I have just dug out my notes on this subject, here we go:
The Stevens’ Study. There have been very few recent studies into the pathology, in particular impact injuries, from light aircraft accidents. However, the RAF Halton Institute of Aviation Pathology’s Peter Stevens conducted his MD thesis in 1967 and released his findings in a book on the subject. In it Stevens studied 42 civil fatal light aircraft accidents and 15 military light aircraft involving over 100 persons ranging from PICs to pure passengers. It makes a very sobering read and I recommend it as a read to those in denial of the effects of an aircraft accident on the human body. Stevens made 2 observations. Firstly that shoulder restraint saves lives in light aircraft accidents and secondly that helmets may make a small percentage of accidents survivable. However, the “may” comes from the fact that many accidents result in multiple injuries (organ damage, severe laceration and impact trauma that is purely un-survivable) that helmets would only really improve the chances of survival in a very small number of cases. Indeed, the design of our aircraft has not kept up with the advances in the motor car industry and only the more recent Cirrus and Cessna aircraft have got airbags, crumple zones and collapsible control columns that we know from our vehicles. The results of his study showed that the accidents had the following break-down of injuries:
Fractures
a. Legs 73%
b. Skull 67%
c. Ribs 63%
d. Arms 56%
e. Spine 53%
f. Face 48%
g. Pelvis 27%
Laceration or Rupture
a. Brain 56%
b. Aorta 39%
c. Lungs 36%
d. Heart 35%
e. Liver 35%
f. Spleen 34%
g. Kidneys 23%
In Stevens’ study some 42% suffered from burns and 25% had penetrating wounds to their chest or abdomen. Stevens was very pro towards a helmet in light aircraft, however, it was in conjunction with shoulder straps. Shortly after his book was released the FAA mandated that shoulder harnesses should be fitted to all new aircraft and the rest of the world followed suit. Recently, this has changed again to a minimum of a 4 point harness and exemptions are made by the CAA to allow the diagonal shoulder harness fitted in older Cessnas/Pipers to be continued to be used. The shoulder harness really was the answer to the injuries that Stevens described in his study and the helmet would only help in <1% of fatalities in the survivable accidents whilst shoulder harnesses would have saved more than 16% of the fatalities that were judged survivable. In his book he concluded:
Shoulder harnesses and protective helmets can only be expected to protect from lethal injury in the potentially survivable accident. If they are truly effective in this function, one would expect that relatively few wearing such equipment would die in survivable accidents; most of those killed while wearing such equipment would be expected to die in essentially unsurvivable accidents.(Stevens 1970)