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
Mitigation Source X Coupling X X Victim E3 UPSETS DEFINED Output Degradation
AIRCRAFT E3 ELEMENTS • COUPLING • Antenna-to-Antenna • Intermodulation (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 • SOURCES • Primary • External • Cosite • Internal • Secondary • Intentional • Unintentional • Conducted • Radiated • Intermodulation • Transients
F-4 PHANTOM II E35,195 BUILT • 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 LESSON LEARNED E3 Control Program Was Required & Effective
- Position Transducer Feedback Gain/Filter SUSCEPTIBILITY OF REMOTED SENSORS AND FLY-BY-WIRE FEEDBACK LOOPS Pilot or Autopilot Command Control Motion + Correction Airplane Electronics Most Common E3 Susceptibility Access Path
SOME WELL-KNOWN FEED-BACK SYSTEMS AUTOMOBILE THROTTLE CONTROL RADIO-CONTROL FOR MODELS
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
Speed Recorders 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.
Position transducer on each aileron F/RF-4 AILERON-RUDDER INTERCONNECT (ARI) RF SUSPECTIBILITY
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 F/RF-4 ARI INTEGRATION & E3 • LESSONS LEARNED • MIL-I-6181 RS Limits Inadequate • RF Saturates Audio Amplifiers • Unbalanced Circuits Are More Susceptible
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 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. UH-60 BLACKHAWK DoD IG REVIEW - 1988
USAF T/CT-43 YAW DAMPER RUDDER POWER CONTROL UNIT YAW DAMPER COUPLER TRANSFER VALVE 1/Q POT MODULATOR AMP YAW ENG CADC POSITION TRANSDUCER (LVDT) YAW DAMPER ACTUATOR AMP RUDDER PEDALS BAND PASS FILTER ELECTRONIC INTEGRATOR ACTUATOR AMP YAW ENG DE-MODULATOR RUDDER YAW RATE GYRO AVIONICS BAY RUDDER INTERFACE Feed-Back Path
BOEING 737-100/500 YAW DAMPER Susceptible Interface Feed-Back 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. 7.4-40/44 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
Narrowband 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! INTERMODULATION
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.
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.
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. “Sleep” Mode Receive Mode COMBAT SURVIVOR/EVADER LOCATOR (CSEL)
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.
USAF CT-43A Combined AIB (AFI 51-503) & SIB (AFI 91-204) USAF RQ-4A GLOBAL HAWK SIB (AFI 91-204) MAJOR INVESTIGATIONS NTSB TWA 800
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
Two 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. THE CT-43A E3 INVESTIGATION
Internal External RF Induced Transient Loads Switching Failure Modes Ground Based Emitters Ship Based Emitters Aircraft Emitters Boeing Lab Work Field Around TWA 800 due to Outside Sources PEDs Boeing Aircraft Work Penetration of External Field Into Aircraft NTSB/NAWC Follow-on Program Effects on FQIS Wiring NTSB TWA 800 INVESTIGATION E3 OVERVIEW
TWA 800 FUEL QUANTITY INDICATING SYSTEM (FQIS) WIRING Only 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.
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
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
AIRCRAFT E3 LESSONS LEARNED • 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 • 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