Approach paths for AAM Vehicles at Vertiports — Standards and Assumptions

Source: NASA AAM NC

By,

Wassaf Akhtar Mohammed | 23/01/2022

What does the Airspace volume look like for UAM vehicles approaching the Vertiport terminal? What are the KPI’s that need to be set so that the Glide path angle (GPA) clarifies the Aircraft performance and its certification basis? How do we envision setting procedures for Quad zero approach (Zero ceiling, Zero Visibility, Zero altitude)? What minimum airworthiness requirements are required to support UAM terminal operations?

This article addresses key assumptions of Vertiport approaches that needs to be considered for different UAM vehicles.

UAM Wheel Airspace Viability:

Viability of UAM “Wheel” to provide for UAM Approaches at 6, 9and 12 degree GPA accounting respectively for 3NM, 2NM and 1.6 NM

The radius wheel as seen above will be defined by vehicle performance characteristics and altitude defined by controlling obstacle. UAM vehicles require high precision Vertiport landing, unique coding and novel approach procedures. Steeper approach capabilities increase operational utility in urban environment. The flyaway assurances requirements increase with steeper GPA capability (This is dependent on UAM business case).

The Approach to IAF:

The initial approach point fix (IAF) is dependent on obstacles, airspeed and winds as the airspace volume flexes and retracts dynamically for on demand departure and approach procedures. Considering in this case if we have a diameter of 3 NM wheel radius, then a 6 degree GPA with V(FAF) of 75–90 KIAS is desired at 3000 feet keeping H(FAF) at 500 feet. The vehicle intercepts at or near V(Cruise), decelerate to V(FAF), standard rate turn to FAF for 6 degree Glidescope path angle (GPA) and Threshold Velocity (V(AT)) at 20 KIAS at H(AT) of 10 feet from the Vertipad. Studies have shown that a 9 degree GPA is most desirable for passenger comfort.

The airspace volume flexes and retracts dynamically as a function of Wind, Obstacle and Airspeed

Conservation of airspace must be considered while allotting a volume of airspace against a particular deceleration. If we look at 3NM wheel and of whatever would be the safe alignment with wind and vertical obstructions for that UAM vehicle to negotiate that procedure, in confined area we can do steep approaches but comes at a cost of requiring high performance characteristics.

Moreover Wind drafts and gusts impact light class UAM vehicles upon approach at Vertiport. How do we account for that extra real estate in tight urban confinement for missed approach and flyaway contingencies? How do we consider the approach paths for Leeward and Windward vertiports? How do we account for Wind/structure “Dynamic interface” in Urban environment?

We need to understand these processes to verify the hypothesis on the existing approach/departure surfaces, constraints that come with it and design standards that are suitable for UAM operational use cases. UAM terminal procedures, airspace standards, infrastructures need to be aligned with UAM category/class vehicle airworthiness requirements. The different category/class vehicle standards must provide assurances that disparate designs will exhibit minimum capabilities in the airspace, if so, we can then conform with lowest common denominator of those class/category, so that they can operate efficiently in the National Airspace. Existing procedures and existing tools cannot be used to create safe UAM environment.

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