WASHINGTON -- Nearly four years after the bombing of a Pa Am flight over Scotland started a search for better ways to find hidden bombs, the widespread use of more advanced detectors is still years away.
The families of victims of the bombing, which killed 270 people, and top aviation security officials say there are signs of progress, but that the prototype bomb detectors being tested in airports have not been developed as swiftly as they want.
Retired Adm. Clyde Robbins, the Transportation Department's top security and intelligence official, said in an interview that he hoped to have high-performance detectors in place at "the most sensitive airports" in two years, but that it would probably be four or five years before they were widespread.
Mr. Robbins was in Albany, N.Y., yesterday to meet with relatives of those who died in the Pan Am bombing to discuss a research program on which millions of dollars are being spent each year, largely as a result of political pressure from the families.
"Of course these things never happen as fast as you like," he said. "It has taken us longer to get the equipment on the street than we would like, but it is very developmental, and much of this equipment is state of the art."
Shortly after the bombing, the Federal Aviation Administration said it would require all big airports to install a new kind of bomb detector, known as a thermal neutron analyzer, which bombards luggage with radiation and analyzes the atomic particles that are emitted in reaction. Six were built and tested, but their performance fell short of expectations.
In 1990 Congress told the FAA not to require any detectors until they are tested and proven reliable at detecting small quantities of plastic explosives.
Since then several new approaches for detecting bombs have been explored by various companies, with financing from the FAA.
This month the FAA for the first time told prospective manufacturers of new equipment what standards their machines would have to meet to be certified for use at airports.
The performance requirements call for equipment to be automatic, sounding an alarm to alert an operator when bomb material passes through. That way, an operator's judgment would not be needed, as it is with existing X-ray equipment used at airports, which cannot reliably detect plastic explosives.
The agency did not disclose the reliability rate required of new equipment and the size of explosives that must be detectable for security reasons.
The FAA said that it was unlikely that any single technology will meet the performance requirements and that combinations of existing technologies will probably have to be used until a breakthrough is made.
In the next two months, according to FAA documents, the agency will begin testing one promising combination of technologies at Delta Airlines and American Airlines terminals at Miami International Airport, using both advanced X-ray machines and vapor-detection equipment that mechanically sniffs out bombs. The trials will include both FAA test baggage and actual passenger baggage.