AIRCRAFT
ELECTROMAGNETIC
ENVIRONMENTAL EFFECTS
(E3) AND SAFETY
Douglas J. Hughes, Full Member
International Society of Air Safety
Investigators
DOUGLAS J. HUGHES
Doug Hughes was an Electromagnetic Environmental
Effects (E3) professional his entire 42-year career, starting
at McDonnell Aircraft in St. Louis after graduation from
the Missouri School of Mines and Metallurgy (Rolla) in
1963 with a degree in Electrical Engineering. He moved to
IIT Research Institute (later Alion) in Annapolis in 1968 to
work on the DoD ECAC support contract. His graduate
Communications Theory degree is from The George
Washington University. He retired in 2005 and moved to
Ann Arbor to be near family.
Mr. Hughes' experience includes database and analysis
model development, sponsor-funded project analysis and
test support, cosite analysis, equipment spectrum
certification, management, and serving as a technical
advisor. He is a full member of the International Society of
Air Safety Investigators (ISASI) with 31 studies or
investigations. All involved aircraft E3, including the
Forrestal fire, two RTCA studies of portable electronics
aboard, the USAF IFO 21 CT-43A accident in Croatia, RQ-4A
AV-2 GLOBAL HAWK, and TWA 800. He continues ISASI
activity in retirement by participating in the Unmanned
Aircraft Systems Working Group. Lessons learned from
the RTCA were presented at the September 14, 2011
meeting, and a few other safety investigations will be
described this evening.
PRESENTATION OUTLINE
PRESENTED SEPTEMBER 14, 2011
• Wireless Aboard Aircraft
– Commercial
– General Aviation
TONIGHT, IF TIME AND INTEREST ALLOWS
• Aircraft Electromagnetic Environmental
Effects (E3)
• Example Accident/Safety Investigations
Involving E3
RECENT PEDS NEWS COVERAGE
 USAToday, December 21 issue, Editorial plus
big article
 CBS This Morning: Is using devices on
planes really dangerous?
 New York Times, January 21, 2011: Interfering
With Flight?
 Wall Street Journal last week
 Scientific American shortly after the Alec
Baldwin A/A episode in December
 Latest Alec Baldwin commercial – “Can you
play games on that?” “Not on the runway”
(Alec)
AIRCRAFT
ELECTROMAGNETIC
ENVIRONMENTAL EFFECTS
(E3)
SOME THEORY SIMPLIFIED
THE E3 EMI ISSUES WITH AIRCRAFT
• Sources of EM Energy Are All Around Us, Yet
Unseen
• Every Wire In The Aircraft Is A Potential Receiving
Antenna – quarter wavelength resonances set up
some interesting coupling opportunities
• Every Wire Connects At Least Two Devices That
Are Potential EMI Victims
• EMI Protection Degrades Over Time
• The FAA’s AGING WIRING Studies Were Eye
Openers
E3 UPSETS DEFINED
Source
Mitigation
X
Coupling
X
Output
Degradatio
n
Victim
X
AIRCRAFT E3 ELEMENTS
SOURCES COUPLING VICTIMS
MITIGATION
Primary
• Frequency
Management
• External
• Cosite
• Internal
Secondary
• Intentional
• Unintentional
• Conducted
• Radiated
• Antenna-toAntenna
• Interface Wiring • Filtering
Input
• Shielding
(IM)-to-Antenna
• Box Penetration
• Physical
• Antenna-to-Wire
• Intentional
Separation
• Box-to-Antenna
Receivers
• Intermodulation
• Box-to-Wire
• Intermodulation• Wire-to-Wire
• Transients
• Receiver
Antenna Input
• Unintentional
Receivers
F-4 PHANTOM II E3
5,195 BUILT
• F-4 Radar-to-RF-4
Side-Looking
Radar
• UHF-to-Nose Gear
Steering
LESSON
LEARNED
E3 Control Program Was
Required & Effective
• “Everything”-toRadar Warning
Receivers
• RF-4 HF Comm-toAutopilot
SUSCEPTIBILITY OF REMOTED SENSORS AND
FLY-BY-WIRE FEEDBACK LOOPS
Pilot or
Autopilot
Command
+
Correction
-
Control
Motion
Airplane
Electronics
Feedback
Position
Transducer
Gain/Filter
Most Common E3
Susceptibility
Access Path
4/8/2015
SOME WELL-KNOWN FEEDBACK SYSTEMS
AUTOMOBILE
THROTTLE CONTROL
RADIO-CONTROL
FOR MODELS
EXAMPLE FLY-BY-WIRE SYSTEM WITH A
FEEDBACK LOOP
4/8/2015
•
Airbus 300-605 Rudder Travel
Limiter
•
Travel limited as airspeed
increases
•
Travel limit set by motor-driven
cam
•
Position sensed by redundant
sensors
•
Position fed back to redundant
computers
F-4 ANTISKID BRAKE RF
SUSCEPTIBILITY
Analog speed recorders on
each wheel hub interfaced to
comparison circuit, which had
failed MIL-I-6181 radiated
susceptibility and required
additional filtering. Wiring,
exposed when wheels down,
also had to be shielded. Early
automobile antiskid brakes
were also RF susceptible.
Speed Recorders
F/RF-4 AILERON-RUDDER INTERCONNECT
(ARI) RF SUSPECTIBILITY
Position
transducer on
each aileron
4/8/2015
F/RF-4 ARI INTEGRATION & E3
• Position Transducers are
Permeability-Tuned Audio
Transformers
• Position Transducers
Integrated in Unbalanced
Circuit
• Position Transducer Signals
Susceptible to UHF Comm
Emissions
• Additional Wire Shielding and
Amplifier Input Filtering
Required
LESSONS LEARNED
• MIL-I-6181 RS Limits Inadequate
• RF Saturates Audio Amplifiers
• Unbalanced Circuits Are More Susceptible
4/8/2015
UH-60 BLACKHAWK DoD IG REVIEW - 1988
Several E3 Upsets
• Master Caution Light Panel
• Hydraulic Pumps Switched
to Backup
• Stability Augmentation
System
• Horizontal Stabilator
Feedback Control RF
Susceptibility
• LVDT Position Transducer
on Stabilator Interfaces
With SAS Amplifier
Forward
4/8/2015
TO 1H-60(U)A-1
NOTE
Flight near high power RF emitters such as
microwave antennas or shipboard radar may
cause uncommanded AFCS and/or stabilator
inputs. Electromagnetic interference (EMI)
testing has shown that the MASTER
CAUTION light may illuminate before or
simultaneously with any uncommanded
stabilator trailing edge movement, with 4 or
5° of movement being the maximum.
USAF T/CT-43 YAW DAMPER
RUDDER POWER
CONTROL UNIT
YAW DAMPER COUPLER
MODULATOR
1/Q
POT
TRANSFER
VALVE
AMP
YAW ENG
CADC
YAW
DAMPER
ACTUATOR
AMP
BAND
PASS
FILTER
POSITION
TRANSDUCE
R (LVDT)
RUDDER
PEDALS
ELECTRONIC
INTEGRATOR
ACTUATOR
DEMODULATO
R
YAW ENG
AMP
RUDDER
YAW
RATE
GYRO
AVIONICS BAY
INTERFACE
RUDDER
Feed-Back Path
4/8/2015
BOEING 737-100/500 YAW DAMPER
Susceptible
Interface FeedBack Path
FAA B737 RUDDER YAW DAMPER EMI
SUSCEPTIBILITY HISTORY
•
Boeing Service Bulletin 737-22-1112 “EMI Effects on Yaw Damper” of
June 18, 1992 corrected EMI from on-board HF
•
European airline electronic technician internet newsgroup report of
B737 yaw damper & analog (GSM) cellular telephone EMI test
•
Boeing proposed fix in NTSB USAir 427 report “Includes improved
wire shielding and isolation to eliminate problems caused by electrical
interference.”
•
FAA B737 Engineering Test & Evaluation Board (ETEB) 11-degree
EMI-induced yaw damper hard over during closed-loop test (pp. 7.440/44 of ETEB Report)
•
AD 97-14-03 to replace B737-100/500 1960’s-era analog yaw damper
coupler with B737-NG digital yaw damper coupler and improved wire
shielding appears to have been effective
•
Old AnalogYaw Damper coupler design very similar to, and same
generation as, F-4 ARI
4/8/2015
INTERMODULATION
Narrowband IM products generated in E-8 JSTARS
VHF communications antenna due to detector in
autotune SWR measuring circuit mitigated via onboard frequency management software
Guam Agana RWY 6L alias glide slope signal detected on
5-6 August 1997 - a distraction to the Korean Air Flight
801 crew Andersen AFB glide slope signal 600 kHz
removed – 609 kHz Broadcast station at base of Nimitz
Hill – 2nd-order intermodulation product – not checked by
FAA!
O’Hare RWY 14R glide slope anomaly during
1996-98 contributed to the 9 February 1998
A/A1340 short landing accident – Middle Marker
75 MHz signal part of a 3rd-order intermodulation
product with Air France VHF transmitter to
produce possible EMI source on 14R glide slope
frequency – not checked by FAA!
4/8/2015
FM IMMUNITY
RTCA DO-176
Problem of long duration. Earlier
joint FAA/FCC solutions using
frequency management
ineffective in Europe where there
are many “pirate” FM broadcast
stations. DoD replaced
VHF/VOR/ILS receivers with units
incorporating better RF filtering.
Lesson Learned - Frequency
management can’t solve all the
E3 problems.
4/8/2015
KOREAN AIRLINES FLIGHT 801
4/8/2015
O’Hare RWY 14R ILS Approach
4/8/2015
AMERICAN AIR FLIGHT 1340
American Airlines, Inc. Submission
NTSB Accident Investigation No.
DCA-98-MA-023
… Flight 1340 was almost directly above the tracks at the point in its
approach where it experienced the most rapid decrease in its pitch
attitude. The close proximity of such a source of possible
intermittent EMI distortion of the Runway 14R glide slope signal
warrants the NTSB’s complete analysis.
… The measurement of potential EMI disruption or distortion at the
altitude and position at which approaching aircraft have reported
glide slope anomalies (such as that encountered by Flight 1340) is
the critical value to be measured.
… Possible causes for the distortion in the glide slope are EMI from
PEDs, EMI from ground-based equipment, and obstruction of the
glide slope signal due to penetration of the ILS critical or sensitive
areas.
4/8/2015
COMBAT SURVIVOR/EVADER LOCATOR
(CSEL)
R a d ia te d E m is s io n L e v e ls in d B u V /m
2 A p r 1 9 9 8 0 9 :3 8 :2 6
Tes t Mo d e: "S leep "
Tes t Mo d e: R eceiv e
A N /P R Q -7
SN: 0 0 0 5 2
Me a s u re d V a l u e s
V er. U 0 2 1 9 C
V ER TIC A L P O LA R ITY
R E 1 0 2 -2 4 6 1 D
70
60
50
40
30
20
10
4/8/2015
1 0 -2
1 0 -1
100
101
Fre q u e n c y i n MH z
102
“Sleep” Mode
1 A p r 1 9 9 8 1 5 :0 4 :2 8
Tes t Mo d e: R eceiv e
Tes t Mo d e: R eceiv e
R a d ia te d E m is s io n L e v e ls in d B u V /m
AFI 11-202 requires that any PED
used aboard USAF aircraft meet the
RE limits of MIL-STD-461, which was
not a design requirement for the
AN/PRQ-7 CSEL radio. Other
military service requirements are
similar. Radiating oscillators, power
supplies, and display sweep circuits
would have failed 461, so a Cockpit
Safety test was required.
A N /P R Q -7
SN: 0 0 0 5 2
Me a s u re d V a l u e s
V er. U 0 2 1 9 C
R E 1 0 2 -2 4 6 1 D
70
60
50
40
30
20
10
1 0 -2
1 0 -1
100
101
Fre q u e n c y i n MH z
102
Receive Mode
CSEL COCKPIT SAFETY TEST
Performed during summer
2001 DESERT RESCUE
training exercises aboard
HH-60G, SH-60F, HC-130,
A/OA-10 and E-2C. Flight
safety avionics were
monitored. The test
conclued that the
AN/PRQ-7 is cockpit safe.
4/8/2015
MAJOR INVESTIGATIONS
USAF CT-43A Combined
AIB (AFI 51-503) & SIB
(AFI 91-204)
NTSB TWA 800
USAF RQ-4A GLOBAL
HAWK SIB (AFI 91-204)
4/8/2015
USAF IFO 21 (CT-43A)
• April 3 1996 Dept. of Commerce
trade mission accident in Croatia
• Complicated Dual NDB approach in
bad weather
• 14 E3 possibilities investigated none were causal
• Emergency beacon coverage
propagation prediction aided the
Search and Rescue (SAR)
investigation
• Results included in 6/6/96 brief to
President Clinton and Vice
President Gore
• E3 institutionalized for USAF
investigations by revising AFI 51503
4/8/2015
THE CT-43A E3 INVESTIGATION
Two on-scene and 12 Annapolis JSC and
contractor staff participated in the
investigation and preparation of the 7,173page AIB/SIB report (60 days).
The historic walled city of
Dubrovnik Croatia.
Crash Position Indicator (CPI) transmitter
remained attached to base of vertical stabilizer
complicating propagation to the northeast and to
SARSAT. The mountain shielded propagation to
the southwest and the Adriatic Sea where SAR
assets were located.
4/8/2015
CPI COVERAGE TO SAR AIRCRAFT AT 2000’
4/8/2015
SINCE IT WASN’T A MISSILE!
TWA 800 BREAKUP SEQUENCE
NTSB TWA 800 INVESTIGATION E3
OVERVIEW
Internal
External
Transient Loads
RF Induced
Switching
Failure
Modes
Ground Based
Emitters
Boeing Lab
Work
PEDs
Boeing Aircraft
Work
NTSB/NAWC Follow-on Program
4/8/2015
Ship Based
Emitters
Aircraft
Emitters
Field Around TWA 800 due to
Outside Sources
Penetration of External Field
Into Aircraft
Effects on FQIS Wiring
TWA 800 FUEL QUANTITY
INDICATING SYSTEM (FQIS)
Only a fraction of the signal energy
will couple onto the FQIS wires. This
WIRING
fraction is a function of the signal frequency, aircraft and cable shielding, and
the wire length.
4/8/2015
TWA 800 E3 LESSONS LEARNED
• Switching transient coupling to FQIS wiring
possible (highest of many measured by NAWCAD was 3 dB below 0.25 mJ threshold)
• PED coupling to FQIS wiring unlikely
• External electromagnetic environment coupling
to FQIS wiring highly unlikely
• NTSB summary on web at:
http://www.ntsb.gov/doclib/reports/2000/AAR0003.pdf
4/8/2015
RQ-4A AV-2 GLOBAL HAWK SIB
SUPPORT
• Flight Termination Data Link Overridden by Signal from the
Nellis Test & Training Range
• Details Available in Accident Investigation Board Report of
13 December 1999
• Two JSC Staff Supported the GLOBAL HAWK Safety
Investigation Board on 13-15 April 1999 at Edwards AFB
• Accurate Propagation Predictions Aided in Conformation of
Accident Cause
4/8/2015
AIRCRAFT E3 LESSONS LEARNED
•Aircraft developments
need E3 control programs
•Unbalanced circuits are
more RF susceptible
•Radiated susceptibility
limits are often inadequate •Frequency-Distance
separations are required
•Wires are unintentional
to mitigate antenna-toantennas
antenna EMI
•Saturated amplifiers are
•Frequency management
detectors
isn’t the solution for all E3
•Intermodulation happens
problems
•Switching transients
•E3 is a factor in air safety
couple
investigations
•Signal propagation can be
accurately predicted
4/8/2015
OPEN FOR
ADDITIONAL
QUESTIONS