Palm Springs Pilots Association - BIRD STRIKES

April 2009 Volume 52 / Number 4

When birds strike

One pilot's experience, and tips for avoidance

Checklist: How to minimize the risk

Before takeoff:

Listen carefully to the ATIS and review the notams at departure and destination airports for “birds in the vicinity” (airports near the water are more vulnerable to bird problems).
Consider asking airport management to disperse any birds on or near the runway.
Familiarize yourself with local and national bird migration routes.
Review Web sites that provide predictive information on bird activity (www.usahas.com; www.usahas.com/bam).
If you will be flying in an area of bird activity and another pilot is on board, discuss the emergency procedures to be followed—especially if windshield penetration results in pilot incapacitation.
Have a pair of sunglasses handy to minimize the likely vision impairment from a possible windshield penetration.

In flight:

Fly as high as appropriate to the mission (less than 10 percent of GA bird strikes occur above 3,000 feet agl).
Avoid low flight along rivers or shorelines (which birds tend to follow).
Avoid low flight over bird havens such as sanctuaries and landfills (where birds tend to congregate).
When you see a flock of birds ahead of you, attempt to pass above them since they usually break downward when threatened.
If flocks are anticipated in an area, keep your speed down until clearing the area. This will provide both you and the birds more time to take evasive action and exponentially reduce the impact energy of a bird strike.
Use landing lights until clear of anticipated bird activity, to make your aircraft more visible.
Consider turning on your onboard radar transmitter during takeoffs and landings since, according to some radar experts, the birds can sense the signal and avoid it. (There is some question about the effectiveness of this technique, but there is no downside to doing it.)
If a collision seems imminent, duck to protect your eyes and head from the bird and flying glass.

The sky was blue, and the day was calm. I was reveling in the joy of flight in my Piper Aerostar at 2,000 feet above the serene landscape. Suddenly, the euphoria shattered. An apparition, materializing out of nowhere, pounced head-on like a monster in a 3-D horror movie. A huge turkey vulture with, it seemed, a look of horror on its face—and its six-foot wings spread over the windshield, as it tried desperately to avoid a midair collision—smashed through my windshield at 200 mph.

This image will remain etched in my mind forever. I instinctively ducked just before the impact.

I felt as if I had been hit by a baseball bat. The right side of my face and my right shoulder and arm were numb, leaving me dazed and dizzy. I found myself looking at—and through—a huge hole, more than two feet in diameter, in the windshield (bizarrely, in the form of an almost perfect circle). My headset had been knocked off.

Handling the emergency

I headed in the direction of the closest refuge, St. Lucie County Airport in Fort Pierce, Florida. Fortunately, I knew the location of the airport, so I was not distracted by navigation requirements. I looked around for some emergency landing sites in case either the airplane or I could not make it to the airport.

In my dazed state, I struggled to retain consciousness—and control. My vision was impaired from blood in my right eye and from the 200-mph wind, more than double hurricane force, screaming through the hole in the windshield.

I made my turns and descent very slowly because I did not want to tax my impaired abilities and did not know the effect of the collision on the aircraft’s flight characteristics. I considered engaging the autopilot but felt that, under the circumstances, it could be more of a distraction than a benefit.

To minimize the debilitating impact of this tempest in a cockpit, I slowed the aircraft, reducing the incoming gale to a mere 150 mph. I lowered my head, flying by the artificial horizon as much as possible and squinting at the real horizon on the other side of that wind only as necessary. I tried to protect my eyes with my hand while wiping the blood from my eye.

The noise was ear splitting. I made no effort to locate my headset because both transmission and reception would have been impossible in that deafening environment. More important, I did not want to distract myself from flying the airplane. Instead, I punched 7700 into the transponder, hoping the tower would clear the airport for me. Even if it didn’t, I was going to land there, one way or another, assuming I made it to the airport.

While I was obviously concerned about my own survival, the possible carnage from an uncontrolled crash into the built-up residential communities below intruded into my other concerns. The mantras “stay calm” and “fly the airplane”—welcome recollections from my many years of Air Force training—kept popping into my befuddled mind as I focused on retaining control.

Since I did not know whether the vulture had been flying in formation with any wingmen, I checked for other damage after I became more comfortable with my control of the airplane. I very gingerly tested the flight controls, flaps, and props to see if there had been any strike damage to them. Thankfully, they responded normally.

Remembering the aerodynamic effect of a thin layer of ice on lift, I decided to increase my approach speed slightly because of the possibility of damage to the wings. Since my vision had improved, I decided to refer to the prelanding checklist in the event that stress or confusion might cause me to overlook a critical step.

Fortunately, I landed uneventfully and turned off the runway at the first taxiway. I put on my abandoned headset to communicate with the tower and taxied to the ramp. An ambulance rushed me to the hospital.

I was covered in blood. As the nurse was cleaning off my face, she found some bird feathers, indicating that only part of the blood was mine. A CAT scan revealed that I had suffered no internal injuries. My main injuries were contusions—including on my right thigh and stomach, which I still can’t understand how they got there.

I considered myself very lucky that the vulture did not strike the airplane just six inches to the left, resulting in a full-frontal mash, which would have ruined my whole day.

After the accident

Having survived the bird strike, a new concern surfaced: What would the inevitable FAA and NTSB investigations uncover? I worried about whether my logbook, POH, charts, GPS data cards, and other records were current and in order, although I am usually meticulous about compliance. I called AOPA and was told that accident investigators had fairly wide latitude to check the airplane for records currency without the pilot being present. Would I come off relatively unscathed from the bird strike only to become embroiled in an enforcement action?

The accident had occurred on a Saturday. I had recovered sufficiently by Monday to drive to the airport (90 minutes away) to check out the damage. When I got there, I learned that an FAA investigator had been there the day before. Fortunately, everything was current.

In short order, I spoke to the FAA, NTSB, tower, and airport management. The FAA examined only the damage. Both the FAA and the NTSB told me that there would be no further investigation because the outcome was uneventful (to them, not to me): No injury plus no structural damage equals no investigation. Whew! Most gratifying were the compliments I received from the personnel of all four of these aviation agencies regarding my handling of the incident. They were amazed at the size of the hole in the windshield, larger than any of them had previously seen. The tower controller expressed surprise that I had turned off on the first taxiway.

Blood and remains were splattered throughout the aircraft, and the stench was nauseating. I took some photos to document the damage for insurance purposes. Viewing the damage, I envisioned how much worse the outcome could have been and reflected about the role that many years of flying experience had played in preventing a disaster. Then I thought about the resistance I had faced from my insurance company because I was an older pilot, disregarding this experience. I smugly wondered how much greater its liability might have been had a younger but less experienced pilot been at the controls when this bird literally came out of the blue.

Before the bird-strike encounter, numerous birds of varying dimensions had whizzed by my aircraft uneventfully. This lulled me into believing—as I’m sure many other pilots do—that birds are not a serious risk, that their survival instincts keep them, and us, out of serious danger. How wrong I was.

Bob Behren is a lawyer, CPA, author, publisher, and former law professor. A former U.S. Air Force fighter pilot and a recipient of the FAA’s Master Pilot Award, he holds ATP and CFI certificates and has logged almost 6,000 flight hours.

Little-known facts about bird strikes

The laws of physics dictate that the greater the mass and velocity, the greater the likelihood that any damage from an encounter will be severe.

The force of the impact on an aircraft generally depends on the weight of the bird, the difference in velocity, and the direction at impact. The force increases with the square of the speed difference—although a low-speed impact of a small bird on a car windshield generally causes no damage, high-speed impacts with aircraft can cause considerable damage.
The impact of a 12-pound bird at 150 mph equals that of a half-ton (1,000 pound) weight dropped from a height of 10 feet (ouch).
Turkey vultures have been identified as the most damaging bird to aircraft, followed by Canada geese and white pelicans, all very large birds. The typical adult turkey vulture is 26 inches to 32 inches long, with a wingspan of 68 to 72 inches.
The number of reported bird strikes was about 6,000 in 2000, about 5,000 in 2006, and more than 7,000 in 2007. About 80 percent of bird strikes go unreported, so the problem is more serious than the statistics indicate.
While wildlife on runways is also a problem, birds outnumber mammals by at least 30 to one.
There is a 15-percent chance that the point of impact on a GA aircraft would be the windshield. This exposes the pilot to a major risk of serious injury from the strike itself.
About 15 percent of bird strikes result in damage to the aircraft. More bird strikes—63 percent—occur during the day than at night (27 percent) and twilight (10 percent) combined.
The vast majority of bird strikes occur during takeoff/climb (35 percent) and approach/landing (50 percent).
The bird-strike risk is greatest during the bird-migration seasons in spring (March and April) and fall (September and October). More strikes occur during fall migrations because large flocks move to wintering areas over a short period of time, whereas spring migrations are slower and more irregular. There is also an increased risk in July and August when inexperienced birds are present and adults molt their flight feathers.
About 90 percent of bird strikes occur on or near airports, with those near water having the worst bird problems. However, birds have also been reported at altitudes as high as 35,000 feet.
In non-migratory periods, more than 90 percent of the reported bird strikes occur below 3,000 feet agl, and 61 percent occur below 100 feet agl. However, strikes at higher altitudes are common, especially during migration.
The altitudes of migrating birds vary with winds aloft, weather fronts, terrain elevations, cloud conditions, and other environmental variables. They generally climb to 5,000 or 6,000 feet, ascending higher as they burn fat. They like it up there because there is less drag where the air is thinner.
There are four major migratory flyways: Atlantic (following the East Coast); Mississippi (following the Mississippi River from Canada); Central (representing a broad area east of the Rockies, stretching from Canada through Central America); and Pacific (following the West Coast). The Mississippi flyway contains the largest number of birds, followed by the Pacific, Central, and Atlantic. Numerous smaller flyways cross these major north-south migratory routes.

How Fast and High Do Birds Fly?

Generally birds follow the facetious advice often given to pilots -- "fly low and slow." Most cruise speeds are in the 20-to-30-mph range, with an eider duck having the fastest accurately clocked air speed of about 47 mph. During a chase, however, speeds increase; ducks, for example, can fly 60 mph or even faster, and it has been reported that a Peregrine Falcon can stoop at speeds of 200 mph (100 mph may be nearer the norm). Interestingly, there is little relationship between the size of a bird and how fast it flies. Both hummingbirds and geese can reach roughly the same maximum speeds.

There is, of course, a considerable difference between the speed at which a bird can fly and the speed at which it normally does fly. When the bird is "around home" one might expect it to do one of two things, minimize its energy use per unit time, that is, minimize its metabolic rate, or m e the distance it travels per unit of energy expended. A vulture loitering in the sky in search of prey might, like the pilot of an observation aircraft, maximize endurance; a seabird traveling to distant foraging grounds might, like a Concorde encountering headwinds on a transoceanic flight, maximize range. Staying up longest does not necessarily mean going farthest. A bird might be able to stay aloft 6 hours at 15 mph (maximum endurance, covering 90 miles) or 5 hours at 20 mph (maximum range, covering 100 miles). Birds can also choose to maximize speed, as when being chased by a predator or racing to defend a territory. Or they can choose some compromise between speed and range.

In order to determine what birds normally do, Gary Schnell and Jenna Hellack of the University of Oklahoma used Doppler radar, a device similar to that used by police to catch speeders, to measure the ground speeds of a dozen species of seabirds (gulls, terns, and a skimmer) near their colony. They also measured wind speeds with an anemometer, and used those measurements to estimate the airspeeds of the birds. (The wind speeds were generally measured closer to the ground than the birds were, which led to some errors of estimation, since friction with the surface slows air movements near the ground.)

Airspeeds were found to be mostly in the 10-to-40-mph range. The power requirements of each bird at each speed could be calculated, and that information was used to establish that the birds were generally compromising between maximizing their range and minimizing their metabolic rates with more emphasis on the former. Airspeeds varied a great deal, but near the minimum metabolic rate rather large changes in airspeed did not require dramatic rises in energy consumption. For example, a gull whose most efficient loiter airspeed was 22 mph could fly at anything between 15 and 28 mph without increasing its metabolic rate more than 15 percent.

Most birds fly below 500 feet except during migration. There is no reason to expend the energy to go higher -- and there may be dangers, such as exposure to higher winds or to the sharp vision of hawks. When migrating, however, birds often do climb to relatively great heights, possibly to avoid dehydration in the warmer air near the ground. Migrating birds in the Caribbean are mostly observed around 10,000 feet, although some are found half and some twice that high. Generally long-distance migrants seem to start out at about 5,000 feet and then progressively climb to around 20,000 feet. Just like jet aircraft, the optimum cruise altitude of migrants increases as their "fuel" is used up and their weight declines. Vultures sometimes rise over 10,000 feet in order to scan larger areas for food (and to watch the behavior of distant vultures for clues to the location of a feast). Perhaps the most impressive altitude record is that of a flock of Whooper Swans which was seen on radar arriving over Northern Ireland on migration and was visually identified by an airline pilot at 29,000 feet. Birds can fly at altitudes that would be impossible for bats, since bird lungs can extract a larger fraction of oxygen from the air than can mammal lungs.

Flying in Vee Formation

We commonly see ducks and geese flying in a regular V-shaped formation, but why they do so remains something of a mystery. One theory has been that all but the lead bird are able to gain lift from the wing-tip vortices produced by the bird in front of them. Those vortices are formed by air rushing up over the tip from the high-pressure area under the wing into the low-pressure area above the wing. The following bird, if it is in just the right position, will remain within the upward flow of the vortices. Calculations indicate that such an advantage could greatly boost the range of a flock of birds over that of a bird flying alone.

Theoretically, to be most efficient, the wing-tip of a following bird should remain within about one-fourth of a wingspan from that of a bird in front of it. Motion pictures of flying flocks reveal, however, that in practice Canada Geese do not travel in formations that allow flight efficiency to be much increased by this mechanism. Instead, scientists have suggested that flying in vee formation is a way of maintaining visual contact and avoiding collisions. Further study is clearly required before the reason for flying in vees becomes clear.

SEE: Skimming: Why Birds Fly Low Over Water.