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Dropping safety – Part 1: Aerial assets

Accidents during the dropping phase

If you got here, you probably started with this LinkedIn post showing a couple of Air Tractor 802’s close calls during the dropping phase,.

If not, it would be advantageous to go back there to gain a deeper understanding of the context in which this entry was originally generated.

Here is the video :

Dropping accidents: reasons for their occurrence

Some of the most common causes of accidents during the dropping phase include:

  • Pilot error: This can include issues such as poor judgment, lack of experience, target fixation, lost of situational awareness, or mismanagement of flight controls.

  • Technical malfunctions: This can include issues with the aircraft’s systems, such as failure of the Firegate, which is unlikely but sometimes could occur. Or something as simple as an altimeter on LATS and VLATS (we have seen VLATS clipping the top of the trees too)

The easy way is to stop here and blame pilots or technicians.

As old as unfair.

Instructors and managers may say:

“We told them so many times! The procedure is crystal clear! – What else can I do?”

Well…

There is a lot we can do as organizations! But let´s leave that until the end of the post and focus on things we can control from now, as individuals.

Focussing on the things we can actually do

Besides the organizational factors, I would like to review two factors that contribute to accidents during the dropping phase, and how to mitigate them next time we jump onboard an aircraft during firefighting missions:

 

Reason 1: The drop is too low

We see too many drops, too low, too often.

This is where I want to pause for a while.

Is there a reason why we are constantly dropping so low?

YES

Because it is easier, and we humans like it simple.

When we are low, hitting the fire is much easier:

  • Our references are closer.
  • The drop is less likely to drift away.

The ultimate goal of an aerial firefighter is not to drop low, hit the fire, and clip some trees every now and then as if that was normal.

Our mission is to drop from safe heights regardless of winds and actually strike the fire.

That is hard!

And that is what we should train in a controlled environment under supervision.

It requires deliberate practice, as well as key personnel such as chief pilots, instructors, and the Director of Operations, emphasizing the importance of dropping from an optimal height.

Let’s refresh our memories by reviewing a few drawings

1- Be careful not to get too low for too long

If we come too low for too long, we are increasing our chances of hitting stuff.

And trust me there is a lot to hit!

Wires, poles, solitaire burnt trees, terrain.

The perspective is so much worse down there.

Sometimes the visibility is reduced.

Play it wise; stay high, get down there only to level off, drop, and up again!

2- “V” drops. Don’t make last-moment abrupt changes on the flight path

If we set up for a deep approach and all of a sudden we pull hard, we risk exceeding our critical angle of attack and getting into an accelerated stall.

As much as it seems a no-brainer, it happens to experience pilots too.

I see it often during training.

Rushing on the base to final turn, terrain constraints, other traffic, external pressure, or tailwind pushing us towards the target on the final turn, are some of the reasons for a messy setup and a V drop as a consequence.

And with a poor setup, high and fast, comes a drop with the engine on idle.

Danger.

The aircraft pitches up after the sudden loss of weight.

You have no power and rush to add it.

The turbine is not a piston, it takes a while, but when power comes, comes together!

A lot of torque and an attitude far from optimal.

The perfect recipe for a LOC-I.

You probably remember this drop as an example of lucky “V” drop.

3- The correct profile

We should come from a position where we have a good perspective of the target.

Try not to lose contact and keep your visual references.

We need to level out, add power and get out.

Make sure to have the turbine engaged (not idling) and that tail well blown!

Drop height and speed: Importance

The height above the ground and aircraft dropping ground speed has a critical effect on the structure, shape, and speed upon the impact of the extinguishing agent.

From a flight safety perspective, airframes may be severely damaged by these cumulative stresses. If too fast on the drop, there is a huge flexion moment over the wing root due to sudden weight reduction.

Airframes will not suffer any damage during regular firefighting if the drop speed is within the manufacturer’s margins, but the wing will flex more after a drop if the speed is excessive.

This stress may not be visible at first, but it will be obvious over time.

Slower drops (within safe limits) are more effective. Drops at high speed break the water into smaller droplets making it some sort of ineffective drizzle.

For our safety and that of others, we must drop at the right speed, according to the manufacturer’s limitations.

We should bring up the small speed window we have for the whole flight while firefighting.

While other forms of aviation allow the pilot to fly at speeds ranging from 140kts to more than 400kts (more than 300% difference), firefighting allows only a narrow window between stall speed and drop speed – Va.

Here is an example showing stall speed at MTOW for varying bank angles:

As seen, the stall speed is 77Kts when the aircraft is straight and level. The dropping speed is 110-115Kts. We just talked about differences of 300% between stall and cruising speeds in other aircraft, but now we are only talking about a difference of 50% between stall and cruising speeds.

As we can see from the table above, the stall speed dramatically increases with an increased bank, which reminds us that while firefighting we spend most of our time banking due to terrain, other traffic, obstacles, and evasive maneuvers.

High G forces are generated by exceeding dropping speed and Va.

This occurs more in the beginning when pilots naturally avoid stalling due to the fear of a stall event while flying low level (a natural and understandable reaction to train and avoid).

Considering the speed window we have and the flight load factor limits, we find ourselves in a kind of “Coffin Corner,” where we are at the mercy of a stall on one side and structural limitations on the other.

Check this video to see a structural failure during the dropping phase.

What is the ideal drop height?

It depends.

This will vary depending on the aircraft.

The intensity and specific circumstances of the fire dictate how the drop should be carried out.

For Single Engine Air Tankers such as the Air Tractors or the Thrush, most of the time 60 to 80 ft / and 110Kts will be a reasonable compromise between safety and efficiency.

Drops from low heights maintain an enormous mass, so they have a high impact speed. Erosion, evaporation, and dispersion of the product are minimized and provide maximum penetration into the forest cover. This is the easiest way but not necessarily the most effective.

Lower is not always better, and it reduces safety margins.

Drops in the lower acceptable range shown in the drawing, are suitable for high winds (low drop = less drift), no ground personnel in the vicinity, and the absence of tall trees (no need to penetrate vertically).

People and equipment on the ground can be at risk from low drops from heavy aircraft. On the other hand, flying low requires more skill from the pilot, but it increases the accuracy of the drop. There is always a projection of air (depending on the mass of the aircraft) when drops are made from very low heights, which causes oxygenation of the environment and a consequent increase in fire intensity.

High drops will reach the ground at low speed, although they can cover a larger area with less impact. Accuracy decreases because there is an increased dispersion of the load and, therefore, a more significant effect of the wind.

Very high drops cover larger areas but will be ineffective due to the lack of penetration of extinguishing products.

As we can see we need to think of the optimum height for the circumstances and safe height, which should not be lower than 60ft as a reference.

The goal is a safe drop, providing the most suitable penetration and maximum amount of extinguishing agent at the designated area.

Some tips to be safer and more effective on the drops

Avoid tunnel vision and excessive target fixation:

And a last and important piece of advice, do not focus so much on the drop and its effectivity that you will lose awareness of the rest.

We might find ourselves doing a spot-on drop as regards accuracy, and find terrain ahead hard to clear, or hit a tree before as we were focussing too much on one single aspect of the drop.

Tunnel vision is a cognitive bias in which a person focuses excessively on a single aspect of a situation, and neglects to consider other important aspects. This type of bias can lead to errors in judgment and decision-making, as it causes pilots to overlook important information and miss out on the surrounding environment.

Do not fly through smoke

We have all done at some point, consciously to try to be more effective, or involuntarily.

Either way it’s a source of trouble.

Drop anticipation

When there is a crosswind, the drop will be wider. Higher values require wider drift corrections (offsets).

Headwind: The drop will be shorter and more compact. The impact on small fires is greater, but visibility is reduced. Hits are more difficult.

When there is a tailwind, the drop will be longer and less compact. There will be less impact on smaller fires, and better visibility. This represents the easiest way to attack larger fires (take energy out at the flank from back to front).

Below is a video showing different drops from different heights.

There is no magic number as the optimal dropping height, as you will see in the video and as we have described above, it depends on the circumstances, but we should always keep our 60ft as minimum recommend. Think of the wingspan of an aircraft flying a knife edge flyby, at least.

Reason 2: Loss of control in flight (LOC-I).

I won’t stop here too much, as we have discussed it several times.

This past article highlights UPRT tailored to our reality as Aerial Firefighters, as the best mitigation to prevent upsets. It will give you some clues linking them to some past occurrences. Please review it if you don’t feel like UPRT and LOC-I are 100% familiar concepts.

You should also watch Wayne Handley’s classic video, Turn Smart, which I’m sure has saved a few lives since it was first published.

Definitely a must.

 

Human error is a symptom of deeper trouble.

Back to beginining of the post, once we have gone through the technical aspects, let’s remember that no one in their right mind goes to work with the firm intention of causing an accident. And if that were the case, we would be talking about a violation or negligence, and not a procedural drift, which still takes us to the next point:

Organizational factors

Connecting people’s behavior with the circumstances that surrounded them points us to the sources of trouble and helps explain behavior.

Organizational factors play a key role and could be the underlying cause on many occasions, as could be the case in the videos.

Some organizational factors could be:

➡️ Unsustainable growth. (Discussed here)
➡️ Not enough instructors or training resources.
➡️ Lack of mentors.
➡️ Inadequate or ineffective safety management systems.
➡️ Pilots left alone on single-crew ops too soon due to contractual needs.

In most cases, those reasons are beyond our control, so we can quit or choose our partners more carefully.

In the event that you feel part of an organization that does not match your values, this article “Slamming the door, a tool for personal growth”, could help clear your mind.

For your safety: we need to SEE the bigger picture

1 –  S – SAFE

2 – E – Effective

3-  E – Efficient

Drop at the optimal height! Lower is not more effective neither more efficient. It cannot be 2 and 3 without 1

If you found this post insightful, you might also enjoy the second part: Dropping Safety part 2: Ground personnel

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2 thoughts on “Dropping safety – Part 1: Aerial assets”

  1. Fantástico trabajo Eder, Absolutamente de acuerdo en todo este análisis. asi es.
    Respecto al lanzamiento en V , muchos incidentes y accidentes por este motivo. Alturas de lanzamiento y comportamiento de la gota perfectamente descrito en tu trabajo.
    La visión de Tubo…. otra de las causas más habituales de accidentes. Arboles secos en nuestra trayectoria que no se ven porque solo se focaliza el objetivo, o factores emocionales que nos atrofian los sentidos perdiendo la capacidad de ver. Vuela tranquilo y conseguiras tu máxima capacidad mental para una correcta toma de decisiones.
    Gracias Eder.

    Reply

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