More USA NTSB Education re low-frequency EMI
It happens - not just in yaw damper position sensor LVDT's.
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NTSB PRESS RELEASE
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National Transportation Safety Board
Washington, DC 20594
FOR IMMEDIATE RELEASE: September 22, 2009
SB-09-53
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NTSB IDENTIFIES SIGNAL FAILURE IN FATAL DC METRORAIL
COLLISION; ISSUES URGENT SAFETY RECOMMENDATIONS TO TRANSIT
AUTHORITY, FEDERAL RAIL AGENCIES, AND CIRCUIT MANUFACTURER
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The National Transportation Safety Board (NTSB) today issued
nine safety recommendations, six of which are urgent, to
address concerns about the safety of train control systems
that use audio frequency track circuits. The recommendations
are the result of NTSB's ongoing investigation into the
collision between two Washington Metropolitan Area Transit
Authority (WMATA) trains on the Red Line near the Fort
Totten station in Washington, D.C., on June 22, 2009.
During the investigation, the NTSB has discovered that a
failure occurred in which a spurious signal generated by a
track circuit module transmitter mimicked a valid signal and
bypassed the rails via an unintended signal path. The
spurious signal was sensed by the module receiver which
resulted in the train not being detected when it stopped in
the track circuit where the accident occurred.
The NTSB made specific recommendations to the Washington
Metropolitan Area Transit Authority and to Alstom Signaling,
Inc., the manufacturer of the track circuit modules at the
Fort Totten station, to examine the WMATA track circuits and
work together to eliminate adverse conditions that could
affect the safe performance of these systems. Additionally,
the NTSB called upon WMATA to develop a program to
periodically determine that the electronic components in its
train control systems are performing within design
tolerances.
Although the NTSB's investigation is not yet complete and no
determination of probable cause has been reached, the NTSB
is concerned about the safety of train control system
circuitry used in comparable rail and transit operations in
other parts of the country. Therefore, the NTSB recommended
that the Federal Transit Administration (FTA) and the
Federal Railroad Administration (FRA) advise all rail
transit operators and railroads that use audio frequency
track circuits in their train control systems about these
findings from the Fort Totten accident investigation.
The NTSB also recommended that the FTA and FRA have transit
operators and railroads that use audio frequency track
circuits examine their track circuits and work with their
signal equipment manufacturer(s) to eliminate adverse
conditions that could affect the safe performance of these
systems, and to develop programs to periodically determine
that the electronic components in their train control
systems are performing within design tolerances.
"After only 3 months, this complex investigation is far from
complete, so we are not ready to determine the probable
cause of the accident on WMATA," said Chairman Deborah A.P.
Hersman. "However, our findings so far indicate a pressing
need to issue these recommendations to immediately address
safety glitches we have found that could lead to another
tragic accident on WMATA or another transit or rail system."
In accordance with NTSB protocol, the letters were addressed
to the heads of each organization with a request for a
response from each organization within 30 days on the urgent
recommendations, addressing the actions taken or planned in
response to the Board's recommendations.
The safety recommendation letter to WMATA may be found here:
http://www.ntsb.gov/recs/letters/2009/R09_15_16.pdf
The safety recommendation to Alstom Signaling, Inc., may be
found here: http://www.ntsb.gov/recs/letters/2009/R09_23.pdf
The safety recommendations letter to FTA may be found here:
http://www.ntsb.gov/recs/letters/2009/R09_17_18_19.pdf
The safety recommendation letter to the FRA may be found
here: http://www.ntsb.gov/recs/letters/2009/R09_20_21_22.pdf