THE LAST 200 FEET A LOW - COST APPROACH TO LANDING AIRCRAFT IN ZERO - PDF document

THE LAST 200 FEET – A LOW - COST APPROACH TO LANDING AIRCRAFT IN ZERO - ZERO CONDITIONS William J. McDevitt III, The Pennsylvania State University, State College, Pennsylvania Windows ™ -based tablet computer. This presentation Abstract will document the testing of this system under Visual Current Federal Aviation Administration Flight Rules conditions in order to quantify the Category I Instrument Landing System approach achievable accuracy and characterize feasibility of minima are a 200-foot above ground level Decision the concept. Height and 2,400-foot Runway Visual Range. The pilot may not commence an approach if the reported Introduction conditions are below these minimums and may only The concept of landing an aircraft on continue an approach below the decision height if the instruments has been in existence since the late- runway environment is in sight. This presentation 1930’s. Subsequently, the most common precision will show that technology exists today to allow a landing aid has been the Instrument Landing System pilot to continue his approach below published (ILS). Most general aviation aircraft are equipped to decision height to touchdown without ever actually perform only ILS Category I approaches with minima ‘seeing’ the runway envi ronment outside of his of a 200-foot Decision Height (DH) and 2,400-foot cockpit. Runway Visual Range (RVR). Decision Height is a Onboard the aircraft, Global Positioning System specified height or altitude in the precision approach enhanced by Wide Area Augmentation System at which a missed approach must be initiated if the typically provides instantaneous positional accuracy required visual reference, such as the runway of less than one meter horizontally and 1.3 meters markings or lights, to continue the approach have not vertically. With this metric even the smallest aircraft been acquired [1]. RVR is the distance over which could determine its location in X, Y, and Z to well the pilot of an aircraft on the centerline of the runway within a fraction of its own footprint. can see the runway surface markings delineating the runway or identifying its center line [2]. While these Using high-precision GPS surveying equipment minima may sound perfectly reasonable to the to perform a real-time kinematic survey, airport layman, in reality they may leave an aircraft in runway locations can be determined with centimeter- extremis if the destination weather conditions are level accuracy, making it conceivable to land an below minimums and the aircraft is low on fuel with aircraft on a specific point on the runway to a very no suitable divert airfield. high degree of accuracy. Precision approaches are aptly named; they Instrument flight with no outside visual cues allow the pilot to precisely know their location on the imparts high levels of stress on the pilot. Landing an approach to landing in three dimensions, X aircraft in zero-zero conditions would add (longitude), Y (latitude), and Z (altitude). For nearly significantly more stress. Synthetic Vision Systems 60 years, the ILS was the most accurate landing that offer the pilot a high-fidelity representation of navigational aid available. But since the advent of the outside world would lessen or preclude this stress. the NavStar Global Positioning System (GPS) Many major universities, government agencies, and satellite constellation and Space-Based Augmentation aerospace corporations are already at work to provide Systems (SBAS) such as Wide Area Augmentation these type systems. SVS will most likely be initially System (WAAS), there is now an alternative designed for commercial, military, and business-class allowing a pilot to precisely know their location in aircraft, and will cost tens to hundreds of thousands relation to the airfield. While the WAAS of dollars. This valuable and life-saving technology specification is for a worst-case accuracy of 7.6 will not be affordable to most general aviation pilots. meters both horizontal and vertical, the actual This paper proposes a reduced-cost SVS system measured accuracy of the system is routinely 0.9 for general aviation, based on a Microsoft meters lateral and 1.3 meters vertical in most of the

continental United States [3]. This level of accuracy Terrain Database would allow the pilot to know their location, even in To be effective, the terrain database must the smallest aircraft, to well within the footprint of present a view that closely mimics the real world as the aircraft. viewed by the pilot. There are two major components to any terrain database: elevation data To accomplish a precision approach, not only does a pilot need to know the aircraft’s location in and imagery. Much of this data is now publically available through various government agencies (e.g. space, they need to acquire the airfield and USGS or state or local government GIS sites) at no accomplish the final approach to landing visually. cost. But technologically, this may no longer be required. By using high-precision GPS surveying equipment to Elevation data can be acquired in many forms, perform a real-time kinematic (RTK) survey, airport but most commonly as digital elevation models runways can be located with centimeter-level (DEM) or digital terrain elevation data (DTED) at accuracy. This would make it conceivable to land an various levels of resolution. The vast majority of the aircraft on a specific point on the runway to a very area in aviation-related terrain databases need only high degree of precision by simply allowing a the coarsest levels of elevation post-spacing (90+ computer to calculate the vector between the aircraft meters between posts). Only when nearing the and its intended touchdown point. ground on approach to landing would a higher resolution (sub-10 meter post spacing) data be While this may be technologically possible, a required. To create a terrain database that can be landing of this type with no outside visual cues would rendered by a computer, this data must be converted certainly impart high levels of stress on the pilot. into polygonal surfaces that represent the surface of The use of a Synthetic Vision System (SVS) that is the earth. tied to the GPS-WAAS-Touchdown Point calculation would offer the pilot a high-fidelity representation of Site-specific satellite or aerial imagery is the the outside world, significantly lessening or second piece required to generate a convincing precluding this stress. Many major universities, texture on the elevation surface. By using real government agencies, and aerospace corporations are imagery that is directly coordinated with the terrain already at work to provide this type of system [4-10]. data, the scene that is rendered by the software SVS will most likely be initially designed for engine will have a very high degree of realism. commercial, military, and business-class aircraft, and Again, the vast majority of imagery used to create the will cost tens to hundreds of thousands of dollars. database need not be of particularly high resolution; This valuable and potentially lifesaving technology publically available 30-meter resolution Landsat 7 will not be affordable to most general aviation pilots. imagery would be more than sufficient for most flight regimes. Only on final approach to landing would Therefore, a reduced-cost SVS system for general aviation pilots displayed on a Windows ™ - higher resolution imagery be justified. based tablet computer is proposed. While a system An alternative or enhancement to high- of this sort could not provide awareness of airborne resolution imagery would be vector-based drawing traffic or runway incursions by vehicles or other features that could be inserted into the database, such aircraft without the addition of an ADS-B (Automatic as runways and runway markings for specific Dependent Surveillance – Broadcast) system, in a life airports. The industry standard for these types of or death situation it could allow the pilot to land the features is the OpenFlight™ format from Presagis aircraft when all other options have been exhausted. [10]. These features can be created and rendered in various modeling tools such as Autodesk 3ds Max or Approach Presagis Creator. Creating runways and markings in this manner would allow a pseudo-high fidelity There are two major components to this system: presentation of the airport without the added a georeferenced terrain database and a synthetic overhead of generating a terrain database using high- vision display. resolution imagery that would vastly increase the size of the database.