Blame Game

Air Safety Week, Sept 20, 2004

Hot words are flying over the causes and consequences of a three-hour radio outage Sept. 14 that left some 400 airplanes out of radio contact with the Los Angeles Air Route Traffic Control Center (ARTCC) in Palmdale, Calf. The airplanes remained under radar surveillance, but controllers at the ARTCC lost radio contact with the airplanes they were following. Basically, the region went instantly to "Free Flight," since pilots were effectively now on their own, particularly in the opening moments of the outage, to provide safe separation from one another. In two cases, pilots relied on their traffic alert collision avoidance systems (TCAS) to take evasive action.

In these two instances, the airplanes passed each other with less than 1,000 vertical feet of separation. Commencing January 2005, domestic reduced vertical separation minimum (DRVSM) operations take effect, reducing standard vertical separation from 2,000 feet today to 1,000 feet for flights at cruising altitudes between 29,000 feet and 41,000 feet. The Federal Aviation Administration (FAA) will not require airplanes entering DRVSM airspace to be equipped with TCAS, relying instead on improved altitude-keeping technology. Pilots unions have strongly criticized the FAA for not requiring TCAS in DRVSM airspace (see ASW, Nov. 3, 2003).

The ARTCC's radio system basically shut itself off at 4:30 p.m. as a result of human error - a technician is supposed to reset the system every 30 days. An improperly configured backup system failed, compounding the error. Some ARTCC controllers used their cell phones to contact colleagues at neighboring ARTCCs to pass messages to pilots. The ripple effect of the sudden loss of ground-to-air radio communications led to massive flight delays.

The FAA was aware of the need for the radio equipment, known as the Voice Switching and Control System (VSCS), to be reset manually every 30 days. The problem is a byproduct of the agency's effort to modernize the national airspace system (NAS). When the VCSC system was upgraded about a year ago, Microsoft code supplanted the original Unix software. The Microsoft code features an internal clock that is designed to shut down the system every 49.7 days to prevent it from becoming overloaded with cached buffer data, according to one account.

A fix to issue a warning well before shutdown is to be installed at all 21 ARTCCs nationwide within the next month.

While acknowledging the failure was serious, FAA officials have been at pains to stress that passenger safety was not compromised.

Officials with the National Air Traffic Controllers Association (NATCA) have challenged the assurance that safety was not eroded. They pointed to the two instances where the 2,000-foot vertical and five-mile horizontal separation minimums were penetrated:

* A Northwest Airlines B757 came with 900 feet vertically and eight tenths of a mile from a Gulfstream III private jet.

* A United Parcel Service B757 came within 100 feet vertically and about 1.7 miles horizontally of a Cessna Citation jet.

The FAA is investigating both cases, as well as the circumstances surrounding the VCSC shutdown.

Tom Brantley, president of the Professional Airways Systems Specialists (PASS), the union of technicians who maintain the gear, issued a pre-emptive strike Sept. 16 against any findings that a PASS technician failed, charging, "The agency continues to build a facade around the problem and blame employees for its system-wide neglect of staffing shortages."

"The 'maintenance check' the FAA mentions is a temporary patch designed to prop up a faulty system," Brantley said. "It is analogous to repeatedly adding air to a flat tire, rather than repairing the hole."

NATCA's Doug Church said, "This was a chaotic, uncontrolled situation."

"Under DRVSM you're still supposed to be under ground control. On Tuesday, we were not under control," he added. "TCAS saved the day, but it's not required for DRVSM."

The overall situation might be characterized as follows:

Pre-DRVSM (today) = Not good enough

Post-DRVSM (next January) = Possible disaster

Much will be reviewed behind closed doors by people who realize how lucky there were. The FAA's Sept. 15 statement that the agency is "aggressively investigating" confirms its concern.

[Copyright 2004 PBI Media, LLC. All rights reserved.]