Preliminary data recovered from the cockpit voice recorder (CVR) and flight data recorder (FDR) from the fatal crash of Yeti Airlines Flight YT691 last month indicate that the propellers of both engines went into feather on the base leg, according to a statement by Nepal’s Accident Investigation Commission. Speaking to AIN, joint secretary of the Ministry of Culture, Tourism and Civil Aviation Buddhi Sagar Lamichhane said the authority will release a preliminary report in the coming days.
A Nepali-language statement released by the ministry on February 6 said investigators will continue their probe while examining “technical and human aspects” of the January 15 crash of the ATR 72 twin-engine turboprop.
Authorities continue to analyze the flight recorders in Singapore with support from that country’s Transport Safety Investigation Bureau (TSIB), France's Bureau of Investigation and Analysis for Civil Aviation Safety (BEA), the Transportation Safety Board of Canada (TSB), Pratt & Whitney Canada, and the European Aviation Safety Agency (EASA).
The provisions guiding all global civil aviation activities appear in the form of the International Civil Aviation Organization’s (ICAO) 19 Annexes to the Chicago Convention, which took effect in 1947—the year ICAO came into existence. Today, 193 countries are signatories to the Convention; individual state laws and regulatory instruments also govern aviation.
First introduced in 1951, Annex 13—Aircraft Accident and Incident Investigation lays out international Standards and Recommended Practices (SARPs) for investigators. It lists technical specifications spread across four parts: Organization and Planning, Procedures and Checklists, Investigation, and Reporting. Complementary documents (Doc) and circulars (Cir) also provide guidance, among them Doc 9973—the Manual on Assistance to Aircraft Accident Victims and their Families.
Under Annex 13, the state of occurrence bears responsibility for initiating an investigation but may delegate all or part of the responsibility to another country or a regional accident and incident investigation organization (RAIO) by mutual consent. Accident and serious incident investigations are not solo acts; as such, the following "Big Four" may appoint an accredited representative and associated advisers: the State of Registry, the State of the Operator, the State of Design, and the State of Manufacture.
Additionally, a country that holds a special interest (i.e., citizens involved) may send a technical expert. In the case of a dangerous goods (DG) aviation occurrence, the State of Origin can also appoint an accredited representative. (Note: Annex 13 provides separate definitions for advisers and accredited representatives.) Beyond Annex 13, states commonly enter into memoranda of understanding (MoUs) with one another to share facilities, equipment, and expertise and frequently participate in multilateral ICAO meetings across the year.
Annex 13 stipulates that investigators should read flight recorders without delay. Doc 10053 guides the protection of sensitive records during investigations. State adoption of investigation-specific legislation and regulations coupled with strong surveillance and regulatory oversight ideally strengthen the protection of records, from witness statements and crew medicals to flight recordings and transcripts.
Protection of CVRs, airborne image recording (AIR), and any related transcripts begins at the time of the accident or incident and continues after the publication of the final report. Protection of other records begins when the investigative authority assumes custody or control and continues after the final report is published, states Annex 13.
There is a caveat.
While records can be made available under Annex 13, their disclosure should hinge on a balance test conducted by a “competent authority” and weighed across nine variables for and against the public interest. Factors include “the requester’s intended use of that record, whether the rights or interests of a person or organization will be adversely affected by the disclosure or use of that record, and whether that record is of a sensitive or restrictive nature,” to name a few.
Annex 13 starkly highlights the sensitivity and complexity of air crash investigations and the significance of collaboration. In the case of Ethiopian Airlines Flight ET 302, the U.S. National Transportation Safety Board (NTSB) and BEA called on Ethiopian authorities to amend the final report on the March 10, 2019 crash of a Boeing 737 Max 8 to address operational and human factors findings. Their requests fall wholly within the scope of Annex 13.
Under Part 4—Reporting, the investigative authority must send a confidential draft of the final report to the Big Four; in turn, states have 60 days to comment. Before public release, the authority shall either amend the final report or attach appended comments. Following this step, the final report is then sent to the Big Four authorities plus any state having suffered citizen fatalities or serious injuries and any state providing information, facilities, and expertise. For DG occurrences and accidents or serious incidents involving an aircraft with a certified maximum takeoff weight (mtow) of 5,700 kilograms or more, the final report also gets submitted to ICAO. The stipulation practically covers all commercial and business aircraft today.
The sole objective of the investigation and the final report is the prevention of accidents and incidents, not to assign blame or liability. While investigations can become highly politicized, Annex 13 calls for states to have an independent investigative authority, structured to “withstand political or other interference or pressure” and functioning separate from any judicial or administrative proceedings, any regulators, and any other entities.