Collisions between birds and aircraft severely threaten aviation and avian safety. To understand and prevent these bird strikes, knowledge about the factors leading to these bird strikes is vital. Collisions between birds and aircraft are as old as aviation. The Wright Flyer III experienced the first recorded bird strike on 7 September 1905. The first fatal accident in India was recorded on 15 August 1962 on a DC-3 aircraft. Indian Airlines flight was in a cruise between Kabul and Amritsar when the crew spotted a vulture (up to 10 kg) above and to one side. The co-pilot was killed when it “attacked” the aircraft and penetrated the windshield. Bird strikes are regular events. Depending on the country, average bird strike rates between 2.83 and 8.19 per 10,000 aircraft movements have been reported in civil aviation for the past few years. In India, as per the 2021 State Safety Programme, against the target of 4.39 bird strikes per 10,000 flights, the actual performance achieved was 7.26.
Even though hull losses in the aviation industry are low, they result in annual costs of at least one billion US $ to the worldwide commercial aviation industry. This is a very conservative figure since bird strikes are often underreported. As accidents have demonstrated, collisions between birds and aircraft also bear the potential for catastrophic outcomes for the involved aircraft. As of 11 November 2019, bird strikes were determined to have caused 618 hull losses and 534 fatalities since the beginning of aviation.
The probability of bird strikes is determined by many parameters such as altitude, time of day, environmental conditions, geographical location, season, and the aircraft itself. The highest probability of bird-aircraft collisions is at low altitudes [28]. According to Dolbeer et al. [29], 88% of the bird strikes in the USA over the past 27 years have occurred below 2500 ft (71% below 500 ft). A European study concluded that even 95% of all strikes occur below 2500 ft (70% below 200 ft), when considering worldwide traffic [30]. The probability decreases with increasing altitude, as Figure 2 visualizes. This corresponds to the flight phases for which most bird strikes are reported: takeoff, initial climb, landing, and approach. While mitigation measures at airports have been shown to be successful in reducing the number and consequences of bird strikes outside the airport boundaries, the options for counteracting measures are limited.
The India Aircraft Rule 1937 has a provision under Rule 91 that addresses issues to tackle the environmental problems that give rise to increased bird activity.
91. Prohibition of slaughtering and flaying of animals, depositing of rubbish and other polluted or obnoxious matter in the vicinity of aerodrome. – No person shall slaughter or flay any animal or deposit or drop any rubbish, filth, garbage or any other polluted or obnoxious matter including such material from hotels, meat shops, fish shops and bone-processing mills which attracts or is likely to attract vultures or other birds and animals within a radius of ten kilometers from the aerodrome reference point : Provided that the Director-General, a Joint Director General of Civil Aviation or a Deputy Director General of Civil Aviation may, if he is satisfied that proper and adequate arrangements have been made by the owners of hotels, meat shops, fish shops and bone processing mills so as to prevent attraction of vultures or other birds and animals, having regard to the vicinity of place of slaughter from the aerodrome, arrangements for disposal or deposit of carcass, rubbish and other polluted and obnoxious matter, grant permission in writing for the purpose.
Hot Spots are identified within a 10km radius of Delhi Airport.
- Illegal waste dumping and accumulation of sewage wastewater at Rangpuri
- legal Meat Selling in Indra Market R. K. Puram and irregular removal of garbage Islaughter waste from drain/area by SDMC.
- Garbage Disposal around Dwarka Area and Railway Track– Runway 9/10/11
- Jai Hind Colony, Vasant Kunj —Runway 29
- Garbage disposal around Dhalao no. 06 in Rang Puri
- Illegal selling of meat in fruit and vegetable market of Dabri Mor (Public Grievance under Rule 91 of Aircraft Rule1937)
Figure 1: Bird Strike Hot Spots in Delhi
In 2017, the residents of RK Puram had a near miss when a GoAir A320 almost crashed into the locality following a bird strike at takeoff. On the 21st of June 2017, M/s Go Airlines (India) Ltd Airbus A320-214 aircraft VT-GOS was involved in an Air Turn Back incident due to a Bird Strike while operating flight G8 – 338 (Delhi- Mumbai). During the take-off roll on Runway 09 at around 115 knots IAS, the aircraft encountered a bird strike on Engine # 2. Both crew noticed an abnormal sound and vibrations, but the PIC decided to continue takeoff, probably wanting to investigate the problem after getting airborne. After takeoff, the situation was incorrectly assessed, and Engine # 1 (unaffected engine) was shut down. The aircraft was climbing with the single-engine, i.e. Engine # 2 (affected engine), for over three minutes. The aircraft stopped climbing at around 3330 ft altitude. The crew realized their mistake and attempted to start Engine # 1 but encountered a Start Valve Fault. The crew carried out appropriate actions, and Engine # 1 was started at an altitude of around 3100 ft. Power from Engine # 1 was found to be available at an altitude of 3108 ft. The throttle of Engine # 2 was later reduced as per QRH procedure and put on to IDLE. Probably, the aircraft lost a considerable amount of energy in the process of starting Engine # 1, which, combined with flying the aircraft in the absence of autopilot due to weather, resulted in the activation of the ALPHA FLOOR. The crew carried out appropriate actions, and ALPHA FLOOR was deactivated after 28 seconds at 2600 ft altitude. The crew requested ATC for a go-around in the first approach as the aircraft was too high on a glide. Subsequently, in the second approach, the aircraft landed uneventfully at Delhi on a single engine, i.e. Engine # 1. The vibration value of N1 of Engine # 2 was above the specified limits for approximately six minutes during the flight.
Countermeasures
To reduce the risk of bird strikes, many measures have been implemented. They can either be ground- or aircraft-related. On the ground, the focus of bird strike hazard reduction in civil aviation explicitly lies on the airports and their direct surroundings. This is related to the altitude distribution of bird strikes with the highest risk at low altitudes.
Landfills and airports have a long history of incompatibility. Birds are attracted to landfills for various reasons including food sources, habitat, and orographic lift. Since landfills can be avian attractants, they are required to be sited at least 10,000 feet away from commercial airports in the United States. Birds are attracted to the landfill site for three main reasons: the presence of food sources in the waste stream; available habitat for food, shelter, water, and nesting areas; and the physical layout of the facility, which provides perching sites and thermal and orographic lift. The area surrounding the landfill is highly industrialized and the landfill represents the best habitat for birds, regardless of consideration of the landfill operations. Airport runway orientation and urban planning need to be coordinated so that the locations of landfills and large garbage dumps are away from the aircraft flight path.
