In the early days of flight, when aviation and avian inhabitants shared the skies as equals, the highly manoeuvrable birds could effortlessly evade the comparatively sluggish aircraft. However, as aircraft technology has evolved, becoming faster and quieter, pilots in New Zealand face a growing challenge in avoiding mid-air collisions with birds, a phenomenon known as "bird strikes."

These avian encounters primarily occur between 50 and 800 feet above ground during the critical take-off and landing phases. While bird strikes at higher altitudes are rare, it's worth noting that the most extraordinary bird strike on record happened over the West African coast, at a staggering 37,000 feet, when a jet collided with a bearded vulture.

Turbine-engine airplanes are particularly vulnerable to bird strikes due to their high speed and quieter engines, which provide birds with limited warning, especially when they take off in alarm and inadvertently cross an aircraft's flight path. In contrast, helicopters, which often fly below 500 feet, seem to have a unique advantage as birds appear to perceive their presence more readily, possibly due to their slower airspeed, greater downwash, and noise.

The aviation industry's pursuit of higher speeds has brought with it increased impact forces and more severe consequences. The physics are clear: doubling the mass of a bird or the speed of impact results in a fourfold increase in the energy of the collision. Even a relatively light aircraft traveling at 90 knots can unleash an impact energy of approximately 536 joules when it collides with a small bird weighing just 0.5 kilograms. The forces generated are enough to cause significant damage, such as denting or tearing aircraft surfaces, shattering windscreens, rupturing hydraulic lines, and more.

While a single bird collision can lead to structural damage, the real menace emerges when a dense flock takes to the skies. Consider the seemingly insignificant starlings, each weighing about 85 grams. A flock of them has been the culprit in at least one serious aircraft accident.

Understanding the problem from a bird's perspective is crucial. Birds rely on their keen senses of sight and hearing to detect potential threats. The more visible and audible an aircraft is, the better the chances that a bird will react and steer clear. However, the scenario changes when an aircraft is in motion, as birds struggle to predict its flight path, leading to unfortunate collisions.

Bird behaviour varies widely in response to aircraft threats. Some birds, like waders, may rest near taxiing or departing aircraft, moving only a few meters if necessary. However, when startled by sudden movements or noise, they may panic and fly directly into the aircraft's path. Other birds might attempt to outfly an aircraft, making last-minute turns to avoid collision. In an intriguing twist, a hawk might perceive an aircraft as potential prey from a distance, only to realise its mistake too late.

The responsibility of avoiding bird strikes at certified aerodromes in New Zealand falls primarily on the shoulders of pilots. Air traffic control can provide guidance when they're aware of potential hazards, and aerodrome operators do their best to manage bird populations. Nevertheless, it ultimately falls to the pilot to navigate this challenge.

The most effective way to enhance an aircraft's visibility to birds is by activating all its lights. Landing lights and strobes should be illuminated when operating at or near an aerodrome, particularly in reduced visibility conditions. For pilots regularly flying below 500 feet AGL, familiarising themselves with bird nesting and feeding areas and high-tide roosting spots in their operational zones can help mitigate the risk. Birds are creatures of habit, often staying within their territory. Even if you're uncertain about the local nesting sites, it's wise to avoid flying too close to harbour mouths or dune banks, which are common breeding and roosting areas for various waders.

New Zealand's coastal aerodromes, which often host larger bird populations, face a heightened bird strike risk. One example is Thames Aerodrome, situated near an ecologically significant bird nesting area along the southern coastline of the Firth of Thames. This area is internationally recognised as a vital wetland for numerous bird species. It's crucial to note that there's an important wader roost and gull breeding area immediately outside the airfield, as well as along the southern shore of the Firth of Thames.

Pilots should make an effort to avoid overflying bird nesting and roosting areas along the coast or other wetlands. Staying at least 1000 feet above these areas can minimise bird disturbance and significantly reduce the risk of bird strikes. However, if weather conditions necessitate low-level flight along the coastline (down to 500 feet AGL), pilots must remain vigilant for potential bird or fishing kite strikes, maintaining a sharp lookout and being prepared to take evasive action.

Birds' nests located under engine cowls or within the fuselage represent a genuine threat to flight safety. For instance, a bird's nest near the engine exhaust system could lead to an engine fire, with potentially disastrous consequences. Similarly, nests disrupting airflow into the engine oil cooler can cause overheating and engine seizure, while those within the fuselage or wings can foul control cables, leading to control surface jamming. Thorough pre-flight checks, especially during the spring, are imperative to prevent such hazards.

Numerous bird control measures have been devised, from loud noises to bird distress calls, which can act as scaring devices to some degree. However, birds tend to adapt quickly, rendering these methods less effective over time. Consequently, periodic shootings are often necessary. Birds are easily frightened, but the need to feed and survive sometimes forces them to endure a certain level of anxiety, causing them to ignore potential threats to their safety.

In cases of aerodromes certified under Civil Aviation Rules, Part 139 Aerodromes, the aerodrome operator must have a wildlife management plan to address bird hazards. To fulfil this responsibility, they require information on bird hazards, near misses, and strikes. Where feasible, aerodrome operators should collaborate with local authorities to mitigate risks associated with bird-feeding sites, such as rubbish dumps or landfills located adjacent to the aerodrome.

At non-certificated aerodromes, the onus of safe flight operation falls on the pilot and aircraft operator. If birds pose a hazard at any of the aerodromes they utilise, operators may need to pressurise the aerodrome owner to rectify the problem.

To reduce the likelihood of nesting, aircraft owners and operators should implement bird control measures to minimise bird populations in their hangars. Such measures are vital in ensuring aviation safety.

The financial implications of a bird strike can be significant for operators, making them eager to report bird hazards and incidents. To secure long-term protection against bird strikes, it's essential to report all bird hazards, near misses, and strikes. Without this data, there is no concrete evidence to warrant bird control measures.

What constitutes a bird hazard? Significant bird populations residing on or near an aerodrome, unpredictable bird behaviour when disturbed by an aircraft, and bird flight paths conflicting with the aerodrome's circuit pattern all fall under this category.

In conclusion, bird concentrations in and around aerodromes present a genuine threat to aviation safety, not only in New Zealand but worldwide. Vigilance, reporting, and appropriate measures are the cornerstones of effective risk mitigation against bird strikes in aviation. By understanding the unique challenges that New Zealand pilots face and implementing.

Further Reading:

Bird strike - anything could happen (CAA)