Frozen chickens and slow climbs: How the aviation industry deals with birdstrikes
A vulture hit an A350 this week as the aircraft neared the end of its flight from Bogotá, Colombia, and made its final approach into Madrid–Barajas Airport (MAD).
The bird, which can weigh around 13 kilograms and have a wingspan of 2.7 metres, impacted the nose of the aircraft, fracturing the radome that houses the weather radar. The aircraft continued its approach, landing safely just over a minute later.
Images circulating on social media show the aircraft arriving onto its parking stand with the unlucky vulture still embedded in the nose. Engineers had to remove the carcass of the bird, revealing the damage to the aircraft structure.
Birds have long been a known concern in aviation. Whilst they have been flying through the air for millions of years, vultures and other birds of prey have only been joined by aircraft for just over 100 years.
As a result, the threat posed by birds to aircraft as they depart and arrive from airfields is something that pilots and airport operations teams take incredibly seriously.
The Miracle on the Hudson
The most famous event regarding birds and aircraft in recent years was that of US Air flight 1549, more commonly referred to as The Miracle on the Hudson.
On a chilly January morning, a routine flight departed from New York-LGA on its way to Charlotte, North Carolina. It was a beautiful day across New York with great views for miles around.
Whilst climbing through 2,800 feet, however, the pilots’ view was suddenly filled with a large flock of Canada geese. A fraction of a second later, the flock impacted the aircraft causing both engines to fail. Taking control of the aircraft, Captain Chesley “Sully” Sullenberger assessed the options. But surrounded by the built-up areas of greater New York, there were few.
He decided that the best bet would be to ditch the aircraft on the Hudson River.
Despite the global headlines, events of this magnitude are incredibly rare. Even though birdstrikes do happen fairly frequently (13,000 annually in the U.S. alone) most usually cause very little damage, if any, to the aircraft.
The physics of impact
How serious the effects of a birdstrike are on an aircraft depends on two factors: the mass of the bird and the velocity at which it impacts the aircraft. This is known as kinetic energy. Of these factors, it is the velocity of the impact which has the greatest effect on the total kinetic energy.
Simply put, the faster the speed of the collision, the greater the damage to the aircraft (and, of course, the bird). Knowing these facts, aircraft designers engineered aircraft in a way to try to minimise the damage caused by bird strikes.
Engine and windshield design
During the testing phase of a new engine, manufacturers must show it is able to withstand the impact of a serious birdstrike. To do this, they fire frozen chickens at an engine on a test rig to confirm that the engine continues to operate normally.
The blades of the engine spin so quickly that they make easy work of smaller birds. When the velocity of impact is greater, however, damage can occur to the blades, resulting in the need for the engine to be shut down.
The windshield of the flight deck is also designed in a way to resist the impact of a birdstrike. Unlike the windscreen on your car, the windshield on an airliner is much more than just a sheet of glass.
On the Boeing 787 Dreamliner, the windshield is made up of three distinct layers. The outer layer is in fact the thinnest layer and is made of strengthened glass, taking advantage of the high damage tolerance of a material named Herculite® II. This layer of glass sits on top of a much thicker layer of stretched acrylic.
At cruising altitude, the temperature outside can be as cold as negative 70° Celsius. When a windshield at that temperature comes into contact with moisture in the form of rain or clouds, it will immediately become covered in ice, reducing our visibility to zero.
To overcome this problem, there is a thin layer of a transparent electrically conductive substance between the outer glass and the stretched acrylic. When an electrical current is applied to this layer it heats up, warming the outer glass, preventing the windshield from icing up. In fact, when sitting on the ground in rain, we often see steam coming off the windshield.
To give the windshield added strength, there is another, even thicker layer of stretched acrylic as the base layer.
Aircraft windshields are designed to take a serious beating, be it from birds or hailstones. The three-layer structure as described above means they can withstand the impact of a large seagull at 400 miles per hour.
Altogether, the windshield is around 4 centimetres thick. Not only does this give it the strength it needs to withstand the worst the external environment can throw at it, but it also makes it light enough to help keep the weight of the aircraft to a minimum, reducing fuel usage and as a result, carbon emissions.
Pilot strategies
There are some common misconceptions about birds and the way in which they behave. Many a rookie pilot will no doubt have been told that the weather radar is an effective way of dispersing any birds on the runway and that the bright landing lights are a good method to scare birds away.
It was also believed that birds don’t fly at night, nor do they fly in bad weather such as low clouds and fog. But these scenarios haven’t been scientifically proven.
The best strategy to prevent a birdstrike is to avoid encountering birds in the first place and, according to the Flight Safety Foundation, there are a number of ways to do this.
On departure, if there are birds on the takeoff path, pilots should inform ATC and wait until the ground operations team have dispersed the birds. They can do this with any number of methods, more commonly using explosives or flares to scare the birds away.
At some airports, they are even using lasers to disperse birds. Not only does this negate the need to carry firearms in the airport environment, but it also means birds can be scared away much more quickly.
If the birds show no sign of shifting, it may be preferable to depart from another runway where the birds are not a threat. The same goes for landing. If bird activity is reported around the runway, it may well pay dividends to delay the approach until such time that they have gone. Or, land on a different runway if one is available.
The way in which we operate the aircraft can also reduce the chances of a birdstrike.
Most encounters with birds occur only 3,000 feet above ground level. If pilots fly in a way that gets the aircraft above 3,000 feet as soon as possible, it will reduce the chance of a birdstrike.
There is also one other great benefit to this method.
In order to climb at a quicker rate, we fly at a slower speed. As mentioned before, the slower the velocity of the impact with birds, the lower the damage to the aircraft. So, by employing this method, not only will the risk of a strike be reduced, if one does happen, the damage caused will be much less.
According to the Flight Safety Foundation, this method “would, in all likelihood, have prevented the US Airways accident.” It was not, however, common practice within the industry at the time.
With that in mind, flying at a slower speed in areas where there could be birds will also reduce the damage should a birdstrike occur.
What happens during a birdstrike?
As the quote from Frank Borman goes, “A superior pilot uses their superior judgement to avoid situations which require the use of their superior skill.”
Still, despite our best preventative attempts, sometimes it just isn’t your day. If a birdstrike does occur, we have tried and tested methods, practised in the calm and safety of the simulator, to put into action.
I’ve had a number of birdstrikes in my career, most of them uneventful. One time, landing at a Spanish airport, we hit a bird at around 200 feet on the approach to land. Flying at 150 miles per hour, things happen pretty quickly. In this case, it was a small bird, maybe the size of a sparrow.
I saw it at the last moment. In the next fraction of a second, it had hit the windscreen, splatting like a bug on a car windscreen, leaving a long streak up the glass.
Another time, we started the takeoff run to see a large bird fly across the nose and down the right-hand side of the aircraft. A moment later a massive bang was our indication that the bird had gone through the engine.
The key in this scenario is to slow everything down in your mind. This is one of the key skills pilots learn as part of their training: The ability to remain calm in a moment of utter chaos and panic, enabling us to think rationally and come up with the correct solution to the problem, exactly as Captain Sullenberger and Senior First Officer Skiles did that day out of LaGuardia.
For the most part, this means not getting distracted and just carrying on with exactly what we were doing before. Chances are, that the birdstrike has caused little if any damage to the aircraft. The greater risk comes from reacting and doing something that will exacerbate the situation.
An example of this is attempting to abandon an approach because of a strike.
According to Airbus and the UK CAA, a better technique would be to fly through the flock of birds with a lower engine speed (as is the case on approach) and allow the bird debris to pass around the engine core without increasing damage to the rear stage compressor blades.
Bottom line
Whilst birdstrikes are common, serious damage to aircraft is incredibly rare. Despite this, pilots and airport authorities are able to do a number of things to reduce the risk of these events happening at all.
Airports keep the grass around runways and taxiways considerably longer than you might imagine. This makes the area less desirable for birds to land and stay.
Pilots, too, can take actions to reduce their chances of encountering birds. Still, if we encounter birds, we know that the chances of them causing serious damage is low.
As a result, our focus is on remaining calm, on flying the aircraft and dealing with any scenario that may develop as a result.
By Charlie Page Charlie Page is an airline pilot flying the Boeing 787 Dreamliner. Each Saturday he gives you a ‘behind the cockpit door’ insight to life in the flight deck.
