The pilot reported that on entering the aircraft during the preflight inspection he noticed a strong chemical odour. Discussion with the duty tarmac engineer confirmed the aircraft had been sprayed for pest control the previous night. During the flight to Emerald the pilot began feeling ill. During the turnaround at Emerald, he contacted company operations and said that he was feeling ill but was of the opinion that he was well enough to return to Brisbane. During the later stage of the flight from Blackwater to Brisbane, the copilot also started to feel ill and described the same symptoms that were affecting the pilot. Both pilots then used the crew oxygen system and began to feel better after about 10 minutes. On arrival Brisbane both pilots were unable to continue duty. Both pilots visited their medical examiners who were of the opinion that the pilots had been exposed to a poisonous substance.
Investigation revealed that the chemicals used to treat the aircraft were "Permakill" and "Permethrin". There are two separate treatments. One treatment is for disinsection, and the other treatment is a surface treatment for cockroaches. The treatments are not normally carried out simultaneously, however, on this occasion they were. There were no instructions that required the treatments to be conducted separately. The chemical constituents of both agents are Dichlorvos and Chlorpyrifos. Both these chemicals are potentially dangerous, and the company has been advised to discontinue the use of such treatments. The recommended procedure for aircraft disinsection is spraying with synthetic pyrethroids which are quite safe for human exposure. The company has opted for this procedure to prevent a recurrence.