June 17, 2009

In this Rotor Roundtable column from the June-July issue of Vertical Magazine, Kevin Nelson shares background, stats, facts and techniques to help avoid the often-occurring, but little-reported situation of bird strikes.

If you’ve been alive these past few months, this is likely not the first story you’ve seen on bird strikes. But, this one uniquely looks at the subject as it relates to helicopters, in the hope that the information provided might minimize the chance of ending up with a mouthful of feathers in flight.

This helicopter was struck by no fewer than four ducks. Statistically, two-thirds of helicopter bird strikes are to the rotors, windscreen and/or nose.

Another Story About Bird Strikes!
Much has been written about bird strikes with aircraft since it was brought to substantial public attention on Jan. 15 of this year. That was when US Airways Flight 1549 lost engine power on its climb out of New York’s LaGuardia Airport, eventually ditching in the Hudson River, thankfully with no fatalities.

In the rotorcraft world, just 11 days prior to the US Airways crash, an accident occurred with one of PHI’s Sikorsky S-76C++ offshore oil transport helicopters, in which eight people died and one survived with serious injuries. While media speculation is that a bird strike caused the crash — fueled by reports that the United States National Transportation Safety Board (NTSB) had brought in additional specialists to examine the wreckage for potential bird remains — the investigation is still ongoing. Suffice it to say, though, a bird strike may have been a causal factor in the accident.

These two high-profile incidents led the Federal Aviation Administration (FAA) to consider protecting the information in its National Wildlife Aircraft Strike Database from public disclosure. It seemed the FAA felt the public was becoming unduly alarmed by the reports and data, and that making the database fully public might jeopardize aviation safety. There was also some fear that operators and airports would hesitate to file reports of incidents if the data was made public.

After a 30-day comment period, and a formal objection from the NTSB, the FAA decided in April it could make the database fully public (see p.16, this issue) — except for a small amount of private information, such as personal phone numbers — “without jeopardizing aviation safety.”

Coincidentally, as I worked on this article, my email inbox received the sixth Concern Network report of an air medical helicopter striking a bird in just three weeks. It made me wonder, is the industry reporting bird strikes more because of public attention? Possibly. Or, is this a time of year for increased bird activity? Definitely.

Appropriately enough, since taking this assignment in March, I’ve personally had two encounters with birds that were significant enough to require aggressive evasive maneuvers to avoid impact.

So, are we being taken over by birds in 2009? Is there an ongoing conspiracy among the bird leadership to ruin our flying desires; a sort of re-monopolizing of the skies by the avian species?

The HEMS mission crew of this AStar made a successful landing after being struck by multiple ducks. Statistically, one in 10 helicopter bird strikes involve multiple strikes.

The NTSB and Transport Canada believe only about 20 percent of bird strikes are reported in all of aviation. That means Transport Canada’s 2007 totals of 1,283 reported bird strikes to airplanes and helicopters could be substantially higher.

That underreporting makes it difficult to estimate the total cost of bird strikes. Although, a 2002 report, The Costs of Bird Strikes and Bird Strike Prevention, by John R. Allan, did try to remedy this. It conservatively estimated that, worldwide, bird strikes cost airlines $1.2 billion US annually in damage and delays. While no similar studies are available for helicopter aviation, one can extrapolate from available data to come up with a total in the multi-millions.

In a 2006 report by Richard A. Dolbeer, Sandra E. Wright, and Edward C. Cleary, titled Bird Strikes to Civil Helicopters in the United States, 1990-2005, statistical distributions and trends of bird strikes with helicopters were studied. The report narrowed the analysis of the 64,734 reported strikes of all aircraft in the U.S. during that period, to the 370 that occurred with helicopters. Analysis showed that 50 percent of those strikes (186) resulted in damage, with 18 percent (67) resulting in substantial damage. Compare those helicopter totals to “all aircraft types,” which showed only 15 percent of strikes resulting in damage and only four percent having substantial damage, and the difference is eye-opening.

Further differences between helicopters and fixed-wing craft included helicopters accounting for 13 percent of the destroyed aircraft and 24 percent of the injuries caused by bird strikes — even though rotary-wing ships made up only 0.6 percent of all reported strikes. Helicopters also had a much higher rate of strikes during the enroute phase of flight, 63 percent, when compared with airplanes, which mostly encounter birds during takeoff, climb, descent and landing, with only two percent of strikes occurring during the enroute phase. The Dolbeer, Wright and Cleary report covered 16 years of data, and had several areas we can study to possibly modify our operations and avoid becoming part of the “Blood, Guts and Feathers Club.”

For instance, the vast majority (72 percent) of strikes happened between one foot and 1,000 feet above ground level (AGL). Only seven percent happened above 2,000 feet AGL. And, nine out of 10 strikes happened at 60 knots indicated airspeed or greater.

Waterfowl and gulls made up 56 percent of the bird species hit in the U.S., while vultures and raptors totaled 17 percent. Also, nearly one in 10 reported strikes involved multiple birds. Areas struck most are the rotors or windscreen (57 percent), with the nose getting 12 percent of the hits.

According to other data collected by aviation sources, more strikes occur during the day (63 percent) than at night (27 percent) and twilight (10 percent) combined. And, this other data confirmed the bird-strike risk is greatest during the migration seasons in spring (March and April) and fall (September and October).

Facial/eye damage is a big risk for pilots and passengers with direct impacts to the front of the aircraft.

Knowing the Risks
The most basic and oldest of aviation rules — see and avoid — is the best one for avoiding bird strikes. But, it takes diligence and steadfast commitment to scan for birds and other hazards, and will certainly not prevent all bird strikes.

Preplanning is key, too. Knowing your operations environment and the areas that present the most bird activity are a must.

Also, helicopters have advantages and disadvantages over airplanes when it comes to bird strikes. On the downside, we compete with birds for airspace more than airplanes do, and we don’t typically fly where there are the bird reduction measures many airports have. But, we do fly slower, are more maneuverable and typically are visual reference, with heads outside the cockpit more often. Further, we are not in pre-calculated, fixed flight paths in and out of altitudes that birds usually fly in. (The famous pilot “Sully” in the case of “US Airways vs. Canada Geese, 2009” fame had little he could do at his phase of flight.)

The impact of a 10-pound bird at 120 knots is almost as much as a 1,000-pound weight dropped from a height of 10 feet. The kinetic energy of the bird is a function of the speed at which it hits you. So, if you reduce the angle of impact and/or reduce the speed of impact — you are well on your way to preventing damage or injuries.

Paul Spring, operations manager at Phoenix Heli-Flight in Ft. McMurray, Alta., said his crews have had many encounters with birds and seen a lot of close calls, particularly with fire fighting and power-line patrol missions.

Recently, on a ferry flight in the bush, Spring had to dodge a last-minute encounter with a bird to avoid taking it in the face through the windscreen of his Eurocopter EC 120. The strike still resulted in $12,000 Cdn in damages. His wife, seated next to him, saw the worst of it, receiving a glancing blow to the other windscreen at the top, cracking it.

After a bird strike, close inspection of the aircraft is required to check for signs of damage. Here the front windscreen frames on an EC 130 were broken by impact with a golden eagle.

“We break it down into three risk areas for our crews,” said Spring, “low-level birds, migratory birds and birds of prey. The low-level encounters are mainly tree-based birds. Owls are the worst: they are fast and fly straight across a power-line patrol flight out of fear. We don’t have good maneuvering room in this envelope.” Spring said small birds are the most prevalent during fire fighting, but seldom do damage. To minimize contact with low-level birds, he recommended avoiding landfills, dumps and bodies of water.

Migratory birds have the highest concentrations during spring and fall. “They typically fly in the 2,000 to 4,000 foot AGL ranges, but descend, land and climb in and out of water areas; and present a particular danger during dusk,” said Spring.

Birds of prey (eagles, hawks and raptors of all kinds), meanwhile, tend to soar on thermals and are not flying to see-and-avoid standards — their focus is on things to eat on the ground. This was the kind of bird Spring hit, at 4,000 feet AGL in cruise flight. “He never knew I was coming, I was flying a pretty quiet aircraft and it surprised him,” explained Spring, who took last-minute evasive actions down and to the right, preventing a direct head-on blow to the pilot’s windscreen.

To help prevent and minimize strike risk and damage, Spring said pilots should always: wear a visor when flying; be vigilant and know their local flying area’s bird habits; fly with lights on — especially pulse lights; and both give and seek out pilot reports of bird activity.

Having a bird at the 12 o’clock position, slightly above your disk and closing, is the ultimate collision risk. If you have a bird in your sights and it is a possible collision risk, I recommend:

• Maneuvering as safely and quickly as possible to position the bird below the horizon (they instinctually dive once they sense danger, to gain speed and maneuverability). So, you should lower the collective and apply aft cyclic, possibly combined with lateral cyclic. This slows you down and loads your rotor disk more — for maneuvering — and helps get the bird closure rate reduced and below your horizon.
• Positioning the bird, if you can, outside of the 10 or two o’clock positions, or aft of your support beam between the forward pilot/co-pilot door edge and the windscreen. This greatly reduces the chance of hazardous impact.
• Being vigilant when avoiding the first bird, as there is a strong likelihood of others nearby. Even eagles soar in groups, as seen in the case of an EC 130 in the Grand Canyon last year.
• Using the see-and-avoid principle early, and keeping a diligent watch to avoid getting in extremis with a bird collision.

New helicopter pilots need to be taught these and other bird-avoidance techniques from day one to ingrain the right habits. So, for all veterans, share your knowledge with the “nuggets” out there, fly safe and avoid bird strikes.