THERE may not be a ''prayer in hell'', according to one well-placed official, that Chek Lap Kok airport will be working by 1997, but that has not prevented Centro Digital Pictures from collecting the Gold Award for Best Promotional or Documentary Film forFlight Path to the Future at the prestigious Mercury Awards in New York. The dazzling, animated visualisation of the projected Chek Lap Kok airport has been shown around the world, to tremendous acclaim. Recognised as the Oscars of professional communications, the Mercury Awards directly address the field of corporate and promotional videos. Gary Thomas, head of graphics at Centro, said: ''This is a major honour for us, and confirms that the work being done in Hong Kong is among the world's very best.'' Now in its seventh year, the award is open to entries from around the world, and is judged in the United States against the highest of standards. This year, more than 650 entries were received from 20 countries, and judging involved 40 agencies and more than 150 industry professionals. Flight Path to the Future was produced under the supervision of the Provisional Airport Authority's Philip Bruce, Karen Cook and Edith Cheng. Centro's production team was Michael Soo, live-action producer; Gary Thomas, graphics producer; and the computer graphics team under Kwok King-cheun and Kelly Kan. Brian Blomfield wrote the script to Noel Quinlan's musical score.