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Substance use: regulatory environment for preventing performance impairment

The detrimental effects of drugs and alcohol on cognitive abilities are well documented. International research suggests the likelihood and severity of accidents increase if people responsible for performing safety-critical tasks use drugs or alcohol. In the New Zealand air, rail, and marine accidents investigated by the Transport Accident Investigation Commission, the consumption of alcohol or use of other performance impairing substances recurs as a contributing factor or a potential impediment to survival. Since the Commission first placed this item on the Watchlist, commercial aviation and maritime operators have been required to have drug and alcohol management plans while regulators are to be given testing powers. However more can still, and should, be done.

What is the problem?

Judgement, decision-making, and reaction time can all be affected by the use of drugs or alcohol. The use of performance-impairing substances by persons performing safety critical tasks in a transport environment is a significant risk. The Ministry of Transport supports zero tolerance of operator impairment; however, industry arrangements are uneven across the sectors and more could be done to manage this risk.

What is the solution?

Regulators and operators need a comprehensive set of measures to prevent impairment by the use of alcohol or drugs of persons performing safety-critical tasks. As a minimum, the aviation, rail, and marine sectors—including recreational boating—should have in place arrangements to:

  • set maximum limits for alcohol
  • prohibit people operating aircraft, vessels or rail vehicles if they are substance impaired
  • require operators to implement drug and alcohol detection and deterrence regimes, including random testing
  • prescribe post-occurrence testing requirements for drugs and alcohol.



The detrimental effects of drugs and alcohol on cognitive abilities have been described and documented by researchers in the transport sector. Australian Transport Safety Bureau research describes how alcohol ‘impairs almost all forms of cognitive function, such as information processing, decision-making, attention and reasoning’ (Newman, 2004a, p.1). Such impairment detrimentally affects the performance of any demanding task.

Cannabis can also adversely affect behaviour, cognitive function and psychomotor performance; ‘complex tasks … are particularly sensitive to the performance-impairing effects of cannabis’ (Newman, 2004b, p.1). In the case of a pilot, for example, flying skills deteriorate, and the pilot makes an increasing number of errors. Pilots are often unaware of their reduced performance.

The risk of accidents increases if people responsible for performing tasks critical to the safe operation of aircraft, vessels or rail vehicles use drugs or alcohol. The Australian research states ‘many studies have shown a significant proportion of aircraft accidents associated with alcohol use’ (Newman, 2004a, p.1); similarly, a US report states, ‘numerous studies have shown that alcohol use increases both the likelihood and severity of boating accidents’ (Lawrence, Miller & Maxim, 2006, p.1).

The consumption of alcohol, or use of other performance-impairing substances, features repeatedly in accidents investigated by the Commission. Since the beginning of 2014, we have investigated twelve occurrences where persons performing safety-critical roles in the operation of aircraft, vessels, or rail vehicles have tested positive for performance-impairing substances (one of these occurrences involved prescription medicines). Forty-two people died in these accidents, including the eleven killed in the hot-air ballooning accident in Carterton, one of New Zealand’s worst aviation disasters.

The Commission has made several recommendations about setting maximum allowable limits for performance impairing substances for people in safety-critical roles, including those in charge of recreational craft; and providing for testing of such levels. Limits should be appropriate to the mode, and reflect the goal of zero tolerance to impairment. These measures are in line with the alcohol and drug testing, including random testing, that is accepted practice in road transport, as well as in other modes in other jurisdictions.

As a result of our recommendations, new measures are being introduced requiring commercial aviation and maritime operators to have drug and alcohol management plans. In addition, the aviation and maritime regulators (the Civil Aviation Authority and Maritime New Zealand) will be given the power to undertake non-notified alcohol and drug testing. This can include random testing, good cause testing and post incident testing. No changes have been made to the recreational boating sector.

When investigating an accident, the Commission cannot require survivors, including those in safety-critical roles, to be tested for performance-impairing substances. This makes it difficult to assess the contribution, if any, of performance-impairing substances to an accident or incident. The Ministry of Transport is still reviewing the need to requiring alcohol and drug testing from survivors of an aviation, maritime or rail accident in the commercial and recreational sectors. We await policy decisions in this area.

The Commission will continue to monitor the incidence of accidents featuring alcohol or drug impairment, and to seek a regulatory environment that supports a zero tolerance for impairment in safety critical transport roles.

References and download


References for further information are given in this .pdf download version.

Version history


First published January 2015 and updated October 2016. This issue’s updates: references to new inquiries; information on new measures and continuing policy work intended to help reduce the risk of drug and alcohol impairment. This update was consulted with: Ministry of Transport, Civil Aviation Authority, New Zealand Transport Agency, Maritime New Zealand.