- Standards Branch
- Aerodromes and Air Navigation
- Wildlife Control
- TP 13549
- Preface to the second edition
- How To Use this Book
- Chapter 1
- Chapter 2
- Chapter 3
- Chapter 4
- Chapter 5
- Chapter 6
- Chapter 7
- Chapter 8
- Chapter 9
- Chapter 10
- Chapter 11
- Chapter 12
- Chapter 13
- Chapter 14
- Chapter 15
- Production Team
- Colour Plates
- An impact-force equation
- Where the aircraft are taking the hits
- The high costs of wildlife-damage to aircraft
- Broader cost repercussions of wildlife strikes
- Legal liability
- Legal-liability case studies
Operating costs in the aviation industry are extremely high, competition is fierce, and in most cases profit margins are small. If resources are to be devoted to the reduction of aircraft damage caused by bird- and mammal-strikes, only a sound business case will ensure the allocation of those funds. This chapter takes the first step toward building that case by explaining the variables that affect the costs of wildlife strikes.
Acknowledging that legal liability is a crucial aspect of wildlife-strike costs—particularly in the event of a complete basic review of the concept of liability and how it applies to wildlife risk.
An impact-force equation
The cost of a wildlife strike is directly related to the part of the aircraft damaged and the magnitude of the damage, which is determined by the impact force created by the collision between the aircraft and bird or mammal.
A precise and configuration, as well as angle of impact. Expressed in an equation, impact force is proportional to bird mass and the square of impact speed (see Appendix 12.1 for additional information on impact force). Applying actual figures, a 4 lb bird that strikes an aircraft traveling at 250 kts will deliver an impact force of approximately 38,000 lbs. At an airspeed of 400 kts, the force increases to 100,000 lbs.
All forward-facing parts of aircraft are at risk of being struck by birds. Aircraft undersides and landing gear are also in danger of impact during takeoff and landing, when aircraft are at higher pitch angles. Close to 75 percent of reported bird strikes, where altitude was reported, occurred within 500 feet of the ground. Mammal strikes, with the exception of those involving bats, are limited to the takeoff and landing roll phases of flight. Transport Canada data show that, where phase of flight was reported, about 90 percent of wildlife strikes occurred during the takeoff and landing.
|Part Struck||% of Reported Strikes
(where part identified)
|All other parts||15|
Table 1.1- Part of the Aircraft Struck in Bird Strikes—Canada and U.S. (1991-1999) Note that the proportion of wildlife strikes involving engines has been gradually increasing over the past several years. This is likely due to the greater frontal areas of larger fan engines in increasing use on commercial jet airliners.
Where the aircraft are taking the hits
The most recent data from Canada and the U.S.—presented in Table 1.1—indicate that, on average, the aircraft parts struck most frequently were the nose, wing and engine.
The high costs of wildlife-damage to aircraft
A number of parameters must be considered when assessing the level of damage that might occur to a turbine engine:
- Size and weight of the bird
- Aircraft speed
- Engine type
- Diameter of the inlet
- Power setting of the engine
- Exact location of the strike on the aircraft
Let’s examine how wildlife strikes affect various aircraft components:
Most individual small birds struck by jet engines are destroyed by the blades of the first stage and pass through the interior of the engine without causing any significant damage. A single strike by a medium-sized bird, and multiple strikes of small birds, frequently result in some engine damage. Blades in the first fan stage may be bent or deformed. Several blades may break in the event of a more serious strike by single or multiple large birds. The broken blades can be ingested into the engine, damaging subsequent engine stages, and possibly leading to complete engine failure or destruction. In a few cases, this has led to an uncontained failure of the engine.
Engine parts, expelled through the engine cowl, can also cause damage to other parts of the aircraft’s systems or structure.
Two conclusions emerge from the increased use of large high-bypass ratio turbofan engines:
- The greater overall engine frontal area increases the chance of single or multiple strikes with flocking birds.
- With up to 80% of inducted air bypassing the gas-generating core of an engine, a portion of bird debris is often directed away from more vulnerable engine components.
In spite of design improvements, the net result is that these new engines suffer damage nearly as often as early generation models.
Today’s jet engines are finely balanced precision machines. Ingesting a bird, no matter how small, requires an inspection at the very least. Even minor damage to the firststage fan section can result in significant costs (USD$16,000 for a new blade in a CFM56 engine) to repair or replace the damaged fan blades. The cost to replace an engine often climbs to several million dollars. In this case, the aircraft will be out of service for a minimum of one day.
Piston, turboprop and turboshaft engines
These engines are generally less susceptible to serious damage from bird strikes. The inlet areas are substantially smaller than those of turbofan engines, and the
Uncontained engine damage to this Falcon 10 business jet resulted
from ingestion of ducks at Lunkin Airport, January 25, 1999.
propeller or rotor blades provide some protection by deflecting bird debris away from engine intakes. Normally, mammal strikes to these types of engines do not directly result in engine damage. Damaged propeller blades, however, can bring catastrophe. With an unbalanced load, the engine can be severely damaged and may separate from its mounts.
The results of windshield strikes range from small bloody smears to large-scale shattering. In a number of cases, when complete penetration has occurred, bird remains and windshield pieces have caused injuries and even death to crew members.
In piston-powered aircraft and helicopters, windshields are often made of a light plexiglass material that is not certified to withstand any significant impact from a bird strike. Even though these aircraft operate at lower speeds than jets, and impact forces of bird strikes are diminished, there have been numerous instances of shattered windshields and cockpit penetrations. Single-engine piston aircraft are somewhat less vulnerable to windshield strikes because of the protection provided by the engine and propeller. In the case of helicopters, the very large windshield area poses more of a risk. In addition, helicopters frequently spend a higher proportion of their total flight time at low altitudes where greater numbers of birds fly.
Windshield replacement costs can be as low as $2,000 for general-aviation aircraft, and as high as $100,000 for a large jet aircraft. Repair or replacement times can range from a few hours to several days, depending on the damage to the surrounding airframe structure.
Wing and tail structures
A strike to the leading edge of the wing or tail components can result in a dent or hole in the skin and possibly torn or crumpled metal. If the bird is sufficiently heavy or dense, and the aircraft speed high enough, the animal may penetrate far enough into the aircraft structure to damage the spar and control cables or hydraulic components. Many wing designs incorporate the use of lift augmentation devices, such as flaps or slats, on either the leading or trailing edge of the wing. These too can be damaged by a bird strike. Damage-repair costs can be negligible in the case of a small dent that requires dressing out, but staggering if significant damage occurs to critical structures or systems.
At first glance, aircraft landing gear appear to be very strong components capable of absorbing significant loads during landing. However, closer examination shows that the main landing gear used on today’s aircraft include a number of vulnerable components such as hydraulic lines, electrical cables, solenoids and micro-switches. Rarely does a bird strike lead to significant structural damage to the undercarriage. However, in the case of mammal strikes, particularly deer, undercarriage damage can be severe. Repair costs to undercarriages range from a few hundred dollars for the replacement of damaged hydraulic lines and micro switches to over $100,000 for structural damage to the main landing-gear components.
Piper PA-44 after impact with a Black Vulture at 2000 ft AGL and 140 knots
near Daytona Beach, Florida, in October 2000.
As described in Table 1.1, many other aircraft parts are damaged—with varying repair costs and times—as a result of bird and mammal strikes. These other components include radomes, landing lights and pitot tubes. Replacement costs for these parts can be thousands of dollars, and repair times range between several hours and several days.
One of the more sinister results of bird strikes is damage that is not immediately apparent or detected. There are documented cases in which aircraft engines struck by birds subsequently failed on later flights, despite basic visual inspections that detected no damage. Frequently, damage is not detected until the aircraft undergoes periodic inspection, and non-destructive testing is carried out on disassembled aircraft parts.
Broader cost repercussions of wildlife strikes
The total cost of a wildlife strike is the sum of the direct, indirect, ancillary, hull-loss fatality and legal liability costs.
The direct costs refer to those incurred in the repair or replacement of damaged parts, and include the actual cost of the parts, labour and the overhead cost associated with the labour.
Industry data on these direct repair costs are available, but limited analysis has been done to isolate wildlife-strike repair costs from other foreign object damage (FOD) costs. The under-reporting of wildlife strikes suggests that the amounts indicated in related repair-cost data will be low. Available data does indicate that repair costs resulting from wildlife strikes are significant. H. Lehmkuhl, of the insurance division of Lufthansa German Airlines, found that in the 10-year period from 1985 to 1994 the airline experienced 2,637 bird strikes, of which 807 (31%) caused damage. During the last five years of this period, the average direct cost of damaging strikes was 45,794 German Marks, or about $31,600. (Lufthansa is unique in compiling complete information on bird strikes involving its aircraft.) In the United States, the Federal Aviation Administration (FAA) reports an average direct cost for damaging strikes between 1991 and 1999 of approximately USD$90,000. These figures do not include any complete hull-loss accidents.
Wildlife strikes can also generate a vast number of indirect costs for aircraft operators. Indirect costs are influenced by the extent of damage to the aircraft, distance from the operator’s nearest repair base, size of the airline fleet and the operator’s type of business (passenger, cargo, charter). Indirect costs can include some or all of the following:
- Fuel used and dumped during precautionary and emergency landing procedures
- Transporting replacement parts and mechanics to the site
- Accommodation and meal costs for repair crews
- Accommodation, compensation and meals for stranded passengers and flight crews
- Replacement aircraft
- Replacement flight crews
- Missed connections and re-booking passengers on alternate flights, often with other carriers
- Delaying effects on highly integrated airline schedules, particularly for airlines employing major hub-and-spoke operations
- Replacement of damaged aircraft on subsequent scheduled flights until repairs have been made
- Downtime costs of damaged aircraft
- Contractual penalties for late delivery of freight
- Lost business opportunities for delayed passengers
- Loss of passenger confidence and goodwill
The indirect costs of bird and mammal strikes are not well documented. Some of the examples listed above are not tracked by airlines. Lufthansa’s H. Lehmkuhl concluded that in many—if not most—cases, the indirect costs associated with a damaging bird strike are greater than the direct costs. However, as an example of the magnitude of some of the above costs, current information shows that flight delay costs can run as high as USD$15,000 per hour. The cost to an airline of a passenger missing a longhaul transcontinental connecting flight can exceed $3,000. Data compiled by the FAA supports the contention that indirect costs exceed the direct costs when aircraft downtime is included. In fact, it is commonly accepted within the industry that indirect costs exceed direct costs by a factor of four.
Ancillary costs are incurred by the airport owner or operator, regulatory authorities, other airport users and emergency-response agencies that must deal with the results of bird or mammal strikes. Ancillary costs include:
- Runway closures
- Airport emergency response
- Off-airport emergency response by ambulances, fire fighters, police, hospital emergency-room standby
- Runway clean-up and repairs
- Flight arrival and departure delays
- Additional fuel used by aircraft during delays
- Airport wildlife-management programs
- Off-airport search and rescue service
- Accident investigations and safety reviews
- Liability insurance
- Administration of regulatory agencies involved with bird and wildlife hazards
Ancillary costs are rarely considered in the analysis of wildlife strikes, although some estimates are available. Costs associated with flight delays have been estimated at between USD$6,000 and USD$15,000 per hour. The cost of major accident investigations such as those for TWA B747 off Long Island, New York, and the Swissair MD-11 off the coast of Nova Scotia, Canada, can exceed several million dollars.
Hull-loss and fatalities costs
Although military aircraft have not been so fortunate (see Chapter 13), there are no known recent aircraft hull-loss accidents involving large civilian passenger jets caused by wildlife strikes. Numerous close calls, however, support the concern that a catastrophic bird-strike accident may happen in the near future. The costs associated with such an accident would be astronomical. New-aircraft costs are steadily rising. In 1996, there were over 1,000 aircraft in operation or on order, valued at over USD$100 million each. A new Boeing 747-400 is valued at more than USD$250 million. Recent passengerliability awards in the U.S. approach $2.5 million per passenger death—amounts that are not likely to decline. Applying these figures, the cost of a bird-strike accident resulting in the loss of a new B747 or similar large aircraft carrying 300-400 passengers could easily exceed USD$1 billion—costs directly associated with an accident and the resulting legal liabilities. As noted earlier, indirect and ancillary costs can also be significant. Even a fatal accident involving an older model narrow-body passenger jet such as a B737-200 or a DC-9 could easily incur costs approaching USD$100 million.
The total annual cost of bird and mammal strikes
At this time, it is not possible to accurately determine the annual cost in any major jurisdiction of bird and mammal strikes to the aviation industry. The required data are either not available or have not been assembled. Several attempts have been made to determine costs in various jurisdictions, but each attempt has shortcomings due to a lack of critical data.
Most available damage-cost information relates to airline and other multi-engine, turbine-powered, commercially operated aircraft. There is little information about damage costs for helicopters and even less concerning damage costs for generalaviation aircraft, which comprise approximately 339,000 privately registered aircraft worldwide. Available estimates of the annual damage costs from wildlife strikes are also dramatically skewed by major hull-loss accidents, which can greatly inflate damage-cost statistics for a given year. Properly documented multi-year data is needed if the industry hopes to determine true long-term average costs.
In spite of limitations, available data still provide sufficient proof that wildlife-strike costs are a significant portion of an airline’s annual aircraft-operating costs. Anecdotal reports provided by executives from a failed North American start-up airline indicate that the cost associated with bird-strike damage to their fleet was a contributing cause of their failure. Recent information supplied by airline executives indicates that 40 percent of United Airlines’ annual costs from FOD were incurred as a result of bird strikes. Robinson (1996) reported that one U.K. airline estimated that birds accounted for about 20 percent of FOD costs. If we estimate 30 percent across the industry as a whole, then the total cost is between USD$64 million and USD $107 million, based on estimated aviation-industry FOD costs of approximately USD$320 million per year.
Again, these are only direct costs. Aviation wildlife-management experts believe that if all other costs associated with wildlife damage are included, then a conservative estimate of the annual cost to the North American aviation industry exceeds $500 million.
In the past, bird strikes were often considered to be acts of God. As a result, in accidents involving bird strikes, no one could be held responsible. Thanks to the work of many natural-science professionals, the idea that wildlife cannot be managed is gradually being recognized as a myth. The behaviour patterns of some bird and mammal species adjacent to airports are reasonably predictable. These patterns can often be changed through appropriate management interventions based on the results of comprehensive wildlife studies. By declining to introduce measures to reduce the numbers of hazardous birds and mammals at and near airports, the responsible organizations and individuals expose themselves to potential liability. This is demonstrated in a brief overview of the concept of liability and the applicable Canadian legislation presented below.
Negligence and liability
The basic principle of liability depends on the proof of negligence. Parties are considered negligent when they act without due care, or when they fail to act, and a person, or persons, whom they ought to have considered, either is affected by their actions or their failure to act. Should a plaintiff prove that a defendant was negligent in their duties, then that defendant will be liable for damages incurred.
Liability has both criminal and civil classifications. The penalties for criminal liability include fines and incarceration. Civil liability penalties in Canada are limited to a requirement to make restitution for the damages incurred. However, in some jurisdictions—particularly the U.S.—civil liability also involves the levying of substantial punitive damages. As discussed earlier, damage costs in the event of a major hull loss assessed against one or more parties could exceed USD$1 billion should negligence be proven.
It’s important to understand that the concepts of negligence and liability apply to all persons and business entities associated with aircraft operations including—but not limited to—airport operators, ATS providers, pilots, airport employees and airport wildlife-management contractors. Even non-aviation related industries can be affected; waste disposal contractors are an example.
In Canada, safe aircraft operation is governed under law by duties and responsibilities— summarized below—imposed on owners, operators and users of aircraft and airports.
Duties and responsibilities in Common Law
Common law relies on precedent, and centres on two key phrases: duty of care and duty to warn. The principles applied to determine whether duties and responsibilities have been adequately discharged are reasonableness and due diligence. A full explanation of these terms would occupy many pages, but the basic concepts are fairly simple. With respect to cases stemming from wildlife-strike incidents, reasonable care must be applied to ensure that an aircraft is operated safely; those responsible must be diligent in availing themselves of up-to-date information and technology that provides adequate warning of any hazards.
For airport operators, this means minimizing the risk of wildlife strikes to aircraft by instituting and maintaining a wildlife-management program and making flight crews aware of unmanaged wildlife risk. Similarly, ATS providers are also responsible both for warning pilots of wildlife hazards at an airport and communicating wildlife activities to airport wildlife-management personnel. Pilots are responsible for adjusting flight operations to avoid known hazards, and for advising airport operators of dangerous situations. Everyone associated with aircraft operation must show due diligence when conducting respective tasks.
Duties and responsibilities agreed and/or imposed by contracts
Contracts impose duties and responsibilities on all signatories—duties and responsibilities that can extend beyond the contracting parties. For instance, contractors providing wildlife-management services to an airport operator may also find themselves responsible for damage that occurs to aircraft operating at the airport. Airport operators are responsible for monitoring the effectiveness of the airport wildlife-management program, and must ensure that contractors meet their obligations.
Particular care must also be taken when defining contracts between airport operators and tenants. Failure to control tenant actions that create hazards may lead to liability for the airport operator should an accident occur.
Duties and responsibilities imposed by Occupiers Liability Legislation
Airports in Canada are similar to all property in that they are governed by individual provincial or territorial legislation. The Ontario Statute, The Occupiers’ Liability Act (R.S.O. 1990, c.322), is quoted below and provides an example of the principles embodied in the act.
- 3. (1) an occupier of premises owes a duty to take such care as in all the circumstances of the case is reasonable to see that persons entering on the premises, and the property brought on the premises by those persons are reasonably safe while on the premises.
- (2) The duty of care provided for in subsection (1) applies whether the danger is caused by the condition of the premises or by an activity carried on the premises.
Note also that there is a clause in this legislation that states “where an occupier has duties imposed by the legislation, they may not be restricted.” This means a contract cannot contain disclaimer language that avoids obligations imposed by the legislation.
In applying this Act, the terms airport owner, operator and user are referred to in the legislation as occupiers, invitees and licensees. In the simplest terms, an airport operator is an occupier and the airline is an invitee. The fact that the airport operator collects landing fees from the airline—and has invited the airline to use the site—imposes a significant responsibility on the airport operator to manage a safe facility.
Legal-liability case studies
These case-law examples may help illustrate the concepts of civil and criminal liability as they apply to wildlife strikes:
Falcon 20 — Norwich, England 1973 On December 12, 1973, a Falcon 20 business jet with nine people on board struck Common and Black-headed Gulls just after takeoff from Norwich airport. The strike caused severe damage to both engines. One minor injury resulted from the crash, which destroyed the aircraft. The judge presiding over the case wrote that the Defendants (the airport operator) owed the Plaintiffs (the aircraft operator and occupants) the common duty of care—a duty to take such care when carrying on their activities at the airport as was reasonable in the circumstances. After weighing the considerable evidence, the Judge decided that the Defendants failed in their duty, and that there must be judgement for the Plaintiffs for damages. In other words, the airport operator failed to show due diligence in managing the airport’s bird hazards.
Sabreliner — Watertown, USA 1975 On June 14, 1975, a NA265 Sabreliner twin-engine jet ingested gulls in both engines at rotation from the Watertown airport. The aircraft crashed. Both wings were torn off and a severe fire ensued. Three of the six people on board were injured and the aircraft was destroyed. The Safeco Insurance Company brought an action against the airport operator, the City of Watertown. The court maintained that the proximate cause of the crash was the failure to warn the pilot of the presence of birds. Judgement for the full value of the destroyed aircraft was entered against the airport operator.
Concorde — New York, USA 1995 An Air France Concorde struck Canada Geese while landing at John F. Kennedy International Airport on June 3, 1995. Two of the four engines on the supersonic jet caught fire and were destroyed. Air France sued the airport operator (Port Authority of NY & NJ) for the USD$6-million cost of the two engines. After significant legal costs for both sides, the parties settled on the eve of the trial for a reported USD$5.3 million. There is anecdotal information indicating that in spite of a sound wildlife-management program, the airport failed to warn the flight crew of known Canada Goose activity.
Falcon 20 — Paris, France 1995 In the fall of 1998, French authorities laid charges of involuntary manslaughter against the Paris Airport Authority and three former officers for their roles in an accident at Le Bourget airport. The charges related to the crash of a Dassault Falcon 20 business jet that struck Lapwings during takeoff from the airport on January 20, 1995. The pilot was unable to control the aircraft after the ingested birds destroyed the left engine. The aircraft crashed, killing all 10 people on board. A subsequent inquiry found that staff failed to perform routine bird-scaring operations prior to the accident. The airport authority was accused of “negligently failing to follow normal security procedures.” The disposition of the case is not known at this time.
In this chapter, we have attempted to build the business case that will support resource allocation and reduce the likelihood of wildlife strikes to aircraft. For the aviation industry, two key messages are clear:
- Damage associated with wildlife strikes costs millions of dollars each year.
- Courts in several jurisdictions have indicated that failure to exercise due diligence in managing wildlife hazards will result in both civil and criminal liability judgments. (Note that a number of other cases have resulted in settlements protected by non-disclosure agreements. To the best of our knowledge, no settlement or judgment has been made in favour of the defendant.)