Issues with PBN Implementation and Trajectory Prediction in ATC Operations

Hassan Shahidi MITRE - USA

Center for Advanced Aviation System Development (CAASD)

Director, Aviation Safety

Issue: Different Implementations of Standards Lead to Path Performance Variations

Due to Flight Management System (FMS) differences, planned and as flown paths vary, resulting in less predictability for controllers

Issue: FMS Performance Differences Flyby Waypoints, Speed Constraints and Wide Turns

• Turns at flyby waypoints – Turn anticipation differences varies

• Speed constraints at waypoints – Some FMSs require an altitude at a

speed constraint; some don’t

• Turns above FL195

– Some aircraft perform wider turns for shorter path length (fuel savings) resulting in bank angles of 5-15 degrees

Issue: FMS Performance Differences Lateral Offsets, Runway Transitions

• Lateral Offset – FMS’s perform Lateral Offset differently

• Some FMS’s may start and end a lateral offset at a waypoint and some cannot

• Runway transitions – Not all FMS’s automatically process

(non tailored) runway transitions • Limiting leg types off the runway

– Heading to Altitude (VA) vs. Heading to Intercept (VI)

– Direct to Fix (DF) vs. Course to Fix (CF)

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Under busy conditions, controllers take airplanes off the PBN procedure and the full benefits are not realized

Project title (Insert, Header & Footer)

Example: Path Prediction

KEPEC

Lateral path prediction impacted most fly-by turn variation

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Example: RF Legs Improve Trajectory Predictions

OAK arrivals (mixed) OAK arrivals (RNP AR)

KEPEC

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Point of Closest Approach (NM)

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The point of closest approach is defined as the distance from the fix to the point where the flight bisects the turn

Example: RF Legs Reduce Variability

• Unconstrained FMS planned descents lead to unpredictability and variability in vertical profiles

Example: FMS Vertical Profile

Potential mitigation – Applying constraints with possible impact to fuel burn and emissions.

Controllers find it difficult to manage CDAs through departure flows and other crossing traffic

The Way Forward Lessons Learned

• Incorporate new understanding of FMS performance into: – Procedure design tools – Improved standards &

criteria – Leverage Automation Aids – Best practices given current

fleet mix – Training (pilots/controllers)

Near Term Future • Improve FMS standardization

– RTCA SC 227 and EUROCAE Working Group 85

– Performance-Based Operations Aviation Rulemaking Committee (PARC)

– Flight Deck Automation Working Group

– CNS Task Force