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Strategies for Prevention of Bird-Strike Events
Strategies for Prevention of Bird-Strike Events

Bird-strike events are relatively common, occur most often on the ground or at low altitude, and are usually benign. However, bird strikes can have significant economic and occasional safety consequences for flight operations. Pilots and operators should be knowledgeable about the hazard, and flight crews should use facts, data, and standard operating procedures to reduce the potential for and consequences of a bird strike.

Flight crews can reduce the possibility and effects of a bird strike by increased awareness and by following recommended procedures.
Bird strikes are a lesser hazard to aviation than other well-known hazards such as loss of control in flight, controlled flight into terrain, and runway excursions, but they can and do present risk that needs to be addressed. The first bird strike was recorded by the Wright brothers in 1905, and the aviation wildlife hazard has been a risk to aviation ever since. The January 15, 2009, ditching of US Airways flight 1549 on the Hudson River in Weehawken, New Jersey, was the dramatic result of dual engine thrust loss arising from an airborne encounter with a flock of Canada geese. Although Boeing airplanes meet and exceed the government regulations for bird strikes, accidents and serious incidents can occur. Aviation wildlife hazards encompass birds on the ground and in flight, terrestrial animals (e.g., deer, coyotes, cattle, camels), and even airborne animals such as fruit bats; however, this article focuses on bird strikes in particular. Operators and flight crews should be aware of the risk of bird strikes, prevention strategies, and actions to take following a bird strike.
This article discusses the characteristics of bird strikes, presents practical information for flight crews, highlights the importance of reporting bird strikes, and provides resources for additional bird-strike information.
Characteristics of bird strikes
According to Bird Strike Committee USA, an organization that was formed in 1991 to facilitate the exchange of information and promote the collection and analysis of accurate wildlife strike data, bird and other wildlife strikes cause more than $650 million in damage to U.S. civil and military aviation annually. In addition, bird strikes put the lives of crew members and passengers at risk — more than 200 people have been killed worldwide as a result of wildlife strikes since 1988. The Bird Strike Committee takes a similar data-driven approach to the bird strike issue that organizations such as the Commercial Aviation Safety Team (CAST) takes to reduce commercial aviation fatality risk. (See www.cast-safety.org.)
Experts within the U.S. Federal Aviation Administration (FAA), the U.S. Department of Agriculture, and the U.S. Navy and U.S. Air Force expect the risk, frequency, and potential severity of wildlife-aircraft collisions to grow over the next decade, based on increasing air traffic, bird populations, and the trend to twin-engine aircraft. (Download PDF.)
While bird strikes usually inflict most damage on the engines, all areas of an airplane can be damaged (see figs. 1 and 2). Airplane damage and effect on flight from bird strikes are closely correlated to kinetic energy, derived from the mass (determined by bird species) and the square of the speed of the collision. (A 20 percent increase in speed raises the kinetic energy by 44 percent.)
Figure 1: Example of bird-strike damage
Bird-strike damage can be quite severe and can shut down jet engines.
Figure 1

Figure 2: Locations of bird-strike damage
Three-quarters of bird strikes involve the wing or engines, but they can damage almost any part of an airplane.

Figure 2

Single or multiple large birds, relatively small numbers of medium-size birds, and large flocks of relatively small birds are all problematic and have resulted in accidents. In the United States, a list of birds most hazardous to flight has been identified: large flocking waterfowl (Canada goose); gulls; pigeons and doves; blackbirds, starlings, and sparrows; and raptors (hawks and kestrels). Most bird strikes occur on or near the ground, highlighting the need for wildlife management on airport grounds and in the vicinity. (Download PDF.)
The aviation bird-strike hazard is a global and industrywide issue affecting all aviation stakeholders, including pilots, mechanics, airlines, airport operators, air traffic controllers, wildlife personnel, aviation safety analysts, airplane and engine manufacturers, flight training organizations, and the traveling public. Boeing participates in national and international groups dedicated to exploring and addressing the problem of bird strikes, and Boeing airplanes meet and exceed regulatory bird-strike requirements. Boeing has many design features, including system separation, system redundancy, and structural attributes, to protect against bird strikes beyond the four-pound regulatory general bird-strike FAA requirement (eight pounds for empennage).
Common misconceptions about bird strikes
A number of widespread misconceptions about bird strikes may give pilots a false sense of security and prevent them from reacting appropriately to the threat of a bird strike or an actual event. These misconceptions include:
  • Birds don’t fly at night.
  • Birds don’t fly in poor visibility, such as in clouds, fog, rain, or snow.
  • Birds can detect airplane landing lights and weather radar and avoid the airplane.
  • Airplane colors and jet engine spinner markings help to repel birds.
  • Birds seek to avoid airplanes because of aerodynamic and engine noise.
  • Birds dive to avoid an approaching airplane.
In fact, none of these statements is scientifically proven.

Preventive Strategies
Airports are responsible for bird control and should provide adequate wildlife control measures. If large birds or flocks of birds are reported or observed near the runway, the flight crew should consider:
  • Delaying the takeoff or landing when fuel permits. Advise the tower and wait for airport action before continuing.
  • Take off or land on another runway that is free of bird activity, if available.
To prevent or reduce the consequences of a bird strike, the flight crew should:
  • Discuss bird strikes during takeoff and approach briefings when operating at airports with known or suspected bird activity.
  • Be extremely vigilant if birds are reported on final approach. If birds are expected on final approach, plan additional landing distance to account for the possibility of no thrust reverser use if a bird strike occurs.
Additional Resources
Additional information is available online through a number of industry groups. Information includes significant strike events, key issues to reduce strikes, risk assessment, system information, papers and newsletters, and discussion forums.
The importance of reporting bird strikes
Flight crews and maintenance and line personnel are encouraged to report all bird strikes because data are essential to quantify and manage the hazard. Reporting bird strikes enables aviation authorities to monitor the risk to aviation and the effectiveness of wildlife hazard mitigation measures. Bird-strike data, together with knowledge of the operational environment, are utilized by Boeing as a basis of many airplane design features beyond regulatory requirements. Bird-strike data also help researchers understand the nature of strikes and develop a scientific approach to reduce the cost and safety consequences of bird strikes.
Aviation stakeholders should report all known or suspected bird strikes to their national or recognized wildlife strike data repository (e.g., the FAA National Wildlife Strike Database in the United States) and share the strike information with the airport operator, the airline safety department, and the aircraft and engine manufacturers. Each of these individual reports will be combined into a single composite data record. Reporters should provide as much information as possible, including:
  • Airplane model and series designation (e.g., 777-300).
  • Airplane serial number or registration.
  • Phase of flight.
  • Speed and altitude of the airplane.
  • Geographical location of the airplane.
  • Date and time of day.
  • Origin and destination airport.
  • Number and species of bird observed and struck.
  • Impact locations of strikes and damage on airplane.
  • Effect on flight (e.g., rejected takeoff, air turnback, diversion).
If bird remains are available, trained personnel should identify the species involved, or the bird remains should be collected using the correct procedure (as outlined here) and bird-strike collection kit and shipped to a qualified laboratory. It is crucial to determine the species of the bird or birds involved in a bird strike and the location of the strike, so that wildlife management can take appropriate actions. Effective wildlife management involves controlling attractants, often species-specific, including food, foraging, roosting, and nesting opportunities. Managing the environment may be necessary, even to the extent of grass type and height, insects, rodents, and invertebrates, along with water sources and land use, such as agriculture.
In the event of a bird strike, maintenance personnel should follow the appropriate maintenance procedures for bird strike inspection in the Airplane Maintenance Manual. Maintenance personnel must be cognizant of the possibility that the bird remains can contain infectious material. The bird strike should be reported by the flight crew in the pilot’s log or by the maintenance crew in the maintenance log. After a bird strike, the airplane should be inspected for possible damage to airplane structure and airplane systems.
In the United States and Canada, bird-strike information can be reported online or via FAA form 5200-7 Bird/Other Wildlife Strike Report.
How airlines can get involved
Airlines and other stakeholders can help address the ongoing problem of bird strikes by participating in local, regional, national, or international aviation wildlife hazard activities, such as bird-strike committees or equivalent groups.
Airlines can also form their own internal aviation wildlife hazard group and designate a single point of contact for coordinating all aviation wildlife hazard activity, both internally and externally.

Bird strikes have always been a part of aviation. While they usually cause no more than minor damage, they can pose a threat to air safety. By being aware of the ongoing possibility of bird strikes and by following recommended procedures, flight crews can reduce the possibility and effects of a bird strike.

Aircraft Brakes

Wheel brakes are normally used to slow the aircraft down during landing roll on the runway and to aid in directional control during ground handling operations as taxi and parking.In small GA aircraft the brakes are connected to the main landing gear only and are operated independently from each other.The brake systems are operated by hydraulic pressure and the rudder pedals have the brakes installed on top and are toe operated. Some aircraft use heel brakes or even with separate levers in the cockpit operated by hand (e.g. DynAero MCR and Tecnam).
With larger aircraft the weight increases but the force pilots can apply will usually about the same for every human being.It is therefore important that the pilot gets help in the form of brake boosters or power assisted brakes.
The wheel brakes are usually made of the disc type, but on some exotic aircraft the drum type with two brake shoes inside is still being used.

Drum type

With this model the two brake shoes are operated by either pneumatic (air) or hydraulic (oil) pressure or maybe even manually with a cable (very rare). You won't see these on modern aircraft anymore. Inside there are a couple of springs attached to the shoes to make sure that the brake contacts the drum evenly as friction will try to move them slightly. The springs also make sure that the shoes retracts when brake pressure is released.

Disc brakes

Very popular as they are lightweight and the disc sits between the braking pads clamping them when brake pressure is applied. For heavier aircraft multiple brake calipers and or multiple discs can be used.The brake disc is made from steel and bolted onto the wheel and rotates. The clamping part, caliper, contains two brake pads and is self centering. When brakes are applied the pressure moves a piston cylinder arrangement inside the caliper and the pads will clamp the disc. With even pressure on both sides.

Brake system

Most light aircraft have two independent brake systems on the upper part of the rudder pedal. This part is hinged and connected to a master cylinder. High pressure tubing is used to connect the master cylinder to the brake cylinder in the caliper. Special hydraulic fluid (DOT4, AeroShell Fluid 41) is used to transmit the brake pressure. Careful: this fluid will eat away paint.Make sure that at the start of the take-off run you place your feet low enough as not to ride the brakes as this would result in a sluggish take-off roll.As the aircraft has two separate brake systems the pilot can use differential braking to help steer the aircraft, some aircraft (Pelican PL, Cessna) have their nose wheel steering connected to the brake system where the first 10° left or right the nose wheel moves and with further rudder movement the main gear will help steer the aircraft, helpful during taxi and parking.

Parking brake

Some aircraft have a sort of ratchet type system where they keep the brake pressure in the system, holding the aircraft in its place. Others use a hydraulic valve and after pressing the toe brakes they close the parking valve, thereby locking the hydraulic pressure. Check the POH to see which type of system is installed.

Power Assist

The simplest system is the boosted brake. In this systems main hydraulic pressure is used progressively through a valve to help the pilot applying the brakes.With power assisted brakes the brake system is fed by the main hydraulic system with a much higher pressure than the pilot can apply. Brake pressure regulates main hydraulic pressure to the wheel and caliper.These power assisted brake systems usually have a backup in case the main hydraulic pressure fails so the aircraft can still be stopped by using the brakes.