comments. Some reports include statements by board members who disagreed, or formal comments from another country that took part. They do not change the official finding, but they show where the evidence was debated.
• “Most likely” is not “certain”. Keep the investigators’ qualifiers when you repeat a finding.
• Cause not established. Some investigations end without a firm cause, usually because key evidence was never found. That is an honest result, not a cover-up. On this site we mark those events “Cause not established” and keep any theories separate, as our How We Check Facts policy explains.
• Old reports may be scans. Older reports, such as the NTSB’s report on Delta Air Lines Flight 191 at Dallas/Fort Worth in 1985 (NTSB/AAR-86/05), are scanned images, so you cannot search the text. The structure is the same: look for the probable cause in section 3.
• Not every report is online. Some older or foreign reports have no official online copy. The Portuguese report on Air Transat Flight 236 (2004) is one we name on its event page without a link, because we could not find a verified official copy.

For the steps that come before the report, read How Plane Crash Investigations Work. For terms such as UTC, CVR and wake turbulence, see our Aviation Glossary.

Sources

• NTSB/AAR-04/04, American Airlines Flight 587, adopted 26 October 2004.
• NTSB/AAR-00/03, TWA Flight 800, adopted 23 August 2000.
• NTSB/AAR-86/05, Delta Air Lines Flight 191.
• TSB Canada A98H0003, Swissair Flight 111.
• ICAO Annex 13 provisions, Uniting Aviation (ICAO), 30 August 2021; ICAO Doc 9756 Part IV, Reporting.
• Report search pages: NTSB CAROL, BEA, AAIB, TSB, PNG AIC, AAIASB.