How did Shallow Fog Result in CFIT During a Go-Around on Night Vision Goggles?

Welcome to the 2nd Episode of the Why Spotlight! 🛸

Today, we’re going to extract all the learning points from a serious incident that involved Controlled Flight Into Terrain (CFIT) while on Night Vision Goggles (NVG).

NVG flight remains one of the highest risk flight categories in aviation.

But why? 👀

Well, there are many reasons.

The nature of the operations that require NVGs is often low level and in uncontrolled environments. However, as with most things, each situation often has its own specific threats that need to be addressed.

Let’s go over this serious CFIT incident, and see what we can learn from it! 💡

As per usual, we’ll cover it all in only about 5 minutes! ⏱️

We don’t publish all our Notes from the Cockpit (like this one) publicly, some are shared only by email. Get the next one sent straight to your inbox ⤵️

CFIT Accident Overview

On the 6th November 2020, an EC135 HEMS crew (a Commander, Technical Crew Member (TCM), and a Doctor) were on their way at night from an industrial site in Slagelse (Denmark), back to Ringsted (EKRS), which was their HEMS operating base.

The crew were aware of an increasing amount of ground fog in the overall vicinity, including EKRS, but were comfortable enough with the quality of visual references.

In the last stage of the final approach, the commander suddenly saw only bright light through his NVGs, lost visual references, and initiated a go-around.

During the go-around, the helicopter unexpectedly impacted the ground in a farm field before resuming flight. The crew initially thought they’d hit the ground at the aerodrome. They were actually 210 meters short of the helipad, in a farmer’s field.

Timeline of Events

The crew departed Slagelse at around 19:00 hrs, late into their shift (about 14 hours). They used NVGs during the departure while climbing to 1200 ft AMSL on their way to EKRS:

While en-route, the crew noticed patches of shallow fog towards the south, as well as halos and glare around lights from cars and buildings (indicating a high humidity, as we’ve discussed here), with an increasing amount of fog patches around the area.

The crew approached EKRS from the west, and activated the runway and helipad lights using the aerodrome radio frequency.

The pre-landing checks and landing briefing were completed, but did not include any go-around criteria. The Commander stated that he would perform “a shallow approach to obtain good references”.

The helicopter established left hand downwind for runway 23, at 600 feet AGL.

As the circuit continued, the helicopter turned onto a left hand base leg, with a groundspeed of about 45 kts:

At this point, the commander flipped down his NVGs, and reported that “everything was perfectly clear through the NVGs”, but noticed there were ground fog patches below the helicopter as well at this point.

The helicopter crossed 200 ft AGL with a groundspeed (GS) of 15-20 kts, which was gradually reducing. Shortly afterwards and without warning, the commander saw only bright light within his NVG.

This resulted in the startle effect.

The commander initiated a go-around, but almost simultaneously, the helicopter impacted a farm field, resulting in these impact marks:

During the go-around, the crew heard the aural indication for maximum power, and the TCM began calling airspeed and altitudes while the helicopter climbed away.

Normal visual references were regained at this point, and the climb continued without further problems, other than a small change in vibration in the helicopter.

The crew thought that they had impacted the aerodrome area, and were not aware that the location of impact was actually a ploughed field north east of the aerodrome, 210 m short of the helipad.

The crew decided to abort their plan to land on runway 23, and instead safely diverted to Slagelse Hospital (EKSE).

Photos of the airframe post impact show that the crossbeam was bent due to the impact force:

Investigation Findings

So what did the investigation find in regards to causal factors? Well, there are few:

1) The flight crew did not properly identify a threat of low visibility due to fog.
2) A decision to perform a shallow approach lowered the vertical distance to any ground fog present below the approach flight path.
3) Visual illusions likely contributed to a loss of flight crew situational awareness on short final.
4) Fog or fog patches most likely caused a NVG whiteout at (or below) an estimated height of approximately 100 ft.
5) Startling effect delayed the initiation of a go-around.
6) Application of go-around power did not stop the helicopter descent in time to prevent a CFIT.

The investigation also concluded:

What can we Learn from This?

So what are the main take-aways here that we can take onboard?

Let’s unpack ⤵️

Integrate Threat Error Management (TEM) in Crew Briefing

Before taking off or landing, actively incorporating TEM into your brief will help the entire crew with:

➡️ Identifying what threats there are
➡️ What can be done to mitigate them

Without this, it becomes very hard to stay ahead of the game and take the correct action when things go wrong.

Don’t Let NVGs and Shallow Fog Trick You

Looking through shallow fog vertically is much easier than horizontally, due to the “amount” of fog in those directions. This can make you think “it’s not that bad’ until you ‘re looking through it horizontally and can’t see anything, like this:

In addition to this, NVGs amplify light. So even if you’re flying in thin layers of cloud, it could be possible that you can see ‘through’ small layers of condensation if the light source behind it is strong enough.

This is why your perception of weather conditions will likely be more positive through NVGs compared to the naked eye.

A good habit to prevent this is to regularly scan underneath your goggles, to perform a gross error check while flying.

Shallow Approaches Reduce References in Fog

The report states:

We are also not sure why a pilot would elect to fly a shallow approach, when ground fog is present. If anything, taking into account legal and company limitations, staying above ground fog for as long as possible could help with keeping visual references.

Black Hole Effect

The black hole effect happens when there aren’t enough light sources in your peripheral vision, which can make you think that you’re higher than you actually are.

To combat most illusions: refer to your instruments and pilot monitoring as a gross error check.

Dealing with Startle Effects

We all get startled if reality does not match our own mental model or expectations. Knowing how to deal with this is crucial, but prevention is key. Situational Awareness and pro-active identification of threats, and strategies for dealing with them, are the main antidotes here.

Communicate Go-Around Criteria

If no go-around criteria are established, it becomes harder to make a decision on whether something is ‘good enough’ or not during an approach.

Especially in multi-crew operations, make sure you’re both on the same mental model, and both pilots are aware of what the criteria are that warrants a go-around.

Conclusion

Shallow fog, NVGs and HEMS at night remain high risk factors in aviation. Hopefully this summary has provided you with a better understanding of how much of a threat shallow fog can be, and that you shouldn’t underestimate its effects.

References

Full Investigation Report

We don’t publish all our Notes from the Cockpit (like this one) publicly, some are shared only by email. Get the next one sent straight to your inbox ⤵️