Immovable human-factors obstacles are a major concern in helicopter safety.
David Learmount/LONDON
THE LIST OF HELICOPTER accidents which, occurred in 1995 (see P43) contains 209 accidents, compared with 272 for the previous year (Flight International, 20-26 September, 1995, P36). As promising as this may sound, however, it may have as much to do with the vagaries of helicopter-accident recording in various parts of the world, as with an indication of a definite improvement in safety.
In the world's largest well-recorded helicopter-operating arena, the USA, however, the optimistic picture would appear to be confirmed. The US National Transportation Safety Board's figures show a 1995 accident total of 162 compared with 207 in the previous year. Similarly, the rates for all accidents have been reduced, from 10.32 per 100,000 flying hours to 7.75, and fatal accidents also have lessened, from 2.39 per 100,000 hours to 1.24. The improvements are all significant but, for fatal-accident rates, they are dramatic.
On the other hand, the previous year was particularly bad for US helicopter safety, and figures as good as those for 1995 have been achieved before in the past five years.
Meanwhile, in Australia, where piston-engined, light-helicopter operations and agricultural flying represent a higher proportion of the total than they do in the USA, the Bureau of Air Safety Investigations reported an accelerating improvement in total accident rates during the 1990s, reducing from 25.6 per 100,000 hours in 1990 to 14.1 in 1995. Australian fatal-accident rates, however, have remained stubbornly resistant to improvement efforts, with the decade to 1995 showing an overall upward trend, even if it is tending now to level out.
The safety chief of the US-based Helicopter Association International (HAI), David Carter, says that an operational area which the HAI is watching with apprehension is the entry into the market of large numbers of retired military machines, particularly the ubiquitous Bell UH-1 (the "Huey"). They are being used for jobs for which they were not designed, such as logging, Carter says, and incidents of problems with tail-rotor gearboxes are increasing. Air claims' accident listing shows two UH-1 engine failures during external-lifting operations (22 April and 18 September). Carter also warns that the ex-military-helicopter sector is particularly vulnerable to bogus-parts trading.
A dramatic bogus-parts incident in the non-military international sector occurred on 26 May, when a Hughes 369D engine-to-transmission drive shaft, removed from a German helicopter after shock-loading and tagged for destruction, turned up in a US helicopter, where its failure nearly caused a fatality.
The immovable flight-safety problem, says, Carter, is not the machinery but the human-factors element, about which he despairs, explaining: "We haven't been successful in controlling human factors. The scary part is that the pilots who are at the best point in their careers - not too old, not too young - who should be the best in the business, just go out one day and do something stupid." He gives as a classic example a 22 April, 1994, Bell 412 controlled flight into terrain (CFIT) accident, of which Carter comments sadly: "It was a two-pilot crew; best pilots, best equipment, best everything." They failed to intercept an instrument-landing system, but flew on in fog (Flight International, 20-26 September, 1995, P42).
Age does not necessarily bring wisdom either. On 3 May (see list) a private Bell Jet Ranger struck trees in darkness, flown by a 67-year-old pilot whose licence was medically endorsed stating that he was not permitted to fly at night.
The Australian Aviation Insurance Group (AAIG) says that it has despaired of certain sectors of the helicopter market, such as search-and-rescue (SAR) and police work. "We don't insure any SAR-type helicopters," says the AAIG: "We believe the rates they are able to get out of [the London insurance market], irrespective of their accident rates, are far too low, given the risk."
Meanwhile, although two years ago the Flight Safety Foundation (FSF) reported that medical-evacuation (medevac) helicopter flight safety had shown an steady improvement over the seven years from 1987 to 1993, accidents, including fatal ones, still happen in that sector. The 20 December event in Switzerland (see accident listing) is a classic example of one of the infinite varieties of problems by which medevac pilots can be overcome, causing fatalities and another accident which, ironically, increases the number of casualties needing rescue. The FSF has reported that "adverse weather and spatial disorientation" tend to feature often in medevac accidents. Now, a Pennsylvania, USA, medevac company, called STAT MedEvac, has been cleared by the US Federal Aviation Administration to set up a network of global-positioning-system (GPS) satellite-navigation-based approach procedures to 13 remote hospitals. This may prove a good move - time will tell - but it is normally near the rescue site that the helicopter accident occurs.
One of the psychological problems for medevac pilots is the pressure for speed to save life. The FSF report quotes an Indianapolis-based medevac company as having adopted a policy which reduces that pressure. "We decided not to tell pilots why they were going on missions. We don't tell [the pilot] that he's going to pick up a critically injured three-year-old. We just tell him there is a mission and let him make his go/no-go decision based on that," it says. The pressure, however, can be re-created by what the pilot sees at the rescue site. It was on departure from the rescue site that the Swiss pilot made his fatal mistake.
Echoing the resigned attitude of the HAI's Carter to intractable human-factors problems, the AAIG says that industry attitudes do not encourage insurer confidence, explaining: "Helicopter people, as a generalisation, seem to be a different sort of breed to the average, fixed-wing, generation. They seem to have a bigger ego and be [resistant to outside criticism]." It is not all bad, however, the AAIG suggests, saying that younger pilots seem to be more safety-conscious than their predecessors.
The AAIG's view on a general lack of safety awareness would appear to be confirmed by the fact that pilots who attend a tailored safety-awareness course are 70% less likely to be involved in an accident.
Certainly, among the accidents recorded this year, pilot error or misjudgment as a causal factor in accidents shows in double the number of events of any other causal category (see table). This is a cautious estimate, showing pilot error as the main factor in 43% of the accidents, but this estimate will probably prove to have been conservative when all the investigations are complete.
Not all pilots have to get airborne to have an accident. On 3 December, an Aerospatiale Ecureil was left by its pilot on the ground with rotors turning at 100% RPM while he disembarked to attach fire-fighting equipment to the belly hook. With wind gusting at 35-40kt (65-75km/h), the helicopter started to get airborne with no pilot. An attempt by the pilot to climb on board as it left the ground destabilised the helicopter and it rolled over and crashed. The pilot was lucky to escape with his life.
External lifting work is one of the potentially most hazardous tasks performed with helicopters, especially when it is carried out in remote and unfriendly environments, as it often is. The accuracy of judgement required of the pilot, together with the need for above-average flying skill and continual alertness to multiple potential hazards during the mission, cannot be maintained over long duty-times. Yet, on 31 September, a Bell 214B helicopter pilot, on a logging job in Canada, who had been working for 8h, finally got himself into a situation which need not have happened (see accident listings). The event has all the hallmarks of the kind of degraded judgement, which fatigue causes, and the fact that the initial accident report highlights that duty time is an indication of the investigators' concern. The equipment-failures total (which includes engine/power failure, "other mechanical failures" and main/tail-rotor failures) comes to 66 events. At least three of these accidents have already been officially determined to have been caused by maintenance error, and many more may yet be. In any case, that results in technical failure being a primary causal factor in 32% of the 1995 accidents listed, with engine failure the most common of failure categories (42 events/20% of accidents).
The fact that helicopters are mechanically complex with highly stressed critical components, compared with their relatively unstressed fixed-wing counterparts, is normally used as the explanation for the high proportion of technical-failure accidents. Whether the industry is satisfied with this as an explanation for quite such a high proportion of accidents is something, which it has to decide. In the US NTSB's 1995 figures, the sum total of engine and maintenance/material accidents is 58 out of 162, which constitutes 36% of all US accidents. In 1994, the same causes were responsible for 34%; in 1993 it was 29% and in 1992, 28%, so the proportion seems to be on the rise. Perhaps it is this, which has caused the HAI's Carter to worry about Hueys in the civil market.
Tail-rotor accidents
In May 1996, the Flight Safety Foundation (FSF) published a study of tail-rotor accidents to turbine-engined helicopters for the period 1988-93. Using NTSB statistics for US-registered helicopters, the FSF reports that there were 74 tail-rotor accidents in the period, and the single most frequent cause (38% of tail-rotor accidents) was "strikes", in which the pilot's manoeuvring caused the rotor to hit the ground or prominent objects such as trees. The second most common cause (31%) was "complete loss of thrust" (CLT), the result of a mechanical failure of the drive, gearbox, or rotor. CLT accidents caused more fatal accidents than strikes, however, and more fatalities.
"Loss of tail-rotor effectiveness," a temporary condition caused by aerodynamic factors (23% of the tail-rotor accidents), is almost always correctable or avoidable by a pilot who understands its causes, says the FSF's report.
The ultimate answer may be to admit the vulnerability of helicopter transmission systems and invent better ones. That is precisely what the US Army has just given Bell Helicopter Textron a $12 million contract to do, at the same time as it is divesting itself of all its old Hueys and the associated problems.
There were 14 listed wirestrike accidents in 1995, which compares well with 28 the previous year. In one accident in Australia in 1995, the wires hit should have been marked on charts, but were not. The NTSB figures again mirror the overall experience as well as contributing to it: wire strikes in the USA dropped from 20 to eight, but it is not possible to determine any encouraging trend in US figures.
The US FAA, referring to a problem endemic to highly automated airliner cockpits, has recently called for "the whole system" (all sectors of the air transport industry) to re-appraise its approach to human-factors issues (Flight International, 9-15 October, P26), rather than producing solutions one by one. Perhaps "the whole system" in the rotary-wing world should do the same; and not just for human factors.
Source: Flight International
