The impact of blunt force trauma in helicopter accident fatalities has remained constant over the last decade despite stricter design rules, according to a study presented by the FAA at the EASA Rotorcraft Symposium last month. The agency is seeking ways to improve post-crash safety.

The fatal accident rate has been stuck in the range of 0.75-0.80 per 100,000 hours, said Lee Roskop, an FAA safety expert. Improvements made between 2004 and 2013 have not been sustainable. “We are treading water,” he said.

Post-crash fire was the most frequently cited sub-occurrence category for U.S. fatal accidents, according to an analysis by the International Helicopter Safety Team. A study of 97 accidents (some of them involving post-crash fires) between 2008 and 2013 revealed that crash-resistant fuel systems strongly decrease the occurrence of fires and associated fatalities in Part 27 (light) rotorcraft.

However, even in case of fire, the cause of death was typically blunt force trauma rather than thermal injuries. So the FAA tried to understand more specifically what kind of blunt force caused death in recent accidents. Such a study, published in 2003, was available for the 1993-1999 period. The FAA searched the 2008-2013 sample for evidence of any change, and found that blunt force injuries–particularly to the skull and brain–remained the same over the two periods.

The agency had hoped to find that the more recent study would show safety had been improved by more recent certification bases. However, too few of the accident helicopters were certified after 2003 for the related death causes to have any significance in the context of certification standards. Furthermore, only 5 percent of the rotorcraft in the data complied with the 1989 standard of Part 27 or Part 29. Approximately 10 percent of the U.S. rotorcraft population now complies, Roskop said. He characterized the evolution rate as “pretty pathetic,” estimating that at this pace it could take 200 years for the entire U.S. fleet to comply.

The FAA is thus pondering what approach to tackle next. It is focusing on how improvements to crashworthiness or survivability equipment can decrease injuries and reduce fatalities in accidents, Roskop said. The agency is also considering retrofits.