Revelations that Costa Rica's president used the jet of a Colombian with alleged links to drugs trafficking have led to three high-profile resignations.
The head of intelligence and security, Mauricio Boraschi, and presidential aide Irene Pacheco stepped down on Thursday. Communications Minister Francisco Chacon resigned on Wednesday.
President Laura Chinchilla travelled twice on Gabriel Morales Fallon's jet.
She said "a few key people" had failed in their duties to protect her.
President Chinchilla is said to have used the jet in March to fly to Venezuela for the funeral of the former leader Hugo Chavez. She then used the plane again last weekend for a private trip to Peru.
But it has since emerged that both the jet, and its owner Gabriel Morales Fallon, were under investigation by Costa Rican intelligence officials for possible ties to drug trafficking.
Mr Morales was "linked to very complicated and complex situations from a criminal point of view", Mr Boraschi said earlier in the week, though he had no convictions and was not subject to any arrest warrant.
The use of the jet came about after Mr Morales reportedly introduced himself to Mr Chacon under a false name.
Mr Chacon has admitted he did not fully vet Mr Morales and the aircraft.
Before his resignation was announced, Mauricio Boraschi, who was also Costa Rica's anti-drugs commissioner, said his agency had not been told that the president was using the private aircraft.
Colombian authorities have investigated Mr Morales over alleged ties to jailed Colombian drug trafficker Luis Carlos Ramirez, arrested in Brazil in 2008. Mr Morales has denied any such links.
President Chinchilla has long been vocal about the need to tackle the drugs threat in the region.
Earlier this month, she discussed the problem of drug cartels with US President Obama during his visit to Costa Rica.