تاثیر تنوع در شیوه های گزارش دهی بر اعتبار فرآیندهای ارزیابی ریسک برخورد پرنده برای فرودگاه   The impact of variation in reporting practices on the validity of recommended birdstrike risk assessment  processes for aerodromes

1. Introduction Collisions between aircraft and wildlife, mostly birds, (hereinafter referred to as birdstrikes) are a serious hazard to all forms of aviation and have resulted in the loss of at least 108 aircraft and 276 lives in civil aviation (Thorpe, 2012). Less serious birdstrikes cause significant operational costs to the aviation industry as a result of repairs to damaged aircraft, delays and cancellations, insurance claims etc. The total cost to world commercial aviation has been conservatively estimated at 1.5 billion US$ per year (Allan, 2002). In order to manage these risks, the International Civil Aviation Organisation (ICAO) requires national aviation regulators to ensure the implementation of effective bird management policies on the air- fields under their control via a number of Standards And Recommended Practices (SARPS) (ICAO, 2012). The guidance material provided by ICAO in support of these SARPS includes a recommended risk assessment process to help aerodrome operators target their bird management effort and resources at those species that cause the greatest risk. This process derives from a paper published in 2006 (Allan, 2006) which has subsequently been adopted, with minor modifications, by International Birdstrike Committee (IBSC, 2006) Airports Council International (ACI, 2013) and a number of national regulators such as the UK Civil Aviation Authority (CAA, 2014a). Other birdstrike risk assessment techniques have also been developed. Most of these employ a variety of ranking processes, * Corresponding author. usually combining factors such as numbers of a particular specieson or around the airfield, their location, their movement in relation to aircraft flight-paths, presence of single birds or flocks, mass of the species, tendency to be involved in strikes etc. The various factors are combined mathematically and weighted to provide a more or less real-time measure of risk that bird controllers can immediately respond to (Allan, 2000; Shaw and McKee, 2008; Soldatini et al., 2010; Yang et al., 2010, Zakrajsek and Bissonette, 2005). These techniques rely on regular and accurate data gathering by bird control staff, who frequently have other duties to perform leaving them unable to devote the time needed to ensure that the necessary data are gathered with the accuracy required. Although having the advantage of providing immediate tactical advice concerning if and when birds need to be dispersed, they have not generally found favour with regulators. The process developed by Allan (2006) provides a longer term strategic view of the risk levels at a particular airport. This, combined with a ‘live risk register’ (a real-time dynamic assessment of immediate risks), provides both strategic and tactical guidance for bird control staff and resource managers. Allan’s process relies on combining, an estimation of the probability of a strike occurring with a particular bird species (using the airports strike record over the past five years) with an estimation of the likely severity of the outcome of the strike incident (using the proportion of strikes with that species resulting in aircraft damage). The data used came from the UK Civil Aviation authority’s birdstrike database for those strikes reported over the period 1976e1996.