IT STARTED with a simple request for a business trip to Vietnam. A senior executive at the Provisional Airport Authority (PAA), Ronald Gunther, believed a three-day trip to Ho Chi Minh City, Vietnam, would help in his job of developing the new Chek Lap Kok airport. He applied for approval from his immediate superior, Richard Judy, the interim commercial and operations director, and the business trip was approved on September 13. Mr Gunther, general manager of development, also confirmed a travel a gent booking for two US$120-a-night (HK$928) rooms and two business-class air tickets for himself and Mr Judy. The men were to depart last Friday. However, Mr Gunther's proposed business trip soon became a ''holiday'', as he says his application was ultimately refused by the PAA. Then, at some stage while the two men waited to board the plane at Kai Tak, the trip was called off. The PAA says the men ''missed the plane'', but legislators are not satisfied and are demanding an inquiry. United Democrats legislator Albert Chan Wai-yip, who has led a campaign in recent months for closer scrutinty of PAA spending, said: ''There are so many unanswered questions. The PAA owes the Legislative Council a full explanation, and its story had better be convincing.'' Mr Gunther had written on his application form for overseas travel that he intended to go to Ho Chi Minh City to inspect its ''economic, transportation infrastructure and tourist development in light of its probable impact on regional and commuter air service to the Hong Kong market due to the normalisation of relations with the US''. The Sunday Morning Post 's investigation into the circumstances surrounding the trip began last Tuesday, when we were informed by a source both Mr Judy and Mr Gunther were planning to go to Vietnam. Documents produced by the source showed Mr Gunther applied to go to Ho Chi Minh City on September 10. The application was approved by Mr Judy three days later. The Sunday Morning Post subsequently asked PAA spokeswoman Norma Fung the purpose of the trip by Mr Judy and Mr Gunther. She was not aware we had Mr Gunther's ''application form for overseas business travel'', with the purpose of his proposed trip clearly spelled out. Ms Fung said both executives would be ''on vacation''. ''Certainly it is a vacation,'' she said, ''it has always been a vacation.'' Requests to talk to Mr Judy were declined, as PAA staff said he would soon be going on a trip. We were, however, able to contact Mr Gunther last Friday - the day of his ''vacation'' to Vietnam. We told him we had been informed he was going on a business trip to Ho Chi Min City. ''That's not true,'' he replied. We then told him our source had evidence he was going on company business, but he maintained: ''It is not a business trip.'' When we then read out to him the reason given on his application form for overseas travel, Mr Gunther said: ''The answer to that is that the business trip application was not approved. And now I am going on a private visit to Vietnam. ''I am paying the air fare myself and I am paying for the trip myself, out of my own pocket.'' He confirmed the following sequence of events as correct - that he and Mr Judy applied for overseas business travel to Vietnam and it had been refused, so they were both going on a personal trip to the country and paying for it themselves. ''Yes. That iscorrect,'' he said. At the airport on Friday afternoon, we were told by Cathay Pacific ground staff we had just missed Mr Judy and Mr Gunther, who had checked in about 1.50 pm for their 3.30 pm flight. It later became clear that neither Mr Judy nor Mr Gunther boarded the flight. On Friday night, PAA chief executive Dr Hank Townsend said ''there was no doubt in my mind'' that Mr Judy was on a holiday, and that he would ''certainly check'' the circumstances surrounding Mr Gunther's trip. We contacted Mr Gunther at home yesterday morning and asked him why he and Mr Judy had not gone to Vietnam. ''I don't know,'' he replied. ''I think we missed the plane. We didn't get there on time.'' When we told him airline staff had said he and Mr Judy checked in almost two hours before take off, he said: ''We did check in, but we did not get to the plane on time. We did not get to the gate in time.'' Asked again, he replied: ''We just did not get to the plane on time.'' We asked whether the PAA had called him back to the office. He said: ''Look, what is this? We missed the plane. Goodbye.'' Dr Townsend said he was informed of Mr Judy's planned holiday to Vietnam. Mr Judy was ''to relax from the heavy workload''. He said he could not comment on Mr Gunther's planned trip, because Mr Gunther did not report directly to him. On the subject of Mr Gunther's application form, Dr Townsend said ''what counts is what the official orders were when he left''. ''So certainly if he went on a vacation trip he would not be reimbursed for any of those expenses.'' Dr Townsend said there was ''no doubt in his mind'' Mr Judy was taking a holiday. When asked to explain why an application form for business travel was filled out by Mr Gunther if he was on a holiday, Dr Townsend said he was not familiar with the situation. ''I will certainly check,'' he said. Swire Travel - the PAA's travel agent - later told us the planned trip by Mr Gunther and Mr Judy was ''a business trip'' and ''a company trip'' and that the invoice would be sent to the PAA. When told of this, Dr Townsend said: ''I wouldn't know because I don't talk to Swire Travel about individual trips.'' He said staff frequently used the same travel agency for business and private trips. He said there was no misuse of PAA funds, because staff on holiday would not be reimbursed. He also said there was no possibility that Mr Gunther's planned vacation would be mistakenly paid for by the PAA, even though it was at one stage approved as a business trip. Asked why ''a vacation'' could be approved as a business trip in the first place, Dr Townsend said: ''I cannot answer that . . . I would certainly check and follow up and see.'' ''I do know Dick [Judy] is going down there on vacation and I would assume before the time they left that it was established Ron Gunther is also going on vacation and not on business. That is all I can really comment.'' Yesterday, Ms Fung could not provide any further information. ''Both Mr Judy and Mr Gunther are on vacation,'' she said. ''No expenditure whatsoever of PAA funds is involved.'' Ms Fung said the authority took a ''strict view for business travelling and we do control it very tightly''. She denied the PAA would be billed by Swire Travel. ''This is incorrect. They [Mr Judy and Mr Gunther] paid personally with their own credit cards.'' She said the bill could go to the PAA but whether it would be settled by the PAA or the individual was up to the PAA. ''. . . whether it is PAA or the individual paying for it Swire Travel wouldn't know,'' Ms Fung said. ''I am telling you they are settling their bills by their own credit cards.'' As to why Mr Judy did not board the flight, Ms Fung said: ''As far as I understand, he missed his flight. He checked in, his plane was delayed and somehow he missed it. ''It seems quite incredible but that was the truth. ''It is incredible. But you know, sometimes when you are thinking 'when do I board', the plane was delayed and you didn't know the plane had left without alerting you. So he missed it.''