Danger is an inherent component of military helicopter missions. Remember the daring mission launched to capture a Somalian warlord on 3rd October 1993 when an American Black Hawk (Super-Six One) was shot down in the city of Mogadishu. Another area of perilous operations is emergency medical missions and oil and gas operations. Two recent reviews highlight the accident statistics in those two types of helicopter operations [1, 2]. Interestingly the former research comes from Germany and the latter from the Gulf of Mexico.
Helicopter Emergency Medical Services (HEMS)
Use of helicopters for emergency evacuation of critically injured started in 1945 . The study by Hinkelbein et al. on accident severity and helicopter model in HEMS accidents in Germany spanned over four decades (September 1970 to December 2009). This was surveyed from the annual accident reports published by the German Federal Bureau of Aircraft Accident Investigation (BFU = Bundesstelle für Flugunfalluntersuchung) . The number of accidents analysed were 99 .
Figure: Bo105 (Left) and Bk117 (Top)
The study included only those helicopter models where there were at least five accidents to avoid random errors. BO105  was involved in maximum number of accidents, accounting for 38.38%, followed by BK117  and UH-1D . Interestingly in terms of severity of injury, 63.6% accidents did not result in any injury and only 9.1% had major injury to at least one occupant (requiring hospital admission for more than 48 hours, sustaining fractures, burns or wounds, not leading to death). It emerged in this study that EC135 (8) and BK117 (5) had largest percentage of uninjured occupants – 100% and 88.2%, respectively.
Tragically there were 19.2% fatal injuries resulting in death up to 30 days after the accident, as compared to 39% reported in US HEMS . Highest fatality was found in Bell222 (9) – 42.9%. Fatality percentage in other helicopters in descending order was 40.0% in Bell412 (10), 35.7% in UH-1D (6) and 15.8% in BO105 (4). Fatality rates were significantly higher during night flying as also during bad weather, as reported by Baker et al. as well in US HEMS .
Figure: Bell412(Left) and Bell222 (Right)
In German HEMS BO105 and UH-1D have been taken out of service over a period of time, and the present fleet mostly consists of EC135 and BK117. Hence the data may seem biased but serves a useful purpose in terms of crashworthiness of the deployed fleet. This is especially so in light of head injury being the commonest cause of fatality in UH-1D helicopters .
Figure: EC135 (Left) and UH-1D (Right)
Acknowledgement Image courtesy Wikipedia