Appendix B - Airport Bird Hazard Risk-Assessment Process

Airport Wildlife Management Bulletins

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Table of Contents

1. Introduction

2. Safety-Risk Framework

3. Classification of Risk

4. Elements of Risk

4.1. Risk Element I – Aircraft Related

4.1.1. Aircraft Types and FAR Certification Categories
4.1.2. Aircraft Movements
4.1.3. Aircraft Lateral and Vertical Flight Paths
4.1.4. Risk Category Classification
4.1.4.1. Aircraft &Engine Certification Standards
4.1.4.2. Aircraft Phase of Flight, Operating Altitudes &Bird Strike Vulnerability
4.1.4.3. Aircraft Flight Crew &Passenger Carrying Capacities
4.1.5. High-Risk Aircraft Flight Paths

4.2. Risk Element II – Bird Species-Related

4.2.1. Bird Hazard Ranking System

4.3. Risk Element III – Land-Use-Related by Hazardous Species

4.3.1. Risk Considerations
4.3.2. Hazardous Land-Uses

5. Airport Bird Hazard Zone Development

5.1. Airport Bird Hazard Zone Definitions
5.2. Airport Bird Hazard Zone Dimensions
5.3. Land Use in the Bird Hazard Zones

Appendix I

Figure 4 – Airport Bird Hazard Assessment Process Map

Table 6 – Summary of FAR Airframe Bird Strike Airworthiness Standards

Table 7 – Aircraft Flight Crew &Passengers

1. Introduction

The goal of wildlife control on and near an airport is to reduce the risk of an aircraft1 accident caused by birds and other forms of wildlife. The bird hazard risk-assessment process contributes to this goal by describing categories of land-use in the vicinity of the airport in terms of the relative risk of bird strikes to aircraft. The process enables those responsible for managing the land to mitigate the safety-risks appropriately, and for those overseeing aviation safety to evaluate the effectiveness of the mitigation.

The risk-assessment process evaluates the relationship among land-use, bird species and aircraft movements in terms of relative risk to aircraft. Figure 4in Appendix I illustrates the risk assessment process. It is applied to a particular airport site using the process map shown in Figure 4 contained in Appendix I. The process enables risk management strategies to be custom-designed and implemented to suit the specific factors that produce risk at a particular airport site. The risk-assessment process is designed to employ data and information on airport movements, local land-use and wildlife species used in the development of Airport Wildlife Management Plans (AWMP). The development of airport bird hazard zones is a key component of an integrated risk-based AWMP that maximizes the effectiveness of the AWMP, by mitigating the risk of hazardous land-use practices in the vicinity of an airport.

The risk-assessment process consists of five steps:

  1. Evaluate the aircraft risks by identifying and analyzing the types, frequency of movement, flight paths and generic phases of flight of the aircraft that arrive, depart and operate in the vicinity of the airport;
  2. Evaluate the bird risks by identifying and analyzing the resident and migratory bird species that could pose a risk to aircraft operations;
  3. Employing information from 1 and 2, categorize the relative risk by aircraft type and phase of flight, and chart this information;
  4. Employing the information from 1 and 2, determine the high-risk bird species and the land uses that may attract them, and chart this information; and
  5. Employing information derived from 3 and 4, plot bird hazard zones by category of severity and land-use.

This document describes the risk assessment process. It can be used to assess the airport bird hazard risks for four possible scenarios:

  1. For an existing airport to form the foundation of an Airport Wildlife Management Program, and to assist in compliance activities associated with the Wildlife Planning and Management regulation; or
  2. During the design phase of a new airport to identify bird hazard zoning requirements; or
  3. During the planning phase for an expansion or modification to airport runways and flight paths; or
  4. During the planning phase for the development of hazardous land uses in the vicinity of an airport.

1 The term aircraft refers to all fixed wing and rotary wing aircraft.

2. Safety-Risk Framework

The Safety-risk Framework links land-use to bird-related risks and aircraft operations. It categorizes the predictable relationships among:

  • The different land uses found near airport sites;
  • Bird species; and
  • The different safety-risks to aircraft during various phases of aircraft flight.

The results are hazard and risk matrices that, when applied to any airport setting, provide risk-based guidance on appropriate land-uses, ranging from prohibited to acceptable.

3. Classification of Risk

The following classification of damage or losses experienced by the aircraft or aircraft occupants is employed in the framework:

Category A – Catastrophic loss, measured as either the complete loss of the aircraft or the loss of more than one life as a consequence of a bird strike even 2,3.

Category B – Major damage, measured as either significant damage to the airframe, failure of one or more engines, one or more aircraft systems, serious injury to one or more aircraft occupants, or the loss of life of no more than one aircraft occupant.

Category C – Minor damage to the airframe, engines, or aircraft systems.

In employing these risk classifications, worst-case circumstances are considered, and subsequently qualified in light of predicted frequencies, or ranges of frequencies.

4. Elements of Risk

To construct the Safety-Risk Framework, it is necessary to understand the steps needed to build the framework. These are the elements of risk and they are described below with each element subsequently described in more detail as follows:

Risk Element I – Aircraft-Related

Identify and categorize areas of exposure and severity (the three-dimensional location of potential risk, and the number of aircraft occupants exposed to the hazard) by:

  • Examining the categories of aircraft that currently, or may in the future, use the airport;
  • Determining the aircraft departure, arrival and transit lateral and vertical flight paths;
  • Determining, based on the aircraft types using the airport, the applicable bird strike certification standards; and
  • Determining the differing degree of risk associated with different phases of flight; in the context of (exposure and vulnerability).

Risk Element II – Bird Species-Related

Identify and categorize the various bird species that could strike aircraft using the airport with regard to the potential severity of impact (i.e. bird weight and behaviour).

Risk Element III – Land Use-Related by Hazardous Species

Identify land-use as it affects nesting, feeding, night roosting, and daily and seasonal flight patterns of hazardous species of birds identified in Risk Element II.

The degree of risk associated with different land-uses can then be determined and applied to the areas associated with the various aircraft operations (probability of loss due to birds attracted by particular land uses).

While it is anticipated that Risk Element II will normally be completed to enable the completion of the evaluation of Risk Element III, a large number of hazardous land-uses have been clearly identified as being applicable to all airport sites thereby enabling a high-level analysis in Risk Element II or bypassing this task completely.

2 The differentiation between more than one death in a Category A accident and one death in a Category B is intended to discriminate between a bird strike event that results in collision with the terrain (Category A) and an event that causes death to a flight crew member after windshield penetration by a bird (Category B). In addition to the greater loss of life, the former will have significantly broader operational, economic, commercial, and political ramifications, and needs to be treated differently than a Category B accident.

3 A bird strike event may include single or multiple bird strikes.

4.1. Risk Element I – Aircraft Related

Evaluating the aircraft-related exposure and severity of bird strike events by determining the types of aircraft that currently (or may in the future) use the airport under examination. This determination is made by documenting:

Exposure

  1. Aircraft types and certification categories.
  2. Aircraft movements – daily and monthly distributions by aircraft type;
  3. The location and dimensions of lateral and vertical flight paths.

Severity

  1. Applicable airframe and engine certification standards associated with the aircraft types determined in 1 above.
  2. Applicable phase of flight, aircraft operating altitudes and bird strike vulnerability information.
  3. Flight crew and passenger carrying capacities for aircraft types identified in 1 above.

4.1.1. Aircraft Types and FAR Certification Categories

Catalogue the types of aircraft that currently (or may in the future) use a particular airport by FAR airframe and engine certification standards. This is done by reviewing the airport aircraft movement logs, assessing the runway lengths and pavement load bearing weights and interviewing representatives of the airport authority and users of the airport.

4.1.2. Aircraft Movements

The number, frequency and distribution of aircraft movements of the various aircraft types that use an airport are critical to the risk assessment process. This can be determined by a review of the airport aircraft movement logs and catalogued using aircraft type and FAR certification categories as described in section 4.1.1.

4.1.3. Aircraft Lateral and Vertical Flight Paths

Aircraft operate to, from, and in the vicinity of an airport with a high degree of predictability, enabling flight paths to be projected and mapped onto the lands around the airport. The airport runways and other landing surfaces are the references from which the flight paths are mapped. The subsequent projections depict the lateral and vertical zones in which, predictably, aircraft operate, and which, therefore, are the “potential” hazard zones for bird strikes.

Local flight paths are influenced by topographical features such as mountains, rivers and lakes as well as built-up areas. These flight paths may be further constrained by noise abatement and air traffic management requirements. Lateral and vertical flight paths to and from the airport (IFR and VFR) are determined by examining applicable aeronautical charts (maps, CFS, CAP), discussions with air traffic service providers and local users, and, by identifying other nearby aircraft landing sites that may be available (e.g. heliports, water aerodrome facilities and nearby airports).

While aircraft flight paths are predictable they are not precise therefore, when depicting aircraft flight paths reasonable margins should be constructed to account for pilot and controller error, environmental conditions (wind, severe weather) and technology errors.

4.1.4. Risk Category Classification

As explained in section 3 the damages or losses experienced by an aircraft or the occupants as the result of a bird strike can be defined as Category A, B, or C. Determining the potential risk categories for the particular aircraft types that use or may use the airport is essential.

4.1.4.1. Aircraft &Engine Certification Standards
Bird strike impact certification standards and aircraft operating performance are defined by the Federal Aviation Regulation (FAR) to which the aircraft or engine was certified. A summary of the engine and airframe FAR bird strike certification standards is contained in Tables 5 &6, in Appendix I.

4.1.4.2. Aircraft Phase of Flight, Operating Altitudes &Bird Strike

Vulnerability

Aircraft operations are divided into defined phases of flight for the purposes of aircraft certification that determines aircraft operating performance, bird impact certification requirements and aircraft system redundancy requirements.

The relevant phases of flight include:

  • take off
  • initial climb
  • enroute climb
  • cruise
  • descent
  • approach
  • landing
  • missed approach

Aircraft are vulnerable to bird strikes in varying degrees during different phases of aircraft flight. The degree of vulnerability is a function of the aircraft type, altitude, operating envelope during a particular phase of flight, and the number of flight crew. Table 1 summarizes the various aircraft categories, approximate altitudes by phase of flight, and Category A or B damage events most likely to occur during these phases. A general description of the phases of flight is included below, ranked from highest to lowest risk.

  1. Take off and initial climb. The highest risk from a bird strike occurs during the take off and could result in loss of aircraft control and collision with terrain. The aircraft is low to the ground; it is often operating at or near the performance limits of the aircraft; it has a large fuel load; and it is at a critical angle-of-attack. Crew activity is high and coordination is imperative. As the climb out progresses and aircraft altitude increases, the risk of loss of control and collision with terrain is reduced. However, the risk of serious damage to the airframe and engine as a result of a bird strike increases because of higher impact forces from increasing airspeeds.
  2. Missed approach. The most severe risk of a bird strike event during this phase of flight is a loss of control and subsequent impact with the terrain. This would likely occur if the bird strike event took place while initiating the missed approach, when the aircraft is low to the ground, the aircraft is in a low energy state, and the flight crew is reconfiguring the aircraft. At this time a Category A event would be possible. However, because much of the initial climb in the missed approach would occur over the runway, the exposure to bird hazard risk may be reduced as a result of airport wildlife management.
  3. Approach and landing. The category of loss in these phases of flight is very much dependant on the aircraft type. For FAR 23 (Commuter Aircraft) &25 aircraft the most severe risk of a bird strike event during the instrument approach is a category B loss. A Category A loss is remotely possible if the event occurs in close proximity to the ground (e.g., a go-around because of unrelated and pressing operational conditions4). For Normal Category Aircraft (FAR 23) and Helicopters (FAR 27 &29), due to the fact that these aircraft have no bird strike impact certification requirements and use only one pilot, the likelihood of windshield penetration and crew incapacitation leading to a Category A loss is dramatically increased.
  4. Descent to approach. For Far 23 (Commuter Aircraft) and 25 aircraft the most severe result of a bird strike event during the descent to the approach is probably a Category B loss. For Normal Category Aircraft (FAR 23) and Helicopters (FAR 27 &29), due to the fact that these aircraft have no bird strike impact certification requirements and use only one pilot, the likelihood of windshield penetration and crew incapacitation leading to a Category A loss is dramatically increased.
  5. En-route climb. For Far 23 (Commuter Aircraft) and 25 aircraft the most severe result of a bird strike event during the en-route climb phase is a category B loss. For Normal Category Aircraft (FAR 23) and Helicopters (FAR 27 &29), due to the fact that these aircraft have no bird strike impact certification requirements and use only one pilot, the likelihood of windshield penetration and crew incapacitation leading to a Category A loss is dramatically increased.
  6. Cruise. For Far 23 (Commuter Aircraft) and 25 aircraft The most severe result of a bird strike event during the en-route climb phase is a category B loss. For Normal Category Aircraft (FAR 23) and Helicopters (FAR 27 &29), due to the fact that these aircraft have no bird strike impact certification requirements and use only one pilot, the likelihood of windshield penetration and crew incapacitation leading to a Category A loss is dramatically increased.

4.1.4.3. Aircraft Flight Crew &Passenger Carrying Capacities

To assess the potential severity of a bird strike event it is necessary to evaluate the number of flight crew operating the aircraft to determine the availability of personnel to operate the aircraft should a crew member become incapacitated and the potential number of passengers on board the aircraft. Table 7 in Appendix I provides a range of values that may be used.

4.1.5. High-Risk Aircraft Flight Paths

Using the information derived above, high-risk aircraft flight paths are developed and superimposed over maps of the local area. These paths represent the flight paths for the various aircraft types where Category A and B events are likely to occur. When constructing the flight paths it is important to provide a sufficient horizontal distance buffer around the direct flight path to account for variations in aircraft speed within the type category, pilot technique and environmental effects such as wind.

4 For instance, in the case of an unanticipated go-around from an altitude below the Minimum Descent Altitude or the Missed Approach Point. An example of such pressing operational conditions occurred during the loss of an Air Canada CL-65 at Fredericton, New Brunswick, in December 1998.

Table 1 – Aircraft Phase of Flight Altitudes (ft. AGL)

Table 1 - Aircraft Phase of Flight Altitudes (ft. AGL)

* Due to the fact that normal category aircraft (FAR 23) and helicopters (FAR 27 and 29) have no bird strikeimpact certification requirements and are flown by only one pilot, windshield penetration and crew incapacitation that leads to a Category A loss is possible.

4.2. Risk Element II - Bird Species-Related

The consequence of a bird strike varies with the weight of the bird, the impact speed and the number of birds that are struck during a bird strike event. Therefore, information regarding the physical characteristics of bird species and their nesting, feeding, flocking, and flying characteristics are needed to establish a generalized category of risk for each species or group.

In the following sections, we develop a generalized ranking system that distinguishes among the bird groups by the degree of risk that they pose to aircraft safety.

4.2.1. Bird Hazard Ranking System

Whereas aircraft fly on very predictable flight paths when operating to and from the airport, bird movements are not nearly as consistent. Their flight patterns vary under differing weather conditions, seasons, and times of the day, to name just a few factors. Therefore, the physical dimensions of bird hazard zones need to be expanded and “rounded out” to account for variations in bird behaviour.

The bird hazard ranking system is based on the size of the birds, their flocking characteristics, and their flight behaviour. The size of the bird is an important determinant of the damage that it can cause to an aircraft. Obviously, large birds cause more damage than smaller birds. The average weight of the bird is used in this system. The weight is more important than the overall size because it is the density of the bird that determines actual damage.

The flocking behaviour of the species is important because it affects the probability that more than one individual is likely to be involved in a bird strike event. A bird strike event involving a flock of birds can lead to birds being ingested into more than one aircraft engine, thereby greatly increasing the risk of an accident. The worst example of this was a Lockheed Electra that ingested a flock of starlings into three of its four engines just after take-off from Boston’s Logan Airport. The aircraft lost power, stalled, and crashed into Boston Harbor, with the loss of 62 lives plus 9 injured. Thus, dense flocks of birds are usually more dangerous than single birds.

The flight behaviour of birds is an important consideration when assessing risk to aircraft. During their annual migrations, birds can fly at high altitudes, often at several thousand feet above ground. These high altitude migrations can pose threats to aircraft safety, but they are independent of local land-uses and are not considered here. However, migratory birds may be attracted to land-uses in the vicinity of an airport as an intermediate stop for food, shelter or water during long migratory flights. In the vicinity of an airport, it is the local movements that occur on a daily basis that are most relevant to aircraft safety. Some species always fly close to the ground, whereas others, such as gulls and hawks regularly fly at higher altitudes of 1000 to 1500 ft agl. Birds at those altitudes can pose a risk to aircraft on approach and departure to the airport.

Dolbeer et al. (2000) have analyzed U.S. civilian bird strike data from the Federal Aviation Administration (FAA) database to rank wildlife species in terms of the damage caused by strikes with each species. The ranking system that has been developed here is consistent with their results.

The general categories used in the Bird Hazard Ranking System are defined below from highest risk (Level 1) to lowest risk (Level 6) based on the mean bird species weight and flocking behaviours in relation to the airframe and turbine engine certification standards and are summarized in Table 2.

The six hazard levels in the Bird Hazard Ranking System are ranked in approximate order from most severe to least severe. Based on the worldwide history of bird strike incidents, it is clear that each of Levels 1 to 4 can present significant safety hazards. The small, flocking birds in Level 4 have caused significant aircraft accidents. The Lockheed Electra brought down by a flock of starlings in Boston was mentioned earlier. Also, a flock of Brown-headed Cowbirds brought down a Lear 24 jet taking-off from DeKalb-Peachtree Airport in Atlanta, Georgia, in March 1973. The aircraft lost power in both engines and crashed with the loss of 7 lives.

Hazard Levels 5 and 6 generally have not caused significant bird strike accidents to civilian aircraft, although some minor damage could occur. There are a large number of strikes with species in Hazard Levels 5 and 6, particularly in the airport environment where both the birds and the aircraft are close to the ground. Many of those strikes go unnoticed by the flight crew and airline maintenance staff, but are detected by the presence of dead birds found on or near airport runways by bird control and runway patrol staff. It should not be assumed, however, that all strikes with Level 5 species are harmless. For example, a single American Kestrel caused significant damage to a Boeing 737 at Louisville Airport in a Category C incident.

Table 2Bird Hazard Ranking System 4.3. Risk Element III - Land-Use-Related by Hazardous Species

Level of Risk Characteristics Illustrative Species
Level 1 Very large (>1.8 kg), flocking Geese, cranes, cormorants
Level 2 Very large (>1.8 kg), solitary or Large (1-1.8kg), flocking Vultures, Mallards Great Black-backed Gulls
Level 3 Large (1-1.8 kg), solitary or Medium (300-1000 g), flocking Red-tailed Hawk, American Crow
Level 4 Medium (300-1000g), solitary or Small (50 – 300 g), flocking European Starling
Level 5 Small (50-300 g), solitary or Very small (<50 g), flocking Eastern Meadowlark, swallows
Level 6 Very small (<50 g), solitary Warblers, vireos, sparrows

4.3. Risk Element III - Land-Use-Related by Hazardous Species

Risk Element II concerns the types of birds that pose the greatest threats and the individual species of concern in the vicinity of an airport. The next step is to evaluate the land-uses that support and attract the bird species of concern; that is, species in Hazard Levels 1 through 4. As discussed at the beginning of this section, a large number of hazardous land-uses have been clearly identified as being applicable to all airport sites thereby enabling a high-level analysis in Risk Element II or bypassing this task completely.

4.3.1. Risk Considerations

Two facts underpin the consideration of risk associated with various land-uses near an airport. These are (1) all lands attract birds of some kind and (2) birds do not pose a threat to aircraft safety when they are on, or close to, the ground on lands adjacent to an airport. The characteristics that cause some land-uses to create a hazard to aircraft safety are discussed in the following paragraphs.

Species

Clearly, the species of birds that are attracted to a particular land-use constitute a key risk factor. The species identified in the previous section are classified by the degree of risk that they pose to flight safety. The species in Levels 1 through 4 are of most concern, in decreasing order from 1 to 4. However, all land-uses that attract these species are of potential concern.

Numbers

The number of birds that are attracted to a specific land-use is an important risk consideration. Sites that attract large numbers of hazardous species are of more concern than those attracting only a few individuals.

Behaviour

The behaviours of the birds attracted to a particular land-use are critical determinants of whether a safety hazard is created. Because birds on the ground do not create a hazard, it is necessary to examine the behaviour of the birds over the site and/or when the birds are flying to and from the site. Some species, such as Turkey Vultures and gulls, soar or tower high into the air above the ground. When that happens, a potential hazard to aircraft safety can be created.

Sites that are used by feeding birds can attract the birds from remote locations. Many of the birds that feed at landfills spend the night at communal roosts. These birds, including gulls, crows, and starlings, make daily flights to and from the landfill, which might be many km from the roost. While in transit, the birds may fly through arrival and departure paths used by aircraft, thereby creating a risk to aircraft safety. That can occur even if the landfill and the night roost are not close to the airport. Gulls regularly fly up to 30 km between a landfill and their night roosts.

Frequency of Use

A key factor for discriminating between high and low risk land-uses is the frequency of visits by hazardous species to a particular land-use. A site that is used on a daily basis creates a higher risk than a site that is infrequently used. For example, a small landfill may be visited by several hundred gulls every day of the year, whereas a recently ploughed farm field may attract that many gulls for a day or two in spring or fall every year. Thus, each of the land-uses attracts the same number of gulls but the landfill is a regular use, whereas the particular farm field is a sporadic use. Clearly, the regular use creates a much higher risk than does the sporadic use.

Location

The location of a particular land-use often determines whether the land-use creates a safety risk. In its most obvious case, a land-use attracting low-flying and feeding birds might create a hazard if it were adjacent to an airport runway, but not create a hazard if it were 2-3 km away from the runway. A less obvious case is that of a major attraction, such as a landfill, that may create a safety hazard if the night roost used by the visiting birds is on the opposite side of the airport, but may not create a hazard if the landfill and the roost are on the same side of the airport. Thus, the specific location of the land-use is a critical determinant of whether a particular land-use will be hazardous to aircraft safety.

Scope of Land-Use

The practicalities of establishing effective bird hazard safety zoning around an airport are affected by the scope of the land-uses involved. It is much easier to zone against a hazardous site-specific land-use such as a Transfer Station or a Hog Farm than it is to zone against widespread agricultural practices such as plowing and cultivating fields. Fortunately, the risks associated with the site-specific land-uses are usually higher than the transitory risks associated with plowing. However, the risks created by gulls attracted to plowed fields are not zero.

4.3.2. Hazardous Land-Uses

This section describes a range of airport-area land-uses in terms of related risks that could be posed to aircraft (see Table 4).

High Risk Land Uses

Putrescible Waste Landfills

Landfills that accept putrescible or edible waste are major attractant of hazardous bird species. These species include Turkey Vulture, Great Black-backed Gull, and Herring Gull (Hazard Level 2), Ring-billed Gull, Rock Dove, and American Crow (Level 3), and European Starling (Level 4). Clearly, putrescible waste landfills are unique in their attractiveness to potentially hazardous birds. They must be a prime focus of the risk assessment.

Food Waste Hog Farms

Hog farms that feed food waste can attract large numbers of gulls (Level 2 and 3 hazards) and starlings (Level 4) on a regular basis. Because of their attractiveness to hazardous species, their regular use, and their ability to attract gulls from long distances, hog farms feeding food waste are rated as high risk hazards.

Racetracks

Racetracks can attract birds. For example, Woodbine racetrack near Pearson International Airport regularly attracts several hundred ring-billed gulls (Level 3) that feed on food discarded by customers and loaf in the infield and on the extensive parking lots. Woodbine has a vast turf course and large areas of lawns that regularly attract several hundred Canada Geese (Level 1) that nest, feed, and raise their young there. The barn areas are home to 1800 horses and many hundreds of rock doves (pigeons; Level 3) that live there. The gulls are attracted from Lake Ontario and the Canada Geese frequent other areas away from the racetrack.

Wildlife Refuges, Waterfowl Feeding Stations

In general, wildlife refuges are often created to attract and protect waterfowl and other large and potentially hazardous bird species. In some locations, these refuges could pose a high risk to aircraft.

Moderate Risk Land Uses

Open Transfer Stations

Open transfer stations are facilities that are not fully enclosed or where waste is transferred outdoors. In those situations, edible waste is often available to gulls and other species. Although the numbers of gulls present is generally not high, the use of open transfer stations is regular. The regular availability of food means that gulls might fly long distances to feed there.

Cattle Paddocks

Ring-billed Gulls (Level 3 hazards) sometimes forage in cattle paddocks adjacent to farm buildings, perhaps foraging for spilled cattle feed. European Starlings (Level 4) are frequently present in paddocks. Cattle paddocks are rated as a moderate risk although in many cases a lower ranking could be applied.

Poultry Factory Farms

Very large poultry operations have a steady mortality of birds. In some operations the dead birds are discarded outside where the carcasses regularly attract substantial numbers of scavenging birds such as vultures (Level 2), raptors (Level 3), gulls (Level 3), and crows (Level 3).

Poultry factory farms are classed as moderately risky operations; however, if the dead carcasses are not discarded outside, then no source of food is created for potentially hazardous birds.

Sewage Lagoons

In the past few decades, sewage lagoons have become important bird habitats. They can attract grebes, geese, ducks, coots, shorebirds, gulls, and swallows. Several of these species can pose a threat to aircraft safety.

Golf Courses

Golf courses contain large expanses of short grass that provide excellent feeding areas for Canada Geese (Level 1 species). The urbanized Canada Geese that are now common in parts of Canada often fly to golf courses to feed on the readily available grass. The geese foul the golf course with their droppings and are actively discouraged by many operators of golf courses, usually with little success. When golfers are present on the course, geese usually leave the fairways and greens. Thus, goose use of golf courses is somewhat sporadic.

Although Canada Geese are very high-risk species, the sporadic use of golf courses means that they should be classed as a moderately risky land-use.

Municipal Parks, Picnic Areas

Municipal parks usually have extensive areas with lawns and often have picnic areas and ponds that attract semi-domesticated and wild waterfowl. The combination of excellent feeding habitat for Canada Geese (grass) and Ring-billed Gulls (bread fed to ducks and picnic scraps) make such habitats ideal for Level 1 (Canada Geese) and Level 3 (Ring-billed Gull) species.

Low Risk Land Uses

Dry Waste Landfills

Dry waste landfills are those that do not accept putrescible or edible food waste. This type of landfill typically accepts construction and demolition (C&D) wastes and other non-edible wastes. Because there is no food available, large numbers of gulls and other birds are not attracted. A few gulls may investigate the site to determine whether food is available. They will move off quickly when they are satisfied that food is not present.

Enclosed Waste Transfer Stations

Waste transfer stations are facilities at which waste is transferred from local garbage pick-up vehicles to long haul trailer trucks that transport large volumes of waste to distant landfills. There are two general types of transfer stations: enclosed and open. At enclosed transfer stations, garbage trucks unload their waste inside a building, where the waste is compacted and reloaded onto transfer trucks. All waste is handled indoors so that no food is available to birds. A properly run enclosed transfer station does not attract birds. However, if waste is spilled outside the transfer station or if the transfer trucks spill waste or leachate, then small numbers of birds can be attracted. Thus, to insure that enclosed transfer stations are operated properly, they are rated as a low risk land-use that means that they will be subject to bird hazard zoning.

Wet/Dry Recycling Facilities

A wet/dry recycling facility is one in which food waste is treated indoors, where it is turned into inedible compost within a period of several weeks. These facilities generally do not attract birds because the food waste is unloaded inside and it is not available to birds. However, if waste is spilled outside by arriving or departing trucks, then birds will be attracted. To insure that this type of land-use is properly operated it should be ranked as a low risk land-use so that it will be covered under the zoning bylaw.

Marshes, Swamps and Mudflats

Wetland habitats can be natural or man-made. These types of habitats often attract substantial numbers of birds, including ducks, rails, coots, and shorebirds. However, the species generally stay in these habitats rather than making regular daily flights to distant locations.

Stormwater Management Ponds

There are increasing numbers of stormwater management ponds associated with various land development projects. Some ponds permanently hold water, whereas others are designed to be dry for most of the time, except during heavy rain events when they may contain water for a few days, at most. The latter ponds are of little concern because they do not provide food for aquatic species and are not regularly used by birds. The former ponds have permanent water that can attract waterbirds, including Canada Geese and gulls depending upon the shoreline and adjacent habitat.

Plowing, Cultivating and Haying

When farm fields are plowed or cultivated, the soil is turned over, and worms, insects, and other invertebrates are exposed and many are killed or injured. Ring-billed Gulls (Level 3) follow the plow and feed on the exposed invertebrates and insects. Gulls find farmers plowing or cultivating their fields, seemingly within minutes of them starting their tractors. The use of any particular field by gulls is transitory. Gulls are present only during the plowing and for a few hours afterward. In some cases, gulls may loaf on that field on the following day or two until a new field is plowed.

Although the use of any particular field is transitory, the overall use of plowed fields in the region is regular and predictable and involves several thousand Ring-billed Gulls. The presence of the agricultural area attracts the gulls inland from the lakes on a daily basis. However, short of banning plowing and cultivating, or requiring that all such activities be conducted at night when the birds are not present, there is little that one can do to zone against these individual transitory events.

If the gulls returned to the same field day after day, then the land-use would be ranked as moderate to high risk. However, the site-specific location varies from day to day, and any particular location is likely to be used for only a couple of days per season (spring and fall). Thus, plowing is rated as a low risk hazard. It is recognized that it is a hazard that will probably have to be accepted given that it is unlikely that this type of farming activity can be prevented.

Haying is the cutting of hay fields, which occurs one to three times per year in southern Ontario. Haying attracts several scavenging species of birds that are attracted by the newly exposed mice, nesting birds, and insects of various kinds. Bird species involved in this activity can include Northern Harrier (Level 4 hazard), Red-tailed Hawk (Level 3), Herring Gull (Level 2), Ring-billed Gull (Level 3), and American Crow (Level 3). This is a very transitory feeding opportunity that lasts for a short period of time, usually during the haying and for a few hours thereafter. Because of the localized nature of the activity, haying does not attract the large numbers of gulls to the area that are attracted by plowing and cultivating, which are much more widespread activities.

Commercial Shopping Malls, Plazas

Shopping malls and plazas often attract gulls, primarily Ring-billed Gulls (Level 3) and starlings (Level 4). The birds are attracted to food scraps that are dropped by shoppers in the parking lots and around store entrances. Also, the large parking lots, light standards, and flat roofs provide excellent loafing habitat for the gulls. Large malls can regularly attract up to 50 gulls.

Fastfood Restaurants

Fastfood restaurants attract Ring-billed Gulls in small numbers to feed on food dropped by customers. This behaviour occurs throughout the range of this species in eastern North America. The attraction is regular, with gulls present every day except in winter. Fastfood restaurants are usually grouped in proximity to other such restaurants, and attractions such as shopping malls and schools. These complexes can attract upward of 50 gulls at a time but the numbers are usually less.

Outdoor Restaurants

Outdoor restaurants and patios can attract Ring-billed Gulls (Level 3) in a similar manner to fastfood restaurants. The habitat is classed as creating a low risk.

Schoolyards

Ring-billed Gulls (Level 3) are attracted to schoolyards to feed on food scraps dropped by the students. The numbers of gulls at schoolyards during the present study was variable. Numbers reached as high as 160, but in 120 observations (schools and dates), only 15 per cent contained 20 or more gulls in a single schoolyard. The numbers present depend on time of day, season, food availability at the particular school, and the number of other attractions nearby. Schoolyards are regularly used by gulls.

Community and Recreation Centres

Community centres and recreation complexes can attract small numbers of Ring-billed Gulls to feed on dropped food items. Larger numbers of gulls are present in complexes that include schools, fastfood restaurants, etc. Facilities that include baseball and soccer fields can attract gulls when people are present and Canada Geese when the fields are not in use. Community/Recreation Centres are classed as low risk (blue zone) when they are part of a complex of attractions.

Limited Risk Land Uses

Vegetative Compost Facilities

Properly operated vegetative composting sites provide no food for birds and are not attractants to them. We have observed vegetative compost facilities in the southeastern U.S. that attracted a few crows because small amounts of food waste contaminated the vegetative matter. However, that does not happen when the facilities do not allow contamination of the vegetation with food waste.

Natural Habitats

There are many natural habitats that attract birds that pose little threat to aircraft safety unless the habitat and its birds are located close to airport runways. These habitats include forests and woodlots, hedgerows, and riparian habitats. Thus, natural habitats are classed as creating essentially no risk.

Inactive Agricultural Fields

Agriculture fields are home to diverse crops and farming practices. In general, most crops and practices create few bird hazards, and most are classed as posing no risk. Some of these practices would be of concern if they occurred on airport property, very close to an airport runway. However, this concern does not apply to the lands to be zoned, which are outside the boundary of the large airport site.

Because agriculture covers such large areas, any low-level attraction can involve a lot of birds because of the area involved. The following sections describe specific practices (plowing, cultivating, and haying) that can attract potentially hazardous birds.

Rural Ornamental and Farm Ponds

Small numbers of Canada Geese (Level 1) nest and raise their young on or adjacent to farm ponds. In late summer and fall, the geese join flocks and feed in other habitats. Unless the farm ponds are on the airport lands, it is unlikely that they will directly cause safety hazards. There may be an indirect effect in that the ponds provide nesting habitat that leads to higher populations, which pose threats in other habitats. Gulls are usually not attracted to these types of ponds.

Other Land Uses

It is not possible to list and discuss all possible land uses that are now or might possibly be planned for the area surrounding an airport. Thus, there may be other land-uses, not discussed above, that attract birds. Any proposed land use within the airport risk zones should be evaluated to determine if hazardous bird species would be attracted to it and appropriate mitigations defined if required.

5. Airport Bird Hazard Zone Development

Integrating the analyses of hazardous bird species, aircraft movements and aircraft flight paths (as described in Risk Elements I, II and III), enables the delineation of bird hazard zones around an airport.

5.1. Airport Bird Hazard Zone Definitions

Airport Bird Hazard Zones are divided into four categories; Primary Bird Hazard Zone, Secondary Bird Hazard Zone, Category B Event Zone and Special Bird Hazard Zone as defined below.

Primary Bird Hazard Zone

The area in which aircraft are at or below 1,500 feet AGL during critical phases of flight. These altitudes are also most populated by hazardous bird species, and where bird-aircraft collisions are most likely to result in a Category A event. For FAR 23 Recreational Aircraft and FAR 27 and 29 Helicopters, due to the lack of bird impact certification standards and their operating altitudes for airport traffic patterns, Category B event flight paths may need to be included in the Primary Bird Hazard Zone.

Secondary Bird Hazard Zone

A buffer zone beyond the Primary Bird Hazard Zone that accounts for variation in such factors as pilot technique, environmental conditions, Air Traffic Control and bird behaviour.

Category B Event Zone

This zone defines the area in which Category B events are most likely to occur. Generally, the Category B Event Zone is used at airports that host a complex range of aircraft, accommodating flight activity and paths that often run in directions that are not parallel to runways (such as those by FAR 23, 27 and 29 aircraft).

Special Bird Hazard Zone

Although land uses within the Primary, Secondary or Category B Event Bird Hazard Zones may attract and sustain hazardous wildlife, activities beyond these zones can also present hazards. Though often distant from airports, Special Bird Hazard Zones encompass specific land uses that, due to their geographic location, may regularly attract potentially hazardous species across other zones. For example, daily flights of gulls may transit through airport arrival and departure paths on their way from nesting sites to feed at a landfill even though neither location falls within either Primary or Secondary Bird Hazard Zones. In this case, the landfill would be designated a Special Bird Hazard Zone.

5.2. Airport Bird Hazard Zone Dimensions

Airport bird hazard zone dimensions and shapes are dependant on the flight paths for the critical phases of flight and the aircraft types that use, or will eventually be accommodated at, a particular airport. The critical phases of flight are those below 1,500 ft. AGL: takeoff, initial climb, approach, landing and missed approach.

Based on the FAR certification standard for the aircraft types, and using the accepted industry standard (normal arrival, departure and maneuvering, lateral and vertical flight paths), predictable shapes with definable bird-hazard zone dimensions can be plotted.

The Primary, Secondary and Category B Event zone shapes are the same from airport to airport regardless of the aircraft FAR certification category; however, the dimensions of these zones varies depending on the aircraft FAR certification category. Special Bird Hazard Zones are site-specific: their location and shape are determined by individual land-use circumstances at each airport.

To facilitate plotting of the bird hazard zones, a dimension-labeling schema is necessary. The zone dimensions are labeled A through H (see Table 3 for a breakdown by FAR category).

The zone shapes with their respective dimension labels are shown as follows:

  • Primary Bird Hazard Zone Figure 1
  • Secondary Bird Hazard Zone Figure 2
  • Category B Event Zone Figure 3

The following principles were applied to develop the bird hazard zone shapes and dimensions:

  1. Departure Paths:
    • Compliance with obstacle clearance requirements for FAR 25 second segment climb; no turns are made below 400 ft. AGL;
    • Aircraft will fly runway heading with no wind drift correction;
    • Wind drift allowance will be made within the bird hazard zone dimensions; and
    • The termination point of the lateral departure path will be the lower of the following two points: where an aircraft reaches 1,500 ft. AGL, or where an aircraft commences a turn to join the airport traffic pattern.
  2. Airport Traffic Patterns:
    • Constructed using accepted industry standard lateral and vertical paths as described in the CARs and AIM.
  3. Arrival Paths:
    • The start point of the lateral arrival path will be the lower of the following two points: where an aircraft would intercept a 3º descent path to the runway at 1,500 ft. AGL, or where an aircraft commences a turn from the airport traffic pattern to the final approach course;
    • Allowance will be made to the bird hazard zone dimensions to compensate for wind drift, and turns from the airport traffic pattern or instrument approach procedure to the final approach course; and
    • Allowance will be made to the bird hazard zone dimensions to compensate for descent paths less than 3º due to shallower glidepaths, non-precision approaches and aircraft descent below the glidepath as a result of pilot technique.
  4. Missed Approach Paths:
    • The start point of the lateral missed approach path will be where the aircraft would commence a missed approach from 50 ft. AGL at the arrival end of the runway;
    • Aircraft will fly runway heading with no wind drift correction;
    • Wind drift allowance will be made to the bird hazard zone dimensions; and
    • The termination point of the lateral missed approach path will be the lower of the following point: where an aircraft reaches 1,500 ft. AGL, or where an aircraft commences a turn to join the airport traffic pattern.

Figure 1
(See Table 3 for a breakdown of measurements by FAR category.)

Primary Bird Hazard Zone

Primary Bird Hazard Zone

Figure 2
(See Table 3 for a breakdown of measurements by FAR category.)

Category B Event Zone

Category B Event Zone

Figure 3
(See Table 3 for a breakdown of measurements by FAR category.)

Figure 3

Table 3 – Bird Hazard Zone Dimensions

Table 3 – Bird Hazard Zone Dimensions

5.3. Land Use in Bird Hazard Zones

Using the analysis of the hazardous land-uses described in Risk Element III, the appropriateness of land-use within bird hazard zones can be determined. The appropriateness of land use within bird hazard zones is described below, and summarized in Table 4.

Primary Bird Hazard Zone Land-Uses

Land-use categorized as high, moderate or low risk is not appropriate in this zone without effective risk mitigation. High-risk land-use, in particular, must be aggressively managed to reduce safety risks to aircraft operations. Land-use judged to be of limited risk is acceptable.

Secondary Bird Hazard Zone Land-Uses

Land-use categorized as high and moderate risk is not appropriate in this zone without effective risk mitigation. Land-use judged to be of low or limited risk is acceptable.

Special Bird Hazard Zone Land-Uses

Land-use categorized as high risk is not appropriate in this zone, and must be actively and effectively mitigated. Land-use that is judged to be of moderate, low or limited risk is acceptable.

Table 4 – Appropriateness of Land-use Within Bird Hazard Zones

RISK LAND USE Land-use Appropriateness by Zone
    Primary5 &
Category B6
Secondary7 Special8
High Putrescible waste landfills No No No
Food waste hog farms No No No
Fish processing/packing plants No No No
Horse racetracks No No No
Wildlife refuges No No No
Waterfowl feeding stations No No No
Moderate Open or partially enclosed waste transfer stations No No Yes
Cattle paddocks No No Yes
Poultry factory farms No No Yes
Sewage lagoons No No Yes
Marinas/fishing boats/fish cleaning facilities No No Yes
Golf courses No No Yes
Municipal parks No No Yes
Picnic areas No No Yes
Low Dry waste landfills No Yes Yes
Enclosed waste transfer facility No Yes Yes
Wet/dry recycling facility No Yes Yes
Marshes, swamps &mudflats No Yes Yes
Stormwater management ponds No Yes Yes
Plowing/cultivating/haying No Yes Yes
Commercial shopping mall/plazas No Yes Yes
Fastfood restaurants No Yes Yes
Outdoor restaurants No Yes Yes
School yards No Yes Yes
Community &recreation centers No Yes Yes
Limited Vegetative compost facilities Yes Yes Yes
Natural habitats Yes Yes Yes
Inactive agricultural fields Yes Yes Yes
Inactive hay fields Yes Yes Yes
Rural ornamental &farm ponds Yes Yes Yes
Residential areas Yes Yes Yes

5 The risk of land-uses that are not appropriate within a Bird Hazard Zone can be reduced if purposeful mitigation is actively employed. The appropriateness and effectiveness of such mitigation must be regularly evaluated, and the mitigation modified when required.

6 Since FAR 23 Recreational Aircraft and helicopters are subject to no bird impact standards, operate at low levels and are flown by only one pilot, Category B events may often become Category A events that result in the loss of aircraft and crew. For this reason, the Category B event zone should be considered a primary bird hazard zone for the purposes of determining land-use appropriateness.

7 See footnote 5.

8 See footnote 5.

Appendix I

Figure 4 – Airport Bird Hazard Assessment Process Map

Figure 4 – Airport Bird Hazard Assessment Process Map

Table 5 – Summary of FAR 33 Turbine Engine Bird Strike Airworthiness Requirements

Mass of Ingested
Birds
Number of Ingested Birds Bird Impact Requirements
3-ounces Maximum of 16 birds in rapid succession Impacts may not cause more than 25% power or thrust loss, require engine to be shut down within 5 minutes, or result in a hazardous situation
1.5 pound Maximum of 8 birds in
rapid succession
Impacts may not cause more than 25% power or thrust loss, require engine to be shut down within 5 minutes, or result in a hazardous situation
4 pound 1 Engine is not to catch fire, burst, or lose the capability of being shut down

Table 6 – Summary of FAR Airframe Bird Strike Airworthiness Standards

Category of Aircraft Airframe Component Bird Impact Requirements
Transport Category Aircraft
(FAR 25)
Entire airplane Able to safely complete a flight after striking a 4 pound bird at design cruise speed (Vc)
Empennage Able to safely complete a flight after striking a 8 pound bird at design cruise speed (Vc)
Windshield Able to withstand impact of a 4 pound bird, without penetration, at design cruise speed (Vc)
Airspeed indicator system The pitot tubes must be far enough apart to avoid damage to both in a collision with a bird
Normal Category
(FAR 23) Commuter Aircraft (10 - 19 Seats)
Windshield Able to withstand impact of a 2 pound bird at maximum approach flap speed (Vfe)
Airspeed indicator system The pitot tubes must be far enough apart to avoid damage to both in a collision with a bird
Normal Category
(FAR 23) Normal, Utility and Acrobatic Aircraft
All components No requirements
Transport Category Rotorcraft
(FAR 29)
Windshield Able to continue safe flight and safe landing after impact by a 2.2 pound bird
Normal Category Rotorcraft
(FAR 27)
All components No requirements

Table 7– Aircraft Flight Crew &Passengers

Category of Aircraft Required Flight Crew Approximate Number of Passengers
Transport Category Aircraft
(FAR 25)
2 - 3 4 - 10 for business aircraft
20 – 500 + for airliners
Normal Category
(FAR 23) Commuter Aircraft
2 10 - 19
Normal Category
(FAR 23) Normal, Utility and Acrobatic Aircraft
1 1 - 9
Transport Category Rotorcraft
(FAR 29)
1 - 2 2 – 30 +
Normal Category Rotorcraft
(FAR 27)
1 1 - 6
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