Project president Mr Oliver Foot hopes that 60 to 100 eye patients will benefit from their three-week stay in China. Many others, however, will have to be turned away.

''That's always one of the hardest things to do,'' Mr Foot said. ''We cannot operate on all patients, only those who are selected for teaching purposes.'' Joining the Orbis team on this mission will be seven volunteer eye surgeons from Europe and America who will be sharing the latest techniques with their Chinese counterparts in glaucoma, retina, corneal and cataract surgery.

The 31-year-old DC-8 will be making its last trip to China before being replaced by a new aircraft later in the year.

The search for a replacement began two years ago. The DC-8 is too small and finding spare parts for it when problems arise has become increasingly difficult, Mr Foot said.

After receiving a donation of US$14 million (HK$109 million) from three people in Hongkong and the US, Mr Foot went to Scotland in 1991 and bought a secondhand DC-10 from a bankrupt airline company.

The DC-10, which is undergoing renovation in Alabama, will have larger operating rooms and classrooms. There will also be a communication centre which provides technology for as many as 300 doctors and nurses, inside and outside the plane, to watch the televised operation and talk to the surgeons.

With an expanded section devoted to lasers, Orbis will be able to give formal training in laser technique on the plane for the first time. The second level of the plane will serve as a biomedical technical training area and house the medical resource library.

In the meantime, Mr Foot is still US$6 million short of the US$10 million need to convert the DC-10. To raise funds, he is selling the new aircraft's 50 seats and nine rooms which will be named after individual or corporate donors.

''The idea of Orbis is to teach doctors sight-saving skills and update them on the latest technologies so they can operate on their own patients after we leave,'' Mr Foot said.

In the past 10 years, Orbis has provided hands-on training to over 24,000 doctors and nurses and restored sight to 13,000 patients on board. In turn, local doctors use their newly-acquired skills to help many who are needlessly blind.

More than 42 million people in the world are blind. Two-thirds of these cases could be prevented or cured with medical treatment which is available in more developed countries.

Of the seven million blind in China, two million could be cured by a corneal transplant, Mr Foot said.

Hongkong people have supported part of Orbis' annual operation cost - US$7 million - for the last three years. There are currently 45,000 local donors who send cheques on a regular basis. Most of their money has gone towards helping the blind in China.

Mr Foot says he keeps his overheads at only 10 per cent of operating costs. As the Orbis team travels around the world, they are able to capitalise on their high-profile charity by soliciting sponsorships from airlines and hotels for free fuel and accommodation.

The idea of an airborne eye hospital was first conceived in the mid-70s by an ophthalmologist from Texas.

To date, Orbis has conducted 129 plane programmes in 61 countries; most of its time is spent in developing countries where the need for eye-care education is the greatest.

There are 25 permanent staff on the plane from all over the world, including six nurses, five ophthalmologists, two pilots, two anaesthetists and three administrators. One of the doctors, Jai Yading, was invited to join the team when Orbis visited China last year.