When it comes to birdstrikes, we don’t need to rely on miracles

Posted: 31 March 2009 | Dr John Allan, Chairman, International Bird Strike Committee | No comments yet

Following the recent events in New York, Dr John Allan, Chairman of the International Bird Strike Committee, looks at the current risk from birdstrikes and what can be done to control it.

Following the recent events in New York, Dr John Allan, Chairman of the International Bird Strike Committee, looks at the current risk from birdstrikes and what can be done to control it.

The newspapers christened the recent accident in New York the ‘Miracle on the Hudson’ when Captain Chesley Sullenberger skilfully piloted his Airbus A320 onto the river without loss of life. Ingestion of Canada Geese into both engines is thought to be the cause of the near catastrophe, but this and other high-profile events, such as the incident in Rome in November 2008 when a Ryanair B737 suffered a collapsed undercarriage after hitting a flock of Starlings on landing, are only the tip of a birdstrike iceberg that involves thousands of airport staff, in a constant battle to keep aircraft safe.

Birdstrikes have been a problem to aviation since the first flights 100 years ago. The first fatality following a birdstrike happened in 1912, when a Wright Flyer crashed into the sea off California after a gull became entangled in the control wires. From those small beginnings, the growth of aviation has been paralleled by a growth in birdstrike frequency. The crash of a Lockheed Electra at Boston Logan Airport after hitting Starlings in 1960 remains the worst aviation disaster caused by birds. Sixty-two people lost their lives in that incident and it resulted in a greatly increased awareness of birds as an aviation hazard.

It was with the advent of jet-powered passenger aircraft that birdstrikes became acknowledged as a real safety issue. The fan blades of jet engines are not as robust as propellers, and increasing pressure for engines to be quieter and more fuel-efficient has presented real design challenges to manufacturers, who need to balance performance with birdstrike resistance. This has led to the development of ever-wider jet fans, capable of swallowing several birds at once, combined with the trend towards twin-engined aircraft, which have a greater chance of ingesting birds into both engines simultaneously.

In order to ensure that engines have adequate birdstrike resistance, regulators require that they pass a bird ingestion test before being allowed into service. The final test for a new engine involves a full engine assemblage ingesting a given number of birds of a particular weight and retaining a specified level of thrust for a given time. These tests, like the design effort that goes into the engines, are inevitably a compromise between what is desirable (complete birdstrike resistance) and what is achievable. For example the Canada Geese that brought down flight 1549 in New York weigh around 3.5kg (7.8 lbs). The engines on the A320 are tested to withstand the ingestion of a 4lb bird and to retain the ability to be shut down safely, not catch fire and not to lose components outside the engine structure.

There is no current engine test that involves a bird as large as a Canada Goose, despite the fact that their population in North America numbers several millions, and there is no requirement for the engines on the vast majority of aircraft flying today to keep producing thrust after ingesting a bird only half that size. Whilst this may seem initially alarming, it is worth noting that Canada Geese are struck every year in North America and in the vast majority of cases engines continue to operate sufficiently well to achieve a safe landing.

It is clear that there is a limit to what engineering can achieve in terms of birdstrike resistance and pilots of larger aircraft using commercial airports are heavily restricted in where and when they fly. Designed tolerance of birdstrikes can only take us so far. Prevention of strikes, especially with the most hazardous species, is the second front of the battle.

Many bird species have to resolve the same problems as aircraft engine designers – to do what they need to do (i.e. fly to find food, find a mate, build a nest etc.) whilst expending the minimum amount of energy. Birds that cannot utilise air currents to glide or soar rely on flapping flight, and need to minimise their energy usage by spending the majority of their time on the ground or perched in trees or other structures. Other than when on migration, when birds may fly at great heights, the vast majority of birds are found close to the ground, most at no more than 3000 feet and that is where the majority of birdstrikes occur. Because most commercial aircraft only descend below 3000 feet when landing or taking off, between 80 and 95% of all birdstrikes happen on or close to aerodromes. The responsibility for birdstrike prevention therefore lies mostly with the airport and, to a lesser extent, its neighbours in terms of keeping the local area as unattractive as possible to birds.

Aerodromes, both civil; and military, have been carrying out bird control for many years and in a lot of cases the techniques used have not changed greatly from those used by our ancestors when they developed agriculture and discovered that birds ate their crops. Simply standing on an airfield and slowly waving your arms up and down still works, and is taught to airport bird controllers as a technique that can be used against some species. Modern bird control is, however, a little more sophisticated.

The two keys to effective bird management on airports are to remove the features that attract birds in the first place, and to select the correct control technique to disperse those that remain. Removing or managing bird attractions should involve about 70% of an airport’s effort, as is achieves permanent reductions in bird numbers. In reality most airports do not put enough effort and resources into habitat management and instead condemn their bird controllers to a routine of chasing away birds that will inevitably come back as soon as their backs are turned, because the airport offers them valuable resources such as food, nesting sites etc.

This emphasis on controlling the problem, rather than its cause, has been reflected in the way that the industry has developed new techniques in recent years. Private companies have seen that there is a market for bird control devices and have invested in developing new approaches such as the use of lasers, bird scaring dogs trained to work on airports, bird repellent chemicals, and radar bird detection. There has been little new work on the management of airport habitat since the development of grass management techniques to deter birds in the 1970s. There is clearly a need for co-ordinated research, funded by governments or aviation regulators, into how to make airports fundamentally less attractive to hazardous birds. The development of alternative types of vegetation between runways and taxiways needs to be considered. Grass has the advantage of being load bearing and relatively cheap to maintain, but could other plant species that are easy to manage and also unattractive to birds be used? Artificial surfaces could also be evaluated. Some load bearing artificial turf suitable for airports is already available, but it would be costly to install and maintain across a whole airfield. Once new techniques are identified they need to be implemented, and this is likely to require regulation, inspection and enforcement by national authorities.

The standard of bird control, both in terms of habitat management and bird deterrence, varies hugely from airport to airport. In part, this is because the numbers and species of birds around each airport are different and the techniques needed to disperse the birds, as well as the level of effort required to deter them effectively, will vary. Nevertheless, there are some basic levels of bird control provision that should be present on all commercial airports, and the International Bird Strike Committee, the professional body for specialists in birdstrike prevention, has developed a set of best practice standards that should, in the opinion of its members, be implemented at all airports that carry regular scheduled passenger flights. These details can be found at, along with a wide variety of other information on the birdstrike issue.

Even the most effective airport managers can be thwarted in their efforts to manage the birdstrike risk, by activities outside the perimeter fence. Inappropriate location of airports in the past has left a number of legacy issues, where airports battle with birds that breed, feed or roost on nature reserves, swamps, estuaries or other sites that they find highly attractive, but which seemed like a good place to put an airport 50 or so years ago. Other problems have arisen as a result of airports being seen as good places to put unattractive developments such as landfills. ‘Put it down by the airport, nobody will mind if it’s there’ seems to have been the philosophy for a lot of urban planning in years gone by.

These days, things are rather more sophisticated, but airport managers still suffer from legacy issues such as these, as well as pressure to ‘green’ the environment around airports. As planners become ever more aware of the need for environmental protection, the requirement for any new development to compensate for any natural habitat that it destroys presents real problems for airports. Problems such as these can very frequently be resolved if consultations take place at an early stage and the developer, the local authority and the airport can agree a way forward that meets everyone’s requirements. Often a modest re-design of proposals, to remove the features that attract hazardous birds, leaving those that benefit small birds, plants and other wildlife, is all that is required. However, if this only comes to light after plans have been finalised, and expensive designs have been paid for, everyone becomes reluctant to compromise and expensive legal wrangles often follow.

The problems with planning control around airports are, in part, self-inflicted. The aviation industry has, for many years, played down the threat from birdstrikes on the basis that they ‘don’t want to frighten the passengers.’ It is not surprising, therefore, that planning regulators outside the aviation industry are sometimes ignorant of the threat that birds pose.

Accidents are mercifully rare, with 104 civil aircraft of all types lost in the history of aviation, an average of about one per year. But the cost of less serious birdstrikes is huge, an estimated US$ 1.5 billion per year in damage and delays to the world fleet. This could only be the tip of a much bigger iceberg, as it is estimated that four in every five birdstrikes go unreported. If the industry as a whole, and airports with particular problems with birds, were more open about the issues, it may prove easier to manage bird attractions in the vicinity of airports, as well as prevent new ones being developed, if the public understood the issues and the potential consequences.

However diligent we are in controlling birdstrike risks, the problem will not go away. Bird populations constantly change in response to changing environmental conditions and improved conservation efforts, whilst the long-term impact of climate change on the birdstrike risk has not yet really been thought about. There will always be new challenges to respond to, and birdstrikes will remain a hazard to aviation until the day that engineers manage to achieve the ‘bird proof plane.’ What is needed, if we are to continue to drive down the birdstrike risk, is a proactive and coordinated approach that will require involvement from regulators, openness about the true nature of the problem and a willingness to invest in the development of new techniques.

The evidence shows that we can control the birdstrike risk to what is, for the most part, an acceptable level, but when things go wrong we should not rely on Capt. Sullenberger being at the controls next time. The consequences of flight 1549 coming down on Manhattan could have been catastrophic. The industry needs to move forward on what is a serious safety issue and not trust to another ‘Miracle.’

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