December 8, 2016
Migratory birds pose real hazard
Migratory birds pose real hazard
Fall has arrived, and with it comes increased potential for bird strikes.
All though most bird strikes do not require immediately discontinuing the flight, the hazard of striking a bird should not be under estimated; after all, each year birds do hundreds of millions of dollars of damage to aircraft.
In addition, the potential for striking birds increases during periods of migration. We are now in such a migration period where many bird types start moving south towards their wintering grounds.
In 2006 Transport Canada received 1,414 reports of bird strikes to Canadian aircraft within Canada. Not surprisingly, the types of birds struck were primarily large ones or those that fly in large flocks. Gulls, perching birds (such as starlings and swallows), hawks, eagles, and vultures account for the bulk of strikes.
Ducks, geese, and swans also see a good number of strikes yearly. July, August, September and October were the key months to have bird incursions.
Hours of the day reported for the majority of strikes were between 6 a.m. and 11 p.m. with average strikes decreasing after 7 p.m., and the least between midnight and 6 a.m. One would think that birds don’t like to fly in the dark, but 17 per cent of the reported strikes occurred at night and another six per cent during dusk and dawn.
When considering the phase of flight were most strikes take place, takeoff and landing were the most dangerous, closely followed by approach. En route, climb and descent received a large number of strikes with most strikes occurring between 1,001 and 5,000 feet. But take caution because some migratory birds have been recorded as high at 20,000 feet. Birds fly as high as safe and efficient for the same reasons that we do!
Most bird strikes occur in the windshield, followed closely by a large number of wing, fuselage, and nose section strikes. Substantially fewer engine strikes are reported, probably because of their relatively small cross-section, but those aircraft with only one engine (e.g. the types most of us fly) get the most engine hits.
Presumably this is because of the high nose impact rate and the fact that most single engine aircraft have their engine mounted on the nose. This lower number of engine strikes does not reduce the inherent danger however. Bird strikes/ingestions to turbine engines can cause catastrophic engine damage.
Since migratory birds pose a greater risk of strikes than solitary birds or those at roost, it is important to know something about their habits during migration. For certain, the altitudes at which they fly vary with winds, weather systems, terrain, and cloud conditions. It is also clear that birds are able to navigate with some degree of precision.
They appear to be keenly aware of day and night cycles and with the help of shadows, they can navigate using the sun as a compass of sorts. For night flight some species are thought to align themselves with the stars in order to distinguish cardinal directions. City lights and other brightly lit areas interfere with this ability and generally cause confusion.
Likewise, during the day, if birds find themselves among tall buildings with reflective windows, many become disoriented and pose additional hazards as they crash into the windows.
Larger birds tend to migrate during the day to take advantage of updrafts and better feeding opportunities. Some smaller birds migrate later in the day in darker conditions so as to avoid potential predators.
Since some birds use terrain features to guide their flight, so expect that rivers, mountain ranges and coastlines will be busier during the migration season. But regardless of where they might be found during their trek to the wintering grounds, spotting them is the key to preventing a strike.
While some larger birds, like geese, fly in partial or full V-formations in order to reduce air resistance, other smaller birds fly in swarms with little or no order. These smaller swarms can be dangerous as they can suddenly change direction and frequently do not appear to be as aware of airplanes near them as some of the larger birds.
But don’t underestimate the destruction power of the larger birds. Their larger mass combined with speed (at least 50 km/hr) means that any impact is a sure guarantee of damage to a light aircraft. And should one of these birds meet your windshield, it is more likely than not to go straight through it!
I recall one case of a goose going through several inches of glass of a fighter planes windshield only to continue on to decapitate the pilot. Today, windshields of fast, high-flying aircraft are heated to prevent shattering during a strike, but sometimes even this is not enough!
The most serious threat from bird strikes to a light aircraft is to the engine or windshield. These two strike areas frequently lead to emergencies due to sudden loss of engine power or engine failure as a result of air intake obstructions, and windshield view obstruction or destruction.
If a bird makes it through the Plexiglas windshield of a light aircraft, the occupants can be easily injured, if not at least messed up a bit with bird guts. Also, with a windshield breach, communications often becomes impossible due to wind noise.
In order to avoid a bird strike, when birds are spotted, climb above the flock. Birds will generally disperse to lower altitudes since by descending they can increase their speed during escape.
However, the best way to reduce the potential of a strike is to avoid over-flight of known bird activity and known migratory routes or flyways. Wildlife refuges are also good places to avoid flying over at the lower altitudes since aircraft noise may also cause large flocks to take flight. And at any time of the year, landfills should be avoided since they attract large numbers of scavengers.
When transiting airports in or near migratory routes, check local ATIS for bird activity in the area. If birds are reported in the area, use extreme caution. Never assume that birds will get out of the way as you approach.
From personal experience I can tell you that some bird types (seagulls for instance) are not at all interested getting out of the way. Many years ago, a wayward flock of seagulls decided to make the centerline of our runway their new home. After several were hit during landings (they didn’t get out of the way even after a dozen planes had landed on them!) the airport authority had to cleanup the carcasses. It was a landing gear vs. birds event, and the landing gear won.
There was some question as to why planes kept landing, but I guess that everyone thought the gulls would notice their friends getting squashed and clear out. No such luck!
If you should strike a bird inadvertently and you survive the experience, be sure to file a formal bird-strike report. It is from these reports that statistics are created to better understand bird activity and warn others of the impending danger.
As an immediate action, tell the nearest ATC facility about the incident so they may warn others of possible bird strike potential.
Later on, in Canada, report a strike using the online form at http://www.tc.gc.ca/.
If in the U.S., use FAA form 5200-7. This form can be obtained from
http://wildlife-mitigation.tc.faa.gov. There is also lots of additional good info about bird strike mitigation at this website that is compiled and maintained by Embry Riddle. Likewise, Transport Canada has a slew of good material on this topic at http://www.tc.gc.ca/civilaviation/AerodromeAirNav/Standards/WildlifeControl.
This month’s Pilot Primer is written by Donald Anders Talleur, an Assistant Chief Flight Instructor at the University of Illinois, Institute of Aviation. He holds a joint appointment with the Professional Pilot Division and Human Factors Division. He has been flying since 1984 and in addition to flight instructing since 1990, has worked on numerous research contracts for the FAA, Air Force, Navy, NASA, and Army. He has authored or co-authored over 160 aviation related papers and articles and has an M.S. degree in Engineering Psychology, specializing in Aviation Human Factors.