Bird Strike Damage
Windshield Bird Strike
Final Report 5078609-rep-03
EUROPEAN AVIATION SAFETY AGENCY
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Approval & Authorisation
Prepared by: N Dennis (fera)
Approved for issue by:
R Budgey (fera)
Authorised for issue by:
A M Whitehead
Record of Revisions
Version Description of Revision
0.1 First Draft for review by EASA
0.2 Second Draft responding to EASA Comments
1.0 Draft Final Report
1.1 Final Report
This document was created by Atkins Limited and the Food & Environment Research Agency under Contract Number EASA.2008.C49 Copyright vests in the European Community.
ATKINS Limited The Barbican, East Street, Farnham, Surrey GU9 7TB
Tel: +44 1252 738500 Fax: +44 1252 717065
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Background to the Study
This report presents the findings of a study carried out by Atkins and the UK Food & Environment Research Agency (FERA). The study was commissioned in 2009 by the European Aviation Safety Agency (EASA), under contract number EASA.2008.C49 [1.]. Its aim was to investigate the adequacy of the current aircraft certification requirement in relation to current and future bird strike risks on aircraft structures and windshields.
Bird strikes are random events. The intersection of bird and aircraft flight paths, the mass of the bird and the part of the aircraft struck are all random elements that will determine the outcome. In managing risk all that can be controlled are the design and testing of the aircraft driven by certification specifications, the aircrafts flight profile and, to a limited extent, the populations of birds near airports.
The bird strike data presented in this report covers US, Canada and UK reported bird strikes from 1990 to 2007. Unfortunately, it was not possible to obtain data from other countries via ICAO, but the data obtained did provide an adequate basis for analysis approximately 11,000 incidents for which complete data on aircraft type, speed and bird species were available. The study also reviewed worldwide accident and serious incident data.
1. Airframe bird strikes are a relatively rare cause of accidents, representing only 0.3% of the total aircraft Fatal Accident Frequency Rate from all causes. However there are significantly more airframe strikes than engine strikes (by a ratio of 4.6 to 1). 51 accidents worldwide have been identified since 1962, of which only 14 (7 of them fatal), fell within the scope of this study. All of these accidents were to CS-23 and CS-27 aircraft. Where accidents have occurred, they have usually been associated with high energy impacts heavy birds (greater than 2 lb/0.9 kg) encountered at relatively high speed, resulting in Kinetic Energies of impact that are often several times the certification values.
2. The main conclusion from this report is that, given the reported level of accidents, the bird strike requirements in CS-25, and 29 are currently providing an adequate level of safety. However there are indications that the accident rate is increasing (although still very low), and that those species that cause the highest kinetic energy impacts are increasing in population (although the number of strikes recorded as involving the Canada Goose is reducing, this may be due to bird control measures near airports). .
3. In CS-23 (excluding commuter) and CS-27 aircraft categories there are currently no specific bird strike requirements and this is reflected in a higher rate of bird strike accidents (particularly windshield penetrations). Based on the accident record to date, a pre-existing requirement that such aircraft withstand collision with a 2lb/1kg bird at
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Vmo/Vh may have significantly reduced the number of accidents to these categories of aircraft by 26% and 66% respectively.
4. It may, however, be difficult to engineer an effective solution to increasing the bird strike resistance of these aircraft at acceptable cost. Additionally, due to the relatively low turn over rate, a change in the regulations may take some time to be effective. The use of helmets and visors might therefore represent a more practical and timely option
5. Other conclusions are listed below.
96% of strikes occur during take off, climb, approach and landing. Strikes en-route are much less frequent but 34% of these result in damage when they do occur. Over 800 ft altitude, strikes and damage are dominated by heavier birds such as Canada Geese and Turkey Vultures and the likelihood of damage is much higher.
The certification requirements for CS-23 Commuter Aircraft (2 lb, windshield only) and CS-29 Transport Helicopters (1 kg) result in an undesirably large proportion of bird strikes (5 to 11%) above the certification value. The equivalent value for CS-25 aircraft is around 0.3%.
Although data is very limited, it is noted that for fixed wing aircraft with certification requirements, the few accidents that have occurred are in the range 2.7 to 6.6 times the certification value.
All those accidents which have occurred have involved bird masses above 0.78kg. Most have involved very high values of Kinetic Energy, well above current certification values, and 90% of accidents involved impact KE above 1500 J.
CS-25 aircraft had the highest rate of reported bird strikes (186 per million flying hours) and the lowest proportion of damaging strikes (9%), probably due to better reporting of all strikes. CS-27 (small helicopters) had the highest proportion of strikes resulting in damage at 49% - predominately windshields.
28% of strikes reported involved multiple birds, and for these the likelihood of damage resulting was approximately twice that for an equivalent single strike. Neither the FAA nor EASA non-engine regulations currently contain any requirements relating to multiple bird strikes of the type that may arise from bird flocking behaviour. Such multiple strikes may result in some pre-loading of aircraft structures and windshields and may mean that the current certification analysis and test regimes are inadequate to model this scenario.
The aircraft parts most likely to be damaged are the nose/radome/fuselage and the wing.
KE is a better indicator of damage likelihood than bird mass. The proportion of strikes with KE above the certification value appears to be a useful safety indicator. The current value for CS-25 aircraft is around 0.3%. The certification requirements for CS-23 Commuter Aircraft and CS-29 Large/Transport Helicopters result in a larger proportion of bird strikes (5-11%) above the current certification KE value, which is undesirable and posses a safety risk.
Windshield penetration was a feature of 50% of all accidents. A detailed analysis of windshield strikes showed a strong correlation between impact KE,
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certification requirements and probability of damage. Increasing the certification requirement is very effective in reducing the incidence of damage.
Detailed analysis of tail strike data shows no reduction in the probability of damage resulting from the higher FAR Part 25 requirements for empennage for strikes between 1.8 and 3.6 kg. However, 100% of the 13 reported tail strikes above 3.6 kg resulted in moderate or severe damage, compared to only 47% of the strikes to wings. There have been no accidents or serious incidents identified as due to bird impact damage to the tail surfaces since the original Vickers Viscount accident in 1962 that gave rise to this requirement. Only 2.7% of reported bird strikes are to this part of the aircraft.
Apart from a single incident affecting an Airbus 320 in 1989, there have been no accidents or serious incidents causing failure of integrated avionics through shock.
The discussion on the effect of bird strikes on aircraft systems concluded that such effect involved mainly external sensors. However 180 US and 32 UK reports of bird strike damage to landing gear and associated electrical and hydraulic components were noted approximately 7x10-7 per flying hour based on CS-25/FAR part 25 aircraft flying hours alone (although this is likely to be a low estimate due to under reporting). Such a strike also resulted in one of the few hull loss accidents to a large transport aircraft.
VLJs have high-speed performance similar to large transport and business jets, but currently have no bird strike requirements. Given the relatively light airframe, single pilot operation and the likelihood that such aircraft will be operated from smaller regional airports and private airstrips, they may be more likely to encounter birds and less likely to be able to withstand the high KE impacts resulting.
The proportion of strikes above the certification value of KE is very similar for the CS-25 Jet and Propeller aircraft (0.27% and 0.31%). Both exhibit very low rate of accidents, so effectively there is no measurable difference in the level of safety provided by CS-25 bird strike requirements between these two categories of aircraft. This confirms that the regulations adequately address the difference in VC between the