In March 2008, two minutes after takeoff from the Wiley Post Airport in Oklahoma (KPWA), a Cessna Citation 500 business jet suddenly entered a steep descent and crashed.
There was no warning of what was to come. The weather was good, the afternoon takeoff uneventful. At 3,000 feet, the crew checked in with Oklahoma City departure, and the controller issued a climb-and-turn instruction, but it went unanswered. About 30 seconds later, on the Wiley Post tower frequency, someone said, “I just saw an airplane crash and explode.” Both pilots and all three passengers were killed and the airplane destroyed by impact forces and postcrash fire.
How the flight came together was complicated and controversial. One week before the flight, United Engines called Interstate Helicopters, a Part 135 charter operation, to transport three United executives from KPWA to Mankato. The plan was to spend the night and come back. United had previously used Interstate Helicopters, as well as some other local charter firms, for occasional company flights. It didn’t know that Interstate had no fixed-wing aircraft on its FAA certificate, meaning that Interstate, according to the NTSB, was facilitating an illegal commercial flight.
While attracting a lot of NTSB and FAA interest, the legalities have no connection to the accident cause.
The left-seat pilot was 44 years old, had about 6,100 total flight hours with type ratings in the Cessna 500, Citation III and Learjet, and was the chief pilot of a FAR Part 91 corporate flight operation. He was trained and legal to operate some Citation jets single-pilot but not this one. During post-accident interviews, pilots who knew him described a “good guy” with a “good reputation” who “loved flying.” The right- seat pilot was 40 years old and had almost 1,400 flight hours, many of which were as PIC in Cessna 340A light piston-twins. He had logged over 70 hours as CE-550 second-in-command but had no record of required SIC training in the Citation. A former missionary in Brazil, he had a reputation as “a planner and a plotter. Everything he did, he thought of the last detail.” Neither had any history of violations or certificate actions.
“It looked for all the world like the plane hit birds and suddenly crashed. Now, eyewitness accounts and initial layman guesses to accident cause are notoriously unreliable. But in this case, first impressions were proven right.”
Departing KPWA was routine. The pilots showed up at about 2 p.m. and readied the jet. A manager from Interstate cleaned and stocked the cabin. Nothing seemed amiss. The weather was good VFR, temperature 52 degrees, greater than 10 miles visibility, clear skies. Wind 150 degrees at 9 knots. The passengers arrived at 2:50 p.m., an Interstate rep carrying their bags to the airplane. All was as it had been several times before. They taxied out at 3:05 p.m.
NTSB Member Kathryn Higgins is correct when she says, “This was an illegal flight that never should have taken off in the first place.” Nonetheless, aside from the legal status, everything here seems benign. No mechanical issues, no weather issues, no ATC issues. No terrain issues, no fuel issues, no procedural issues. Competent, rested pilots at the controls. Still, fate was the hunter that day, and minutes after takeoff, all five occupants would be dead.
The cockpit voice recorder was not working, but the NTSB does have all the ATC tapes. At 3:06, the pilots received their IFR clearance: “…on departure, turn right heading 200, maintain 3,000, expect flight level 270 ten minutes after departure. Oklahoma City departure frequency 124.6, squawk 3403.” Six minutes later, the tower controller cleared them for takeoff from runway 17L. Handed over to OKC departure, they checked in, reporting out of 2,000 feet for 3,000. The controller was busy on a landline coordination call and didn’t respond. The Citation checked in again, now level at 3,000 feet. The controller radar identified them and issued clearance to “climb and maintain 15,000 turn right heading 290.” There was no response. “Citation three sierra hotel, did you copy?” “Citation three sierra hotel, how do you hear?” “Citation three sierra hotel Oak City approach, how do you hear?”
There’s no flight data recorder information, but OKC approach control has good radar coverage in this area and captured the event. A STARS computer using an ASR-9 radar at the Will Rogers World Airport first dis- played the jet climbing through 1,500 feet. It leveled at 3,000 feet and flew straight on the assigned 200 heading, from Wiley Post airport over wooded countryside and Lake Overholser. Suddenly, there was a steep descent. A ping at 2,400 feet, then no further returns. Observers, wreckage analysis and simulation studies all agreed that a sudden left roll continued through 290 degrees. Eyewitness accounts and security camera footage show the plane descending in a 60- to 70-degree nose-down attitude, trailing white or gray smoke. It impacted the ground inverted at a pitch angle of 53 degrees. There was an immediate large fireball.
A person by the lake heard a bang and saw the plane diving as well as what appeared to be bits of bird and feathers floating down. Another witness saw remains of two large white birds in the water. It looked for all the world like the plane hit birds and suddenly crashed. Now, eyewitness accounts and initial layman guesses to accident cause are notoriously unreliable. But in this case, first impressions were proven right. At the location where the aircraft disappeared from radar, NTSB radar analysis found “a trail of primary targets consistent with birds.” During 10 minutes covered by the radar data provided by the FAA, there were an amazing 5,985 primary targets observed by the OKC airport surveillance radar. We share the sky with many flying friends. It’s not always a peaceful coexistence. Bird remains were all over the wreckage.
The jet probably lost power in the right engine and likely breached the left wet-wing fuel tank. It was likely fuel streaming out the left wing that was the “smoke” seen by eyewitnesses. The Board determined that damage to the airplane’s flying and/or control surfaces produced “pitching and rolling moments that could not be compensated by pilot control inputs,” even worse than losing an engine and a fuel tank. A perfectly good airplane had instantly become unflyable.
After the accident, the NTSB delved deep into aircraft- bird impact certification. What it found is not comforting. It’s not that Citations don’t meet FAA standards, but, rather, “current airframe certification standards for bird strikes are insufficient.” The Board found regulations “are not based on bird strike risks to aircraft derived from analysis of current bird strike and bird-population data and trends” and allow for varying levels of bird strike protection on different structures on the same airplane. The Citation’s departure from controlled flight likely resulted from wing structure bird damage, “which far exceeded the airframe’s design certification limit.”
In compliance with FAA transport category airplane requirements, the windscreen and wing structures of the Cessna 500 are certificated to withstand an impact from a 4-pound bird while cruising at normal cruise speeds at sea level (for this Citation that’s 287 knots) without damage that would prevent safe flight and landing. The empennage must withstand an 8-pound bird at the same speed. The problem is that many large birds are heavier than 4 or 8 pounds. The Citation impacted a flock of American white pelicans, where each bird can weigh up to 20 pounds. The energy of a 20-pound object hitting at “just” 200 knots was calculated by the NTSB as 34,416 ft-lbs. That’s well over double the general structure certification energy value of 14,586 ft-lbs. It’s rare in aviation that a certification parameter can so easily be exceeded, and extremely rare we can casually exceed it by a factor of two.
Building an airplane invincible from bird strikes would result in a tank too heavy to fly efficiently. In safety, they are few absolutes and lots of compromises. Most bird strikes cause little damage. Wipe the blood off and go fly again. The American white pelican is an exceptionally big bird, bested in wingspan only by the California condor. Captain Sully ditching an Airbus A320 into the Hudson River after hitting a flock of Canada geese (also at 3,000 feet) was a unique, once-in-a-movie-universe event.
Only it turns out that seriously damaging bird strikes aren’t that rare. It was just 17 months after Sully that a Royal Air Maroc Boeing 737 smashed into a flock of geese while climbing out from Amsterdam’s Schiphol Airport, causing a huge amount of damage. The crew did a fantastic job to return safely to Schiphol. The airline industry was lucky to be saved, again, by great pilots.
Since the first reported bird strike in 1905—by one Orville Wright—planes have hit a lot of birds. The total damage, according to one recent study, is 618 hull losses and 534 fatalities. Our feathered friends are estimated to be causing over a billion dollars of damage a year to aircraft. And it’s getting worse. The Board cites research showing that in North America, the population of large bird species, with body masses greater than 8 pounds, has increased significantly in the past 30 years.
A lot more could be done as an industry to mitigate the bird strike hazard. Stopping the building of bird sanctuaries next to airports would be a start. A few years after the “Miracle on the Hudson,” New York City built the North Shore Marine Transfer Station, a bird-attracting garbage facility just 2,200 feet from runway 13/31 at LaGuardia Airport. There exist practical bird-sensing radar systems that can alert ATC about active flocks in the air. Drones, lasers, mirrors, effigies, pyrotechnics, falconry and more can discourage birds close to runways. Stronger certification standards of airframes and engines might be warranted.
There’s some good news in recent research. Studies find that painting an aircraft in bright colors helps, as does installing pulsating exterior lights. Engines on the right side of multi-engine aircraft get fewer bird strikes than those on the right, a phenomenon believed to be caused by avian eyes being more sensitive to the green navigation light than the red. Changes to the frequency spectrum of red navigation lights, making them more visible to birds, might reduce the impacts on that side.
The KPWA ATIS noted “birds in the vicinity of the airport,” but these always-on blanket warnings are designed more by lawyers to shield liability than for pilots to enhance safety. It’s like your vehicle navigation system warning you there are cars in the vicinity of the road—every time you start the engine. It’s not actionable information. While there’s been amazing progress bringing high-quality weather, navigation and traffic information into the cockpit, there’s been nothing new for birds. Neither the internet nor the iPad has helped us with this problem.
What can we do as pilots? Not a lot. Probably the best precaution is to slow down. Kinetic energy of impact goes up as the square of the airspeed, so every few knots here help a lot. In a brightly painted plane with exterior lights flashing, going slower gives birds more time to maneuver themselves away. For jet pilots, the 250-knot speed limit below 10,000 feet is relevant here, and 200 knots or less may be better if you suspect flocks of birds. All of us can slow down a bit and plan on limiting flying through known danger areas like over lakes or active migratory bird paths.
There are some concepts for birdstrike avoidance, but none are ready for market. Until that time, birds are a threat we manage alone, mostly blind, using best guesses and luck.