The history of helicopter safety
The early 1900s saw the first experimental helicopters being flown in various European countries, with many different concepts being tried and tested. However, it wasn't until Sikorsky started building R-4 helicopters for the US Army Air Corp, with the first delivery in 1944, that a real production run of helicopters began.
The first civil helicopter in the world to be certified was a Bell 47B, serial number 1, registry number NC-1H, on May 8, 1946.
However, the early years of the fledgling helicopter industry were marked by many accidents, with seven civil Model 47 and one Army YR13 accidents occurring in the first year of 1946. Three of the Model 47s involved in accidents were experimental helicopters, one of which was involved in a fatal accident on August 10, 1946. The next year, 1947, saw 33 accidents.
While this may sound alarming by today's standards, it's important to note that the helicopter industry was still in its infancy, and accidents were not uncommon for any civil or military model helicopter built by any manufacturer in their first few years.
Helicopter pilot training, like designing and building helicopters, was also in its early stages during this time.
The known flight experience of the helicopter pilots involved in three of the eight accidents in 1946 were only 7 hours 15 minutes, 9 hours 30 minutes, and 61 hours 50 minutes. The pilot with the highest flight time and experience was actually involved in the fatal accident, which was an experimental helicopter with the highest airframe time of the accident group at 275 hours.
Despite the difficult early years, things started to improve in many areas, including pilot training, maintenance, and aircraft improvements. As a result, the accident rate eventually settled down to a constant level, with the fluctuations since 1976 in the annual accident rates being related to changes in the FAA flight hours estimate process.
Even though the Bell Model 47 helicopter has been out of production for over 30 years, the accident rate for this model has been holding fairly constant since the early 1950s.
The worldwide fleet of 47 series helicopters for the period of 1947 through 1996 shows that most accidents had several cause factors, but the initiating cause factor is used for this chart. Interestingly, engine failures were less frequent than the Non-Engine Airworthiness failures and even maintenance-related failures.
This may be due to the fact that the engine was well developed with experience in airplane use, whereas the aircraft itself was a new concept with a lot of dynamic components that required considerable new types of maintenance. The majority of accidents were due to human or unknown causes. However, there were a lot of "lessons learned" during those early years, as the helicopter was more expensive, slower, and had much lower payload than an airplane.
Nevertheless, the helicopter could do missions that were impossible for an airplane, thanks to its ability to hover, making it a valuable asset in certain situations.
The helicopter industry started to make significant safety improvements in the 1960s. Turbine (turboshaft) engines were introduced, providing more power per pound of weight than reciprocating engines, which improved payloads. Both reciprocating engines and turbine engines continued to improve and initiate accidents less frequently. The most recent improvement has been the use of electronic controls, which has made engines less of a safety issue.
The aircraft itself has also improved over time, with early helicopters like the R-4 and 47 using tubular frame construction, while later models progressed to aluminum bulkheads and skins. Some models also feature composite materials like carbon fiber and Kevlar.
In addition to structural improvements, modern helicopters also incorporate advanced avionics and computer systems. These systems include digital flight controls, GPS navigation, and electronic displays that provide pilots with real-time information on the aircraft's performance and surroundings.
The development of these advanced technologies has made helicopters more capable and safer to operate. For example, the use of digital flight controls has greatly reduced the workload on pilots, making it easier for them to fly the aircraft in complex conditions. GPS navigation systems have also made it easier for pilots to navigate in difficult terrain or poor weather.
Another significant development in helicopter technology has been the evolution of rotor systems. Early helicopters used simple rotor systems with two blades that rotated in opposite directions. Today's helicopters, however, use more advanced rotor systems that incorporate multiple blades and sophisticated designs that reduce noise and vibration.
One such design is the "fenestron" or "fantail" rotor system, which uses a shrouded tail rotor that provides improved control and reduced noise. Another design is the "NOTAR" system, which uses a fan to create a boundary layer of air around the tail boom, providing anti-torque control without the need for a tail rotor.
Overall, the evolution of helicopter technology has made these aircraft more capable, efficient, and safer to operate. As technology continues to advance, it is likely that helicopters will continue to play an important role in a variety of industries, including search and rescue, law enforcement, and military operations.