Helicopter safety is about more than not having accidents.
David Learmount/LONDON Ramon Lopez/WASHINGTON DC Paul Phelan/CAIRNS
Although helicopters, like fixed-wing aircraft, often emerge from dangerous situations without harming the people on board, they are particularly vulnerable to damage which could be described as self-inflicted. As one helicopter pilot observes: "There's so much energy in a hovering helicopter that, in a relatively non-dangerous situation, it can put down and thrash itself to pieces."
A hard landing in a fixed-wing aircraft might merely call for a gear inspection, but in a helicopter it might cause the main rotor to sever the tail boom, and the aircraft to roll over, causing further damage, which makes the hull a write-off for the insurers.
The latter is a dramatic example, but not rare, as the following accident list (PP39-51) shows. Comparisons between fixed- and rotary-wing safety, however, can have only limited validity because the two types are used in such different roles. Almost always, if a fixed-wing aircraft can carry out a task efficiently, it will be chosen in preference to a helicopter because of its greater speed and lower operating cost over a given distance. If a helicopter is used, it is because a fixed-wing aircraft would not be suitable for the task.
Helicopters are used usually for non-standard jobs. This makes setting standards and drawing up standard operating procedures (SOPs) more difficult for regulators and operators. In addition, helicopter pilots are more likely to be faced with situations for which there are no SOPs.
In the case of rescue or medical evacuation (medevac) flights in dangerous conditions, the pilots can be faced with ethical as well as operational decisions - do you go on and risk everything for the patient, or abandon the rescue?
The accident list shows the result of decisions to continue a rescue, with no margin for error or sudden wind-change. The accident in Colorado on 9 July is an example of a no-margin exercise, but there are 12 medevac events listed, each of which represents not just an accident, but a rescue failure.
David Carter, director of safety and flight operations at the Helicopter Association International (HAI) says: "The human factor - that's where we've got to look. The machinery is rarely the problem."
The 1994 accidents list would suggest that Carter is talking in relative terms: there were at least 21 fatal and 83 non-fatal turbine-helicopter accidents in the year, apparently precipitated by serious engine or other mechanical failure. That makes 104 out of the 270 recorded here, and that total does not include the events, which, as yet, have yielded no clues as to their cause.
Capt. Lew De Marco, head of helicopter flight operations at the UK Civil Aviation Authority, agrees with Carter on the human element, saying: "Airworthiness-related catastrophic events have been superseded by operational events."
David Chapman, head of rotorcraft in the CAA's design and manufacturing standards division, observes that the demands imposed by the offshore oil-support industry in the hostile North Sea, perhaps the world's most demanding large-scale rotorcraft operation, has made the North Sea a fertile breeding ground for advanced-safety thinking - and learning.
It was this environment which spawned the widespread voluntary installation of helicopter health and usage monitoring systems (HUMS) by North Sea operators. Chapman points out that the UK helicopter-accident rate, calculated on a five-year moving average, peaked at four accidents per 100,000 operating hours in 1983-7 and, since then, has dropped continuously, reaching a low of 1.5/100,000h for the 1990-4 period - the most recent assessment available.
De Marco says that offshore operators are still learning about the HUMS. "Every flight downloads masses of data...there's an awful lot of learning going on about what stage indications for any given unit become significant," he says. The operators say that, in cost terms, the HUMS is still a two-edged sword: it can provide warnings improving safety and enabling preventive maintenance, but also gives "warning symptoms" whose significance is little-understood.
France's Bureau Enquetes Accidents does not attempt to estimate helicopter operating hours, so cannot produce estimated accident rates for French-registered aircraft. It has however, provided accident numbers from 1990 to 1994, which show a public transport sector, which suffers an average of 1.8 accidents a year (0.6/year fatal accidents) and no trend up or down, an air-work sector averaging 25.8 accidents (three fatal) annually, but a promising 1994 with only 14 events and a private sector with an average 22.8 accidents a year (seven fatal) and a slight downward trend.
The last time that the Australian Bureau of Air Safety Investigation (BASI) carried out an extensive analysis of helicopter safety was in 1990, tracking performance of Australian-registered aircraft over the decade to 1988. It was probably the most detailed analysis of helicopter accidents ever carried out by any authority, and revealed some generic truths which appear not to have changed significantly in the last five years - at least in Australia's environment:
Turbine-powered and piston-powered helicopters are proportionately equally vulnerable to given accident causes or contributory factors: eg, pilot error is a factor in about 60% of accidents in both types, terrain in 20% to both types;
BASI found that the same was true for the proportions of accidents related to flight phase. The message is that the degree of vulnerability to any given accident category is the same for piston- and turbine-powered helicopters;
Over a seven-year period, the highest risk was for agricultural flying (69.5 accidents per 100,000h), with rates decreasing as follows: test and ferry flying (42.7), training (38.6), private/business (29.4), stock mustering (cattle herding) (19.3), mapping/photo/survey (16.7), with charter the safest at 12.7 events/100,000h. Fixed-wing general aviation, where roles were the same, was always safer by a considerable margin, the highest differences being in training (fixed-wing five times as safe) and agricultural flying (more than twice as safe).
Perhaps partly because of the analysis, the current Australasian rotary-wing industry seems more self-critical, with operators obviously under pressure from insurance costs and public-safety perceptions. Australian and New Zealand helicopter-safety statistics are still recognised as worse than the world average, but activities such as deer shooting and cattle mustering are still confirmed, contrary to popular belief, as not being the worst "culprits".
The Helicopter Line, a high-profile New Zealand tourism operation, has suffered two fatal accidents in the past two years because pilots disregarded SOPs, and the company acknowledges that it will not stay in business if this is allowed to continue. In the USA, the tourist-helicopter industry in Hawaii, is under intense scrutiny by the US Federal Aviation Administration and the appearance of Hawaiian accidents ten times in the 1994 list, shows why this scrutiny is needed.
The New Zealand CAA (NZCAA) director Kevin Ward signaled in 1994 that he was unhappy with the number of helicopter accidents, totaling about 30 a year that the authority is aware of, in a fleet of about 360 aircraft.
New Zealand helicopter flying has been increasing, and the NZCAA, giving a "best estimation", says that operators are now flying a total of about 100,000h/year."
Ward says that New Zealand's current helicopter-accident rate, based on insurance claims, is about 41 per 100,000h for private operations and 28 for revenue operations, commenting: "We intend to reduce this to 25 for private operations, 15 for aerial work, and 5 for air transport by 2000. Most of the accidents are in the Robinson R22 and Hughes 269 field, where overloading and other excursions from good practice seem to be a routine event."
Barry Payne, a consultant and chief pilot at the Helicopter Line, says: "We're in the process of implementing what we call an enhanced safety environment, highly targeted at the identification of hazards and latent failures, running it on the Reason model. We've just joined an international programme called TOPS [tour operators' programme for safety]...including about 12 US operators. We'll be the first international operator to go with the programme. It's almost a Part 121 standard for helicopter operations." The TOPS programme is being coordinated by the HAI.
According to US National Transportation Safety Board figures going back to 1975, helicopter accident-rate trends for the USA do not look good. Turbine-powered helicopters provide the best figures, but the trend shows no significant improvement since the 1970s. The total turbine-powered accident rate was 2.06/100,000h for 1994, but 6.06 the year before, and the 1994 fatal accident rate for the category was 0.77.
Piston-engined helicopters provide the bad news, with NTSB figures for 1993 (the latest year analysed) showing a total US accident rate of 26.49/100,000h and a fatal accident rate of 4.32. The fatal accident rate trend is worsening and the total accident rate is where it was in 1979.
A report, expected to be published by the US National Transportation Safety Board (NTSB) in the near future, should lay to rest the long-running, much debated saga about the safety of the highly commercially successful Robinson R22/R44 family of piston-engine-powered helicopters. A Government source close to the NTSB says that the report, which studies 27 in-flight break-ups caused by main-rotor contact with the tail boom, is expected to tone down its earlier recommendations, but not to eliminate them.
The NTSB admits that there is still no evidence as to why the "mast-bumping" occurred, and for that reason wants testing to continue. What is really under fire is the FAA's certification testing procedure. The US Government source says: "The dilemma is that these helicopters fly 100,000h in the USA before an accident occurs. The FAA questions the need to ground an aircraft which the majority of pilots are operating just fine." In other words, the accident rate is not unduly high - a fact, which the UK CAA's Chapman confirms is true for the 200-strong UK-registered Robinson fleet.
Chapman and the HAI's Carter both insist that the Robinson's low cost and commercial success have brought in new pilots whose low experience makes them accident-prone as a group. Chapman and the NTSB, however, describe the aircraft respectively as "unforgiving" and "sensitive", and believe that these characteristics, combined with low pilot experience, hold the key. Human factors, is the dominant theme again, but not the only one.
Source: Flight International