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When Birds Strike

By Caterina Hessler

 

Birds are a severe danger for pilots. Especially when flying at low altitudes with high speed – a profile that is typical for helicopter flights.. What can be done to prevent strikes and to save lives and costs?

 

On the 30th of December 2005, a pilot was flying a Bell 206 near Washington, LA at approximately 500ft. While doing a quick scan of his instruments, a large vulture crashed into his cockpit. The bird shattered the windscreen and came to a halt inside the cabin. The pilot was instantly blinded by blood spraying into his eyes. After partly regaining his vision and control over the helicopter, he tried to land in a nearby field. Since he was barely able to see the ground and read the instruments, he crashed the helicopter. The pilot was taken to a hospital and had to undergo several surgeries to repair the severe damage to his face, his teeth and his eyes. The B206 was completely destroyed.

 

As this case demonstrates, collisions with birds can be quite dangerous. The main problem is that pilots have only a few seconds to discover the birds and react. There are no guarantees, but there are a few simple rules to help avoid the danger of a bird strike.

 

Although fewer bird strikes occur during take off and landing, one should consider the surroundings of the helipad or heliport. It should be as unattractive as possible for birds. This means there should be no bushes with fruit or berries, no possibilities for nesting, no ponds or ditches and the grass should be mowed short.

 

Over 80 percent of all bird strikes happen in a height lower than 1000ft. So it is useful to use a higher cruising altitude, although it should be mentioned that there are reports about swans and goose flying at heights of 30, 000 ft and higher. Furthermore, pilots should know some facts about the behavior of birds. Most birds have a natural reflex when being approached by a bird of prey or a helicopter. They will start a sudden climb and they will slow down. This is because birds have learned that most raptors try to catch them by diving down on them from a greater height. Only pigeons will speed up. Compared to airplanes, helicopters are much more maneuverable and pilots should take advantage of this fact and try to avoid a bird strike by evading. If pilots see a bird on collision course they should try to dive away. While these measures will help to avoid collisions with most birds, there are some species which are much more aggressive and might mistake a helicopter or plane for a rival. Hawks as well as lapwings have been reported to attack aircraft. Areas where these birds are sighted should be avoided.

 

Depending on your geographic location, the number of strikes in summer is higher than in winter, but most of the birds are small and do not cause severe damages to aircraft. The reason for the high number of collisions during the months of summer, in many regions, is that migratory birds such as swallows and starlings have returned from the warmer lattitudes where they resided during winter and there are many inexperienced young birds claiming the skies.  There are less strikes during fall and winter, but the damages caused are considerably higher, since larger birds, such as swans, geese, and ducks, are involved.

 

Last but not least, if possible, pilots should plan their routing well. In summer large raptors, such as buzzards or vultures, will soar on thermals generated over forests – you will not find them over water. While flying over expanses of water, birds like seagulls or ducks are most likely to be encountered. Smaller birds such as swallows will fly deep over grass to catch insects. So look out for large birds while flying over forests, avoid coast sections and fly in moderate height while passing over grass fields.

 

Real consideration should be given to appropriate personal protective equipment worn by pilots and crewmembers. The absolute best protection one can have is a helmet and glare-shield. This protects the eyes and may also keep the pilot from being knocked unconscious or receiving a serious head injury if struck in the head by a bird coming into the cockpit. At the very least, pilots should invest in high quality protective sunglasses with military grade, polycarbonate lenses for eye protection.

 

To learn more about the behavior of birds it is necessary to report every bird strike, even if only a small bird was involved and the damage to the aircraft was minor. Many bird strike associations offer online forms for an easy and fast way to report a strike. Take for example this resource provided by the US Federal Aviation Administration:

 

http://wildlife-mitigation.tc.faa.gov/wildlife/default.aspx

 

Many of the organizations have experts who can categorize a bird by its remains, even if it is only one feather. In order to support these groups, send them a sample of feathers if you find one on your helicopter after a strike and document the damage with photographs.

 

Editor’s Comments: In recent years I have had the experience of working in a coastal flight department that had two bird strikes. Both caused significant aircraft damage, as well as injured people inside the helicopter. Both incidents also involved single pilot operations of the Agusta A109E and soaring birds. Since both involved two different pilots, we felt it had little to do with pilot technique and more to do with our operational profile. I served on the team that evaluated our profile and wrote the SOP that changed how we flew our helicopter. Here is a brief summary of our analysis.

Facts

Wildlife studies showed us that over land, 90% of all birds fly at or below 1500’ agl. Over ocean, nearly the same percentage of sea birds, like gulls and pelicans, will remain within 1 mile of the shoreline.

Speed of Helicopter

In our case speed was important for two reasons. First, there is a difference in reaction time afforded (for bird and pilot) between a B206 cruising at 110 kts and an A109E going 140kts. Faster aircraft means higher risk of striking a bird. Secondly, knowing what speed the aircraft windscreen is bird strike tested to, can help in shaping policy. In our case, we were told by the OEM, that our windscreen was tested at 120 knots with a bird carcass up to X lbs. The downside is that the Agusta can go much faster than 120 kts and the buzzards in Florida are much bigger than the test dummy bird used by the OEM in testing.

Altitudes & Route

Aside from a diligent pilot scan, altitude selection is the single largest factor in reducing bird encounters. Bottom line: if over land, fly enroute legs above 1500’ agl. Additional benefits may include cooler air and less noise for the purpose of flying neighborly. When following a shoreline, do so greater than one mile offshore. Also, when choosing a route, steer clear of known areas of bird concentration, such as waste landfills.

The net result of our research was to begin flying with two pilot crews. We also adusted our operational cruise speeds to remain less than 120 kts whenever we were below 1500’ or within a mile of the shore line. By flying higher over land or further offshore, we drastically reduced the number of bird encounters, hence reducing the risk. – Editor In Chief, Lyn Burks

Posted in: Safety

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