At least four pilots of Indonesian airlines have been stripped of their flying licences in recent weeks after being tested positive for hard drugs. Two of those pilots were arrested over the drug charges.

The country's anti-narcotics agency says there are more pilots using narcotics but has not disclosed any more details.

According to the Indonesian Pilot Federation, there has been a major rise in drug usage among the country's pilots due to stress caused by increased work loads.

Al Jazeera's Step Vaessen reports from Jakarta.