Delta V = 0.7V = 85,000 irate travelers
Article Abstract:
On Sep 17, 1991, an AT&T protective meter-relay that was wrongly set triggered at 52.8 V instead of at 53.5 V, and consequently, telephones went down and air transport was disrupted. The area affected included much of the northeastern United States. One of the most significant things about this system failure is the fact that it was caused by so minor a malfunction. Further investigations have revealed that the failure of the meter-relay device initiated a series of other failures and mistakes, so that faulty maintenance and poor judgement compounded the original problem. For example, in one location, an alarm light did not work because its bulb was burned out, and in another place, an audible alarm did not sound because one of its wires had been cut, and in yet another place, a standard-procedure maintenance walkthrough was not done as it should have been. AT&T is working to put practices and equipment in place to ensure that such a sequence of events does not occur again. The Federal Aviation Administration (FAA) is working to strengthen its own backup and emergency-communications arrangements. And a panel convened by New York Mayor David N. Dinkins recommends a 'carrier diversity' plan, so that if one carrier encounters a problem, several others would be available to help with its traffic.
Publication Name: IEEE Spectrum
Subject: Engineering and manufacturing industries
ISSN: 0018-9235
Year: 1992
User Contributions:
Comment about this article or add new information about this topic:
Three little bits breed a big, bad bug
Article Abstract:
There were eight incidents involving signaling equipment failure between Jun 10 and Jul 2, 1991, and 20 million telephone customers lost service. A six-month investigation led by Bellcore (Bellcore Bell Communications Research Inc) demonstrates that the cause of the problems was a failure in signal transfer point (STP) software. In fact, the problems have been traced to a flaw involving only 3 bits: what should have been a binary D (1101) was a binary 6 (0110). The STPs, which are manufactured by DSC Communications Corp, function as a part of Signaling System 7. DSC had tested its code, but apparently not sufficiently. When failures occurred, they did so in a way that tended to initiate a domino effect, shutting many systems down. The outages that were consequent caused nationwide concern, and both the US House of Representatives and the Federal Communications Commission demanded investigations. Changes in the Signaling System 7 protocol are one probable outcome, and better quality assurance procedures at DSC Communications is another.
Publication Name: IEEE Spectrum
Subject: Engineering and manufacturing industries
ISSN: 0018-9235
Year: 1992
User Contributions:
Comment about this article or add new information about this topic:
TCAS sees ghosts
Article Abstract:
The Federal Aviation Administration (FAA) ordered 200 of the 700 $150,000 TCAS units installed in US aircraft to be shut down because the devices were seeing and issuing evasion commands to avoid phantom aircraft. The TCAS systems send a continuous stream of interrogation signals to other aircraft with the same systems to determine each other's distance, altitude and approach rate. All 4,000 large aircraft in the US are supposed to carry TCASs by the end of 1994. The failures were determined to be the absence of five lines of range correlation code in the TCASs manufactured by Rockwell International Corp's Collins Defense Communications Division (Dallas, TX). The code had been disabled during testing at Collins, and not re-enabled prior to shipping to the airlines. Collins will reload the code and return the systems within 90 days of the discovery of the problem. TCAS units made by other companies did not encounter the problem.
Publication Name: IEEE Spectrum
Subject: Engineering and manufacturing industries
ISSN: 0018-9235
Year: 1991
User Contributions:
Comment about this article or add new information about this topic:
- Abstracts: Designing fast for the future. Steel makes lightweight fibre sandwich. The car's the star
- Abstracts: Large computers. Kwajalein's new role: radars for SDI
- Abstracts: Cray Computer suffers competitive blow. How cheap can it be and still give you 3-D? The main event
- Abstracts: The specialties. The specialities
- Abstracts: Expert observers define top priorities to ensure safe and accessible skies. Improving the world's largest, most advanced system: a system-wide upgrade races to replace two-decade-old equipment