What are the most Common Causes of Helicopter Crashes?

Helicopter incidents, accidents, and even fatal crashes are unfortunately still way too common, especially compared to the fixed wing world. Every month or so there are still news articles featuring the latest unfortunate helicopter events. These are then followed by safety reports on how to prevent it in the future, but things are seemingly not improving as much as we would like. So what are the most common causes of helicopter crashes nowadays? What does the data show, and what can we learn from it?

For us in Europe, EASA publishes an annual safety review every year. It features the latest stats and learning points for everyone to learn from. We’ll be referencing the data from the annual safety review 2020, which you can download here. Keep in mind that all these stats are based on flights in Europe from 2009 to 2019. Full credit to EASA for the reference material and graphs.

Please keep in mind that this official data is not corrected for total flights / hours. This means that numbers might go up or down because of total flight time, not just industry trends.

To answer these questions, we’ll divide our attention between these helicopter industry segments:

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Commercial Air Transport Flight Accidents

The first category we’ll look at is Commercial Air Transport (CAT). This is just a fancy term for operations that are conducted under an Air Operators Certificate (AOC). EASA defines it as:

An aircraft operation to transport passengers, cargo or mail for remuneration or other valuable consideration.

This usually includes offshore flights, as well as onshore HEMS, sightseeing tours, air taxis or any other operations where passengers or an organisation are paying a company a fare to get from A to B.

Let’s have a look at the first bit of data showing the accidents per year within CAT.

As you can see, over the last decade, things have not really improved in a very obvious way. In 2009, we had 1 serious incident, 5 non-fatal accidents, and 4 fatal accidents. Compare that to the 2019 figures and you’ll see that things have actually got worse.. Not a positive picture.

Let’s zoom in a bit. What type of operations are most commonly involved in accidents?

To no one’s surprise, HEMS is involved in the most accidents both on average and in the last year for this data: 2019. After HEMS, it’s offshore, then air taxi and the unknown category.

But when do things actually go wrong? Here is the data that breaks it down by phase of flight.

The cruise phase and landing phase are the most involved in accidents.

But why? What are the causes for accidents during these flight phases?The key risk areas are:

And the winner is.. Aircraft upset! What does this mean? Let’s look at the EASA definition.

An aircraft unintentionally exceeding the parameters normally experienced in line operations or training, normally defined by the existence of at least one of the following parameters:

a) A pitch attitude greater than 25 degrees nose up;
b) A pitch attitude greater than 10 degrees nose down;
C) A bank angle greater than 45 degrees; or
d) Within the above parameters, but flying at airspeeds inappropriate for the conditions.

Most of the ‘aircraft upset’ category is often caused by Inadvertent Entry into Instrument Meteorological Conditions (IIMC), i.e flying into clouds / fog / degraded visual conditions. This is currently still the highest risk area for helicopters in the CAT category. This risk area is followed by obstacle collisions and airborne collisions.

To finish this flight category, let’s have a look at what EASA considers the highest risks based on actual occurrences and consequences:

While system failures is at the top, most categories that follow all belong to the ‘human factors’ category. Notable ones here are:

• Perception / situational awareness
• Decision making / planning
• Degraded visual environment
• See and avoid
• Airborne separation
• Flight path management

All of these can be grouped and induced by pilot error, which is still the main cause of helicopter accidents in Europe.

Specialised Helicopter Operations

Specialised operations.. You might wonder what that means exactly? Well, EASA defines it as:

Any operation other than commercial air transport where the aircraft is used for specialised activities such as:

Agriculture
Construction / sling loading
Photography
Surveying
Observation / patrol
Aerial advertisement

For this category we are expecting more accidents per flight movement as the operation itself is usually exposed to slightly more risks. Risks such as nearby obstacles, flying low level, and often the helicopter types used are non-complex and single engine.

As you can see in the table below, there is a noticable trend downwards when it comes to incidents and accidents.

One thing to note here as well is that the amount of accidents is higher, but the ‘fatal accident’ category is at a lot lower ratio compared to the CAT category.

What about the type of operation jumps out the most? Well, let’s have a look at the graph below.

The construction / sling load category hold by far the most accidents, which probably isn’t surprising given the conditions and the common environmental factors that come with this type of operation.

When it comes to flight phase, the manouvring phase is the most risky. Again, this is expected as the amount of risk undertaken is the highest when actually performing the work / activity such as long lining or constructing a large mast.

Then moving on to the actual reasons for accidents within this category, let’s have a look at the actual causes:

Aircraft upset, again, is the leading cause of accidents, followed by obstacle collisions / injuries to personnel, and terrain collisions.

Finally, the root causes for these are laid out here:

The main difference here compared to the CAT category is that ‘system failure’ is not at the top. Instead, it’s perception / situational awareness (information processing), see and avoid, flight path management, and intentional low flying that are the most common.

Non-Commercial Helicopter Operations

The non-commercial category is very big in the helicopter industry, as it comes with less regulations, requirements and limitations. The type of flying included in this segment are mainly flight trainin, VIP flights, ferry flights, and test flights.

What does the trend look like in the last 10 years?

While there was a slight downtrend until 2016, the figures have increased since then. Not only that, but if you look closely, you can see that even the ‘safest’ year still had about the same accidents at the most unsafe year for the other segments discussed earlier..

What type of flying is the most risky according to the data?

Training flights and pleasure flying, followed by the ‘unknown’ category. It’s probably to be expected that flight instruction is still one of the riskiest environments. Most of the helicopters used in this sector are small, basic, and equipped with 1 engine.

On top of this, the flight enveloppe that they’re being exposed to presents more risk as well. Think about engine off landings, practice forced landings, advanced autorotations.

Because of these factors, the riskiest flight phases are actually quite spread out, as you can see here:

The riskiest phase here is still landing, likely due to the manoeuvres discussed earlier which can be characterised as ‘landing’, although this is not confirmed to be the case.

What about leading reasons for these accidents?

Aircraft upset, again, is the main cause for these accidents, followed by runway excursions, injuries to personnel, airborne collisions, and terrain collisions.

Finally, let’s have a look at the accident root causes again:

Flight path management is the leading cause here. This is likely because of the quick planning skills required for some of the manoeuvres practiced in flight training. This one is followed by system failures, situational awareness and experience / training / pilot competence.

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Conclusion

To summarise, no matter which helicopter segment we looked at here, ‘aircraft upset’ is by far the most common reason for helicopter accidents. This can be caused by human factors (discussed here) as well as system failures, but the data and history both suggest human factors are still the leading cause for aviation (and helicopter) accidents.