Comparing Hazardous States and Trigger Events in Fatal and Non-Fatal Helicopter Accidents

16th AIAA Aviation Technology, Integration, and Operations Conference, Jun 2016

Helicopter safety literature generally focuses on identifying the causes and contributing factors for fatal accidents. It identifies the top mechanical and crew-related problems that lead to fatal accidents, and intervention strategies to reduce fatal accidents and improve cash survivability. In this paper, we argue that data from non-fatal accidents is an underused resource that could be used to better understand the reasons for several types of fatal accidents. If fatal and non-fatal accidents share similar stories, we can leverage information in non-fatal accident reports to reduce not just the number of fatal accidents, but rotorcraft accidents overall. We seek to identify and compare the top hazardous states (e.g., loss of control) and trigger events (e.g., incorrect cyclic input) in fatal and non-fatal accidents. We analyzed 5051 helicopter accidents that occurred in 1982–2008. Fatal accidents constitute a small proportion of accidents (15.2%), while the remaining 84.8% were non-fatal. Inflight loss of control (LOC), controlled flight into terrain/object (CFIT), weather, failure to maintain physical clearance/altitude from objects, and system/component failure comprised the top five hazardous states, which accounted for nearly 90% of fatal accidents. Poor inflight planning/decision making by pilots was most likely to trigger both fatal and non-fatal accidents LOC accidents. Decision-making errors also frequently triggered fatal CFIT accidents. The high proportion of non-fatal accidents provides an opportunity for in-depth interviews of pilots to understand the rationale behind the decisions and the actions that followed. Seven out of eight system/component failure trigger events involved the main rotor system and the rotor drive system, highlighting the importance of these systems for rotorcraft operations. Critical flight components such as tail rotor blades and gearbox, and transmission drives were equally likely to fail in both fatal and non-fatal accidents. In some cases the nature of terrain, phase of operation, and on-board protective gear were the difference between life and death.

Rao, A. H. and Marais, K., “Comparing Hazardous States and Trigger Events in Fatal and Non-Fatal Helicopter Accidents”, AIAA AVIATION, 16th AIAA Aviation Technology, Integration, and Operations Conference, AIAA Paper 2016-3916, Washington D.C, 13-17 June 2016,