Helicopter Safety

Compared to airplanes and jets, helicopters are more mechanically complex and fly more dangerous missions. For this reason, safety in helicopter operations is critical. In this article we discuss helicopter safety including accident rates, leading causes of accidents, and technologies/strategies for improving safety.

Accident rates

Helicopters have advantages over other aircraft including the ability to land in remote areas without runways or improved surfaces, fly low to the earth, and hover. These are exactly the conditions where aircraft are most vulnerable to accidents. Combine this with the increased complexity of a helicopter over a fixed wing aircraft, and you might expect them to be much more dangerous. Surprisingly, accident rates do not back this up.

How should we measure this? Just counting the total number of helicopter accidents would be misleading. The average person spends a lot more time in automobiles and fixed wing aircraft than helicopters. Even if helicopters were much more dangerous, the total number of accidents could be much lower. We instead use accidents per hour flown or accidents per mile flown to be more meaningful. For automobiles, we compare to accidents per hour or mile driven.

Organizations like USHST maintain data for helicopter accidents. Their reports indicate about 4 accidents, including 0.6 fatal accidents, per 100,000 flight hours. They have further data on accidents subdivided by mission and helicopter model if you’re interested.

Let’s compare this to automobiles first. Data from the Texas Dept. of Transportation shows 1.55 deaths per hundred million miles driven (other states are lower on average). If we assume an average speed of 33mph, this equates to 1.55 deaths per 3 million driving hours, or 0.05 deaths per 100,000 driving hours. Yikes, that’s saying helicopters are 12x more deadly than to cars (per hour)!

Of course, a helicopter can complete a trip much faster than a car, so comparing deaths per hour may not be fair. Let’s compare per mile death rates, assuming helicopters fly an average of 100 kts or 115 MPH. At this speed, 0.6 fatal accidents per 100,000 hours corresponds to 5.2 fatal accidents per hundred million miles flown—3.4X as deadly as an automobile (per mile).

Let’s compare to non-commercial fixed wing aircraft (airplanes and jets). According to the AOPA, these have about 1 fatal accident per 100,000 flight hours. Surprisingly, this means fatal crashes are 70% more likely (per unit time) compared to a helicopter! Of course, including commercial jets drops the fixed wing accident rate significantly. The FAA estimates that the total helicopter accident rate (including non fatalities) is 30% higher than fixed wing.

Now let’s look at the leading causes of helicopter accidents.

Weather

In 2020 basketball star Kobe Bryant, along with 8 other people, lost their life in a helicopter accident. This accident was primarily caused by weather, when the helicopter flew into low clouds with little or no visibility. The presence of these clouds was known and air-traffic controllers had steered the helicopter around most of the weather and kept them at low altitude. However, at some point the pilot decided to climb through a large layer of clouds to a higher altitude. In this phase the helicopter began flying erratically and eventually crashed into a hillside.

Unfortunately, the circumstances of this crash are not rare. It’s reported that bad weather played a role in 28% of fatal helicopter accidents in the US from 2008 to 2018. More recently, the crash that killed the president of Iran was also blamed on bad weather.

Poor visibility, likely the key in Kobe’s crash, can cause pilots to be disoriented and lose control. It can also cause pilots to run into power lines or other structures.

High wind speeds are another big risk, particularly in takeoff or landing. As with any aircraft, ice accumulation can change a helicopter’s performance and make it dangerous to fly. With any of these conditions, pilots must not be shy about delaying or canceling a flight.

Pilot training

Pilot error is the leading cause of helicopter accidents, accounting for about 70%. What many people don’t realize is that training is about much more than just controlling the aircraft. Let’s discuss some of the other important aspects, above just handling/controlling the aircraft to fly the maneuver desired.

For one, pilots must know what maneuvers and flight conditions are dangerous. For example, flying at high speeds close to the ground, or low speeds high above the ground, are very dangerous (see e.g. the “dead man’s curve”). Likewise, high descent rates with low airspeed can lead to a dangerous condition called vortex ring state.

Pilots must also be aware of how much weight their helicopter can carry and how this weight must be distributed. For example, putting excess heavy cargo in the back of the helicopter can move the center of gravity significantly and turn an otherwise safe mission into a deadly one. There are many such things to consider, and some details are model specific. It’s critical for pilots to know all this information to fly as safely as possible.

Another big item is emergency protocols. If you fly long enough a malfunction will occur in flight. A hydraulic system may leak, an engine may catch on fire, or an actuator may fail. You may be surprised to know that some pretty scary malfunctions are survivable. However, quick and specific pilot action is often needed (quicker than a fixed-wing aircraft). For example, if torque is lost in flight, a pilot may only have seconds to reduce the torque required (by some combination of dropping the collective and flaring) to autorotate. Otherwise, rotor speed will drop below a fatal threshold with no hope of recovery. Likewise, a fire may require quick use of extinguishers to prevent disaster. Ideally, pilots practice such emergency scenarios frequently (e.g. in simulators).

Finally, communication is important. Clear and constant communication between the pilot, co-pilot, air traffic control, and ground crew is vital for maintaining safety. In the Kobe Bryant crash, air traffic control had steered the pilot around the clouds that eventually caused the crash. Perhaps more communication would have led the pilot away from the cloud layer that caused the crash.

Regular emergency drills, along with a calm and prepared mindset, can make all the difference during a critical situation.

Passenger training

Passengers also play a role in safety. In an extreme example, a passenger touring the Grand Canyon in an EC130 attempted to pull the rotor brake in flight, which could have killed everyone onboard.

It’s often not practical to extensively train passengers, but at a minimum they must be calm, follow pilot instructions, and not do anything to significantly distract the pilot during flight. Pilot instructions should cover the use of seat belts, emergency exits, and protocols for handling in-flight emergencies.

Maintenance

As we’ve said before, helicopters are very mechanically complex. This complexity can make them hard to inspect and maintain. Fortunately, operators are aware of this and generally maintain helicopters with very strict guidelines. For this reason, the number of accidents associated with poor maintenance has been kept surprisingly low, below 20%.

Examples of helicopter accidents attributed to maintenance include the 2022 crash of firefighters in New Mexico and the 2022 crash of a Bell 407 in New Jersey.

Regulations

In the United States, helicopter operations are governed by the Federal Aviation Administration (FAA) and other national aviation authorities. Compliance with regulations such as airworthiness standards, operational guidelines, and pilot qualifications is essential for minimizing risk. Additionally, operators should adhere to industry safety standards like those outlined by the Helicopter Association International (HAI) and the European Union Aviation Safety Agency (EASA).

Technology to improve safety

As you might expect, many technologies are increasing helicopter safety. Below is just a short list.

• Improved flight control systems reduce pilot workload. This reduces pilot fatigue and allows them to better focus on other critical issues.
• Terrain awareness systems (TAWS) reduce collisions by warning pilots of upcoming terrain and fixed obstacles.
• Traffic collision avoidance systems (TCAS) provide instructions to help pilots avoid other moving aircraft.
• Synthetic vision systems may help pilots better see their surroundings and avoid hazards.
• Redundant components. Having double or triple redundancies for critical actuators, hydraulics, … saves lives when failures occur.
• Predictive maintenance. Algorithms may be able to predict components that need early replacement based on the history of a particular helicopter.
• More reliable engines. Engine failure is an extreme emergency that requires an immediate landing in single-engine helicopters. When such failures occur far from safe landing zones they are deadly.
• Wire strike protection systems.
• More reliable rotor systems. Complex rotor systems with joints, hinges and dampers are more prone to failure.
• Self-sealing fuel tanks.