The seizure of a bag of methylamphetamines from a light plane at a Perth airport on Tuesday is the biggest Western Australia has seen, police say.

The bag was allegedly found along with 8.85 kilograms of ecstasy - or 35,000 tablets - when crime squad detectives intercepted the plane on arrival at Jandakot Airport around 5pm on Tuesday afternoon.

The drugs have an estimated street value of $77 million.

The plane has now been seized under proceeds of crime legislation, while the pilot and his passenger have appeared in court.

They faced Perth Magistrate's Court yesterday charged with possession of methylamphetamine with intent to sell or supply, and possession of MDMA (ecstasy) with intent to sell or supply.