The hostage complained of feeling ill and was allowed to leave the jet after a period of intense police negotiation.
Witnesses said they saw a figure wearing mustard-coloured clothing and a head scarf descend from a ladder at the rear of the jet and walk towards two police armoured Land Rovers.
A police spokesman refused to disclose any more details at a press conference half an hour later.
Negotiators working to free more than 150 hostages held on board have begun discussing "issues" which could lead to an end to the crisis, police disclosed this morning.
However, senior police officers stressed that the hijackers had so far made no specific political demands during more than 31 hours of negotiations. "There have been no specific requests other than for food, water and medication - what we would term house-keeping requirements," Essex assistant chief constable John Broughton told a news conference at the airport.
"It has always been our intention to seek a safe resolution without anybody getting hurt and we are working towards that," he added.
A total of 157 people, including 21 children, 17 women, 14 crew and an unconfirmed number of hijackers, remained on board the aircraft today after spending their first full night on the ground at the Essex airport.
The jet, operated by Afghan carrier Ariana, touched down shortly after 2am yesterday following a flight lasting almost 24 hours across the former Soviet Union and Western Europe.
The English-speaking gunmen seized the aircraft on Sunday morning shortly after it had taken off on a domestic flight from the Afghan capital, Kabul, for a flight of less than an hour to the provincial city of Mazar-e-Sharif.
Essex police denied that a news blackout had been imposed on any details of political demands made by the hijackers, who were earlier reported to have requested the release of Ismail Khan, a key opposition figure jailed in 1997 by the Taliban, Afghanistan's ruling Muslim fundamentalist regime.
"We are not being evasive, there have been no specific demands. But issues have been talked about generally, there have been broad issues talked about," said an Essex police spokeswoman.
At about 8am a police vehicle drove out to the isolated concrete apron where the jet has been held since touch-down to deliver a breakfast of mushrooms and omelette to those on board.
Earlier, a second electricity generator was delivered to the plane after a generator delivered yesterday began to fail.
Mr Broughton said it appeared that the hostages appeared to be receiving good treatment from their captors, but said conditions on the plane after three days would be difficult.
"We are obviously concerned for the comfort and welfare of those on board," he said. "They have now been on board for some considerable time and obviously we want to make the negotiations as comfortable as possible.
"Conditions must be very difficult but we are told the atmosphere is calm and that the negotiations are business-like."
It also emerged that police, as well as delivering food and sanitary supplies, had also made available medication for stomach upsets being suffered by some of those on board the jet.
Meanwhile, police were expected to continue debriefing the hostages who were released in two batches yesterday as they worked to gain further intelligence about the hijackers.
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