The seriousness of unruly airline passenger behaviour has worsened even though the number of cases has dipped.

Alcohol and drugs are the main cause of bad behaviour on flights, media were told by the International Air Transport Association in Geneva.

''Intoxication either by alcohol or by narcotics continues to be a significant issue. The problem here relates to drinking prior to boarding the aircraft or consuming duty free alcohol purchased at airports onboard without the knowledge of the crew,'' said Tim Colehan, the association's assistant director of external affairs.

The level of intoxication may not be apparent at the time of boarding.

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The latest figures are from last year when 9837 instances of poor behaviour from all causes were reported, a drop from 10,854 the previous year.

Further analysis of drunk passengers showed most of the bad behaviour was level one - the least serious, but 444 were level two involving physically abusive or obscene behavior, verbal threats of physical violence and tampering with emergency or safety equipment.

''These can be more challenging to manage in the confines of an aircraft.''

The proportion of the more serious episodes had risen from 11 per cent of incidents in 2015 to 12 per cent in 2016.

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Colehan said almost four billion passengers would safely fly this year. Over 24 hours more than 100,000 flights will take off and most will land without trouble.

''But there are a tiny minority of passengers whose unruly and disruptive behaviour can disrupt the flight experience and travel plans of countless other passengers and adversely impact the work place for cabin crew. Unruly passengers remains a significant daily issue around the world,'' he said.

But there are a tiny minority of passengers whose unruly and disruptive behaviour can disrupt the flight experience and travel plans of countless other passengers and adversely impact the work place for cabin crew

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The data came from reports submitted by about 190 airlines.

Non-compliance with safety regulations was also a key issue, Colehan said.

Nearly 55 per cent related to smoking onboard, 34 per cent to compliance with regulations such as turning off or not using electronic devices) and 14 per cent related to compliance with seat belt signs.

The biggest obstacles to deterring bad behaviour were international laws.

Although the state where the aircraft was registered had jurisdiction over unruly passengers on flights, unruly passengers often landed at a foreign destination where police were powerless to deal with them.

''Too often those accused of unruly and disruptive behavior are released without charge,'' said Colehan.

The association wanted more guidance for states on the use of administrative or civil penalties in certain cases. This is already in use in some countries such as New Zealand and the United States where aviation security officers can impose spot fines.

''Think of this as like a speeding tickets for motorists. You get an infringement notice and you can either pay a fine or appeal it. We believe this is an important opportunity in some cases for unruly passengers to face the consequences of their actions, again acting as a better deterrent.''

IATA had issued comprehensive guidance to member airlines on unruly passenger prevention and management and responsible service of alcohol.

The guide is being updated next year.

''Unruly passengers remain a significant issue for the industry and the only way to deal with this problem is for governments, airlines and other stakeholders to continue to work together to resolve it.''