Mystery surrounded a Chilean Air Force plane yesterday as it sat on the runway at the airport, waiting to leave for the UK to pick up former Chilean dictator Augusto Pinochet.

The plane, a Boeing 707 named "Aguila'', arrived on the Island on Tuesday evening from Chile and was due to land at Brize Norton Royal Air Force base, in Oxfordshire, England yesterday afternoon.

An article in Chile's Santiago Times noted that General Pinochet's doctor, Henri Olivi was on board the plane, along with a team of 15 nurses and paramedics to take care of the 84-year-old ex-dictator during the long trip home.

The flight crew and medical team stayed at the Grotto Bay Hotel on Tuesday night, according to the resort's manager J.P. Martens.

Last night they moved to Clear View Guest House in Hamilton Parish. This is the third plane to have been sent to the UK by the Chilean Air Force to pick up General Pinochet since his October 1998 arrest.

It has been dubbed "Operation Return'' by Chilean state television.

But with the plane still sitting on the airport's windswept tarmac, it seems as if the process of General Pinochet's release may be hitting some obstacles.

British Ministry of Defence spokesman Ben White denied any knowledge of the cause of the aircraft's delayed departure.

He told The Royal Gazette : "We gave permission for the Chilean Air Force to land their plane at Brize Norton this afternoon but we were notified this morning that there was a delay.

"We are not aware of the cause of it and any questions of that nature should be directed to the Chileans themselves.'' And Airport Operations duty officer Skip Tatem confirmed yesterday that the delayed departure was not due to mechanical problems.

But the human rights group Amnesty International have launched a legal challenge against documents which state that the general is unfit to stand trial for alleged torture crimes in the 1970s, the proceedings of which could have caused the delay in departure.

And a story by the Chilean newspaper La Tercera said the plane was "awaiting instructions'' from Britain as to Home Secretary Jack Straw's final decision.

General Pinochet has been the focus of media attention since October 1998 when he was arrested while receiving medical treatment in Britain.

His arrest was requested by Spanish Judge Baltasar Garzon who wanted to try him for human rights abuses dating from the latter part of his rule, between 1973 and 1990. Mr. Straw announced last Wednesday that the general, who has been under house arrest at his mansion near London for the last 15 months, was "unfit'' to stand trial.

But Amnesty International criticised the Home Office for not releasing to human rights groups the results of recent medical tests performed on General Pinochet.

A story by Reuters news agency reported Amnesty International spokesman Brendan Paddy as saying: "If he is being released for medical reasons, we would like to see that evidence.'' On Friday, Amnesty International announced it would make a formal submission to the Home Secretary against his decision, which was subject to representations within seven days by any interested parties, including Spain and Chile.

The deadline for such appeals to be sent was Tuesday at 5 p.m. UK time.