The Aeronautical Accident Investigation Process

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As of May 21, 2021

Airplanes are a means of transportation that even today causes fascination and amazement that something so heavy can fly carrying passengers and tons of cargo every day. Air transport is undoubtedly very safe, a result of numerous safety protocols, which start from the development of a new aircraft, manufacturing, testing, certification, redundant systems, maintenance and inspection requirements, and many others besides the aircraft itself such as the airports, air traffic control, navigation systems, location and weather conditions involved, to name a few.

Even with the great apparatus that sustains aviation safety, several accidents have already happened, and statistically new accidents might happen since the system involves machines, processes and mainly people. But aircraft accidents are a source of much commotion and media appeal, especially when a plane crash results in dozens or even hundreds of casualties. No matter where a fatal air crash occurs, it will likely be reported worldwide and can be in the media for several weeks and months, and remembered even after a few years, given the impact and commotion an accident can cause. However, the fact is that aviation is what it is today because of accidents that occurred in the past, whose causes were investigated, and corrections and improvements were implemented in aviation.

Do you know how the investigation process for aeronautical accidents or incidents works? There is also a protocol that generally defines the rules and responsibilities for the investigation process. This article seeks to explain the investigation processes where an accident or incident has not been caused by intentional reasons such as terrorism, attacks, sabotage, or criminal acts.


ICAO is responsible for providing international standards and recommended practices for the investigation process, through a document called Annex 13. The first edition was published in 1951, and it defines how each country should have an organization responsible for investigations, how an investigation should proceed, who should be responsible for the investigations, and what is expected as a result.

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Figure 01 – Cover of ICAO Annex 13 document

What is the purpose of the investigation?

“3.1 The sole objective of the investigation of an accident or incident shall be the prevention of accidents and incidents. It is not the purpose of this activity to apportion blame or liability.” (ICAO)

It is a very simple but very important definition, and where the result of each investigation contributed to the countless changes in projects and requirements in aviation that has been making it increasingly safer.

One of the most basic rules is that the investigating body must be totally independent and impartial, that is, it cannot be part of a country’s civil aviation authority, or linked to any aircraft manufacturing company, for example. In many countries the civil aviation authorities are civil government organizations and the investigating bodies are military organizations, but this is not a rule, just an example, but the full independence of the investigation must be respected.

As defined, the investigation reports will not point out the guilty, but the causes and/or factors that contributed to a given accident and will always propose safety recommendations so that accidents with these same causes and/or contributing factors do not happen again. On the other hand, there will also be civil and criminal judicial investigations aimed at the compensation of the parties and even the criminal conviction of those responsible, work that is done by other entities and a situation that is clearly outside what is expected by an investigation aimed at safety.

Investigation Responsibilities

As defined by the ICAO, the responsibility for leading an investigation rests with the country where the accident/incident occurred, and which will receive support from other investigative bodies, such as the country of registration of the aircraft, the country of the operator and the country of manufacture of the aircraft and engines for example. Normally the aircraft manufacturer will provide all technical and documentary support during the investigation as well as suppliers and maintenance companies as they are necessary during the investigation process. ICAO defines an entire notification protocol by the country where the accident occurred for the other affected countries, which rigor is required for the investigation to be carried out as it should be done.

The agency responsible for the investigation in the country of occurrence must ensure by possible means of protection and safety where the plane or its wreckage is located so that the information is preserved in the best possible way and does not interfere in the investigations, especially access to flight data recorders and voice.

Many countries have fully trained investigative bodies with diverse resources that ensure a smooth investigation progress. But an accident can occur in a small country with few resources and which would not be able to lead the investigation. In these cases, the investigation leadership can be delegated to other investigation bodies, preferably linked to the crashed plane (country of registration / operator, country of manufacturer).

Once the leadership of the investigation is defined, authorized representatives (persons) will be designated by each entity to carry out the investigation itself, which will become accredited representatives with specific responsibilities and obligations.

Common steps of an Investigation

The investigation process can take months and, in some cases, even years, and the process involves the following steps in general:

  • Location of plane or wreckage.
  • Witness information.
  • Survey of various information, especially manufacturing documentation, maintenance records, and any or all records of other activities (supply, releases, mechanics and pilots training records, etc.) that may be relevant to the investigation.
  • Analysis of flight data recorders and voice records in the cabin and with air traffic control, as well as analysis of satellite location records and environmental/weather data.
  • Conducting tests on materials and simulating flights under the same conditions as the accidental flight when necessary.
  • Construction of the possible failures observed and identification of all the reasons that allowed failures to occur.
  • Issuance of the final report with safety recommendations.

Generally, an investigation report must be issued within twelve months, but more complex investigations can occur that can take much longer, and so interim reports can be issued. Situations can still occur where a very serious failure is identified early in the investigation and a preliminary report with some safety recommendations is issued so that the airline industry can take immediate action to prevent a new accident, the most recent example is the case of the Boeing 737 Max which, right after the second accident, posed a serious doubt as to the safety of the aircraft, which left this model of aircraft banned from flying again for around 18 months, conditioned to modifications and additional training.

The figure below illustrates the investigation process in a visual and more interesting way:

Figure 02 – Investigation Process Illustration

Normally, an investigation is able to have access to all the necessary data, and with this it is able to reproduce the accident scenario and identify all the contributing factors for that accident and the issuance of safety recommendations address actions that will prevent new accidents with the same causes. But the investigation is not always able to gather all the necessary information, and some of the situations below may occur:

  • Aircraft without flight data and/or voice recorders, in the case of simple and non-commercial aircraft, often making it difficult to conclude what led to the accident.
  • Aircraft that had its flight data and/or voice recorders damaged due to the accident and its information ends up not being recovered. Or even a very long delay in locating these recorders, especially when an aircraft has an accident at sea, an example of the accident with the Air France AF447 that crashed into the Atlantic ocean between Brazil and Europe and which had its data found two years after the accident, in which case it was still possible to retrieve the data and complete the investigation.
  • Missing aircraft, as an example of the Malaysia Airlines MH370 aircraft that disappeared and was never found, making the investigation of this accident limited and based mainly on hypotheses and a few satellite data records that managed to track an unscheduled route change.

As can be deduced, the cost of investigation is always very high, as it involves many countries and many resources, especially when trying to locate missing debris in vast areas such as the sea and large forests. The MH370 for example was responsible for one of the largest searches ever carried out either on the surface as well as underwater and covering vast areas, estimating a cost of 133 million euros.

Final considerations

The investigation of aeronautical accidents is fundamental to guaranteeing an ever-safe aviation experience and it is impressive how this protocol has been working very well since the 1950s, when this constant search for accident prevention began. The investigation report data provided is of such quality and accuracy, resulting from a highly standardized industry and whose protocols are followed as best as possible.

But there is still a misuse of the final investigation reports that are civil and criminal effects, a situation that can interfere in future investigations if people are more concerned about being punished than about contributing to safer aviation. But this question has been asked for many years and does not appear to have significantly affected the results of an investigation.

There are many safety programs that aim to prevent accidents before they occur, but an investigation is in essence a means of learning from errors, which is why it is very important because it would no longer be acceptable for the same error to happen again, but it also manages to emit in the final additional recommendations that prevent other dangerous situations from occurring.

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