Why does it take months, sometimes years, for the BEA and NTSB to complete aviation accident investigations?
When it comes down to it, accident investigations involve lots of coordination between many different groups, companies, and agencies, often around the world. These groups may range from helpful and responsive to completely uncooperative.



Visiting the Site - First there will be a team that heads to the incident site to collect information. If the site is easily accessible, this may be a fairly quick process. If the site is tough to access, or takes a while to find, this will of course take much longer. This is generally the part most visible to the public, but is only the tip of the iceberg in generating a useful report.

Research - There is also a lot of research that must go on behind the scenes. Especially if a possible cause is not clear, investigators must look into many factors to rule out the options. This can be a lot of information and may involved many different groups around the world:


Previous maintenance done on the plane
ATC and weather information about the flight
Information about the crew, the passengers, and the cargo on the flight
Many individuals may also be interviewed


If any of this initial information provides clues as to possible causes of an accident, they will also be gathering information about related aircraft design and functions. This can be a lot of information and may involve working with many different groups. The process of narrowing the focus of the investigation may involve tracking down different leads which end up being irrelevant. It may take a lot of effort just for the report to end up saying "X was not a factor."

Flight Recorders - Gathering the flight recorder data is not always as simple as plugging it in and reading the data. If there is damage, extracting and repairing the memory may take time. The FDR data must be analyzed and it may take additional work to investigate and verify the parameters. The CVR must be read out and then transcribed. Transcription is also a long process, involving different parties to the investigation, and must be synchronized to ATC and FDR information.

Analysis - Once the information has been collected, it must all be analyzed. Investigators may need to contact and work with many different groups and experts to develop an understanding of parts and processes that took groups of engineers years to analyze and design. Components may need to be analyzed down to a microscopic level. This is generally the longest part of the process. Investigators may realize that they must go gather more information. This may involve running tests on equipment to recreate issues. It may take a lot of work to not only explain what failed, but also the reasons behind the failure and how it could be avoided in the future. Most reports will find issues in many different areas, including human factors, regulations, procedures, and aircraft design.

The Report - The investigators will eventually need to come to some conclusions among themselves. This must all be written up in a report. Some reports can be quite lengthy. If you've ever had to write something like this, you might know that writing the report can easily take much longer than the work that went into it. There will also be an opportunity for parties to the investigation to make comments and provide feedback before the report is released. This is where the investigators get to share the results of all their hard work, and it will be published to get picked apart by the whole world, so it's worth taking the time to get it right.

Law - While most agencies like the NTSB focus on producing a factual report and not assigning blame, lawyers may also need to get involved. Investigations may involve dealing with proprietary or sensitive information, or groups that are reluctant to divulge information (see "completely uncooperative" above). Some accidents may involve criminal investigations as well, in which case organizations like the FBI may also be involved.

Followup - It's not even over after the report has been released. The agency will still need to follow up with regulatory agencies (like the FAA) about recommendations made in the reports and determine whether the responses are adequate.

Additional Duties - On top of all this, many investigators will not be working on one incident full time. Agencies like the BEA and NTSB investigate many smaller incidents as well. So imagine that at any given time, an agency may have many active investigations at different points in the above process. In the case of the NTSB, all of this is accomplished by about 400 people with a budget of around $100 million per year. While aviation safety is the largest part of this with about 130 employees, the NTSB also investigates highway, marine, and railroad/pipeline/hazardous material incidents. Employees also spend time on other things such as educating the public about safety issues, looking for ways to improve safety, and producing additional types of reports.