The Downwind Approach: A Silent Killer

After decades of learning from accidents and improving aviation safety more and more, there is still a silent threat that poses a significant risk in both the fixed wing and rotary industry: the downwind approach.

Downwind approaches continue to be a cause for concern and a subject that demands attention globally, and various regulators are doing everything in their power to raise awareness to tackle these types of accidents.

Today we’ll highlight the dangers associated with downwind approaches, with the aim to increase awareness amongst pilots. We’ll cover the reasons behind the risks, and explore the potential consequences of disregarding the need to conduct an approach with a headwind component. We’ll also talk about the mitigations that we can use to eliminate accidents caused by downwind approaches.

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Why is a Downwind Approach Dangerous?

Let’s start with refreshing the basics, why are we trained to NOT fly an approach downwind? There are quite a few reasons, let’s break it down:

A reduced airspeed or an increased groundspeed

When flying downwind, your indicated airspeed will always be lower than your groundspeed. If you’re in the cruise, this is a benefit. Outside the cruise phase though, not so much.

This means that to achieve a certain constant “closure rate” or “apparent groundspeed” during an approach (which is still taught in modern flight training programs), you’ll have to fly a lower airspeed than normal to achieve the same groundspeed.

Or if you want to look at it the other way around:

If you fly your “normal” airspeed, you are moving significantly faster over the ground. This forces you to slow down.

At lower airspeeds though, helicopters are more susceptible to instability, loss tail rotor effectiveness, but more importantly, an:

Increased Power Requirement

Depending on the phase of flight, this can have major consequences. Have a look at the graph below. Normally, in most helicopter, you are here during most of the approach phase (the area fairly close to Vy):

However, with a tailwind component and you having to slow down, you often get to a speed that’s lower than Vy, which means you are now here on the power curve:

This requires more power, but it doesn’t end here. During a normal approach, the disc is usually tilted slightly backwards to decelerate the helicopter throughout the approach, which means that vertical thrust is slightly lower than the total rotor thrust:

But because you are flying the approach downwind, you will have to tilt the rotor disc backwards even more, to reduce the closure rate. This reduces your vertical component of rotor thrust and results in an even higher amount of power required:

As you slow down, at some point the airspeed will be 0, but you are STILL moving across the ground! The helicopter will basically perform as if it’s in the hover while still travelling forwards! This is because you’re now here on the power curve:

This now requires even more aft cyclic, which tilts the disc even more and reduces vertical thrust even more. This is probably the most efficient way to run out of power in any helicopter, which can result in:

Settling with Power

As the amount of power required increases rapidly, you will start descending quickly if the power setting is constant.

To counteract the descent, you will want to raise collective, but as the engines are likely already giving everything they can, all that will happen is a decay in rotor RPM and a reduction in total rotor thrust.

Settling with power and vortex ring state are often mixed up, but at the start of settling with power you are already using your maximum available power available.

Vortex Ring State (VRS)

Probably the largest threat for any helicopter pilot. A situation where the helicopter has entered its own downwash and an increase in power will only result in higher rates of descend.

Most literature quotes these 3 conditions for VRS to occur:

In reality, these figures will be slightly different for each helicopter, depending on the downwash speed, disc area, and shape of the fuselage. We’ve covered the ins and outs of VRS in this article.

Higher Risk of Loss of Tail Rotor Effectiveness

Most helicopters (especially ones with Fenestrons), benefit from an effect called “Weathercock Stability”. Simply put, the air coming from the front of the helicopter while moving forwards, helps with both the yaw stability and the amount of “free” generated anti-torque thrust by the tail rotor. This normally helps keep the power required as low as possible:

At lower or negative airspeeds associated with downwind approaches, this effect is significantly weaker or even completely gone. This then increases power required even more!

Larger required landing distance

Both normal and emergency landings require more space while downwind. Even if nothing goes wrong throughout the approach, you will need a significantly larger area to land safely due to the increased groundspeed.

If one engine does fail, this becomes an even bigger issue as the landing distance required will be even larger.

Why do Downwind Approaches Happen?

So why do they even happen? Why do we see so many helicopter crashes due to downwind approaches? In summary: Situational Awareness (SA) and the way we process information.

Mixing up where North is after a few orbits and a few distractions is more common than we might want to admit, even though we have a heading indicator clearly showing us where North is.

On top of this, quite a lot of FMS’s show a wind vector, which can be misread as ‘this is where the wind is coming from’ rather than a vector that represents the wind direction itself.

If approaches aren’t properly planned and briefed, it will be easier to come in downwind without realising.

How can you Mitigate the Risks of a Downwind Approach?

It all starts with wind awareness. Some pilots are always on top of where the wind is, some are more relaxed about it. Especially for those who fly single engine helicopters under performance class 3 (PC3), you always need to be ready to lower that collective and immediately turn into wind.

You could argue that vigilance and readiness are just as required for pilots flying twin engined helicopters, but you might have noticed that PC3 does bring out that extra amount of vigilance in most pilots due to the higher amount of risk involved.

By the time you’ve entered the helicopter, you should already be aware of what the wind looks like that day. On top of this, you have plenty of wind indicators to get a grasp on the local wind direction if your nearest METAR station is further away:

Another great way to mitigate the risk is by having a vigilant pilot monitoring in multipilot operations. Situations where a turn to a final leg are made, and the pilot monitoring catches the fact the helicopter is positioned downwind, are not unheard of across various high paced operations such as HEMS or SAR.

For operations to and from airports, there is an extra safety layer in place, as the active runway should always come with a headwind component. This is why rotary pilots are at higher risk of flying a downwind approach.

Accidents Caused by Downwind Approaches

There are quite a lot of horrible crashes on the record that have happened partly because of downwind approaches. Here are the most relevant ones:

Private EC130 T2 Crash

In 2018, an EC130 T2 lost control and crashed in Nebraska. The NTSB concluded that “the pilot’s inadequate and incorrect anti-torque pedal application during a tight, decelerating turn while downwind, which resulted in a loss of yaw control”.

Private Robinson R44 Crash

In 2022, a private Robinson R44 crashed due to not having enough power in the later stages of the approach. The pilot had flown the entire approach downwind and caused a decay in RPM when he raised collective to attempt to correct the rate of descent.

Patrolling NH90 Crash

In 2020, a Dutch NH90 patrolling the Caribbean crashed due to a lack of power while flying downwind. This wasn’t the only contributing factor, but it played a role in the crash.

Private Hughes 269A-300 Crash

In 2008, a private Hughes 269A-300 crashed due to a main rotor overpitch situation caused by being downwind and running out of power (starting to see a theme here?)

There are plenty of others, but we purely wanted to give the most typical kinds of accidents that are related to flying downwind.

Conclusion

Being downwind while not aware of being downwind carries a huge risk for any pilot, whether fixed wing or rotary. The problem with rotary is that there are more opportunities and less controls in place to mitigate for downwind approaches. Vigilance and wind awareness are by far the most important factors to prevent further crashes in the future.