Electro-Magnetic Interference v avionics
 

Does anyone know from where I can glean the latest Electro-Magnetic Interference/Compatability EMI/C data and regulations? I was just wondering how the shielding and protection of our avionics systems countered the transmission levels and interference patterns of modern mobile phones/MP3 players/palm-tops/wi-fi etc.
I am sure there has been a lot of research done out there by various boffins/organisations but I get the impression we take for granted (just a little bit) the immunity of our modern ac from such 'wiggly-amps'.

Thanks in anticipation

flipster

In Europe there is the EMC Directive which is downloadable from the Europa website, which applies to Machinery. This is backed up by Standards which are not downloadable, and cost a lot from the likes of BSI. The Standards list the levels of emissions and immunity, and it depends upon what the equipment is. We wouldn't have aviation Standards for example.

The company I work for does EMC testing and we find that most manufacturers don't bother doing it, relying on 'good electrical practice'. The majority of machines we test anyway fail first time. This does not necessarily mean they are dangerous, but could be subject to unexpected movements - not a problem generally on the ground, but could be at 40,000 feet.

Anything with variable frequency drives is likely to cause problems, many conveyor systems and some GSE have issues. We tested some equipment used to build bridges, as it was considered they could be a danger to low flying aircraft in the vicinity...

I was on a 747 in the middle of the Atlantic when a message came over the tannoy about turbulence. It caused all of the video equipment to freeze and had to be reset - the EMC engineer with me told me it was an EMC problem on the aircraft, not what I wanted to hear at that moment.

I do think it is a growing problem, because so many people ignore it, and it is not policed very well in the UK, less so in the rest of Europe, although I believe Russia are very hot on it.

PA always has priority over IFE, its a legal requirement for the video system to pause during a PA. Nothing to do with EMC:ok:

I know that IFE normally freezes during announcements, then carries on, but this caused channels to change and the system had to be reset, it wasn't a normal occurrence, it was a definite fault. It wasn't an old aircraft either.

I suspect that the IFE just had a hiccup because of the interruption during the PA.
If its anything like the rockwell collins IFE on some of ours I'm surprised it ever worked again.:uhoh:

Thanks for input peeps. However, it does seem as if there is dearth of widely-available knowledge out there. There seems to be anecdotal evidence that may indicate that things are not all as rosy as we would like. Some pilots may wish to know such things like:

How do you physically protect electronic/avionic eqpt from EMI - how is this done and maintained?

How does this protection work and can it be compromised?

What frequencies/powers are most dangerous and where in the cabin is the effect greatest?

How does such interference manifest itself and is there a pattern - eg comms, nav, warning systems, fire detectors etc?

How do mobiles/ipods/wiFi/PDAs etc differ from country to country, along with any differences in EMI protection?

Just how good is the 'flightsafe' mode of the average mobiles - how does it work?

What research studies back this?

Do recent studies take into account the effect on the EM intensity and subsequent interfernce patterns by the proliferation of the number of mobile phones on each flight? These days, the likelihood is that almost every passanger aboard will have a mobile phone/laptop/ipod/PDA with WiFi etc, while most pax will not even listen to the welcome PA, never mind switch off their 'toys'?

and so on....

Any pointers gratefully accepted.

flipster

Pick up a copy latest revision of RTCA DO-160 (RTCA Products) . It contains enviromental and EMC testing standards for avionics equipment.

Portable Electronic Device Generated Electro-magnetic Fields on Board a Large Transport Aeroplane
http://www.caa.co.uk/docs/33/CAP756.PDF

Aircraft EMI - susceptibility
 

flipster, during a 42-year career, most on-aircraft susceptibilities experienced were due to:
on-frequency emissions coupled to an avionic receiver antenna
undesired high-intensity fields coupled to wires connected to remoted sensors or part of an analog feed-back loop. The latter were often parts of flight and engine controls. Best fixes were to run the signal on the digital bus rather than analog. If analog, filter and wire shield. Twist wires from multi-phase sensors such as synchros.

w3hoDoug, ISASI MO4415

EMI Elements
 

There are four:

1. Source
2. Coupling
3. Victim
4. Degradation

Mitigation involves breaking the chain in one or more of many ways.

Thanks for help peeps!

I am getting the impression that few understand the severity of the threat and the possible interference by the 'RF soup' with our aircarft systems. I, for one, will be keeping a weather eye open for the slightest suspicion of EMI and will also be modifying my welcome PAs. CAP 756 is interesting reading as are many of the references within - rather scary if you ask me!

Flip

If analogue - also good practice to avoid close parallel cable runs, especially if unscreened cables (if feasible) - preferably crossing analogue cables at or near right angles - ensuring correct cable shield grounding (often from source end only) - utilising star grounding & running twisted cables tight to common grounded areas where possible - use of ferrite to dump RF (see the bulge in your PC monitor cable)

Usa Ntsb & Emi
 

The NTSB engineers are learning.

************************************************************
NTSB ADVISORY
************************************************************

National Transportation Safety Board
Washington, DC 20594

July 23, 2009

************************************************************

THIRD UPDATE ON NTSB INVESTIGATION INTO COLLISION OF TWO
METRORAIL TRAINS IN WASHINGTON, D.C.

************************************************************

The National Transportation Safety Board continues to make
progress in its investigation of the June 22, 2009,
collision of two Washington Metropolitan Area Transit
Authority (WMATA) trains on the Red Line in Washington, D.C.
The Board has developed the following factual information:

Two signal companies, Ansaldo STS USA (US&S) and Alstom
Signaling Inc. (GRS), that designed and manufactured the
automatic train control components for the WMATA system, are
providing technical assistance to the NTSB investigation.

As previously reported, an impedance bond (#15) for the
track circuit where the accident occurred was replaced on
June 17th, 2009, five days before the accident. Continued
review of the maintenance logs has identified that the
impedance bond (#14), located on the other end of the same
circuit, was replaced in December 2007. WMATA records reveal
that this track circuit's train occupancy signal has been
intermittently fluctuating since the replacement was
installed in December 2007.

The NTSB has requested trouble tickets for the last 18
months to see if these problems had been reported, and
seeking records to see if any operators reported problems on
this circuit.

The investigation is identifying possible sources of
interference affecting the automatic train control (ATC)
operation. These potential sources include Electromagnetic
Interference (EMI), traction power harmonics and signal
crosstalk, communication lines, and system upgrades and
changes.

Following the accident, WMATA began to review operations
data and identified some problems at other circuits. These
anomalies are being examined by NTSB and WMATA to determine
if they are the same kinds of problems as were found in the
location of the accident site.

Testing has identified that the circuit problems are
occurring more frequently during the rush hour time period.
As a result, the NTSB and WMATA testing at the accident
location on the Red Line is continuing. These tests may
result in occasional delays on the Red Line in the Fort
Totten area. All testing in the Fort Totten area is closely
coordinated with WMATA and is scheduled to minimize delays
on that area of track during rush hour.

On Saturday, July 18, the NTSB conducted a sight distance
test at the accident location. Information collected from
the test will be correlated with rail markings documented
after the accident, the braking characteristics of the
striking train, and the speed information gleaned from the
WMATA Operations Control Center records.

More USA NTSB Education re low-frequency EMI
 

It happens - not just in yaw damper position sensor LVDT's.

>>>>>

************************************************************
NTSB PRESS RELEASE
************************************************************

National Transportation Safety Board
Washington, DC 20594

FOR IMMEDIATE RELEASE: September 22, 2009
SB-09-53

************************************************************

NTSB IDENTIFIES SIGNAL FAILURE IN FATAL DC METRORAIL
COLLISION; ISSUES URGENT SAFETY RECOMMENDATIONS TO TRANSIT
AUTHORITY, FEDERAL RAIL AGENCIES, AND CIRCUIT MANUFACTURER

************************************************************
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

EMI Confirmed by NTSB today
 

************************************************************
NTSB SAFETY RECOMMENDATION
************************************************************
National Transportation Safety Board
Washington, DC 20594
August 11, 2010
************************************************************
NTSB Safety Recommendations R-10-8 through -22
************************************************************
The National Transportation Safety Board makes the following
safety recommendations to the Washington Metropolitan Area
Transit Authority:

Because of the susceptibility to pulse-type parasitic
oscillation that can cause a loss of train detection by the
Generation 2 General Railway Signal Company audio frequency
track circuit modules, establish a program to permanently
remove from service all of these modules within the
Metrorail system. (R-10-8)

Establish periodic inspection and maintenance procedures to
examine all audio frequency track circuit modules within the
Metrorail system to identify and remove from service any
modules that exhibit pulse-type parasitic oscillation. (R-
10-9)

Review the process by which Metrorail technical bulletins
and other safety information are provided to employees and
revise that process as necessary to ensure that (1)
employees have received the information intended for them,
(2) employees understand the actions to be taken in response
to the information, and (3) employees take the appropriate
actions. (R-10-10)

Completely remove the unnecessary Metrorail wayside
maintenance communication system to eliminate its potential
for interfering with the proper functioning of the train
control system. (R-10-11)

Conduct a comprehensive safety analysis of the Metrorail
automatic train control system to evaluate all foreseeable
failures of this system that could result in a loss of train
separation, and work with your train control equipment
manufacturers to address in that analysis all potential
failure modes that could cause a loss of train detection,
including parasitic oscillation, cable faults and placement,
and corrugated rail. (R-10-12)

Based on the findings of the safety analysis recommended in
R-10-12 incorporate the design, operational, and maintenance
controls necessary to address potential failures in the
automatic train control system. (R-10-13)

Implement cable insulation resistance testing as part of
Metrorail's periodic maintenance program. (R-10-14)


Work with the Tri-State Oversight Committee to
satisfactorily address the recommendations contained in the
Federal Transit Administration's March 4, 2010, final report
of its audit of the Tri-State Oversight Committee and the
Washington Metropolitan Area Transit Authority. (R-10-15)

Require that your safety department; representatives of the
operations, maintenance, and engineering departments; and
representatives of labor organizations regularly review
recorded operational data from Metrorail train onboard
recorders and the Advanced Information Management system to
identify safety issues and trends and share the results
across all divisions of your organization. (R-10-16)

Develop and implement a non-punitive safety reporting
program to collect reports from employees in all divisions
within your organization, and ensure that the safety
department; representatives of the operations, maintenance,
and engineering departments; and representatives of labor
organizations regularly review these reports and share the
results of those reviews across all divisions of your
organization. (R-10-17)

Review the Hazard Identification and Resolution Matrix
process in your system safety program plan to ensure that
safety-critical systems such as the automatic train control
system and its subsystem components are assigned appropriate
levels of risk in light of the issues identified in this
accident. (R-10-18)

Develop a formal process by which the general manager and
managers responsible for Washington Metropolitan Area
Transit Authority operations, maintenance, and engineering
will periodically review, in collaboration with the chief
safety officer, all safety audits and open corrective action
plans, and modify policy, identify and commit resources, and
initiate any other action necessary to ensure that the plans
are adequately addressed and closed within the required time
frame. (R-10-19)

Remove all 1000-series railcars as soon as possible and
replace them with cars that have crashworthiness collision
protection at least comparable to the 6000-series railcars.
(R-10-20)

Ensure that the lead married-pair car set of each train is
equipped with an operating onboard event recorder. (R-10-21)

Develop and implement a program to monitor the performance
of onboard event recorders and ensure they are functioning
properly. (R-10-22)
************************************************************
http://www.ntsb.gov/recs/letters/2010/R-10-008-022.pdf
************************************************************
The complete recommendation letter is available on the Web
at the URL indicated above.
The letter is in the Portable Document Format (PDF) and can
be read using the Acrobat Reader 5.0 or later from Adobe
(http://www.adobe.com/prodindex/acrobat/readstep.html).

An archive of recommendation letters is available at
http://www.ntsb.gov/recs/letters/letters.htm.
Electronic versions of letters may or may not include
enclosures; however, related publications, accident
briefs, and aviation accident synopses may be found
on the NTSB website.
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