IMC, pilot error cited in rotorcraft mishaps

 - January 23, 2008, 10:07 AM

If all flights took place in flawless conditions, in ideal weather and with perfectly designed aircraft that are maintained to impossibly impeccable standards and flown by only the most skilled of pilots, there would still be accidents.

Why? Because try as we might, humans (and the machines they design) have a long way to go before attaining perfection. This holds especially true for the men and woman who fly helicopters in the Part 135 environment.

A study of 147 accidents from 1991 through 2000 involving Part 135 helicopter operations has revealed that some long-held assumptions about IMC flying are true, as are some not so well known facts. An analysis conducted by Dr. Patrick Veillette and recently published by the FlightSafety Foundation offers a wide-ranging roundup of safety insights.

For example, Veillette found that 58 percent of the fatal accidents recorded between January 1991 through December 2000 occurred in IMC, with human error cited as the primary causal factor in 66 percent of the accidents. Most of the human error-related accidents studied occurred during the en route phase of flight and shared various degrees of three different accident causes: inadequate in-flight planning, poor decision-making or inadequate evaluation of weather information.

During the period studied, there were 147 accidents and 306 incidents involving Part 135-operated helicopters within U.S. airspace. Forty-three of these accidents resulted in fatalities, 29 percent of the total. Of the 616 people aboard the accident helicopters, 22 percent (for a total of 133 people) were killed, 66 people (11 percent) were seriously injured and 112 people (18 percent) received minor injuries. A total of 311 people (50 percent) involved in these accidents were uninjured.

Just one of the 147 accidents involved a collision between two rotorcraft, hence the total number of accidents examined involved 148 helicopters. Of those, 48 helicopters (32 percent) were destroyed, and 97 helicopters (67 percent) were substantially damaged.

In analyzing the data digested for his paper, Veillette combined reports from both the FAA and NTSB, as well as from NASA’s Aviation Safety Reporting System (ASRS), which brought into the examination process information on a further 306 Part 135 helicopter incidents and 457 ASRS field reports. Sifting through this data, Veillette, himself a professional pilot with more than 13,000 hours, found that:

• Forty-two of the 147 accidents (29 percent), including 25 (58 percent) of the 43 fatal accidents, took place during IMC. Thirty-six percent (15) of these were controlled flight into terrain (CFIT) accidents. Another 13 involved loss of control and/or spatial disorientation.

• An astoundingly high percentage of the total number of accidents took place during en route flight– 82 out of the 147 accident total, including 32 (74 percent) of the total fatal accidents. Additionally, no fewer than 169 of the 306 incidents took place during the en route phase. This trending has surfaced in other helicopter safety studies, most recently an exhaustive examination of aeromedical accidents conducted by University of Chicago researchers. Forty-three of the en route accidents recorded by the FAA (52 percent of total accidents) had causes traced to human error. Thirty-two (39 percent) of the en route accidents occurred in low visibility, and 22 (69 percent) of those accidents were fatal.

• The accident rate for approach and landing, traditionally considered the most dangerous part of the flight regime, continued to be hazardous, with a full 22 percent (33) of the accident total and five fatals (12 percent of the total) taking place at that time.

• Twenty-nine accidents (20 percent of the total), including five fatal accidents (12 percent), and 41 incidents (13 percent) occurred during takeoff. Of those accidents, 24 (83 percent) were the result of human error. Eight takeoff accidents (28 percent) resulted from collision with obstacles. Five takeoff accidents (17 percent), two of which involved fatalities, occurred in low visibility.

• Forty accidents (27 percent) and 98 incidents (32 percent) involved engine failures.

• Of the 306 incidents, 165 (54 percent) resulted in only minor damage to the helicopters; 141 incidents (46 percent) resulted in no damage at all.

Down Where the Danger Is
The Part 135 helicopter does not cruise at 35,000 feet at Mach 0.80. It flies down in the weeds, often in uneven terrain and uncertain weather conditions. “The vast majority of the missions are conducted with one pilot,” Veillette wrote, “pilots typically under pressure to maintain high utilization rates, provide reliable on-demand service and respond quickly to humanitarian missions. This results in frequent operations into marginal VFR conditions and IMC, as well as landings and takeoffs from marginal sites, such as roads flanked by power lines, trees, hillsides.”

On top of the need to operate from unconventional landing and takeoff sites (because isn’t that what the flexibility and versatility of the helicopter is all about?), another factor adding to the overall riskiness of Part 135 operation sits right in the front seat of most rotorcraft. It’s the pilot.

Pilot Personality Traits
Veillette cited a special report prepared for the Canadian Minister of National Heath and Welfare by O.W. Skjenna entitled Cause Factor: A Treatise on Rotary Wing Human Factors, in which it was noted that helicopter pilots showed a pattern of basic personality factors that are conducive to an increased tendency to take risks. The helicopter pilots tested showed a lower tendency than other pilots to conform and a high tendency to achieve. Helicopter pilots generally are goal-oriented individuals. “This characteristic adds motivational pressures, largely self-induced, to conduct a flight when requested, to complete the flight as planned, to please the passengers, to meet schedules, make money and impress peers,” wrote Veillette.

Quantifying these factors with hard numbers is difficult and too often imprecise. However, Veillette extrapolates some data from the NASA ASRS program that shows that when it came to self-examination and constructive self-criticism, the support of “to thine own self be true” was definitely in command.

Of the 457 reports examined in the study, 39 percent were submitted by EMS pilots, 29 percent were submitted by on-demand pilots, 18 percent were submitted by air-tour pilots and 13 percent were submitted by offshore helo pilots. A full 58 percent of the reports dealt with nonadherence to regulations. Other incidents dealt with near-midair collisions (39 percent), inadvertent encounters with IMC (29 percent), wire strikes, unauthorized flights into controlled airspace, violations of ATC clearance and mechanical malfunctions.

Eighty-one percent of the reports submitted by air-tour pilots involved nonadherence to regulations. Almost one-fourth of those violations concerned aviators busting the air-tour minimums established by SFAR 71, the regulations group that govern air-tour ops in Hawaii. One of SFAR 71’s major requirements is that no air tour be conducted less than 1,500 feet agl and no closer than 1,500 feet from any person or property. Since getting the customers close to what they want is a large part of the air-tour experience, it’s easy to see how such minimums could be broken.

It’s the many ways in which a helicopter can be operated that make it so attractive. Often that multifunctional capability gets helicopter cockpit crews in trouble. High workload was cited in 63 percent of the ASRS reports, with a single pilot often tasked with controlling the aircraft, navigating, monitoring multiple radio frequencies and sometimes even conducting passenger briefings. This concentration of duties prompted 77 respondents to claim they were overloaded with work.

This work overload carried over into communications problems cited by 49 percent of the ASRS respondents. In descending order, pilots complained of having to monitor several frequencies (75 reports), having to sort out congested frequencies
(63 reports) and inadequate radio reception (47 reports). The remaining 38 reports cited interference from intercom calls from passengers or crew.

Late or Low: a Dangerous Combination

Of course, the whole reason to travel via helicopter is to save time, and time pressure was cited in 170 (37 percent) of the responses, the vast majority of them penned by aeromedical pilots (119 out of that 170 total) who tied the time pressures to concerns about the medical condition of their patients.

The keenness of the whip with which time lashes us is evidenced by the results of a human-error study conducted by James Reason and presented to the 22nd International Seminar of the International Society of Air Safety Investigators in Canberra, Australia.

Reason found that the probability of human error is increased by a factor of 11 by time pressure; by a factor of eight in circumstances involving inadequate human-systems interface or the irreversibility of error; by a factor of six in circumstances involving information overload; and by a factor of four in circumstances involving misperception of risk. These results favor much of the current stress/safety thinking.

When it comes to helicopters, what they do best they do low–patrolling powerlines, serving as camera platforms for TV stations, aiding law enforcement or hovering with mammoth loads slung underneath, their pilots struggling to place that huge office-building air conditioner into place.

Not surprisingly these sorts of low-altitude operation claim their share of helicopter accidents, according to the FAA/NTSB numbers. Of the 147 accidents cited, 65 (44 percent) occurred at or below 100 feet agl; 104 accidents (71 percent) at or below 500 feet agl; and 130 accidents (a whopping 88 percent) at or below 1,000 feet agl.