Vulture Disaster: Bad Luck, Poor Planning or Fate?

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A final report published earlier this year by the Spanish civil aviation accident and incident investigation commission lays out the heart-wrenching end to a family of four out for an adventure in their four-seat general aviation aircraft. 

The report is not new – it came out in March – but not much has been reported on its results.

Was their fate avoidable? 

A basic tenet of pre-flight planning is to “become familiar with all available information concerning that flight….” That’s a tall order given the ever-growing glut of information available, and one that I have to admit I do not always carry out 100%, particularly for a pleasure flight on a known route.

But in the case of the family in a Socata TB-20 (EC-ESK) flying home to Leon, Spain, the afternoon of January 16, 2016, after a Saturday in Alicante on the Mediterranean coast, did it prove to be fatal?

Two key pieces of pre-flight information or knowledge about the flight over the beautiful Serrania de Cuenca Natural Park would have been critical, both of which are relatively obscure. 

- The Spanish aeronautical information publication (AIP) showed a “bird gathering area” along the route. 

- The impact energy when hitting one of those birds goes up with the square of the aircraft’s velocity.

Radar tracking of the aircraft showed it to be flying at a ground speed of 140 kt. and 2,000 ft. when it struck a griffin vulture.

Given the winds at the time, the aircraft likely had a headwind, so actual airspeed would have been 140 kt. or greater. The adult bird, which most likely had a wingspan of 7.5-8.7 ft. and weighed from 13-20 lb., hit the leading edge of the left wing, which then detached from the aircraft, falling to the ground along with the bird. The aircraft went out of control and crashed.

Data from the radar track was overlaid on the bird concentration map published in the AIP, and the accident location coincided with “an area identified as having one of main vulture breeding colonies,” according to the final report. Griffon vultures glide between 6000 ft. – 11,500 ft., but sometimes climb to as high as 20,000 ft. 

The low-time pilot (334 hr. flight time) appeared to be conscientious, filing a flight plan and talking with air traffic control, but was he aware of the AIP and the griffon’s? Investigators talked to his friend and partner, who said he flew the route often. 

What’s an AIP anyway ? It’s an ICAO-recommended document published by a country’s air navigation service provider (in our case, the FAA) every six months with updates in-between covered by Notams. To be honest, I’d never looked at one until reporting this story. I do however regularly look at the FAA’s Airport/Facility Directory, which has much of the same information, but the AIP is a bit broader and includes, among other information, some generic wisdom about birds, including:

“Avoid overflight of known areas of bird concentration and flying low altitudes during bird migration. Charted wildlife refuges and other natural areas contain unusually high local concentration of birds which may create a hazard to aircraft.”  FAA AIP 23rd Edition Amendment 3 (May 26, 2016)

Being aware of bird hazards is one thing, but avoiding them in flight is another. In this case, investigators think the setting sun may have been in the pilot’s eyes, making avoidance difficult if not impossible. When pilots do see birds, particularly in flocks, the AIP recommends climbing to avoid a collision “because birds in flocks generally distribute themselves downward, with lead birds being at the highest altitude.” It also recommends putting landing lights on in areas “where flocks of birds may be expected”

Even if the pilot had expected to encounter griffon vultures in the area, did he understand the certification criteria for his aircraft with respect to bird strikes or the relationship between his cruise speed and impact energy? 

Possibly not. 

The Spanish safety board notes that the TB-20, like all Part 23 light aircraft, does not have to undergo bird impact analysis or testing as part of certification. For commuter aircraft certified under Part 23, the aircraft must handle (without penetration) the impact 2 lb. bird at the aircraft’s maximum approach speed with flaps extended (Part 25 aircraft – airliners – have more rigorous requirements).

Investigators note that the kinetic energy (KE) of a 2 lb. bird at the maximum flaps extended approach speed for a commuter like the Fairchild SA-227 Metroliner is 5,566 Joules.

Based on the size of a mature griffin vulture, the aircraft would have had to handle a KE of 15,561-23,342 Joules, depending on the bird’s weight (13-20 lb). “Therefore, normal, utility, acrobatic and commuter category airplanes are not certified to withstand impacts with a kinetic energy as high as that delivered by this impact with the vulture,” the final report states. Click HERE for an excellent NTSB analysis of how to minimize bird-strike damage.

However, if the pilot had throttled down for a cruise speed to 100 kt., the velocity-squared effect would have lowered the KE to 7,803 – 11,704 Joules, a hefty decrease that may have helped here. 

My condolences to anyone who knew this family. We can only hope that their story might help others avoid the same fate.

Discuss this Blog Entry 11

on Oct 11, 2016

The author should understand headwind/tailwind does not change airspeed, only groundspeed!! It would not change impact speed.

on Oct 11, 2016

The ground speed was 140 kt.; add the headwind to 140 for the air speed. Evidently, the ground speed was derived from the radar track. The author got it right.

on Oct 13, 2016

The aircraft's air speed with a headwind was certainly greater than 140 kt ground speed. But what about the vulture's speed and heading at the time of impact? We know nothing about it so all this discussion about relative speeds doesn't make any sense.

on Oct 11, 2016

The author didn't word it well, but he is correct. The groundspeed was registered as 140kts, therefor, in a headwind, the airspeed would have been greater than 140kts.

on Oct 11, 2016

Was their fate avoidable? In this case of course it was. As the author mentions: 'pre-flight planning is to “become familiar with all available information concerning that flight…”'. The pilot in this case obviously didn't fulfill his obligation concerning this requirement and his family paid for his complacency with their lives.

Mountain climbing, scuba diving, GA flying and other similar high risk activities all have a common thread: a single mistake can be fatal for the individual and also for anyone associated that is dependent on their planning (including people on the ground).

Risking one's own life is a decision of the individual, risking others lives is a calculated responsibility of preparation that is shirked only with fatal results. This individual could have easily flown a different route. He may have had to take longer or even stopped overnight, but his family would have survived.

Accident Cause: Pilot Error. In reference to 'faasafety.gov':

"Pilot Error Causes More Than 80% of Aviation Accidents...effective risk management starts with flight planning. Good flight planning can help pilots avoid becoming an accident statistic. FAA statistics suggest these accident categories have produced high fatality rates... [including] poor pilot judgment...and deficiencies in basic airmanship."

on Oct 11, 2016

So, did the wing separate from the fuselage or just the leading edge ?
"hit the leading edge of the left wing, which then detached from the aircraft, falling to the ground along with the bird. "

on Oct 11, 2016

As written, the entire wing separated. Losing just the leading edge would make control difficult but not impossible.

on Oct 11, 2016

The author could have made the article better if he had avoided mixing SI and Imperial units of measurement, also including the formula for calculating kinetic energy ((0.5 * mass) * (v * v)) the v*v bit is what does the damage; would have allowed any reader unused to mentally comparing systems to work out an answer in their prefered units. For example a 15lb Vulture hit at 140 kt equals an impact energy of 248062 ft/lbs/sec. As a comparison an AP shell from an A-10 has 2908 ft/lbs/sec

on Oct 11, 2016

Comment removed by staff.

on Oct 12, 2016

Hitting a large bird at high speed can ruin your day. Back in 1987, a B-1B flying over Colorado struck a large bird on a wing leading edge. The bird penetrated the wing, severing fuel and hydraulic lines. Three of the six men on board died (two instructors riding in jump seats and the copilot).

on Oct 13, 2016

In this report, everyone is talking about the people in the plane. Did the vulture choose to die ?

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