Pilot Perceptions of Wire Strikes in Agricultural Aviation Operations

METHODS

RESULTS

Overall, 32 wire-strike events were reported across focus groups; 7 pilots (32%) reported more than 1 wire-strike event, with a range of 2–3 events each among them. Collectively, the focus group subjects reported experiencing 21 (66%) wire-strike events in a fixed wing aircraft and 4 (12.5%) wire-strike events in a helicopter. Seven events were tallied as “unclear”. The dialogue in these events lacked distinctive terminology, such as references to the fan blade or the tail boom, that would indicate whether they involved in a fixed wing aircraft or rotorcraft. Eight distinct risk factors were identified to describe subjects’ responses to Question 1: “What conditions or events contributed to the in-air collision event?” These eight factors were grouped into two higher order categories: situational risk factors and cognitive risk factors. Situational risk factors refer to environmental conditions and aspects of flight that may increase the risk of a wire-strike event occurring. In order of prevalence, situational risk factors included: A) technically difficult operations, B) flight stages/aspects of flight, C) internal risk factors, and D) environmental risk factors (Table I). Alternatively, cognitive risk factors include discrete events that happened during flight that involve different aspects of decision-making and pilot performance. In order of prevalence, cognitive risk factors included A) splitting attention/distraction, B) judgement call errors, C) performance pressures, and D) breaking their own rules (Table II).

Table I.Situational risk factors contributing to wire-strike events.

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Table II.Cognitive and personal risk factors contributing to wire-strike events.

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For situational risk factors, subjects repeatedly mentioned technically difficult operations (see Table I). Overall, 12 subjects (55%) reported that a technically difficult maneuver or field condition was associated with their wire-strike event. These included flying a field that had multiple wires, or a field that required “jumping a wire,” described as a pilot briefly flying over a wire located in the middle of a field.

Over half (55%; N = 12) of the subjects identified specific flight stages and aspects of flight as being related to the wire-strike event. The most frequent flight stage was making “trim” or cleanup passes around the edge of the field or other part of the field that was missed during the planned and executed flight path. Other stages of flight included wire strikes occurring when a pilot entered the field or exited the field.

Subjects also discussed a variety of internal risk factors as contributors to their wire-strike event. These factors included fatigue, heightened emotional states (e.g., excitement about the birth of a child or grief due to loss), being inexperienced or new to flying, and being unfamiliar with the particular aircraft flown. Altogether, 11 subjects (50%) reported some internal risk factor as contributing to their wire-strike event.

Table I also shows that environmental risk factors were reported by 6 subjects (27%) and included night flying, flying with poor visual conditions, and the occurrence of distracting weather conditions. There were 19 subjects (86%) who provided a response indicating at least 1 of the 4 situational risk factors contributed to their wire-strike event.

Cognitive and personal risk factors identified by subjects included discrete events that affected situational awareness, decision-making choices, and pressures that, in turn, may have affected pilot performance during flight (Table II). The most commonly reported cognitive risk factor was splitting attention or being distracted, which was reported by 13 subjects (59%).

Specific examples of splitting attention/distraction included being focused on another obstacle in the field, being focused on avoiding and protecting owner property such as a garden, thinking about other aspects of work or future work tasks, and having some discrete event (e.g., a radio call) that brought the pilot out of focus.

The next cognitive risk factor reported was making judgment call errors, which was reported by six subjects (27%). Subjects in these situations reported that they knew the wire was there but misjudged the proximity to the wire when trying to maneuver around it, suggesting a perceptual error in HFACS taxonomy.⁵

Six subjects (27%) also reported performance pressures as a risk factor in wire-strike events. Often, these pressures were described in terms of doing the highest quality work possible (e.g., spray all the edges of the field that were previously missed). Other pressures reported by subjects included internal pressures to hurry or complete the field in a timely manner.

Finally, two subjects (9%) also attributed their wire-strike event to breaking their own established rules. The factor “breaking their own rules” applied to instances where subjects explicitly reported a reference to breaking one of their own personal flight rules, such as flying the first pass at a certain height. Overall, 19 subjects (86%) reported at least 1 of the 4 cognitive risk factors as contributing to their wire-strike event.

Subjects reported a number of immediate and secondary recovery steps in response to Question 2: “What were your recovery steps immediately following the air collision event?” The researchers identified eight immediate recovery steps that were reported by subjects; these steps were ranked in order of prevalence in Table III. The most commonly reported recovery step was related to maneuvering the aircraft, which included keeping the aircraft flying level or changing altitude to avoid other obstacles. There were 15 subjects (68%) who reported this immediate recovery step, often mentioned in alignment with the general aviation maxim, “aviate, navigate, and communicate.”¹⁶ Along with this immediate focus on continuing to fly the aircraft properly, six subjects (27%) reported monitoring gauges, five subjects (23%) reported assessing the situation, and three subjects (14%) reported maintaining airspeed. Subjects across all focus groups reported implementing at least one of eight immediate recovery steps following the air collision event.

Table III.Immediate recovery steps following wire-strike events.

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There were 10 subjects (45%) who reported assessing damage to their aircraft immediately after collision and while still in the air, such as looking out the window at the wings or circling around to see if they could spot the wire that they flew through. Alternatively, three subjects (14%) explicitly reported assessing for damage following landing.

There were 16 subjects (73%) who reported making the decision to fly to a nearby airport (often referred to as “home” or “home base”) rather than making an immediate landing. In this group, some subjects even reported making an informed decision on which airport to go to, such as in the following scenario:

“I got an airport 6 miles away. I know it’s unattended. It’s 6 o’clock in the evening. What do I have underneath my airplane? Do I have landing gear? Do I have anything? …I can go back to this airport. Possibly land there, with no landing gear. And lay out there for God knows how long at this airport because they’re not going to come look for me for another probably 45 minutes. And why would they look for me at an airport. So I thought, well okay, I’m going home. I’m going home. At least if I can’t get ahold of anybody they’re going to see me pancake this thing on the runway and at least get me help.”

Subjects also reported communicating with personnel in the area over radio following their wire strike (27%; N = 6). These cases often involved inquiring whether others on the ground could help assess the condition of the aircraft, such as potential damage to landing gear, to assist in landing decisions.

When asked Question 3 (“Were you aware of the obstacle before it happened?”), subjects indicated that they were previously aware of the wire before the accident occurred in 21 out of the 32 (65%) wire-strike events reported across focus groups (Fig. 1). These subjects reported explicit awareness such as, “I was 100% aware of it” and “Yeah I pulled up over that wire, 39 times. I trimmed next to it two times. And I hit it on the 40^th time.”

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Alternatively, subjects reported not being completely aware of the wire in 11 of the 32 (35%) wire strikes. For example, one subject reported that they were not “paying close enough attention and didn’t see it until the last minute, until it was too late to pull it,” while another subject reported that “It was not visible and I did a recon so I never saw it until I was down… I didn’t even see it. I felt it. I didn’t see it.”

Three actions were identified from responses to Question 4: “What could you have done differently that would have prevented the collision?” In order of prevalence, these actions included: A) check conditions/situational awareness, B) avoid deviating from plan, and C) don’t break own rule (Table IV).

Table IV.Steps that could have prevented a collision.

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Overall, 19 subjects (86%) suggested that their wire-strike event could have been prevented with better checking of conditions at the field (e.g., reconnaissance, surveillance) before spraying it to maintain better situational awareness and focus during each pass of the field. Subjects also suggested avoiding deviation from their plan (23%; N = 5). These reports included examples of pilots changing their minds midflight about procedures, such as the direction in which they will fly passes or waiting as planned for the rest of the crew to arrive. Finally, similar to the cognitive factor reported as a contributor to the wire-strike event, three subjects suggested that breaking their own rule may have also contributed to wire-strike events.

DISCUSSION

Subjects identified a number of situational risk factors that they believed may have contributed to their wire-strike events, such as environmental conditions and aspects of flight. For example, the frequency with which “trim passes” were identified as a key stage of flight during their wire-strike events indicates that pilots should be more attentive to potential wire strikes during these passes, or evaluate them preflight to assess the potential risk of a wire strike occurring. While the importance of staying vigilant during “trim passes” is a situational risk factor unique to agricultural aviation operations, most of the other identified risk factors offer insight for general aviation accidents more broadly.

Internal risk factors including heightened emotional states (either positive or negative), lack of experience, or lack of familiarity with the aircraft are important factors that subjects reported as having contributed to their wire-strike events. Subjects reported that environmental risk factors such as night flying or poor weather, along with technically difficult operations such as flying fields covered in wires, contributed to the wire-strike event. Future research could look explicitly at how much the level of flying experience in general, or within that specific aircraft, may factor into these events.

Subjects also reported several cognitive and personal risk factors that may have affected their performance and thus contributed to their wire-strike event, such as situational awareness, decision-making choices, and pressure (internal or external). Some of these factors can be mitigated partially by emphasizing a positive safety culture, such as mitigating performance pressures to do the best work possible without compromising safety (see Key et al. for a review of safety culture).¹⁷ This increased emphasis on safety would also need to address pilots’ self-imposed performance pressures; wire-strike events tended to involve pilots who were in a hurry or were performing to the highest standard possible. Trainings specific to avoiding wire strikes, such as those offered by the NAAA, may help address some of these pressures.¹⁸ Other factors such as mental distractions also may be addressed through attention management training and reflecting on how any current internal risk factors, such as fatigue or heightened emotional states, may increase the risk of an event. However, certain cognitive risk factors are not necessarily something that pilots can evaluate effectively preflight and, therefore, must constantly monitor during flight. Additionally, risk assessment decisions, such as judgment calls or breaking one’s own rules, occur during flight. However, there are likely times that deviating from a given plan would be the safer decision, thereby highlighting the complexity of decision-making in aviation.

Understanding the recovery steps that pilots took immediately following the wire-strike event is critical to promoting successful recovery from such events. Subjects reported immediately assessing the situation and maintaining control of the flight while in-air (e.g., adjusting airspeed, maneuvering aircraft, monitoring gauges), as well as later assessing the damage postflight. Overall, while these specific recovery examples were limited to wire strikes that occurred during agricultural operations, the lessons learned from these successful recoveries offer insight to all aviators that operate at low altitudes.

Immediate recovery strategies typically aligned with the general aviation maxim, “aviate, navigate, and communicate,” implying that the first priority of the pilot should be continuing to fly and maintaining control of the aircraft.¹⁶ Subjects reported an immediate focus on maneuvering the aircraft to a safer flight path, regaining situational awareness of the field and their surroundings, and monitoring gauges. Subjects reported focusing on communication to ensure a safe landing, also in line with this general maxim.

Of particular interest, the majority of subjects (73%; N = 16) reported that they made the decision to fly to a nearby airport rather than seek immediate landing. These subjects even reported making informed decisions about which airport to land at, sometimes choosing a further airport if they felt landing would be safer there (e.g., a nearby airport would have fewer resources to assist with any landing emergencies). One pilot reported that the decision to land at the local airport was based on concerns about damage to the plane. The pilot noted, “I got back home to land on my runway and I suppose I was, I know I was nervous, there’s no supposing about it… I knew I didn’t have any brakes. Because I had touched my brake pedals.” Overall, these results highlight the difficulty of making in-air decisions that follow wire-strike events.

Whether or not the pilot was aware of the wire obstacle before the collision has important implications for prevention strategies. Subjects reported already being aware of the wire in 65% (N = 21) of wire-strike events. This is in line with a previous analysis of in-air obstacle collision accident reports, where about half of pilots were aware of the obstacle before the collision.⁷ Together, these results indicate that better surveying the field and other preflight preparations would have been effective mitigation strategies in some, but not all, wire-strike events. For cases where pilots are already aware of the obstacle, other prevention strategies such as those described below may be more effective. Additionally, wire markers and a range of additional tools are available to pilots that may assist in keeping track of wires throughout flight, including Electronic Flight Bags, the Wire Strike Protection System, and the Obstacle Collision Avoidance System (see Chandrasekaran for review).¹⁹

The focus group subjects reported a number of strategies that they believe would have prevented their collisions with wires. As noted above, some of these reports were related to better field scouting, where subjects suggested that better reconnaissance passes could either have alerted them to a previously unseen wire or would have made them more confident overall that they were aware of all obstacles while flying passes in the field (i.e., thus minimizing that distraction). Besides improving awareness of the position and orientation of wires, other suggestions for preventing wire-strike events included not spraying the field in the first place due to safety risks or paying better attention to where they were in the field at the time of collision. Many subjects mentioned this idea of staying present, minimizing distractions, and focusing on each current pass. While the individual facets of situational awareness proposed here are specific to the conditions of each event, the overarching suggestion of staying “in the moment” may be useful advice for pilots across all aviation operations.

Additional strategies for preventing wire strikes included avoiding both deviation from the plan and breaking personal rules for flying. Both of these strategies relate to the prevalence of wire strikes occurring during nonnormal flight conditions, such as during clean-up “trim” passes or following in-the-moment decisions to deviate from a flight path. Breaking personal rules were also explicitly mentioned as a contributing factor to wire-strike events and could interact with other contributors, such as performance pressures (e.g., doing a good job cleaning up the edge of a field) or judgment call errors. Overall, these prevention strategies highlight the importance of pilots following their own predefined plans and trusting their own safety expertise and instincts.

There are several limitations in the current study worth discussing. First, survivorship bias is a factor, and the current results should be interpreted from the lens of wire-strike accidents that were not fatal.²⁰ According to NTSB data, 15% of reported wire-strike accidents in Part 137 Agricultural Operations were fatal.² Similarities noted in the current sample might involve human factors differing from those of fatal accidents, which cannot be compared in the current study.

Given the sensitivity of the topic and the lack of accurate base rate information pertaining to wire-strike events, it is difficult to get the full picture of the scope of human factors issues involved. An accurate fatality rate of wire-strike events may be difficult to determine, as wire strikes may go unreported to the NTSB if damage to the aircraft or other property is minimal. As well, the sample only includes subjects that were willing to discuss their accidents. Pilots that were uncomfortable discussing their experiences in a focus group setting may also have experienced other contributing factors not discussed here.

The nature of the focus group itself can affect the quality of group interactions and discussions. For example, one person may drive the conversation, leading to single-minded responses, especially in groups with a high propensity for information-sharing.^20,21 Group characteristics such as size and experience also can influence responses within the group.^21–23 The moderator’s style (e.g., direct or active, indirect or passive) and disposition (e.g., sensitive or outward personality), also can influence responses within the group.^23,24 Finally, it is also possible that different content would have been elicited from subjects if they were questioned in structured interviews rather than focus groups or whether they were questioned individually in a one-on-one setting.²⁵

Finally, focus group questions did not include any events or circumstances prior to takeoff (e.g., flight planning, level of experience, familiarity with the field, ground inspection). Future research should consider the impact of preflight events and circumstances on wire-strike incidents; as it stands, it is not clear how a discussion of such circumstances during the focus group could affect the findings noted here.

Furthermore, the raters’ lack of familiarity with operational rules makes it difficult to assess whether an action caused the pilot to deviate from their plan versus break their own rule. For example, if operational rules only address how pilots operate the aircraft (e.g., weight and balance, fuel load), then any missteps involving these operations would be in violation of the operational rules and not personal rules.

Altogether, the current study provides insight into “how” and “why” wire-strike events occur during agricultural operations. Subjects identified a number of human-factors-related issues in these operations, including situational and cognitive risk factors, which could inform pilot decision-making in all stages of flight. Reported recovery steps and proposed preventive strategies may help future pilots mitigate and recover from these events, should such incidents or accidents occur. Further, subjects frequently reported being aware of the wire pre-collision. This highlights the need to scope the human factors issues involved in wire-strike events properly, ultimately to minimize or prevent such events in the future in agricultural aviation operations and general aviation more broadly.