Radio Altimeter Industry Coalition Coalition Overview David Silver, Aerospace Industries Association

7/1/2021 2 Background

• The aviation industry, working through a multi-stakeholder group formed after open, public invitation by RTCA, conducted a study to determine interference threshold to radio altimeters

• The study found that 5G systems operating in the 3.7-3.98 GHz band will cause harmful interference altimeter systems operating in the 4.2- 4.4 GHz band – and in some cases far exceed interference thresholds

• Harmful interference has the serious potential to impact public and aviation safety, create delays in aircraft operations, and prevent operations responding to emergency situations

7/1/2021 3 Goals and Way Forward

• To ensure the safety of the public and aviation community, government, manufacturers, and operators must work together to: • Further refine the full scope of the interference threat • Determine operational environments affected • Identify technical solutions that will resolve interference issues • Develop future standards

• Government needs to bring the telecom and aviation industries to the table to refine understanding of the extent of the problem and collaboratively develop mitigations to address the changing spectrum environment near-, mid-, and long- term.

7/1/2021 4 Coalition Tech-Ops Presentation

John Shea, Helicopter Association International Sai Kalyanaraman, Ph.D., Collins Aerospace

7/1/2021 5 What is a Radar Altimeter?

• Radar altimeters are the only device on the aircraft that can directly measure the distance between the aircraft and the ground and only operate in 4200-4400 MHz • Operate when the aircraft is on the surface to over 2500’ above ground

Radar Altimeter Antennas Radar Altimeter Antennas Photo credit: Honeywell Photo credit: ALPA

7/1/2021 6 How Does a Radar Altimeter Work?

1. The radar altimeter transmits a signal toward the ground 2. The signal bounces off the ground 3. The radar altimeter receives the reflected 1 3 signal 4. Round-trip time is translated into distance 2 Photo credit: Garmin

7/1/2021 7 How Does a Radar System Differ From a Communication System? • In a communications system, a receiver listens for signals that are generated by a transmitter and sent directly to the receiver. • Transmit power can be increased to compensate for local conditions • In a radar system, a receiver is listening for a transmitted signal that has reflected from an object or terrain • Transmit power is generally fixed and operates over a wide frequency range (up to 200 MHz) • Type of reflective surface can cause the return signal to vary widely in strength. The receiver must be very sensitive to receive signals reflected from tall grass, plowed fields, water/waves, snow, ice, etc. • Achieving this increased sensitivity means that radar receivers are inherently more sensitive to interference from strong signals in adjacent bands

7/1/2021 8 How Does Radar Altimeter Information Get Used? • Radar altitude is shown directly to the pilot during approach and landing • Essential to safe operation during heavy workload, and the pilot needs absolute trust • In addition, multiple other systems on the aircraft are fed the information directly: • Flight Controls • Automatic Landing Photo credit: Radio Nederland Wereldomroep, CC BY 2.0 • Advanced Aircraft Flight Control Modes Turkish Airlines 1951 crashed at AMS, in part due to • Terrain Awareness and Warning Systems a false radar altitude reading, which caused • Aircraft autothrottle to go to idle at inappropriate altitude • Helicopters • Other Warning Systems and Aircraft Systems

7/1/2021 9 Radar Altimeter Use on Helicopters • Helicopters operate at low altitudes in an even more challenging environment than airplanes • Approaches to random points-in-space and hospitals • Below fixed-wing obstacle protection surfaces • Congested urban areas • Radar altimeter critical for sling load operations / tall building construction • Search-and-Rescue and Medevac • Terrain / buildings / obstacles • Offshore platforms in all weather • Platforms will also be equipped with 5G wireless • Erroneous radar altimeter readings have been causes of numerous incidents/accidents

7/1/2021 10 Scenario 1a: Airliner or GA Visual Approach and Landing – Illustrative Example of Some RA Functions

Even in good weather flying, without use of the autopilot, the radar altimeter is used for many important functions, such as: 1 2

1 At 2500’, radar altitude display active 3 At 2300’, Predictive Wind Shear activates (deactivates at 50’) 2 4 From 1550’ – 1000’, Traffic Alert Collision Avoidance System (TCAS) alerts change 5 3 At 900’ TCAS Resolution Advisories are inhibited (not shown due to lower priority) 6

4 At/below about 800’, many status and caution messages are inhibited to prevent distraction during landing; other warnings may be enabled at these altitudes (e.g. landing gear not down). (Note: similar warning changes during takeoff) 5 At 200’, “rising runway” symbol and landing visual cues are shown on flight instruments and Heads-Up Display / automatic altitude callouts to touchdown – e.g., 50, 40, 30, 20, 10 and “rising runway” animation At about 100’, some aircraft may transition to a “Flare and De-rotation” flight control law for enhanced handling qualities. Radar 6 altitude is also used in the arming and activation of ground spoilers, thrust reversers, and other landing systems

For Illustrative Purposes – not all uses of radar altitude in airliner or GA visual approaches are described; the exact systems and altitudes vary by aircraft type Scenario 1b: Airliner or GA AUTOLAND, Visual or Low Visibility “CAT II/III”

1 Radar altimeter functions in addition to all of the items from the Visual Approach Scenario 1a:

2 Prior to approach, pilots select the approach in 3 1 the Flight Management System – includes “Decision Height” (e.g. 100’ radar altitude) 4 Selecting a different approach is disabled below a certain radar altitude; 5 2 manual tuning of the ILS system may be locked out below certain radar altitudes 6 Once a CAT II Autoland approach starts, loss of radar altimeter data usually requires the approach to 3 be abandoned (missed approach)

4 Autopilot sensitivity on ILS beam reduces with radar altitude, as ILS Localizer beam width narrows

5 At the specified Decision Height, the pilot must have the runway touchdown zone in sight or execute a missed approach

6 AUTOLAND will transition to Flare and Rollout modes at about 100’ radar altitude.

For Illustrative Purposes – not all uses of radar altitude during AUTOLAND or CAT II/III approaches are described; the exact systems and altitudes vary by aircraft type Scenario 2: Windshear Encounter and Escape • Windshear is a weather phenomenon that causes aircraft to experience a rapid decrease in airspeed, due to wind flows near the ground • Hazardous during takeoff and landing. • Upon encountering a windshear, the Pilot Flying executes an “escape maneuver”: pitch to a nose-up attitude, and increase engines to full power • Aircraft can still lose altitude during the escape maneuver Windshear • The Pilot Monitoring continuously calls out radar altitude Warning to give the Pilot Flying critical situational awareness to help with decision making to avoid ground contact • Loss of, or incorrect radar altitude would greatly impair a Radar Altitude successful safe outcome Display

7/1/2021 13 Image Credit: Airbus Airliner Interference Hazards • Each use of the altimeter has a functional hazard assessment • Hazards for loss of or erroneous altitudes vary by application • Hazards range from ‘Major’ to ‘Catastrophic’ depending on phase of flight • Hazards from multiple affected functions could occur simultaneously and combine

7/1/2021 14 Scenario 3: Helicopter SAR Operation

Helicopter operations often deal with demanding environmental factors • Typically Entire Flight at Low Altitude • Day/Night Conditions • Weather • Unfamiliar Areas • Obstacles • Time Critical Radar Altimeters feed a wide array of data/control systems designed to enhance safety:

• GPWS/HTAWS • Aural Safety Warnings § 135.160 – Operable Radio Altimeters Required for Part 135 • TCAS • Descent Operations • Auto Pilots & Automatic Flight Control Systems • Flight displays §135.605 – HTAWS Required by Regulation for all Helicopter Air Ambulance Operations • Flight Directors – Including approach/hover modes

7/1/2021 15 Scenario 3: Helicopter SAR Operation Radar Altimeter interference can result in lost/inaccurate/erroneous/unreliable data that will be DETECTED or UNDETECTED:

______Detected______Undetected______. Hazardous flight profiles . Increased risk to aircrews . CFIT . Loss of situational awareness . Loss of aircraft control . Increased crew workloads . Distraction . Loss of mission

Response to Detected Interference Effectiveness of Actions . Situational – dependent on flight operations/environment . No equivalent replacement for loss . Actions driven by risk-based analysis of altitude data . May be driven by company SOP or Regulation . Asking crews to operate at risk . Final response may range from continued flight to abort mission

7/1/2021 16 Where Can I Find More Information? • The RTCA published a report in October 2020: “Assessment of C-Band Mobile Telecommunications Interference Impact on Low Range Radar Altimeter Operations” • Section 5.3 describes specific aircraft systems that depend on radar altimeter information, and the effect of radar altimeter interference on those systems • https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-Interference-Assessment- Report_274-20-PMC-2073_accepted_changes.pdf

7/1/2021 17 RTCA/EUROCAE Current Status Sc-239/WG-119 Low Range Radar Altimeters Jean-Luc Robin, Airbus Seth Frick, Honeywell

7/1/2021 18 RTCA Report: methodology and conclusion

Methodology

RTCA Report concluded that 5G operations present a risk of harmful interference to at least some heavily deployed RAs across a wide variety of aircraft types, with far-reaching consequences and impacts to aviation operations "(c) 2021 EUROCAE, (c) 2021, RTCA, Inc." RTCA Report: Scope and Limitations

The receiver ITMs (Interference Tolerance Masks) for each of the 3 Usage Categories used in the RTCA Report were based on aggregated measurements from multiple widely-used RA models in each category. Therefore, while at least some RA models would be susceptible to 5G interference, this may not be true for all models. Evaluation of individual RA models was outside the scope of the RTCA report, since this was not necessary to determine whether or not a risk of harmful interference exists

The 5G signals and operations were characterized as follows:

- Waveform used for interference tolerance testing: 3GPP Test Model 1.1, with 30 kHz subcarrier spacing and 100 MHz channel bandwidth. This is expected to be a reasonable worst-case, but many other waveform configurations are possible, and network dynamics will play a significant role in the interference levels seen in the real world. - 5G operational parameters such as base station antenna patterns and scan angles for active phased array antenna systems were based on nominal implementations anticipated by wireless industry engineers. Off-nominal conditions, and potential future applications with different characteristics, were not evaluated. - Only a single 5G base station (with 50% downlink duty cycle) was considered. Scenarios with multiple 5G base stations were not evaluated. - 5G fundamental emissions and 5G spurious emissions (within the 4.2–4.4 GHz band) were evaluated separately. In the real world, both will be present simultaneously. "(c) 2021 EUROCAE, (c) 2021, RTCA, Inc." MOPS WAY FORWARD Aircraft 5G – AERO collaboration proposal operational scenarios 5G operating rules/regulations Aggregated Power Flux Density (emissions limits, frequency (dBW/m²/MHz) for arbitrary points bands, spurious limits, etc.) in space where aircraft may MOPS RA receiver Mask per operate altitude (ITM) 5G Experts RTCA/EUROCAE from MOPS Special wireless 5G Waveform Comittee industry SC239/WG119 5G modeling tools - Note1: Fixed Wing aircraft mask could differ from helicopter mask - Note2: Receiver masks will account for all Existing Accuracy Realistic worst- known interference sources near the RA Realistic worst-case 5G signals interference criteria case RA band, which may be more than just 5G scenario sources operating - Note3: ITM in the MOPS is expected to be - Several UEs onboard the aircraft? valid for the next 30 years (Ownship conditions - Aircraft crossing a 5G BS AAS beam created by several UEs in the direction of RA…) (terrain the aircraft ? reflectivity, Legend - Max. scan angle above the horizon for aircraft pitch/roll, Aviation industry active phased array base stations? etc.) needs help and - Worst-case secondary lobes directed collaboration from above the horizon in base station antenna 5G experts patterns? "(c) 2021 EUROCAE, (c) 2021, RTCA, Inc." Industry way forward

STREAM Continued Airworthiness wrt in-service events with existing equipment (aviation authorities) 1

Short Term Mitigations STREAM (e.g: 5G restrictions around airports, aircraft operational Decisions made restrictions, aircraft retrofits… ?) 2 based on the Classification of Potential Decision the criticality and Update urgency MOPS RA receiver Mask per altitude (ITM)

Input RTCA Behavior of RA Impact at output (RA STREAM from MOPS aircraft manufacturers) 3 5G delivery level YEARS

1st July 2021 ? End 2022 2023 >30 years MOPS release plan "(c) 2021 EUROCAE, (c) 2021, RTCA, Inc." CONCLUSION 1. RTCA/EUROCAE MOPS is focusing on Radio Frequency Coexistence with 5G a) Additionally, new MOPS will improve standardization and documentation of key Rad Alt performance characteristics needed for future coexistence evaluation

2. RTCA/EUROCAE MOPS will be released once the ITM is agreed within aeronautical community. The ITM will be defined once the 5G aggregated level is defined. The target release date is Q4 2022.

3. There is a need to get the 5G aggregated level from 5G community in order to build the MOPS on validated, sound, resilient and long-term assumptions. a) This same effort helps with the development of near-term mitigations as well, not just the long-term solution (new MOPS). "(c) 2021 EUROCAE, (c) 2021, RTCA, Inc." Fixed Wing Perspective Ben Ivers, The Boeing Company

7/1/2021 24 Fixed Wing Perspective • Airframe OEM’s support 5G and its deployment • The aviation industry (including UAS/AAM) expects to be a big user of 5G • Harmonization is key to ensure public safety and to ensure Aviation / Telecom joint success • There is variation in the interference effect on aircraft. Variation depends upon: • Level of integration of the radio altimeter with other aircraft systems • Radio altimeter model number • Crew workload in specific phases of flight • External environment • Preliminary safety analyses of airplane level effects of interference are consistent with RTCA report: • Under specific conditions, interference could result in hazards levels up to and including catastrophic

7/1/2021 25 Fixed Wing Perspective

• Some radio altimeters should be resilient to 5G signals while others will need upgrades • Confirmation needed once RTCA global threat characterization is complete • Collaboration with 5G industry is needed to validate 5G assumptions • Radio altimeter updates will take time to be incorporated

• There is a need for near-term mitigations in the form of 5G implementation guidance • These mitigations would be temporary until updated MOPS and altimeters are available • These mitigations will ensure public safety while long-term solutions are put in place

7/1/2021 26 Radio Altimeter Rotorcraft Modes and Hazards Nick Kefalas, Lockheed Martin Sikorsky

7/1/2021 27 Radio Altimeter Rotorcraft Modes and Hazards

7/1/2021 28 Radio Altimeter and the Modern Flightdeck Wes Googe, American Airlines

7/1/2021 29 Flight Crew Requirements • Knowledge • National Airspace System • Aircraft Systems and Procedures • Skillset • Judgement • Training • Experience

7/1/2021 30 Flight Crew Dependencies • Standard Operating Procedures • Aircraft Basic System Reliability • Navigation Data Accuracy and Integrity • Aircraft Safety System Reliability and Integrity

7/1/2021 31 Radio Altimeter Integration • Flight Operations Use • Safety of Flight Items • Approach Minimum • Terrain Avoidance • Aircraft Collision Avoidance • Wind Shear Avoidance • Aircraft Operating Envelope Protection • Navigation, Warning System Functionality • Auto Land Operations

7/1/2021 32 Radio Altimeter RFI • Flight Crew Aircraft Concerns • No RFI Detection Capability • Loss or Degradation of Certain Safety Systems • Unplanned/Unintended Aircraft Operation • Flight Crew Operation Concerns • Approach Success Uncertainty • Significant Reduction in Safety During WX or Terrain Events • ATC Mitigation • Loss of Low Visibility Runway Operations • Reduced Airport Access

7/1/2021 33 Summary • Aircraft Operational Impacts • Under Review • Training Preparation • Under Review • Flight Operational Consequences • Under Review

7/1/2021 34 Mitigating Radio Altimeter Interference: Restoring Safety and Operational Integrity Robert Ireland, Airlines for America

7/1/2021 35 Mitigating Radio Altimeter Interference: Restoring Safety and Operational Integrity • Detailed characterization of expected issues, iterated by real-world findings • Revised/new system designs (3-5 years) • For ALL aircraft types that are susceptible, starting ASAP • Certification and STC approvals (months to years for all aircraft models and new or revised LRUs) • Procurement cycle • Installation (3-5 years of major airlines, unless otherwise mandated) • Dependent on extent of mods (i.e., LRU, +writing?,+antennae changes??) • Maintenance visit coordination (routine or special routing?)

7/1/2021 36