The Forrestal incident occurred during the Vietnam conflict, July 1967. It was pretty much as you describe except I would not say EMI was not controlled. All DOD services had EMI requirements at his time. In fact, 1967 was the year that MIL-STD-461 was adopted as a Tri-Service requirement superseding Service-unique standards. The actual mechanism was that a shield termination on a pyro actuation circuit on one fighter was degraded or broken and radar illumination of it fired a weapon inadvertently, into another fully loaded, and fully fueled fighter. That was the cause of the disaster. In September 1967, MIL-E-6051C, Aircraft EMC was updated to the "D" revision. In "D", for the first time you have 20 dB safety margin demonstration on pyro electrical actuation. Coincidence?
---------- >From: [email protected] >To: [email protected] >Subject: EMC-related safety issues >Date: Thu, Jan 3, 2002, 9:57 AM > > > > > The key word in EMC is "compatibility". This implies that electrical and > electronic > equipment are (ideally) designed so that each can operate normally in the > presence > of another. This requires limiting both the emissions and sensitivity of such > devices. > > Historically, only a limited number of product types have been subject to EMC > limits. > Most EMC requirements are based on the assumption that the emission of specific > frequencies is more likely to interfere with other equipment than "white" or > broad > spectrum emissions. For example, the FCC rules apply to devices using clocked > frequencies of 10K and above, but place no limits on vacuum cleaners, blenders, > arc welders, etc. unless they contain clocked electronics. > > The exclusion of so many products from emission/susceptibility requirements is > often > the cause of EMC related "accidents". Some years ago, in one of the U.S. > Southwestern > states, the local public safety (police/fire/etc) communications were often > disrupted by an unknown source. The source was eventually traced to a pin ball > machine in a roadside tavern. The owner was told he must get rid of the > machine. A few weeks later, the noise re-appeared. It turned out that the same > pinball machine was placed in service at another pub in the county. > > In some cases, the interaction of two devices is not exactly foreseeable. We > once > received reports of one of our typewriters typing occasionally without human > assistance. It turned out that the typewriter was in use fairly close to an > airport radar beacon. When the radar beam swept the area of the typewriter > installation, it could cause the capacitor coupled keyboard to create false > keystrokes. We added a large grounded template to cover most of the interior > keypad area, to increase its immunity. > > There can be, and have been, safety related consequences of EM incompatibility. > In the 1980's (as I recall) a U.S. aircraft carrier suffered a major EMC > disaster. The powerful on-board electronics, particularly the radar units, > triggered the launch of a missle from one of the on-deck planes. The missle > struck the bridge tower, resulting in a fire costing millions of dollars in > repairs and the loss of some lives. I cannot find my copy of this event, > reported some years ago in one of the electronics magazines. > > In general, Navies are far more sensitive to EMI due to the concentration of on- > board electronics. As a result, the U.S. Navy version of the Blackhawk > helicopter > had few EMI problems, while the Army version had several early crashes due to > interference from nearby radio stations. > > The moral, if there is one, is that emissions and susceptibility of unregulated > devices is more often the problem than the emissions or susceptibility of a > regulated device. > > George Alspaugh > Lexmark International > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > No longer online until our new server is brought online and the old > messages are imported into the new server. > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
