Bird strikes explained: hazards, deterrence and the Hudson landing

A short dull thud, sometimes a bang from the engine, a few feathers on the runway – and shortly afterward a bird control vehicle rolls across the apron. If you regularly stand at the fence, sooner or later you notice that aircraft and birds share the same airspace. Usually that ends well. Sometimes it does not. This guide explains what a bird strike is, why it happens especially on takeoff and landing, how airports work against it and what famous cases like the ditching on the Hudson reveal about technology and training.

Bird strikes: the short answer

A bird strike is the collision of an aircraft with one or more birds. Experts often speak more generally of wildlife strikes, because mammals like deer or foxes also wander onto runways. The vast majority of these collisions have no consequences for the aircraft. It becomes critical when large birds or entire flocks get into the engines or hit cockpit windows – and that in a phase of flight where little altitude and little time remain.

That is why bird strikes are mainly a topic near airports. During the takeoff roll, the initial climb, the final approach and touchdown, aircraft are moving where most birds also fly, feed and rest. Exactly this area is what you observe as a spotter.

Why takeoff and landing are the critical phases

Birds stay mostly at low altitudes. Around airports, there is also whatever attracts birds: large, open grass areas, insects, mice, often water or fields in the surroundings, plus a clear view of approaching predators. Gulls, starlings, crows, pigeons, birds of prey and geese find ideal conditions here.

For the aircraft, these phases are doubly tricky:

• Little altitude: If an engine fails shortly after takeoff, there is hardly any room to maneuver. With two failed engines at low altitude, every second becomes a decision.
• High engine power: On takeoff, the engines run at takeoff thrust and draw in enormous amounts of air – and with it everything flying in front.
• High workload: Takeoff and landing are the most work-intensive phases in the cockpit anyway. An incident hits the crew when they already have a lot to do.

Ruled out entirely at high altitude, however, bird strikes are not. During bird migration in spring and fall, many species also travel at night and at greater heights. In its bird migration forecasts, the German association DAVVL points out that most species stay below 10,000 feet, but geese and cranes can climb to cruising altitudes.

Which parts of the aircraft are at risk

Almost all bird strikes hit the front of the aircraft. What happens depends on where the bird strikes.

Component	Typical consequences	Why it can be critical
Engine	Damaged fan blades, vibrations, loss of thrust, at worst failure	Ingesting larger birds can deform or break blades – with flocks, in both engines
Cockpit windows	Cracks, impaired visibility	In the worst case the crew loses sight in a critical phase
Radome (nose)	Dents, damage to the weather radar	A frequent point of impact, usually without danger to the flight but expensive to repair
Wing leading edge and flaps	Dents, damaged slats	Can impair aerodynamics and requires inspection
Landing gear	Damaged lines or sensors	Often only noticed during the check on the ground

Twinjets like the Airbus A320 or the Boeing 737-800 dominate short- and medium-haul traffic today (how the A320 variants differ is shown in the guide Telling the A320 family apart). They are designed to keep flying safely with one engine out. The worst case pilots fear is therefore a simultaneous hit in both engines – exactly what a flock of geese can cause. How to tell engine families apart on an aircraft is explained in the guide Identifying engines.

What certification requires

In type certification, engines and airframes must show that they can withstand bird strikes within a defined scope. Put simply, there are two categories of tests:

• Large bird: After ingesting a single large bird, the engine must be able to be shut down safely without breaking up uncontrollably or catching fire. It does not have to keep delivering thrust in this test. How heavy the test bird is depends under today’s rules on the inlet size and ranges from around 1.8 to around 3.6 kilograms. For engines of the CFM56 generation, 4 pounds, or about 1.8 kilograms, was the standard.
• Small and medium birds: Here the engine must keep running after the hit; under current US rules, it may permanently lose no more than a quarter of its thrust.

The airframe and cockpit windows are also designed for the impact of a bird of about 1.8 kilograms, the tail for a bird of about 3.6 kilograms. The crucial point: a Canada goose weighs about 3.6 kilograms on average – significantly more than the test bird for engines like the CFM56 – and almost never appears alone. A flock of heavy birds is therefore beyond what a single engine has to withstand safely. This gap was at the center of the discussion after the Hudson accident.

Manufacturers like CFM International, whose CFM56 powers both the A320 family and the Boeing 737 Classic and Next Generation, must therefore demonstrate their engines in firing tests: birds or substitute bodies are shot into the running fan with compressed-air cannons.

Deterrence at the airport: how wildlife management works

Every larger airport runs a wildlife or bird strike management program. The goal is not to keep every bird away – that would be impossible – but to make the grounds as unattractive as possible for the dangerous species: large birds and species that appear in flocks.

Habitat management: the habitat decides

The most effective measure is unspectacular and easy to see from the fence: the grass. Many airports deliberately keep the areas between runways and taxiways long. In tall grass, gulls, starlings and crows find food less easily and feel unsafe because they cannot spot predators early. The DAVVL also points out that freshly mown areas attract starlings, crows and birds of prey – which is why the timing of mowing is planned carefully.

More building blocks:

• Water: Open bodies of water, puddles and stormwater retention basins attract geese, ducks and gulls. They are avoided, covered or secured with nets and wires.
• Food: Waste, fallen fruit or crops in the immediate vicinity are taboo, and insect and mouse populations are monitored.
• Buildings: Nets, spikes and structural details keep birds from nesting or roosting in hangars and on terminals.
• Surroundings: Landfills, bodies of water or certain field crops in the area can trigger bird movements across the approach and departure routes. Airports therefore also get involved in planning outside the fence.

Active deterrence

If birds still show up on the grounds, bird control moves out. Typical means are:

• Pyrotechnics and bird-scaring cartridges – loud, effective in the short term, but birds get used to it if it is used too often.
• Acoustic signals, such as played-back warning and distress calls of the respective species.
• Vehicles and patrols that deliberately flush flocks before an aircraft arrives.
• Falconry at some airports – birds of prey signal danger to other birds.
• Lasers in certain cases and only with caution, because they pose a risk of their own near aircraft.

In Germany, airports rely on habitat management and, when needed, pyrotechnic deterrence; lethal measures are not used. It is different in other countries: in New York, for example, Canada geese were killed on a large scale after the Hudson accident, and as early as the early 1990s a culling program at JFK had drastically reduced the gull population in the area.

The DAVVL: bird strike prevention in Germany

In Germany, the DAVVL e.V., which now calls itself the association for biological flight safety, bundles the expertise on the topic. The association, formerly known as the German Committee for the Prevention of Bird Strikes in Air Traffic, has dealt with the subject since the mid-1960s. Its tasks include:

• the documentation of bird and wildlife strikes and maintaining a bird strike database,
• the identification of feather remains – and when no feathers are available, by DNA analysis too,
• bird migration forecasts and BIRDTAM warnings that alert airlines and air traffic control to periods of increased bird strike risk,
• expert reports on birdlife at airports as well as training for bird control staff and for airlines.

Feather identification is more important than it sounds: only those who know which species hit an aircraft can counteract in a targeted way. A hit with a common buzzard calls for very different measures than a flock of starlings.

The Hudson landing: US Airways Flight 1549

The best-known bird strike in aviation history happened on January 15, 2009 in New York. An Airbus A320 of what was then US Airways, registration N106US, took off from LaGuardia in the afternoon toward Charlotte. Shortly after takeoff, at about 2,818 feet, roughly 4.5 miles north-northwest of the airport, the aircraft flew into a flock of Canada geese. Both CFM56 engines lost nearly all their thrust.

Captain Chesley “Sully” Sullenberger and First Officer Jeffrey Skiles had only minutes. The crew immediately started the auxiliary power unit (APU) so the onboard systems kept receiving power – a step the US accident investigators later explicitly rated as a good decision. Given the altitude and time, the crew did not consider it feasible to reach an airport safely. Less than four minutes after the bird strike, Sullenberger put the A320 down in the middle of the Hudson River, level with Midtown Manhattan, not far from today’s Intrepid Museum.

NY Waterway ferries were on the scene within a few minutes, and shortly afterward more boats from authorities and shipping. About 25 minutes after the ditching, the last person was off the aircraft. All 155 occupants – 150 passengers and five crew members – survived, despite freezing air and water temperatures of around five degrees Celsius. About 100 people were injured, five of them seriously, but nobody lost their life.

What the investigation found

The NTSB determined as the probable cause that large birds had entered both engines and that these lost almost all their thrust. DNA analyses confirmed the Canada geese. Simulator tests in which pilots attempted to return to LaGuardia turned out differently – only some succeeded, and with a realistic reaction delay the attempt failed. The investigators concluded, however, that these tests did not reflect the real delays for recognizing and deciding, and rated the ditching as the right decision.

The final report of 2010 contained numerous recommendations, including on:

• engine tests with bird strikes at lower rotational speeds as well,
• checklists for the failure of both engines at low altitude,
• life vests on flights that do not cross long stretches of water too,
• the training of water landings,
• research into brace positions in the cabin and into wildlife management.

The case became world-famous under the name “Miracle on the Hudson” and was turned into the film “Sully” in 2016 by Clint Eastwood with Tom Hanks. The aircraft itself now stands, engines included, in the Sullenberger Aviation Museum in Charlotte. If you visit New York, you can incidentally watch the departure area from Planeview Park in Queens right at LaGuardia.

Other well-known cases

Flight 1549 is not the only case in which birds made history. A few examples show the range:

Case	Year	What happened	Outcome
Eastern Air Lines 375, Boston	1960	A Lockheed L-188 Electra flew into a flock of starlings shortly after takeoff, three of the four engines failed or lost power	Crash into Winthrop Bay off Boston, 62 of the 72 people on board died – one of the worst bird strike accidents
US Airways 1549, New York	2009	A320 loses both engines after colliding with Canada geese	Ditching on the Hudson, all 155 occupants survive
Ural Airlines 178, Moscow	2019	An Airbus A321 hits gulls shortly after takeoff from Zhukovsky, both engines ingest birds and lose power	Belly landing in a cornfield, all 233 occupants survive
Jeju Air 2216, Muan	2024	A Boeing 737-800 reports a bird strike on approach, goes around and lands on the second attempt without the landing gear extended	Collision with a concrete structure beyond the runway, 179 dead; the investigation is disputed and not complete

The case of Jeju Air in particular shows that a bird strike is often only the trigger of a chain of events. What role crew decisions, technology and the design of the facility beyond the runway played was, as of this article, the subject of the Korean investigation and public controversy. Reliable statements about the causes belong in the official final report – not in speculation. You can read more about how runway ends are secured in the article Runway safety.

What happens after a bird strike

Most bird strikes are unspectacular. The crew notices a thud or sees remains on the windshield, checks the engine indications and continues the flight or returns as a precaution. Depending on the situation, the following steps happen:

For you as a spotter this means: if an aircraft flies a loop shortly after takeoff and comes back, the fire department stands ready at the runway or a runway is suddenly closed, a reported bird strike is not infrequently behind it. How the airport fire department is set up for this is shown in the article Airport fire department. If a flock is on the runway during an approach, a go-around can be the result as well.

What to keep in mind as a spotter

• Safety before the photo. If you witness a serious incident, stay on public ground and keep escape routes clear. What applies in such situations is covered in the guide Witnessing an emergency landing or incident.
• Know the limits on photos. Pictures of injured or helpless people are legally delicate – more in the article Photos of aircraft accidents and emergency landings.
• Do not feed animals. Leaving bread roll scraps behind on the spotters’ hill attracts crows and gulls – exactly the species airports want to keep away. You can read more about animals around the fence under Nature at the airport’s edge.
• Report anything unusual. If you see large flocks right in the approach area or an injured animal on a public road by the fence, you can inform the airport. You do not enter the grounds yourself.
• No remote diagnoses. A burst of fire from an engine after a hit looks dramatic but says little about the cause. Leave the assessment to the experts.

Conclusion

Bird strikes are part of flight operations like wind and weather. The vast majority of collisions have no consequences because engines, windows and airframes are designed for hits and crews train for engine failures. It becomes dangerous with flocks of large birds at low altitude – the Hudson landing of 2009 showed that impressively, and it also showed how much good training and quick decisions matter. On the ground, airports work quietly and steadily against it: with long grass, dry areas, deterrence and precise documentation.