Sources said the aircraft, with two crew members - including a woman - took off from Bangkok and was on its way to Karachi. It landed at the Calcutta airport for fuelling and minutes after taking off from there disappeared from radar. The plane reappeared on radar after 40 minutes and the crew sought the permission of ATCs to land for refuelling. After the aircraft landed around 1.30 am on Wednesday, the AAI, Customs and Immigration officials checked it and reportedly found it equipped with high-frequency cameras and other electronic goods.

Immediately, the crew was detained and their passports seized. The crew have been put up at a five-star hotel in the city and are notbeing allowed to move out from there, sources said.

Sources revealed the aircraft is registered in New Zealand and belongs to a private American company, Cooper Airlines. Of the two crew members, G C J Cooper is a Briton and the woman pilot, Contong, is an Australian citizen. The aircraft has been sealed. Sources said AAI officials also sought the advice of ISRO experts on the devices. The ISRO experts confirmed that the plane was carrying some photographic device and added that they were not functional and had also been disconnected. Sources said the crew and aircraft would be released after getting clearance from Director General of Civil Aviation, New Delhi, which is expected on Monday.