David Learmount/LONDON Paul Phelan/CAIRNS
Turbine engined helicopter accident numbers for last year are well up on those for the previous year: 239 compared with 171 in 1997. Comparison with 1996 also shows an increase, although less dramatic, from the 218 accidents that year.
In 1997, only 17 accidents were caused by engine failure, but that figure more than trebled last year, to 57. The US Federal Aviation Administration has targeted turbine engine failure in its safety improvement campaign for airlines. Perhaps that effort should be extended to rotary wing operations.
Health and usage monitoring systems (HUMS) could have warned of the faults leading to many, if not all, of the 57 engine failures and subsequent serious damage which occurred last year - and not just to those in the engine, either. A total of 13 main or tail rotors also failed, some failures occurring in the blades, but more usually in the drive or gearbox.
The 6 June incident (see tables) involving an Aerospatiale AS350B, which occurred just after landing, may have been prevented by HUMS.
Capt Peter Gray, helicopter safety specialist for Geophysical Safety Resources, says there has been a 25% increase in the number of deaths worldwide in oil support operations. Over the past 10 years, the fatal accident rate for non-public transport helicopter operations, from three fatal events per 1 million flying hours, to nearly 35, while that for fixed-wing aircraft has dropped. "Non-public transport helicopters are steadily becoming less safe," says Gray. "The present rate is unacceptable and something must be done to stem the tide."
The HUMS, pioneered to monitor helicopters servicing the oil platforms in the North Sea, is coming of age. When operators began to use the system in the late 1980s, they said that they did not know what to do with all the data produced. Another early problem was that vibration - endemic in helicopters - is a primary source of diagnostic information, but what was normal had to be established before warning could be given of abnormalities and exceedances.
Ten years on, systems are becoming smarter, more generic - and therefore cheaper - and capable of identifying more potential failures. For example, Smiths Industries Aerospace offers a multi-aircraft generic (GenHUMS) system, using off-the-shelf airborne and ground technology. Recently, the UK Ministry of Defence selected the GenHUMS for the Boeing Chinook.
The GenHUMS provides conventional HUMS capabilities, plus rotor track and balance, failure detection, flight regime recognition, alert generation, system configurability, and a user interface. All the required airborne data acquisition and processing, including crash survivable cockpit voice recorders (CVRs) and flight data recorders, are combined in a single line replaceable unit. This reduces space, weight and power requirements, making the GenHUMS cheaper to operate and maintain. On the ground, PC-based equipment can handle the data extraction and analysis.
Maintenance data
As well as warning of potential equipment failures, the GenHUMS collects data for routine maintenance. It monitors and records nearly 200 parameters, and acquires, processes and stores data in cartridge form for routine maintenance. The system also has a crash-survivable memory and CVR to support incident analysis.
Sensors around the airframe provide input on engine and gearbox vibration, rotor track and balance, avionics and overall aircraft performance. Essential health data is provided to the flightcrew. Smiths says that future developments will include an upgrade which will enable fatigue prediction in real time. If, however, all the evidence of impending failure is there and the organisation still does not take it seriously, there is no point in having it. The 18 July fatal accident to a Sikorsky CH-54A (see tables) is a reminder of the way in which tragic decisions to take a serious risk are made, which, in this case, also contravened regulations.
It is essential to reduce mechanical or system failures, and the HUMS can do that. Taking unreasonable operational risks, however, is not something the system can influence, except to provide accurate detail of the resulting mishap. This review could reasonably add a new category to its summary of accident causes: undertaking unacceptably high-risk tasks. If the category were to be added for 1998 accidents the number of events could total 13.
Helicopters are unique in the variety of tasks they can perform and in the types of site at which they can be carried out. Sometimes, the helicopter is the only means available, which can put extreme pressure on a crew. Some medical evacuation companies make a point of briefing the crew only on the destination for a mission, but intentionally do not go into detail about the evacuees or their condition. The pilot's job should be to arrive safely, pick up the evacuees and leave safely.
Within the category, there would have to be differentiation between those high risks for which a pilot's tactical decision were responsible; those missions on which the helicopter should not have been dispatched that day because the weather was below minima for the task, or because a proper landing/operating site survey had not been completed, and finally, those contracts which the operator should not have accepted. Without the final accident reports, it is difficult to determine where the fault lay in most cases, unless there was an obvious tactical misjudgment by the pilot - which tends to be clear from the circumstances. What can rarely be ascertained, however, is how much a pilot misjudgment about acceptable risk is influenced by pressure from the employer.
Perhaps the most frequently occurring accidents in which the operational wisdom looks suspect involve work on overhead power cables, either slinging them or repairing the wires, or towers (see accident list, 3 February). The requirements for precision flying are high, the visual cues poor, and the price of a mistake, or a gust of wind, is heavy. Site surveys are vital for safety in the case of agricultural work and planned landings at off-base sites, but there is little evidence that they are often done well.
Aviation authorities report that one of the top accident causes every year, in general aviation fixed and rotary wing incidents, is that of continuing visual flight rules flight into instrument meteorological conditions, generically known as continued flight into deteriorating weather. This begs the question as to which standard operating procedures companies follow.
Training accidents increased, from nine to 25, over the year. Most of the mishaps follow practice autorotations and result in severe damage or write-offs. This represents an expensive mistake, which ought to be avoidable. The exercise is complex for early trainees, and even for type-raters in unfamiliar aircraft.
Australasia
Australia has twice the reported helicopter accident rate of that of the USA, although the air safety community claims that this is largely because of differences in how an accident is defined. New Zealand, with similar definitions, has about twice the Australian accident rate. New Zealand reported 34 accidents from a fleet of 350 helicopters, or about a 10% rate, while Australia reported the same number of accidents from a fleet of 800.
New Zealand has a large helicopter population and a broad spectrum of operating standards, ranging from highly professional to non-compliant, say safety consultants. The terrain and the nature of some operations make some New Zealand helicopter flying more than usually hazardous, they say. Of the accidents during the year, 11 involved turbine powered aircraft. About 20% of the fleet is uninsured.
Pat McLaughlan, of Boston Marks insurance broker in Auckland, observes that New Zealand helicopter safety statistics are relatively static. He says there is a high degree of self regulation, with which compliant operators are becoming frustrated because the situation provides the non-compliant - virtually untouched by the authorities - with a commercial advantage.
The insurance industry, says McLaughlan, is depressed, because a relatively large number of operators rely on agricultural work, which has more than its fair share of accidents. Some 14 of the reported Australian accidents last year occurred during stock mustering operations.
John Funnell, managing director of Helicopter Services (NZ), speaks for the larger operators, saying: "The Aviation Industry Association has set up an advisory council in which senior industry figures approach pilots conducting dangerous or illegal activity. We talk to these people and try to educate them in the error of their ways and try to encourage them to change their operating techniques, more in line with standard procedures."
John South, an Australian aviation safety advisor to major companies, says: "The major commercial helicopters have mature quality assurance, into which are incorporated equally mature safety management systems. The control of documentation is well audited internally. The emphasis is more on safety than general compliance. Both the major offshore helicopter organisations [Bristow and Lloyds] look on the regulatory standards as a minimum."
Source: Flight International
