AIRCRAFT ELECTROMAGNETIC ENVIRONMENTAL EFFECTS (E3) AND SAFETY Douglas J. Hughes, Full Member...
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Transcript of AIRCRAFT ELECTROMAGNETIC ENVIRONMENTAL EFFECTS (E3) AND SAFETY Douglas J. Hughes, Full Member...
AIRCRAFT ELECTROMAGNETIC
ENVIRONMENTAL EFFECTS (E3) AND SAFETY
Douglas J. Hughes, Full MemberInternational Society of Air Safety
Investigators
DOUGLAS J. HUGHESDoug 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 OUTLINEPRESENTED 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
Output Degradatio
n
Source
Coupling
Victim
Mitigation
X
XX
AIRCRAFT E3 ELEMENTSSOURCESPrimary•External
•Cosite
•Internal
Secondary•Intentional
•Unintentional•Conducted
•Radiated
•Intermodulation
•Transients
COUPLING
•Antenna-to-
Antenna
•Intermodulatio
n (IM)-to-
Antenna
•Antenna-to-
Wire
•Box-to-Antenna
•Box-to-Wire
•Wire-to-Wire
VICTIMS
•Receiver Antenna Input
•Interface Wiring Input
•Box Penetration
•Intentional Receivers
•Unintentional Receivers
MITIGATION
•Frequency Management
•Filtering
•Shielding
•Physical Separation
F-4 PHANTOM II E35,195 BUILT
LESSON LEARNEDE3 Control Program Was
Required & Effective
•F-4 Radar-to-RF-4 Side-Looking Radar
•UHF-to-Nose Gear Steering
•“Everything”-to-Radar Warning Receivers
•RF-4 HF Comm-to-Autopilot
04/19/23
SUSCEPTIBILITY OF REMOTED SENSORS AND FLY-BY-WIRE FEEDBACK LOOPS
Pilot or Autopilot Command
+ControlMotionAirplane
Electronics- PositionTransducerFeedback
Gain/Filter
Correction
Most Common E3 Susceptibility Access Path
SOME WELL-KNOWN FEED-BACK SYSTEMS
RADIO-CONTROL FOR MODELS
AUTOMOBILE THROTTLE CONTROL
04/19/23
EXAMPLE FLY-BY-WIRE SYSTEM WITH A FEEDBACK LOOP
• 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
Speed Recorders
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.
04/19/23
Position transducer
on each aileron
F/RF-4 AILERON-RUDDER INTERCONNECT (ARI) RF SUSPECTIBILITY
04/19/23
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
04/19/23
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
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.
TO 1H-60(U)A-1NOTE
UH-60 BLACKHAWK DoD IG REVIEW - 1988
04/19/23
USAF T/CT-43 YAW DAMPER
YAW RATE GYRO
DE-MODULATO
R
BAND PASS
FILTER
MODULATOR
CADC
1/Q POT
ELECTRONIC INTEGRATOR
AMP
AMP
AMP
YAW ENG
YAW ENG
YAW DAMPER COUPLER
TRANSFER VALVE
YAW DAMPER
ACTUATOR
POSITION TRANSDUCE
R (LVDT)
RUDDER
ACTUATOR
RUDDER
PEDALS
RUDDER POWER CONTROL UNIT
AVIONICS BAY RUDDERINTERFACE
Feed-Back Path
BOEING 737-100/500 YAW DAMPERSusceptible
Interface Feed-Back Path
04/19/23
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. 7.4-40/44 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
04/19/23
INTERMODULATIONNarrowband IM products generated in E-8 JSTARS VHF communications antenna due to detector in autotune SWR measuring circuit mitigated via on-board 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!
04/19/23
FM IMMUNITYRTCA DO-176Problem 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.
04/19/23
KOREAN AIRLINES FLIGHT 801
04/19/23
O’Hare RWY 14R ILS Approach
04/19/23
AMERICAN AIR FLIGHT 1340American 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.
04/19/23
COMBAT SURVIVOR/EVADER LOCATOR (CSEL)
10
20
30
40
50
60
70
10-2 10-1 100 101 102
1 Apr 1998 15:04:28 AN/PRQ-7 SN: 00052 Ver. U0219C Test Mode: Receive Test Mode: Receive
Rad
iate
d E
mis
sion
Lev
els
in d
BuV
/m
Frequency in MHz
Measured Values RE102-2 461D
10
20
30
40
50
60
70
10-2 10-1 100 101 102
2 Apr 1998 09:38:26 AN/PRQ-7 SN: 00052 Ver. U0219C Test Mode: "Sleep" VERTICAL POLARITY Test Mode: Receive
Rad
iate
d E
mis
sion
Lev
els
in d
BuV
/m
Frequency in MHz
Measured Values RE102-2 461D
“Sleep” Mode
Receive Mode
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.
04/19/23
CSEL COCKPIT SAFETY TESTPerformed 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 theAN/PRQ-7 is cockpit safe.
04/19/23
MAJOR INVESTIGATIONSUSAF CT-43A Combined AIB (AFI 51-503) & SIB (AFI 91-204)
USAF RQ-4A GLOBAL HAWK SIB (AFI 91-204)
NTSB TWA 800
04/19/23
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 51-503
04/19/23
THE CT-43A E3 INVESTIGATIONTwo on-scene and 12 Annapolis JSC and contractor staff participated in the investigation and preparation of the 7,173-page 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.
04/19/23
CPI COVERAGE TO SAR AIRCRAFT AT 2000’
SINCE IT WASN’T A MISSILE!
TWA 800 BREAKUP SEQUENCE
04/19/23
NTSB TWA 800 INVESTIGATION E3 OVERVIEW
Transient Loads
Boeing LabWork
Boeing AircraftWork
Switching
PEDs
Ground BasedEmitters
Ship BasedEmitters
AircraftEmitters
FailureModes
RF Induced
Internal External
NTSB/NAWC Follow-on ProgramEffects on FQIS Wiring
Field Around TWA 800 due to Outside Sources
Penetration of External FieldInto Aircraft
04/19/23
TWA 800 FUEL QUANTITY INDICATING SYSTEM (FQIS)
WIRINGOnly a fraction of the signal energy will couple onto the FQIS wires. This fraction is a function of the signal frequency, aircraft and cable shielding, and the wire length.
04/19/23
TWA 800 E3 LESSONS LEARNED•Switching transient coupling to FQIS
wiring possible (highest of many
measured by NAWC-AD 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
04/19/23
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
04/19/23
AIRCRAFT E3 LESSONS LEARNED•Aircraft developments need E3 control programs
•Radiated susceptibility limits are often inadequate
•Wires are unintentional antennas
•Saturated amplifiers are detectors
•Intermodulation happens
•Switching transients couple
•Signal propagation can be accurately predicted
•Unbalanced circuits are more RF susceptible
•Frequency-Distance separations are required to mitigate antenna-to-antenna EMI
•Frequency management isn’t the solution for all E3 problems
•E3 is a factor in air safety investigations
OPEN FOR ADDITIONAL QUESTIONS