Electromagnetic Interference with Aircraft Systems:
why worry?
11 July 1997, modified 13 July, 20 October 1997
Everybody knows how difficult listening to the radio or watching TV becomes when someone is using the vacuum cleaner in the next room. The vacuum cleaner causes significant interference with the radio signal. I used to live in a house in Kensington, CA, with an electric garage door opener, activated from the road by a small radio device carried in my car. The door would occasionally open by itself, early in the morning, on some rainy days when SFO was using RWY 19 for arrivals, and the flight path came more-or-less overhead. Now, there's an anecdote. I don't know it was aircraft transmissions; I don't know it wasn't a passing taxicab whose driver was talking to base; I don't even know it wasn't a fault in the door opening mechanism. We may presume that the system was not very well shielded from electromagnetic interference, and it is certainly not certified to the same rigorous standards as avionics (aviation electronics).
Nevertheless, there are similar worries in aviation at the
moment. Passengers use electronic devices on board aircraft, including
some such as cellular phones that they shouldn't in any case be
attempting to use, and pilots have reported anomalies with their
navigation equipment that seem to correlate with use of personal
electronics in the cabin. An overview of the technical issues may be
found in.
There have been to my knowledge no reports so far of interference
with electronic flight control on the Airbus A320/330/340 series or the
Boeing B777. These systems are shielded very well against electronic
signals, because they have to fly through radar beams and other
electromagnetic fields that may be occasionally very strong. There is
nevertheless some experience with electromagnetic interference with
electronic flight controls. Five crashes of Blackhawk helicopters
shortly after their introduction into service in the late 1980's were
found to be due to electromagnetic interference from very strong radar
and radio transmitters with the electronic flight control systems.
So concern about this phenomenon is not purely the result of
speculation. It has actually happened, and it is appropriate to be
concerned about the possibility of similar phenomena in transport
aircraft.
Bruce Nordwall, writing in Aviation Week and Space
Technology in September 1996, reported on the topic of an RTCA report
to the FAA Administrator. At the request of the FAA, RTCA Special
Committee 177 was formed in 1992 to look into the possibility of
interference with aircraft systems from electronic devices operated by
passengers during flight. Such devices include laptop computers,
Gameboys and, more insidiously, portable personal telephones employing
cellular technology.
Nordwall reported the RTCA advisory group to be worried that no
group was testing or systematically tracking the potential effect of
passenger electronics on avionics. The group was also concerned that
the flying public is not being educated about the potential hazard, and
that the airlines must largely figure out how to deal with the issue
themselves. Most airlines in the US already prohibit use of passenger
electronics of any sort below 10,000ft altitude. There is most concern
for the future; that rapid increases in the technology of personal
communications may allow passengers to bring aboard with them, and
inadvertently or surreptitiously use, devices such as personal
satellite phones that may be capable of significant levels of
electromagnetic radiation. The RTCA report recommends developing and
installing devices in aircraft cabins that could detect and locate
potentially harmful radiation coming from within the aircraft. John
Sheehan, the chairperson of RTCA SC-177, kindly provided the Executive
Summary of SC-177's report, RTCA DO-233 (RTCA96). The Summary is
included here as Appendix A.
Navigation systems are particularly vulnerable for two reasons:
they have parts devised to detect and act on signals coming from outside;
radio-based systems are particularly susceptible to low levels of interference.
Aircraft control systems are located entirely within the aircraft and are shielded from absolutely any signals not coming from one of their own devices; they are also not radio-based, but are based entirely on electrical signals conducted through wires as are most computer networks (in the future, maybe also light signals conducted through glass-fibre cables). Navigation avionics, on the other hand, must have some designed sensitivity to environmental radio signals in order to perform their function. Nordwall says
THe antennas of radio-based avionics may be affected by [electromagnetic] field intensities of only microvolts per meter. But being outside the aircraft, the antennas get some protective attenuation from the fuselage of radiation originating inside the aircraft. Non-radio systems generally have higher signal levels, and so are less susceptible to low levels of interference.
The hull of a metal aircraft forms an effective electromagnetic boundary between the outside and the inside of an aircraft. Electromagnetic signals find it hard to get in, or to get out. That is why the navigation and radio antennae on an aircraft need to be placed outside the aircraft hull. But while outside they must be sensitive, the navigation electronics inside the hull can be in principle just as well and securely shielded as control avionics, because there is no reason at all for navigation systems to be sensitive to electromagnetic signals coming from inside the aircraft indeed, very good reasons for these systems to be very insensitive, namely, that there is lots of other electronics working there as well.
The Regulatory Environment
US Federal Aviation Regulation 91.21 prohibits the use of any
portable electronic devices on board aircraft, with the exception of
voice recorders, hearing aids, heart pacemakers, shavers, and any other
device that the operator of the aircraft has determined will not cause
interference with the navigation or communication systems of its
aircraft:
91.21 Portable electronic devices
(a) Except as provided in paragraph (b) of this section, no person may operate, nor may any operator or pilot in command of an aircraft allow the operation of, any portable electronic device on any of the following U.S.-registered civil aircraft:
(1) Aircraft operated by a holder of an air carrier operating certificate or an operating certificate; or
(2) Any other aircraft while it is operated under IFR.
(b) Paragraph (a) of this section does not apply to
(1)Portable voice recorders;
(2)Hearing aids;
(3)Heart pacemakers;
(4)Electric shavers; or
(5)Any other portable electronic device that the operator of the aircraft has determined will not cause interference with the navigation or communication system of the aircraft on which it is to be used.
(c) In the case of an aircraft operated by the holder of an air carrier operating certificate or an operating certificate, the determination required by paragraph (b)(5) of this section shall be made by that operator of the aircraft on which the particular device is to be used. In the case of other aircraft, the determination may be made by the pilot in command or other operator of the aircraft.
The regulation puts the responsibility firmly on an individual
airline to determine that there is no interference. However, as
Nordwall points out, Compact consumer electronic devices have
proliferated in numbers that defy cataloguing, let alone testing. The
question is what would constitute an appropriate determination of no
interference. In contrast to the US Federal Aviation Regulations, the
International Civial Aviation Organisation (ICAO) has no regulations
relating to portable electronics.
US airlines implement a general ban on using any portable
electronic devices (PEDs) below 10,000ft. According to former FAA
associate administrator for regulation and certification, Tony
Broderick, this action was first initiated by Northwest Airlines, and
other airlines quickly followed suit. Broderick notes that use of PEDs
during takeoff and landing phases is to be discouraged anyway, not only
because of possible consequences of EMI but also to encourage
passengers to pay attention to the cabin crew in case an emergency
should arise during these critical phases of flight (a
commercial aircraft is below 10,000ft usually only during the takeoff
and landing phases of flight, and according to the Boeing statistics,
20.9% of all fatal accidents to jet aircraft have happened during
takeoff and initial climb, and 46.6% during initial and final approach
and landing ). Broderick also believes that the FAA, in
cooperation with the industry, will need to determine if there is
indeed a problem with PEDs on board aircraft, and that it will soon
become commonplace to have PEDs on board that are doing things (for
example, transmitting) that their owners aren't really aware of.
Some Issues Particular to Cellular Phones
Cellular phones, often called Cellphones in the US and Handy's in
Germany, are a particular source of problems because, regardless of
whether they may interfere with aircraft systems, the technology on
which cellular telephones are based precludes their effective use on
aircraft. This applies to all cellular phones, including the analogue
technology in the US and the digital GSM technology in Europe. It may
be worthwhile first to explain the known problems associated with
attempted use of cellular phones while flying.
The technology of cellular phones is based on small local ground-based
reception areas called cells. A cellphone user is served by just one
cell, and when reaching the boundary of a cell, will be handed over to
another cell which (s) he is about to enter. The topology of coverage
is based on the assumption that the user is on or near the ground, and
it is a technical assumption on which the entire system is based that a
user will be within sight of just one cell except when nearing a cell
boundary. When in an aircraft, however, a user is within radio sight
of many cells, simply because (s) he is way off the ground. An
attempted
call or reception from an aircraft would activate many if not all cells
in the local area, which breaks the technology – it causes many
transmission problems and the system is disturbed. Therefore the
various communication authorities, such as the US Federal
Communications Commission (FCC), ban the attempted use of cellular
phones while on board aircraft. However, such attempted use is not ipso
facto rendered dangerous. It is technically inappropriate and
antisocial, as well as mostly futile.
On Saturday 1 March 1997, German Transport Minister Matthias Wissmann
was reported in the German and international press as wanting a fine
and up to two years in jail for people attempting use of cellular
phones on board aircraft. He was reported as saying that
In order to further increase air transport safety there will be new regulations in the use of these dangerous things [...] In future the use of electronic equipment by passengers in aircraft will be banned.
Herr Wissmann's comment mentions the danger of attempted cellphone use. He therefore seems to be speaking about the possibility of interference with aircraft systems, which if true is certainly dangerous, rather than simply the problem that it causes the cellphone technology to malfunction.
While one may applaud Herr Wissmann's proactive stance in
addressing a potential hazard, one may also query the wisdom of
publically declaring aerial cellphone use to be dangerous in the
absence of any concrete proof. My colleague Prof. Dr. Klaus Brunnstein
of the University of Hamburg, who avidly follows various potential
public computer risks, commented that
[...] German law still forbids mobile communication (with specific exemptions) [...] It is interesting that airlines don't specifically refer to this law when announcing that [attempted use of] mobile telephones [is] not permitted on board.
Brunnstein is not aware of any concrete proof of electronic interference on German aircraft, but reports that EUCARE has more than 60 pilot reports of potential cases of interference, including some with cellphones. He laments the anecdotal nature of these cases, since one requirement for accurate forensics, as he aptly terms it, is verifiability of the source data.
General Worries on Interference
Nordwall reports that the RTCA Committee 177 inquiry found 137 incidents (pilot reports, anecdotes) reported either to them, or to the FAA/NASA Aviation Safety Reporting System (ASRS) program, or to the International Air Transport Association (IATA). VOR reception (2) was affected in 111 incidents by far the most common occurrence. From the 33 reports direct to RTCA, 21 incidents related to laptop computers and only 2 to cellular phones. Navigation systems were affected in 26 of those incidents; fuel systems, warning lights and propulsion reported one incident each. Rough correlation of suspect with effect by turning the suspect device on and off was found in 14 cases, on-off-on in 6 cases, and no correlation in 13 cases.
Some Anecdotes and Discussion
Jim Irving is a colleague who flies B737 aircraft for a major US carrier. He has an anecdote:
[...] One day departing Portland Oregon we noted that the FMC [Flight Management Computer] Map display showed a disagreement with the "raw data" VOR position. Our training is such that we would normally immediately switch over to raw data and assume the FMC was in error.
We would have done that except that it was a beautifully clear
day and I looked out the window and was able to determine that the FMC
seemed to be right on. I called back to the cabin and asked the flight
attendants to check for someone using a cell phone or computer. A few
minutes later they called back to say that a man had been using his
cell phone and it was now off. Strangely (?) our VOR and FMC map now
agreed.
Later in the flight the flight attendants called back and said
that they had caught the man using his cell phone again but this time
we had not noticed any problems, perhaps because we were in cruise far
from the ground and not paying as much attention.
André Berger (who also has a homepage) is a colleague who flies B737 aircraft for a major European airline and who has had first-hand experience of some of these incidents. While interference is not proven, he believes it gives considerable cause for concern; and that while it may be difficult to demonstrate the relationship using Brunnstein's forensic criterion, this could be due to the fact that the equipment needed to do so is not on board the aircraft at the times the incidents occur. Berger monitors the IATA confidential incident reports, and also has some experience of his own to contribute:
In our company we recently had a Localizer deviation (out of tolerances) on a B737-200 related to a GSM (mobile phone) being operated by a passenger (who was disregarding our company regulations). When requested by the cabin crew to switch off his GSM, localizer indications became normal. Is this scientific proof? Certainly not, but good enough for me as a captain to insist that all the electronic toys, computers, mobile phones, etc., are OFF during critical phases of flight. [...]
I had fuel indications on the FMC going crazy on board the B737,
that returned to normal when all electronic stuff in the back was
switched off. I suspect a Gameboy electronic game device to have
interfered, but this is no more than a guess. No, I did not ask to
switch the toy back on again and investigate more in depth as I was
responsible for the safety of 140 passengers and this would have been
extremely irresponsible! This is not a situation in which to do such
testing! This [ever-present responsibility accounts for why] there is
no proof of the relationship.
I also recall experiencing impossible mode annunciations on the
FMA (flight mode annunciator) on B737. Having both the autothrottle AND
the pitch channel of the autopilot trying to maintain speed (both in
MCP SPD mode) for example, not programmed by the pilot (you cannot
program that). After an expensive in-depth troubleshooting session by
our maintenance department, the incompatible mode annunciations were
traced to a ... faulty cockpit window heat wiring. This caused
electronic interference with the auto flight system.
Berger has also recounted two more incidents:
June 07, 1997. B737-300: Verify position was indicated on the
CDU. Both IRS and radio position were correct, the FMC position was
not. The difference rapidly increased to 8 nautical miles. After
switching a GSM in the cabin from STBY to OFF, the FMC updated
normally. FMC was correct for the remainder of the flight and on the
return flight.
April 30, 1997. B737-400: During level cruise, the AP pitched up
and down with ROC/ROD of 400 fpm indicated. Other AP was selected: no
change. Cabin was checked for PC's and other electronic devices:
nothing was found. Requested passengers to verify that their mobile
phone (GSM) was switched OFF. Soon after this request all pitch
oscillations stopped.
Just glitches or did interference really occur? Don't know, but
EMI (electro-magnetic interference) is a problem that needs more
research.
Apparently, there are also some incidents with older aircraft. Here is Berger's response to a query from another colleague:
> Has anyone heard of EMI incidents involving older Aircraft, i.e. 707,
> DC9,747-200, where system signal strengths are larger, and a lot more
> are analog?
[There was one incident reported with a] B737-200. During
approach to MAN (Manchester International, UK), the LOC for landing
runway 24 oscillated and centered with the aircraft not on track (but
offset), confirmed visually. Ground equipment was monitored and working
normally. When a GSM in the cabin was switched off, all indications
became correct.
Frank McCormick, an aerospace engineering colleague who is also a
FAA Designated Engineering Representative, wonders about the physics of
such possible incidents:
The threat levels presented by the gadgetry in question – personal computers, cellular phones, compact-disk players, hand-held video games and so on – are mere background noise compared to the threat levels that must be demonstrated during environmental qualification testing [of the aircraft systems]. How could an FMC [Flight Management Computer] pass, say, DO-160C [standard certification] tests, yet lose its mind in the presence of a cell phone on standby?
and Peter Mellor, of the Center for Software Reliability at City University in London, reports that
The cabling on the A320 has not only been tested for resilience to normal EMI, but for its ability to withstand the much greater pulse that would result from the aircraft flying through a powerful radar beam, for example.
While doubting that the suspected-EMI phenomenon is ubiquitous,
McCormick suggests that some sort of systematic investigation could
proceed by inviting protagonists (actual airplane, pilots, customer
with suspect device) to participate in attempts to reproduce the
incidents. Berger reports that in fact very few systematic tests are
performed anyway: he asked a major portable phone manufacturer's
representative what tests they performed for EMI from their devices in
aircraft. The manufacturer performed none because use of cellphones is
illegal in aircraft. Berger notes that nevertheless such tests are
relevant, because these phones are frequently used surreptitiously or
inadvertently on aircraft. He also notes that most electromagnetic
interference testing is bench-testing, performed on independent
subsystems, and that this may suggest an interesting suspect point of
weakness in the aircraft, namely the system interconnections. Recall
one of the incidents he noted above: neither the electronics nor the
well-shielded wiring itself, but the wiring connections seem to have
been problematic. He reports incidents to specific aircraft (whose
registration tail numbers are also given in the reports):
On a specific B737-300, a MCP (mode control panel) was doing
weird stuff intermittently during several flights. I mean really weird:
like letting both pitch and autothrottle fight each other to maintain
speed. Nearly all boxes involved (MCP, FCC, several AFDS boxes) were
changed before a clever mechanic found out that the windshield heat was
not correctly grounded. This is located just a few inches from the MCP
and is one of the big consumers on board. Tightening a few nuts solved
an engineers nightmare.
On a specific B737-400, the FMC was doing weird things, mainly in
cruise. Some pilots reported that after a request to the passengers to
switch off electronic equipment, the problem was solved, others said it
did not help anything even with every electronic gadget switched off in
the cabin. Others reported nothing abnormal with CD's, PC's, Gameboys
and more of that stuff trying to jam the system unsuccessfully.
Troubleshooting was done and it was decided to replace another black
box that was suspected. It was pulled out but, no spare was available.
So the same black box was pushed in again. Problem solved, it never
happened again!
Connections are a possible weak point. And difficult to duplicate
if a problem exists. Can an imperfect connection make a tested system
EMI susceptible or not?
He emphasises, as do the RTCA and the other correspondents, that more research and systematic methods of testing are urgently to figure this situation out.
John Dimtroff is an electrical engineer on the Transport Standards
Staff of the FAA Transport Aircraft Certification Directorate in
Seattle. He is also a member of the Joint Airworthiness
Authority/Federal Aviation Administration Electromagnetic Effects
Harmonization Working Group. He has been a Federal Communications
Commission investigator and inspector, a Boeing RF design engineer and
a US Air Force Radar Specialist. Dimtroff reports some incidents
first-hand:
...even the aircraft's own certified airborne equipment can play games on itself. [A few] years ago I was involved in identifying the source of [navigation instrument indicator] needle swings and voice modulations in the pilot's headset. [The culprit turned out to be a] certified airborne-authorized telephone broadcasting on a frequency which just happened to be commensurate with a piece of [navigation] equipment.
[Another case involved] the Flight Guidance Computer/Air Data
Computer [which was] radiating unwanted signals, the 15th, 20th &
22nd harmonics of 6 & 8 MHz clock frequencies, [which are] right on
the 120MHz & 132MHz VHF band! [But] each piece of [this] equipment
met all the required RTCA DO-160 level testing [requirements].
...my experience with the FCC has taught me [to wonder] how many
[PED] devices transmit with a clean, zero-spur signal, especially after
being dropped, banged, klunked, fondled and sat upon. [In] my former
FCC investigative days, [I saw] a number of devices (computers,
stereos, TV's, etc., etc.) which purportedly met FCC Part 15
requirements as indicated by their label, [but] were either bogus
marked, illegally imported or were just outside the manufacturing
quality bell curve. [My personal view is] that every carry-on
electronic device is suspect until it has been individually tested,
which, of course, is impossible.
[My experience suggests to me that] it is nearly impossible to
predict/replicate an EMI event on an aircraft when the event involves a
portable carry-on device (PED). Location, orientation, power output,
modulation, inconjunction with ALL the other
PED's/electronics/electrics/avionics active at that time all play a
role in the EMI event. And we must not exclude the terrestial based
emitters (radars, etc).
ARSR Summary of Reports, 1986 – June 1994
The following summary prepared by the ASRS was forwarded by Peter Mchugh of the FAA's Office of Aviation Safety, taken from Quick Response No. 271 dated November 30, 1994.
The following synoptic analysis of passenger electronic devices incidents was accomplished by the ASRS staff [at the request of the FAA]:
There were a total of 46 passenger electronic devices related incidents in the ASRS data base covering the period Jan 1, 86 thru June 30, 94. This number is in contrast to the 51,337 full form reports covering all types of incidents reported to the ASRS during the same period.
Passenger electronic devices incidents comprise .08 percent of the total full form reports in the ASRS database. Full form reports receive full analysis processing and include the reporter's narrative as part of the database record.
45 incidents involved passenger carrying operations. 33 of the incidents involved aircraft in the 60,000 – 300,000 lbs. weight classifications.
33 of the incidents referenced alleged aircraft systems
interference from an onboard passenger electronic device. 10 of the
incidents referenced alleged interference from an unknown onboard
source. The remaining 3 reports make reference to FAA policy about the
use of passenger electronic devices.
The breakdown of aircraft systems {reported} affected by passenger electronics devices interference included: nav equipment (37 incidents), aircraft communications equipment (9 incidents), radar altimeter equipment (1 incident) and fly-by-wire throttle controls (1 incident).
21 passenger electronic devices were specifically identified to be the sources of the aircraft systems interference. The reporters noted the interference ceased after the devices were turned off. The identified passenger electronic devices included:
Cell phones (4)
Laptop computers (4)
Portable AM/FM Radio Cassette Players (4)
Portable CD Players (3)
Electronic Games (3)
HF Radio (1)
Heart Monitor (1)
One report cited interference from 23 passengers using AM/FM radio cassette players.
One report cited unknown onboard interference causing ILS signal interference resulting in two missed approaches.
Two reports cited passenger use of cell phone as a cause of dual VOR nav failure.
None of the passenger electronic devices incidents had a critical impact on the safety of the flight.
Mchugh urges caution in interpreting the data. It has limited
statistical significance because
reporting is voluntary and there is no statistical understanding of the total reporting population or any way of estimating what the actual number of events might be;
reporting is subjective and influenced by biases, including that reporters gain protection from FAA regulation-enforcement procedures and it is undoubtedly the case that some reports are generated mainly for that reason, and this may affect the quality of the report.
(Indeed, many private pilots I know, including myself, carry ASRS reporting forms with us in our flight bags on every trip!) Accepting these caveats, however, the ASRS assembles many more anecdotes than other systems, and Mchugh notes that it is in many cases the only game in town. And the personal, subjective nature of the reports can provide insight into the human factors issues resident in some events.
Social and Administrative Pressures
The physical phenomenon of EMI interference seems to be relatively emphemeral. It is hard to determine if specific incidents are examples of the phenomenon, partly for the reasons Dimtroff remarks. In this respect, as McCormick points out, it distinguishes itself from other recurring problems such as icing, controlled flight into terrain (CFIT), and cargo-hold fire prevention and detection. These latter problems have clear, undisputed instances, and the question is what to do to prevent them. The question with EMI is what kind of a problem it is, and how to obtain clear instances.
There may be social and legislative pressures on participants which may
color their response to this situation. Consider the following
circumstance. US airlines may only allow use of PEDs if they are known
to the airline not to cause interference (FAR 91.21). As we have noted,
it is largely impractical to submit devices to stringent test,
considering the number of devices on the market, and the varying
condition of individual devices. Suppose a US airline reports and
investigates an incident, suspected to be EMI. Ipso facto, that airline
cannot therefore be deemed to have determined ... non-interference,
as required by FAR 91.21. Just the opposite, in fact – they have
suspected interference! Therefore, FAR 91.21 prohibits use of such a
device on board that aircraft. A strict reading of the legislation thus
leads directly from suspected-incident report to prohibition on that
airline.
However, other airlines permitting use of such devices could
legally continue to do so until they themselves were subject to an
incident. A US airline fastidious about reporting and pursuing alleged
EMI incidents could therefore find itself at a competitive disadvantage
as it must prohibit PED use, and laptop and Gameboy users and cellphone
owners with a penchant for not turning their devices off might well
move their custom to rival airlines. Thus may airlines find themselves
in a situation in which they must downplay reports or risk losing
business, as a consequence of requirement FAR 91.21.
In Europe, many aircraft and crews are certified for the demanding
automated approach procedures known as Category III (CAT III), in which
the autopilot, following navigation signals, flies the aircraft on
landing all the way to main gear touchdown on the runway. A reported
incident of suspected EMI with PEDs on board such an airplane could
seriously bring into question the aircraft's CAT III certification,
since the aircraft electronic systems must be demonstrably highly
reliable in order to exercise CAT III authority. An airline reporting
such incidents officially could suffer the loss of CAT III
certification on the incident airplane until the problem is discovered
and rectified. Since EMI incidents, as we have remarked, appear to be
very difficult to reproduce on the ground, one could imagine a scenario
in which an airline reporting a suspected EMI incident is unable to
trace the source, and therefore cannot exercise the CAT III capability
on that airplane again. This would be a serious service limitation in
the European environment. Again, this situation reveals a potential
competitive disadvantage to airlines which take suspected EMI incident
reports seriously.
If social pressures exist for airlines to downplay potential EMI
incidents, one could also foresee the possibility of pressure from
airline management on line pilots also to downplay observed avionics
anomalies in service. It is easy to see that both of these social
pressures could result in general underreporting and underinvestigating
of suspected EMI incidents.
Finally, the pilot in command is directly responsible for the safety of
those on board the aircraft. As André Berger has remarked, this
responsibility includes avoiding all potential safety degradations, no
matter how minimal. Thus, if EMI from a passenger PED is suspected, the
only appropriate recourse, according to this legislative
responsibility, is for the pilot to require the device immediately be
turned off completely. This precludes any kind of correlation testing,
benign or otherwise. However, recycling the device and trying to
reobserve the interference is the most obvious simple test one can
perform, and could be deemed benign in many circumstances. A fastidious
interpretation of regulations concerning pilot responsibilities will,
however, preclude it.
Since the current regulatory situation may thus unwittingly discourage
reporting and investigation of suspected EMI incidents, there is a
significant role for regulators to play in encouraging both reporting
and investigation of such phenomena. I see five proactive ways for
regulators to help:
in limiting the regulatory pressures towards underreporting and underinvestigating noted above;
in establishing reporting standards for such incidents;
in providing guidelines for, and allowing, if not encouraging, in-flight impromptu tests by the flight crew if certain sorts of benign influence from passenger electronics is suspected;
in providing guidelines for ground-based testing procedures in the wake of such incidents, possibly involving also the suspect PED equipment and its owner/user;
based on a classification of reports of the incidents, in clarifying which kinds of incidents would be considered to constitute a maintenance problem, and of which sort, and how those kinds would be considered to alter the certification status of the aircraft (particularly with regard to no-go and CAT III status).
The last of these measures, of course, could only be taken in a regulatory environment in which an absolute ban such as that in FAR 91.21 did not apply. The question of just what such an environment could look like is the topic of the first measure.
Conclusions
There are plentiful anecdotes of possible electromagnetic interference with aircraft systems. While the systems are subjected to thorough bench-tests under conditions of electromagnetic interference to demonstrate adherence to certification standards, there appears to be no systematic process for investigating and attempting to reproduce in-flight incidents, although the British Airways BASIS system, ASRS and EUCARE provide systematic logging of such reports, as one presumes do individual airlines for internal use.
Possible explanations of the lack of reproducibility of such
incidents center on the environmental differences between the bench
tests for certification, in which individual subsystems are tested
independently, and the integrated aircraft environment. While entire
aircraft are also subjected to some testing during certification, there
may be individual differences between aircraft: if wiring connections
are susceptible to interference, for example, then aircraft with a
longer maintenance record may be more prone to interference incidents
than brand-new ones.
While there is considerable disagreement amongst experts as to
whether the phenomenon or phenomena are indeed cases of
electromagnetic interference from passenger electronic devices, the
call for more systematic testing appears to be unanimous. I have argued
that some change in the regulatory environment will help. Nevertheless
it appears clear that, whatever one's view on the reality of the
phenomenon, an increasing number of reports on correlation will
continue to appear at ASRS, BASIS and EUCARE.
Peter Ladkin