A Lufthansa Boeing 737 recently became the first aircraft to use Mode S capability to transmit its radar identification (flight ID), without the use of secondary surveillance radar (SSR) code. Rod Marten, who oversees mode-S operations at Eurocontrol, said that air traffic controllers typically assign a four-digit SSR code to a target on the radar screen then manually correlate the aircraft information with the electronic flight plan data. Using mode-S capability, the 737 flight crew entered a 24-bit code into the aircraft computer, which automatically correlated the aircraft’s flight plan data. The transponder then issued a flight ID to controllers. Because of the short supply of SSR codes–there are 4,096–European controllers make an average of 20,000 code changes a day, Marten said. “There aren’t enough,” he said. “You find that there are code duplications, with different aircraft using the same code.” There are approximately 17 million 24-bit codes, however. Marten said that there have been “a few problems” during test phases when pilots entered the wrong 24-bit code, but he added, “It’s going to be an evolutionary way of improving identification of traffic.”