THE Provisional Airport Authority (PAA) has tightened rules on overseas business travel following an aborted trip to Vietnam by two senior executives. Instead of requiring only approval by the employee's supervisor and department head, all applications must now be approved personally by the Chief Executive Officer Hank Townsend, according to a letter from PAA Chairman Hamish Macleod to legislator Albert Chan Wai-yip. Mr Macleod said the criteria for deciding whether a trip was necessary included a requirement that it be of real benefit to the authority. This could include visits to other airports overseas where lessons could be learned to the advantage of Hong Kong, attendance at industry conferences and seminars and meetings with overseas airport authorities, airline and industry bodies, he said. ''In each case, an individual assessment is made of the application in question. No blanket approvals are given,'' Mr Macleod added. Last month, the Sunday Morning Post revealed that the PAA's Interim Commercial and Operations Director Richard Judy and Chek Lap Kok Airport Development General Manager Ronald Gunther failed to board a flight to Vietnam. While the travel agent said the trip was booked for business reasons and the PAA would be charged, PAA spokeswoman Norma Fung insisted the trip was personal and the pair would bear the cost. The letter to Mr Chan did not indicate whether any disciplinary action had been taken against the pair. Ms Fung declined to say whether the aborted trip would undermine Mr Judy's chances of becoming permanent commercial or operations director. Mr Judy was not available for comment. A source close to the PAA said board members had been surprised to read the newspaper report on the aborted trip. In his letter, Mr Macleod, also the Financial Secretary, revealed that the pair had submitted applications for business travel to Vietnam. Mr Gunther's stated ''purpose of travel'' on his application form was ''to inspect Ho Chi Minh City's economic transport infrastructure and tourist development in light of its probable impact on regional and commuter air service to the Hong Kong market .. . '' His application had been approved by his superior, Mr Judy, whose application, however, was later rejected by Mr Townsend, according to the letter. As a result, Mr Gunther's application was turned down too. The subsequent decision to travel on vacation to Vietnam was made by Mr Gunther and Mr Judy in their private capacities, Mr Macleod said. ''No expenditure whatsoever of authority funds was involved,'' he said. Mr Chan said he hoped the new rules would prevent further controversies.