The groups transported the hashish to remote farms in the southern province of Malaga on Spain's Costa del Sol and then shipped it overland to other European nations, police said in a statement.
The smuggling ring employed a “veteran flight instructor who was an expert in mountain rescues and night flights,” the statement added.
The flight instructor, who had experience in mountain rescues in the French Pyrenees and the Swiss Alps, would then recruit and train other pilots employed by the smuggling ring.
— Guardia Civil (@guardiacivil) October 15, 2015
He was detained after being caught smuggling delivering 600 kilos (1,300 pounds) of hashish into Spain by helicopter while also training another pilot for the ring.
Police detained seven French nationals, six Spaniards and two Moroccans and seized 810 kilos of hashish and three helicopters worth €2.5 million ($2.85 million) as part of the operation.
The 15 suspects were charged with drug trafficking, membership of an organised crime group and illegal possession of arms.
The authorities opened their investigation in May 2014 when a helicopter loaded with hashish crashed at night after hitting electrical cables in southern Spain, killing its pilot.
Spain's proximity to north Africa, a key source of hashish, and its close ties with its former colonies in Latin America, a major cocaine producing region, have made it a major gateway into Europe for drug traffickers.