Accident Probe: Flocking Together

Hitting one or more birds with your airplane doesn't always have a miraculous ending.

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I hit a bird once. I was flying a Piper Arrow II, on short final, with landing gear and full flaps extended, when I saw the bird ahead of the airplane. It was maneuvering and, from my perspective, flew in a circle as we neared each other, then disappeared under the left wing. I heard a muffled thump as it went by. I still had three green lights and the airplane remained controllable, so I landed.

After shutting down, I inspected the left wing and landing gear, finding a trace of blood and a very small feather associated with a slight depression in the wing’s leading edge. The bird hit the outboard portion of the grille covering the left wing’s fresh-air inlet, where the wing root fairing joins the Arrow II’s leading edge. History did not record its fate. It did, however record that the first reported bird strike involved Orville Wright, in 1905. In other words, bird strikes have been a “thing” since the beginning.

Birds and other wildlife pose a distinct threat to aircraft of all sizes and types. Just ask retired US Airways captain and former U.S. ambassador to ICAO Chesley “Sully” Sullenberger if you’re not convinced. Also, aircraft most often encounter them near airports. Weird, huh? Not really. According to the FAA’s Aeronautical Information Manual, 90-plus percent of reported bird strikes occur at or below 3000 feet AGL, although ducks and geese “are frequently observed” as high as 7000 feet AGL during migration, which typically occurs March through April, and August through November.

Airframe damage is the predominate threat birds pose to piston aircraft, while almost anything powered by a turbine engine is at greater risk for engine damage or failure. According to AOPA, turbine engines “are able to ingest about three small birds (one and one-half pounds) or one medium bird (two and one-half pounds) without failing. The FAA currently considers a large bird to weigh more than four pounds. There is no aircraft engine certified to ingest a large bird without shutting down.”

Bird strikes involving personal aircraft can certainly ruin your day, but they typically aren’t fatal. This month’s accident is pretty much the worst-case scenario.

Background

On May 11, 2019, at about 1530 Eastern time, a Piper PA-30 Twin Comanche was destroyed when it collided with terrain near Naples, Fla., apparently out of control. The solo private pilot (male, 71) was fatally injured. Visual conditions prevailed. The flight departed Key West, Fla., at an unspecified time and operated on an IFR flight plan.

The en route and initial approach flight phases were apparently uneventful, and at about 1528, the pilot advised the tower he was on a 5.5-mile final to Runway 23, which was his last communication. At that point, the airplane was at about 2185 feet MSL. The airplane continued toward the airport until 1529:42, when it began a gradual, arcing, left descending turn. The last radar target was recorded at 1529:55, when the airplane was less than a quarter nautical mile from the accident site, at 750 feet. The airplane collided with terrain about 4.3 miles and 052 degrees from the approach end of Runway 23.

All structural components necessary to sustain flight, and all primary and secondary flight controls remained attached or were located at the accident site. Examination of the right aileron bellcrank revealed neither stop was damaged. Examination of the flight control cables for roll, pitch and yaw revealed they exhibited either tension overload or were cut for recovery; there was no evidence of preimpact failure or malfunction.

The flap actuator jackscrew was extended 1.750 inches, or 11 threads, which equated to between fully retracted and 10 degrees of flap extension. Both main landing gear were retracted in their wheel wells; the nose landing gear actuator position could not be determined due to impact damage. There was no evidence of preimpact failure or malfunction involving the engines and propellers.

The rear seat headrest and two inflatable life vests were located about 440 feet north-northwest of the accident site. A dead Black Vulture, weighing 3.8 pounds, was located among the wreckage. Feathers were found adhering to a blanket located near the separated inboard section of the right wing. Swabs from the headrest and life vests contained either DNA and/or microscopic feathers from a Black Vulture.

The airplane was certificated under Civil Air Regulation 3 (CAR 3) by the FAA’s predecessor agency, the Civil Aeronautics Administration, which did not include a minimum standard for window or windshield structure strength, or bird penetration. The two-piece factory windshield was 0.125-inch thick, with a center post. It was replaced in 1979 with an STC’d one-piece windshield and the center post was removed. There was no requirement for the new windshield to exhibit bird strike resistance. Maximum thickness of the windshield pieces recovered from the accident site was 0.250 inch. The pilot’s autopsy noted the presence of black bird feathers.

Probable Cause

The NTSB determined the probable cause(s) of this accident to include: “Incapacitation of the pilot due to a birdstrike through the windshield in front of the pilot’s position, while on approach to land.”

The NTSB amplified its theory of this accident, stating, “Because the Black Vulture was located among the wreckage and because the airplane’s flight path deviation was unannounced, it is likely that the Black Vulture directly impacted and then penetrated the windshield in front of the pilot’s position, which incapacitated him, resulting in an uncontrolled descent.” The NTSB also noted, “The airplane was certificated in accordance with Civil Air Regulation 3, which specified no minimum standard for window or windshield structure strength, or bird penetration.”

If there was any doubt about whether the Black Vulture took down this Twin Comanche, the feathers observed during the pilot’s autopsy should be sufficient evidence. And if you think you’re immune to this kind of accident because you fly a newer airplane—one whose standards generally exceed CAR 3—the only birdstrike resistance required of the windshields aboard Part 23 small airplanes involve those certificated in the Commuter category.

This time of year, birds are especially active in North America. For some tips on where you might find them, and on avoiding them once you do, see the sidebar below.


Minimizing Bird Encounters

  • According to the Aeronautical Information Manual, four major migratory flyways exist in the U.S.: The Atlantic flyway parallels the Atlantic Coast, the Mississippi Flyway runs south from Canada through the Great Lakes and follows the Mississippi River, the Central Flyway stretches from Canada through Central America and the Pacific Flyway follows the west coast.
  • Turbine engine ingestions may result in sudden loss of power or engine failure. Review engine-out procedures, especially when operating from airports with known bird hazards.
  • When encountering birds en route, climb to avoid colliding with them. This is good practice because flocking birds generally distribute themselves downward, with lead birds being at the highest altitude.
  • Avoid overflight of known areas of bird concentration and flying at low altitudes during bird migration. Charted wildlife refuges and other natural areas contain unusually high local concentrations of birds which may create a hazard to aircraft.

Aircraft Profile: Piper PA-30 Twin Comanche

Not accident aircraft. Image: André Wadman

OEM Engines: Lycoming IO-320-B1A

Empty Weight: 2408 lbs.

Maximum Gross Takeoff Weight: 3725 lbs.

Typical Cruise Speed: 169 KTAS

Standard Fuel Capacity: 90 gal.

Service Ceiling: 18,600 feet

Range: 1100 NM

VS0: 60 KCAS


This article originally appeared in the May 2022 issue of Aviation Safety magazine.

For more great content like this, subscribe to Aviation Safety!

Jeb Burnside is the editor-in-chief of Aviation Safety magazine. He’s an airline transport pilot who owns a Beechcraft Debonair, plus the expensive half of an Aeronca 7CCM Champ.

11 COMMENTS

  1. Birds are where you find them. There’s really no viable method to avoid colliding with one, or even a flock, if they’re ‘destined’ to do so. Our military base had one method to chase those flocks away. We would obtain a Very Pistol, and shoot the flares toward those flocks. Sometimes it worked.

  2. LHR-AMS is a short 40+mins flight in a B757-236 with RB211- E4 engines. On approach a smell of roast duck came through the left aircon pack into the flight deck. BA crew catering was not known for roast duck or indeed anything so exotic. After shut down our ground engineer invited me to inspect the No1 (left) engine intake, sure enough a fan blade was slightly bent and the aroma of roast bird, type unknown, very evident. The RB211 was strongly built, the blade fixed and we continued on our return sector to LHR, thus avoiding an unplanned night stop in AMS with the appropriate generous cash allowance for 2 pilots and 6 cabin crew.

  3. Had the misfortune of 3 bird strikes. 1st descending into Randolph AFB at dusk in a C21 hit a bat creasing 10’ of the right fuselage. Bracken Cave, on the northern outskirts of San Antonio (our approach), is home to the world’s largest bat colony, with more than 15 million Mexican free-tailed bats with dusk/dawn high activity. At that time marked on the sectional. 2nd was descending IMC over Cincinnati taking a goose under the nose. This is a common migration route. Several years earlier two Learjet pilots killed in same area with a goose strike. 3rd was out performing aerobatics coming out of a loop took a red tail hawk thru the canopy. Obviously both saw each other as it tucked and dived while I was ascending. Fortunately had a shard of canopy remaining able to tuck behind to see and make a nearby emergency landing.

  4. I lost track maybe 10 total mostly in the US Navy flying low level at 350+ Knots. A good reason for visor down and mask on. The last was a dramatic encounter with a Canadian Goose (we think) on short final into Toronto Peterson at 700′ 165 KIAS. Hitting squarely in L1 I had to look around the remains to finish the landing, thank goodness there is a chicken cannon that tests the windscreens to withstand such encounters! Technicians estimated the poor bird was at least 8 pounds!
    I read a publication of strange encounters airplanes have had like a snake strike at 5000′!

  5. Was skydiving in Jeanerette, Louisiana in 1990 and while at about 250 feet setting up for landing when a flock of about 6-7 Canadian geese flew underneath me and I could distinctly hear their hard breathing. They ARE everywhere.

  6. There aren’t many things that can get your attention faster than burning odor in the cockpit over the mountains on a moonless night than a (unknown at the time) bird in the engine compartment, slowly cooking. There’s not a lot worse mess to clean up either.

    When birds are small enough, they don’t make much noise or enough of an impact to feel. But I believe they expand geometrically upon heating.

  7. While flying a friends’ Twin Bonanza at night from a DAL dinner-out with friends, my friend Ray was sitting right-seat and our wives visiting in the back. My wife was responding to the other wifes’ remark about how interesting it was to fly at night when it was so cool and smooth…. My wife was apparently thinking herself jocular when she responded, “George has sometimes said he expects to die on a night-flight when a meteor or a goose comes thru his windshield.”
    We were descending thru 8K’ into our home field at CLL and my friend looked over at me as if to say, “I wish she’d not talk like that to Fran… This is Fran’s First Flight in a personal airplane.”
    At that very moment a Huge BANG shattered the smooth descent and Ray and I involuntarily ducked beneath the glare-shield and the wives both screamed.
    Only a few miles from CLL we continued the descent and the post-flight inspection showed a 10” HOLE in the left wing-root between the fuselage and the left engine. A mass of meat, feathers and one dangling web-foot hanging out of the hole. That thick Beech leading edge looked like a cannon-ball had entered it.