Bird Strike Committee USA

Understanding and Reducing
Bird Hazards to Aircraft

 

 

 

 

Signficant Bird Strikes

Home

 

Risk Assessment - Frequently Asked Questions

 

Overview in relation to bird strikes

It is important to distinguish between hazard and risk in discussing wildlife and aviation.  Canada geese are a definite hazard to aviation because of their large size (8 pounds or more) and flocking behavior.  About 57% of goose strikes result in damage to aircraft in USA (Cleary, Dolbeer and Wright 2006).  Rock pigeons (feral pigeons) are an intermediately hazardous species in that about 12% of strikes cause damage.  In contrast, only about 1.4% of strikes with swallows result in damage to aircraft. 

 

Risk is a measure of how frequently an event is likely to occur (i.e., probability) times the level of hazard of that event.  Thus, Canada geese are always a hazardous species, but if the likelihood of geese being in the path of aircraft at a specific airport is low, then the overall risk posed by geese at that airport is low.  Although pigeons are a less hazardous species than Canada geese, pigeons may pose a higher risk than Canada geese at an airport if the probability of encounters between pigeons and aircraft is high. 

 

Thus, in developing management plans at airports to mitigate wildlife risks to aviation, it is important to distinguish between hazard and risk.  The goal is to document the species found at the airport, rank these species by hazard level (i.e., probability of causing significant damage in a strike event), and determine the probability of each species being struck (based on past strike history at airport, numbers of birds, flight paths across airport, behavior in relation to aircraft, and other factors).  By combining hazard level and probability of a strike event, the risk for each species can be determined.

 

Listed below are three publications of direct interest to the subject of risk and hazard related to bird strikes followed by a more detailed discussion of risk assessment in general.

 

Allan, J. R.  2000.  A protocol for birdstrike risk assessment at airports. Proceedings International Bird Strike Committee. 2000; 25:29-46.

 

Cleary, E. C., R. A. Dolbeer, and S. E. Wright. 2006. Wildlife strikes to civil aircraft in the United States, 1990-2005. U.S. Department of Transportation, Federal Aviation Administration, Office of Airport Safety and Standards, Serial Report No. 12, Washington, DC., USA. 63 pages (Table 13 lists the probability of a strike causing damage for over 300 North American bird and mammal species).

 

Dolbeer, R. A., S. E. Wright, and E. C. Cleary. 2000. Ranking the hazard level of wildlife species to aviation. Wildlife Society Bulletin 28:372-378.

Detailed explanation of risk and hazard


What is Risk?
A common definition of risk is that it is the combination of a specific hazard and the likelihood that the hazard occurs (probability)x(hazard) = risk. That likelihood may be expressed as a rate or a probability. For example the risk of an aircraft accident (hazard) can be expressed as one accident per million flights (likelihood).

Risk can be objectively defined so that two people can take the same data and come up with a similar result. Risk can be expressed in many ways, so long as it combines a hazard with a likelihood. The concept of risk exists in aviation, finance, human health, and many other areas. One can use the methods of science, engineering, and math in order to define risks.

What is Risk Assessment?
Risk assessment is the process of analyzing potential losses from a given hazard using a combination of known information about the situation, knowledge about the underlying process, and judgment about the information that is not known or well understood.

Risk is defined as the product of a hazard (such as damage costs) and the probability that this hazard occurs. In other words, (probability)x(hazard) = risk. The first two values must be known or at least estimated in order to define risk.

What are the Goals of Risk Assessment?
The basic goals of risk assessment include the following:

  • Identify potentially hazardous situations,
  • Apply appropriate methods to estimate the likelihood that a hazard occurs, and the uncertainty in that estimate,
  • Provide alternative solutions to reduce the risk,
  • Estimate the effectiveness of those solutions,
  • Provide information to base a risk management decision, and
  • Estimate the uncertainty associated with the analysis.

What is the Procedure for Performing a Risk Assessment?
Risk assessment consists of four general steps:

  1. Hazard Identification,
  2. Evaluating relationship between exposure to a risk and adverse effects,
  3. Exposure assessment - evaluating the conditions that lead to exposure to a risk,
  4. Risk characterization - describe nature of adverse effects, their likelihood, and the strength of the evidence behind these characterizations (often done by using probability and statistics).

How Do I Estimate Risk?
Estimating risk can be done in several ways:

  • With historical data,
  • By modeling,
  • If no data is available, by breaking down the system into known subsystems using techniques such as event trees or fault trees,
  • By analogy with similar situations, or
  • By comparison with similar activities.

What is the Point of Doing a Risk Assessment?
The risk assessment for a particular issue forms the foundation for making a decision about future actions. That decision may be to perform additional analyses, to perform activities that reduce the risk, or to do nothing at all.

What is Risk Management?
The process of combining a risk assessment with decisions on how to address that risk is called risk management. Risk management is part of a larger decision process that considers the technical and social aspects of the risk situation. Risk assessments are performed primarily for the purpose of providing information and insight to those who make decisions about how that risk should be managed. Judgment and values enter into risk assessment in the context of what techniques one should use to objectively describe and evaluate risk. Judgment and values enter into risk management in the context of what is the most effective and socially acceptable solution

How Do You Combine Risk Assessment with Risk Management?
The combined risk assessment and risk management process can be described as a six step process. The first three steps are associated with risk assessment and the last three with risk management.

  1. Formulate problem in a broad context - Do this by answering questions like: What is the problem?, Who must manage the problem?, Who are the stakeholders? Also, establish relationships among the problems and rely on stakeholders for problem identification and characterization.
  2. Perform the risk analysis - Evaluate the risk in order to determine the hazard, the likelihood of the hazard occurring, and any uncertainties in the estimate
  3. Define the options - Determine what can be done about the risk issue and the ways that it could be done. Determine potential consequences, costs, and benefits.
  4. Make sound decisions - Determine the best solutions and how they could be implemented in ways that are feasible, cost effective, and socially acceptable.
  5. Implement decisions - Find out what actions are needed to implement and deal with any objections or reassessments.
  6. Evaluate actions taken - Determine what is an acceptable and effective means of evaluating the effectiveness or appropriateness of the risk management actions.

Home