Devices will be used to detect runway debris; other applications are possible.

The FCC seeks comment on radar operations in the 78-81 GHz band, and in the meantime, has granted a waiver for limited use.

There has been a lot of regulatory interest lately in radar devices above 75 GHz, up in the “nosebleed” portion of the spectrum. Back in 2009, the FCC considered, and later granted, a waiver to allow the Atlanta airport to use 77-76 GHz radars to track aircraft and vehicles on the ground. The beginning of 2010 saw a proposal to use 78-81 GHz to measure the levels of substances inside large industrial tanks; there, too, the FCC granted a waiver, while a rule change is still pending. Last May, the FCC proposed to relax the rules for vehicle radars at 76-77 GHz, which provide for automatic braking when the car senses an obstacle ahead.   That rule, too, is still under consideration.

Now the FCC has revisited the airport environment, with a proposal to authorize 78-81 GHz radars to detect “foreign object debris,” or FOD – apparently a term of art in the airport business. We are all in favor of FOD detection, remembering that a stray piece of metal on the runway, dropped from an earlier plane, tripped up an Air France Concorde in 2000 at the cost of 113 lives. Apparently aircraft shed parts more often than most of us realize. Other common forms of FOD include misplaced tools, equipment and supplies, rocks and pavement fragments, luggage, and wildlife.

A close reading suggests the FCC is determined to approve FOD radars. But it is not sure how: whether to authorize 78-81 GHz radar on an unlicensed basis, like cordless phones, or under license, like taxi radios. Another question is whether to restrict the band to use at airports, or to permit other applications as well. A third question is whether radar users should have to coordinate their operations with others who share the band.

All of these questions turn in large part on the need to protect radio astronomy from interference. Radio astronomers have a primary allocation across most of the band, which they use to identify molecules in remote stretches of space. The good news is that radar signals at these frequencies tend to form narrow beams and do not propagate well, thus cutting the risk of interference. On the other hand, though, radio astronomy facilities use exceedingly sensitive receivers, and so can be disrupted by even a very low level of interfering signal.

While the rulemaking proceeds, the FCC has granted one company a waiver to market equipment in the band, solely for FOD detection at airports, and only under a license.

Comments and reply comments are on a relatively short fuse: 30 and 45 days, respectively, after publication in the Federal Register. We will post the actual due dates when they become available.