to fly too close together, after a radio system shut down because a routine inspection was skipped, the Federal Aviation Administration said Wednesday.
Angeles Air Route Traffic Control Center, caused widespread disruptions. The system shut down while 800 planes were in the air, and forced delays for 400 flights and the cancellations of 600 more.
While there were no accidents, there were five incidents in which planes flew closer than rules allow.
In two cases, "controllers could see the two data blocks superimposed on each other," said Doug Church, a spokesman for the controllers union, the National Air Traffic Controllers Association, said, referring to the block of letters and numbers on the radar screen that locates a plane. "It was about thelongest 12 seconds of their life," he said.

Rick Day, the acting vice president of the F.A.A.'s Air Traffic Organization, said that the airplanes were supposed to be separated by five nautical miles laterally, or 2,000 feet in altitude. While Mr. Church, the union spokesman, said one set of planes came within a mile of each other, the aviation agency said two pairs of planes had come within two miles laterally and were separated by 1,100 feet and 1,400 feet. But he added that in January, standards will change and planes will be allowed to come within 1,000 feet in altitude of each other, informs the NYTimes.

According to News10, Air travel on the West Coast remained snarled well into Wednesday morning after a radio failure grounded planes for more than three hours Tuesday night.
On Tuesday afternoon, air traffic controllers at an FAA control center north of Los Angeles found they could monitor planes on radar but couldn't talk to them. At about 5 p.m., the FAA decided to ground aircraft at airports in and around Los Angeles and at other West Coast airports, including Sacramento International. Planes that were in the air were allowed to land at those airports.
The FAA fixed the radio problem by about 9 p.m., but by that time there was a long backlog of delayed flights. Although there were massive delays and at least one close call, no accidents occurred during the outage, according to the Federal Aviation Administration.

Airports most severely affected by the radio failure were those in Southern California and Las Vegas.
Two separate human errors caused the breakdown in radio communications that brought Southern California's major airports to a near-stop on Tuesday and led to at least five instances where planes came closer to each other than regulations allow, Federal Aviation Administration officials said.
'A loss of communication is a serious matter and it should not have occurred,' Mr Rick Day, a senior FAA official, said on Wednesday.
FAA officials said its radio system in Palmdale, in the Mojave Desert, shut itself down on Tuesday afternoon because a technician failed to reset an internal clock - a routine maintenance procedure required every 30 days by the FAA.
Then the back-up system failed, also as a result of technician error, officials said.
On Tuesday, FAA officials had insisted that the more than three-hour system shutdown
posed no safety risks. But they acknowledged on Wednesday that they are investigating five incidents in which planes lost the required separation distance during the first 15 minutes of the communications breakdown.
In two cases, large airliners came more than twice as close to small corporate jets as federal guidelines allow, requiring at least one pilot to take corrective action, reports AsiaOne.

FAA Says Fixes Will Prevent Repeat Of Radio System Failure FAA officials say they are moving quickly to ensure there is no repeat of the radio communication failure that disrupted hundreds of flights in Southern California this week. A five-hour shutdown of the voice communications system Tuesday at the en route ATC center in Palmdale, Calif., meant flights had to be grounded or diverted to other airports. The outage caused about 400 delays and about the same number of cancellations. Radar coverage was never lost, and aircraft were handed off to other centers. The agency said it is "aggressively investigating" the shutdown, and although its systems generally have greater than 99% reliability, any failure "is unacceptable because of the inconvenience to air travelers and cost to the airlines." The primary voice communication system shut down at about 5 p.m. Pacific Time, and the secondary system failed soon after. Operations were restored gradually when the system was brought back on line. The Professional Airways Systems Specialists (PASS) union said only one technician was on duty at the time of the outage, and an off-duty specialist had to be brought in to fix the problem. FAA said the primary system shut down automatically because a required 30-day maintenance check was not performed, and the outage would have been avoided if procedures had been followed correctly. The secondary system "was not configured properly to ensure its availability," the agency said. The agency said it will review its maintenance checklists and protocols to make sure maintenance procedures are up to date and are being followed. It will add new feature to prevent service disruptions if periodic maintenance is not performed. A PASS official told The DAILY that this problem has occurred at other en route centers, and FAA is working to install a patch to correct an anomaly in a recent system upgrade. The PASS official said the new system's synchronization expires every 50 days, and it does not automatically reset itself. An American spokeswoman said the FAA problems contributed to a "crazy day" on Tuesday. American had 31 flights either diverted or canceled due to the voice communications outage, and 44 flights were diverted because of thunderstorms in the Dallas/Fort Worth area.