FCC action follows interference to airport weather radar.

The FCC has confirmed a fine of $25,000 against AT&T for operating a Wi-Fi-type device that caused interference to a weather radar at a Puerto Rico airport. Yes, it appears that AT&T slipped up. But we think the FCC fined it for the wrong offense.

The problem stems – as do many FCC problems – from the fact of an overcrowded spectrum. Almost every useful frequency is shared by multiple users. Part of the FCC’s job is to set priorities among them.

One such choke point occurs in the band at 5470-5725 MHz. Since 1998, the FCC has allowed relatively high-powered devices to use highly directional antennas in this region, all without a license. The band is popular among companies – called “wireless Internet service providers,” or WISPs – that provide Internet service to locations not easily reached by other broadband facilities.

A 2003 expansion of the band produced an overlap with frequencies also used for radars that detect “wind shear” near airports. This condition is potentially dangerous to aircraft flying close to the ground, as when approaching the runway to land, so the radars are important to flight safety. They operate at 5600-5650 MHz, squarely within the 5470-5725 MHz WISP band. The initial rules for WISPs (and other unlicensed users of the band) required devices to (a) sniff the air for radar signals, and (b) if those signals are found, to avoid the frequencies on which they occur  – a capability the FCC calls Dynamic Frequency Selection (DFS). After interference occurred anyway, the FCC worked with device manufacturers and radar operators to clarify the rules. When some interference persisted, the FCC refrained from shutting down the WISPs, as it had a right to do, and instead sought the WISPs’ cooperation in heading off the problem.

Then came the AT&T event.

According to an FCC notice back in February 2011, AT&T’s transmitter was certified for use under a different set of rules at 5735-5840 MHz, but was operating outside that band, at 5605 MHz, and had no working DFS. The 5605 MHz frequency is inside the weather radars’ operating range. Based on that fact and other data, the FCC concluded the AT&T facility was responsible for the reported interference to the nearby weather radar.

Inasmuch as the transmitter was not certified for 5605 MHz and had no DFS, the FCC could properly have dinged AT&T for using non-certified and noncompliant equipment. In fact the FCC proposed a fine for that offense. But it also did more. Since a transmitter operating outside its certification does not qualify for unlicensed operation, the FCC reasoned that AT&T needed a license. Since AT&T did not have one for 5605 MHz, the FCC added on the more serious charge of operating without a license.

We thought that was wrong. Under the FCC’s rules, AT&T’s transmitter could not possibly qualify for a license at 5605 MHz. The only licensable services at that frequency are maritime radionavigation, meteorological aids (weather radar) and radiolocation (other radar). AT&T’s WISP operation does not fit any of these. So the FCC proposed to fine AT&T for not doing something it could not legally have done. This is a little like a police officer ticketing me for not using my siren at an intersection – I being an ordinary citizen not allowed to use a siren.

A year and a half later, the FCC has now confirmed the fine and ordered AT&T to pay the money. AT&T did not raise our issue about the impossible-to-obtain license. Instead it presented evidence that it was not operating on the 5605 MHz frequency claimed by the FCC, but rather on 5685 MHz. Unfortunately that frequency is also outside the certification, and apparently also lacked DFS, making AT&T just as culpable. In AT&T’s favor, though, a 5685 MHz transmitter could not have interfered with the airport radar. But the FCC stuck to its story, insisting its field agents had detected AT&T operation at 5605 MHz.

In a footnote, the FCC even explained how AT&T could have falsified its frequency data. Frankly, we think this is out of place. The FCC has had reason to doubt the veracity of some respondents in the past, but we don’t think AT&T is one of them. The FCC should have taken AT&T’s assertions at face value. It could still have disagreed as to the operating frequency, but did not have to imply that AT&T may have been deliberately untruthful.

Now AT&T has three basic options: it can pay the $25,000 and move on with life; or it can pay the fine and then challenge the FCC’s order in the U.S. Court of Appeals; or it can wait to be sued for the money and raise its defenses.  (In some parts of the country, AT&T’s legal options may be limited, as explained in this earlier post.)

Simultaneously with the AT&T order, the FCC issued a public notice reminding WISPs and others to avoid interfering with weather radars, and mentioning the potential penalties for noncompliance, up to and including imprisonment.

To the best of our knowledge – and we try to keep track of these things – the FCC has not yet jailed anyone for operating an unlicensed device on the wrong frequency. But WISP equipment transmits in both directions. So if you rely on WISP service for watching videos of insanely complex Lego contraptions, the threat of imprisonment is definitely something to keep in mind.