Beware of Birds - Bill Read looks at the dangers and consequences of birdstrikes and the steps that airports and airside safety providers are taking to reduce the risk

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At 9.15 am on 29 April 2007, a Thomson Fly Boeing 757-200 with 221 passengers on board took off from Manchester airport on a flight to Arrecife, Lanzarote. Seconds after the aircraft had left the ground, two birds were sucked into the aircraft's right engine causing a flameout and black smoke to issue from the Rolls-Royce RB211-535E4 power plant. The pilot continued the takeoff on one engine and declared an emergency. After dumping excess fuel, the pilot returned to the airport and was able to make an emergency landing using one engine at 10.30.

The incident was not an isolated one. Statistics published by the UK's Civil Aviation Authority (CAA) reported a total of 1,299 birdstrikes in UK airspace during 2007. In the USA, figures from the US Federal Aviation Administration (FAA) and Department of Agriculture reported a total of over 56,000 birdstrikes at 1,300 US airports between 1990-2004. However, the FAA estimates that the actual figure may be five times higher, as up to 80% of strikes go unreported.

According to the FAA, only 15% of strikes result in damage to the aircraft. However, when they do, the consequences can be severe. A birdstrike, also known as a BASH (bird aircraft strike hazard), poses a danger to aircraft in two ways. Firstly, there is the problem of kinetic energy. Because aircraft travel at such high speeds, a collision with a bird can cause significant damage to the airframe (kinetic energy being defined by the equation Ek = 0.5mass X velocity2). For example, the impact of a 5kg bird at 150mph has been estimated to be equivalent to a 1/2 ton weight dropped from a height of 10 feet. Birdstrikes have caused serious damage to forward-facing edges such as a wings, nose cones, engine cowlings or inlets and cockpit windows. However, worse problems occur when birds fly into jet engines. Since jet engines operate at a very high rotation and speed, a bird hitting a fan blade can cause it to be displaced into another blade causing a cascading failure and the engine to cease working.

In theory, a large commercial aircraft should be able to continue flying on a damaged engine or by using the remaining engine. Certification tests for large commercial aircraft power plants include a test in which a 4lb bird carcass, or high density gelatin block, is fired into an engine from a gas cannon. The engine does not have to survive the ingestion, just be safely shut down. Modern jet aircraft structures, including cockpit windows, must be able to withstand collision from a 41b bird while the tail must withstand a 8lb bird collision.

However, many larger birds weigh over 4lbs while many birds fly in flocks which can be ingested into more than one engine. The Thomson Fly Boeing 757 mentioned above was lucky in that it was able to continue its takeoff and then land using its remaining undamaged engine. Not all aircraft have been so fortunate. In October 1960, an Eastern Air Lines Lockheed L-188 Electra crashed into Boston harbour with the loss of 62 lives after the aircraft flew into a flock of starlings after takeoff which damaged all four engines. While rare, fatal accidents resulting from bird strikes have accounted for the loss of 400 lives and the destruction of 420 aircraft worldwide.

Birdstrike damage to the windshield of an Israeli Air Force UH-60 helicopter.

Military aircraft are particularly vulnerable to birdstrikes. In July 1996 a Belgian Air Force C-130 about to land at Eindhoven in The Netherlands struck a flock of birds and crashed short of the runway killing all four crew members and 30 out of 37 passengers. Also in 2006 a USAF T-38 trainer was lost after hitting ducks while the US Navy T-45 jet trainer went down in October 2007 after a collision with a bird. Birdstrikes have also been responsible for the loss of two E-3 AWACS, a US Air Force B1-B bomber and an RAF Nimrod.

The problem is not confirmed to birds in the air. Many aircraft have been damaged or have crashed as a result of colliding with birds and other wildlife while still on the ground. Indian airports have reported an increasing threat from animals that stray onto the runways, as their natural habitats decrease. These have included leopards, antelopes, deer, cheetals and wild boars. In the early months of 2008, a Kingfisher ATR 72-500 hit a dog during take-off at Bangalore, an Indigo aircraft hit a deer at Nagpur and an Air India regional flight hit a nilgai while landing at Chakeri airport. There was also an incident in June 2006 where a plague of hares caused Milan city airport to be closed.

Even if a birdstrike only causes minor damage to an aircraft, it can result in significant costs to an airline as the aircraft has to be taken out of revenue service to be repaired. Furthermore, minor damage to airliners not always covered by aircraft hull or engine insurance. The UK Central Science Laboratory estimates that bird strikes cost airlines worldwide around $1.2 billion a year in repairs and aircraft downtime. There are also the costs of delays to passengers caused by aborted take offs and emergency landings.

Amateur video image of flames coming from the engine of Thomsonfly Boeing 757after it suffered a birdstrike.

Regulatory recommendations

The most common place for birdstrikes to occur are at airports when aircraft are close to the ground, either descending, approaching or climbing. US civil aircraft statistics show that around 41% of reported strikes occur while an aircraft is on the ground during takeoff or landing and 75% of strikes at less than 500 feet above ground level. This is also the time when aircraft are at their most vulnerable as they have limited room to recover in case of an emergency.

Aware of the problem, the International Civil Aviation Organization (ICAO) has published a set of standards and recommended practices (SARPs) that address the risks of birdstrikes in the vicinity of airports which has been promulgated in the UK in the CAA CAP 772 Birdstrike Risk Management for Aerodromes.

Although not binding, the ICAO standards recommend that member countries should establishment a national procedure for aircraft operators and airport personnel to record and report bird strikes to aircraft and that an appropriate authority should take action to decrease the number of birds constituting a potential hazard to aircraft operations in the vicinity of an aerodrome. The 'vicinity' can refer to areas within 13km of an airfield.

Airport operators are encouraged to develop a bird control management plan (BCMP) to assess their birdstrike risk and to define and implement appropriate control measures. A BCMP should include details of roles and responsibilities of airport management and bird control personnel, together with policies and procedures for risk identification and assessment. The plan should also record results of birdstrike risk assessments and specify risk mitigation measures that are in place.

The International Bird Strike Committee (IBSC) has also published a set of bird and wildlife control best practice standards for airports carrying regular scheduled commercial air traffic. These recommend that airports should review areas on their property which might attract birds and develop a management plan to reduce its quantity. It also suggests that airports appoint a manager to be responsible for bird control and that a trained and equipped bird controller should be on hand during all daylight hours or, at less busy airports, at least 15 minutes prior to any aircraft takeoff or landing. Bird control staff should be equipped with appropriate bird deterrent devices and have proper training in their use. They should also keep records of areas of the airport patrolled, numbers, location and species of birds/wildlife seen, action taken to disperse the birds/wildlife and the results of the action.

Habitat management

There are three main techniques used to discourage birds from the vicinity of airports:

  1. making the environment unattractive for birds (habitat management)
  2. scaring them away (bird control) or
  3. killing them.

The third solution is only used as a final resort, as endangered bird species are protected under law and culling one type of bird will only result in another taking its place.

Habitat management consists of identifying and removing vegetation and other potential food sources attractive to birds, together with objects which could serve as roosts. This work might include cutting down trees and bushes, trimming hedges, emptying skips, sealing empty buildings, removing derelict aircraft, covering watercourses, draining ponds and cutting grass to a particular length (birds like both very long and very short grass). Unfortunately, removing such features can also result in making the surrounding landscape less attractive from an environmental conservation point of view.

Another problem faced by for airport authorities is that that aircraft can be threatened by birds attracted to areas outside the airport perimeter ' for example, lakes, woods, public parks farmland, sewage source or landfill site, or even to people feeding pigeons or waterfowl or planespotters with sandwiches. It is often difficult to control such areas, but the CAA encourage UK airport authorities to develop working relationships with local landowners and encouraging them to adopt measures to reduce the attractiveness of the site to birds or to mitigate the risk, especially in the immediate approach and departure areas. Airport operators are also expected work in consultation with local planning authorities to prevent developments which might increase bird numbers. In some cases it may be impossible to resolve the conflicting interests of flight safety and conservation, but airport which try to do so will be in a better position to show due diligence in the event of an future accident or legal claim.

Bird scaring for beginners

Airports use a variety of bird control methods. Manchester Airport uses many techniques including falcons, as does JFK in New York and Oporto in Portugal. Beijing Airport sounds gongs while Nairobi airport in Kenya uses slingshots. One of the most effective methods is the use of bio-acoustic systems which broadcast recorded bird distress calls. 'Birds react to signals from other birds that indicate danger, distress or death,' explains Tom Diamond, group commercial manager of UK-based Scarecrow Bio-Acoustic Systems. 'Distress calls are only ever emitted by birds when they are being attacked by a predator. Broadcasting distress calls extracts an inherent physical response. These are most efficient if the distress call is appropriate to the bird species. Operators therefore need a good working knowledge of ornithology to identity what type of birds they are dealing with.'

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