**Human Factors and Operations Issues in GPS and WAAS Sensor Approvals:
A Review and Comparison of FAA and RTCA Documents**

April 1997

#   {#section .unnumbered}

#   {#section-1 .unnumbered}

# PREFACE 

This report is the culmination of the first task in a project to assist
aviation certification specialists in the evaluation of human factors
and operations issues in the approval of Global Positioning System (GPS)
Class C and GPS/Wide Area Augmentation System (WAAS) Class Beta
equipment. This document was submitted by Monterey Technologies, Inc.,
under a contract with Battelle (Subcontract No. 87929 (477302)). Dr.
Michael McCauley served as the program manager for Monterey
Technologies, Inc. Mr. Donald Eldredge served as the program manager for
Battelle. Mr. Tom Hazard of Monterey Technologies, Inc., reviewed and
provided comments on the initial draft of this document. The
contributions and support of Dr. McCauley, Mr. Eldredge, and Mr. Hazard
are greatly appreciated by the author.

This report is part of a continuing effort at the John A. Volpe National
Transportation Systems Center (Volpe Center) to assist the Federal
Aviation Administration (FAA) aviation safety professionals in the
understanding and application of human factors principles in GPS
applications. Special thanks to Dr. Thomas McCloy (AAR-100) for
monitoring this effort. Dr. Daniel Hannon and Ms. Colleen Donovan
directed this project for the Volpe Center. The direction and support of
Dr. Hannon and Ms. Donovan in this effort are greatly appreciated.

Several FAA aviation safety professionals, including aircraft
certification specialists and the Northwest Mountain Region Aircraft
Certification Office and members of the FAA Satellite Operations
Implementation Team (SOIT), provided invaluable input to this effort.
Special thanks are extended to Peter Skaves of the Northwest Mountain
Region Aircraft Certification Office and Bruce DeCleene and Susan Cabler
of AIR-130. Thanks also are extended to Rachel Daeschler, Catherine
Gandolfi, and Rosanne Ryburn of the Northwest Mountain Region Aircraft
Certification Office for their input on this project.

Questions concerning this document should be directed to:

Colleen Donovan

GPS/WAAS Human Factors Program Manager

U.S. DOT/Volpe National Transportation Systems Center

55 Broadway, DTS-45

Cambridge, MA 02142-1093

phone: (617) 494-2474

fax: (617) 494-3306

email: donovan@Volpe1.DOT.GOV

# TABLE OF CONTENTS

**[Section]{.underline} [Page]{.underline}**

1\. INTRODUCTION

2\. SYSTEM DESCRIPTION

2.1 Global Positioning System

2.2 Wide Area Augmentation System

3\. APPROVAL OF GPS AND GPS/WAAS SENSOR EQUIPMENT AND INSTALLATION

4\. GPS AND GPS/WAAS TSO EQUIPMENT CLASSIFICATION

5\. REQUIRED NAVIGATION PERFORMANCE

6\. GPS, GPS/WAAS, AND RNAV EQUIPMENT AND INSTALLATION APPROVAL
DOCUMENTS 13

6.1 RTCA DO-208 - Minimum Operational Performance Standards (MOPS) for
Airborne Supplemental Navigation Equipment Using Global Positioning
System (GPS) (RTCA, 1991)

6.2 TSO-C129A - Airborne Supplemental Navigation Equipment Using the
Global Positioning System (GPS) (FAA, 1992)

6.3 RTCA DO-229 - Minimum Operational Performance Standards for Global
Positioning System/Wide Area Augmentation System Airborne Equipment
(RTCA, 1996)

6.4 AC 20-130A - Airworthiness Approval of Navigation or Flight
Management Systems Integrating Multiple Navigation Sensors (FAA, Draft)

6.5 RTCA Paper No. 192-96/SC 181-061 Minimum Aviation Performance
Standards: Required Navigation Performance for Area Navigation Draft 8
(RTCA, 1996)

6.6 Supporting Documents

7\. HUMAN FACTORS AND OPERATIONS ISSUES, SIMILARITIES AND DIFFERENCES
WITH GPS VERSUS GPS/WAAS EQUIPMENT 19

7.1 Comparison Tables of Human Factors, Operations, and Accuracy Issues
for GPS and GPS/WAAS Requirements Documents 19

7.2 Differences in Approval Requirements Between GPS and GPS/WAAS

7.2.1 Traditional Human Factors Issues.

7.2.2 User Interface Functional Characteristics.

7.2.3 System Integrity, Annunciations, Alerts, and Accuracy.

7.3 Impact of RNP on the Approval of GPS and GPS/WAAS Sensors

8\. CONCLUSIONS AND RECOMMENDATIONS 35

REFERENCES 37

# LIST OF TABLES

**[Table]{.underline} [Page]{.underline}**

1\. GPS Equipment Classification 9

2\. GPS/WAAS Equipment Classification 10

3\. Human Factors, Operations, Accuracy Requirements/Issues 21

4\. Summary of Requirements 26

# EXECUTIVE SUMMARY

This report is the culmination of the first task in a project to
evaluate human factors and operations issues associated with the
integration of Class C Global Positioning System (GPS) sensors and Class
Beta GPS/Wide Area Augmentation System (WAAS) sensors into navigation
systems in low-end transport category aircraft. The objective of the
project is to provide aircraft certification specialists with
information that will help them in the evaluation of GPS and GPS/WAAS
sensors within integrated navigation systems. The first task of the
project was to compare the requirements of the various FAA and industry
documents currently used in the approval of GPS and GPS/WAAS sensor
equipment and installation. The impact of the use of required navigation
performance (RNP) standards on approval also was evaluated.

This document describes both the GPS and GPS/WAAS navigation systems and
equipment classifications. The major difference between GPS and GPS/WAAS
systems is improved accuracy, integrity, continuity, and availability of
GPS/WAAS systems (through the use of differential corrections) over GPS
systems. Class C GPS sensors, together with an integrated navigation
system, may be approved as supplemental means of navigation, while
GPS/WAAS Class Beta sensors, when combined with an integrated navigation
system, are expected (in the near future) to be approvable by the FAA as
a primary means of navigation.

The GPS and GPS/WAAS equipment approval process is described. Five
approval documents --- 1) TSO-C129A, 2) RTCA DO-208, 3) RTCA DO-229, 4)
AC 20-130A, and 5) RTCA 192-96 --- and three supporting documents were
reviewed. The review served two main purposes: 1) evaluation of the
approval process and the identification of problems within the process
and the documents, and 2) a detailed comparison of the requirements of
the different documents for GPS and for GPS/WAAS sensors.

The evaluation of the documents and discussion with FAA personnel
revealed potential areas for improvement of the approval documentation.
Some of the documentation is difficult to understand and apply.
Individuals at different Aircraft Certification Offices (ACOs) as well
as manufacturers and operators may have different interpretations of the
same information. At the time this document was prepared, not all of the
FAA policy documentation regarding GPS/WAAS equipment was available.
With GPS equipment, the documentation is difficult to use because it
requires a great deal of cross referencing. Another problem is the
distinction between technical standard order (TSO) authorization of
equipment and approval of installations. TSOs are intended only to
address equipment requirements, and cannot address installation
requirements. TSO-C129 specifies requirements that apply to the
multisensor system with which the equipment is to operate. This ensures
that sensors provide an acceptable interface, but it also places a
burden on the applicant who must use an FMS in order to demonstrate
compliance. In many cases this situation is further complicated by the
fact that the applicant is not the manufacturer of the FMS. In addition,
some ACO engineers interpret the equipment interface requirements of
TSO-C129 as installation requirements and are unsure how to approve
equipment (in accordance with a TSO) independent of an installation.

The comparison of the requirements specified in the documents is
presented in table form and major differences are discussed. The
comparison revealed a high level of similarity between GPS and GPS/WAAS
sensor requirements. While many requirements are the same, they are
organized and worded differently, so the only way to identify common
requirements is to carefully read each document. There were a number of
differences between the GPS and GPS/WAAS requirements that did not
appear to be specifically related to conceptual differences between the
systems. Rather, many of the differences may be due to the increased
availability of information at the time of the GPS/WAAS publication
(1996) than at the time of the GPS publication (1991). One difference in
requirements that was due to technological differences between the two
systems was the treatment of accuracy and integrity requirements,
including alerting and annunciation of accuracy or integrity problems.

The impact of required navigation performance for area navigation (RNP
RNAV) on GPS and GPS/WAAS approvals also was considered. RNP RNAV is a
concept intended to enable user-preferred trajectories and to promote
free-flight by specifying minimum accuracy and integrity requirements
for these operations. GPS and GPS/WAAS manufacturers may want to meet
RNP RNAV requirements as well as GPS equipment requirements. A
comparison of GPS and GPS/WAAS requirements with RNP RNAV requirements
(as described in RTCA 192-96) revealed a few requirements unique to RNP
RNAV approvals though GPS/WAAS requirements include requirements that
are equivalent. Other than a requirement for parallel offsets and
additional holding capabilities, equipment that meets the human factors
and operations requirements of RTCA DO-229 for GPS/WAAS should meet the
requirements of RNP equipment. Equipment approved to TSO-C129 rather
than TSO-WAAS will have to be evaluated more carefully to ensure that
all of the additional requirements of RTCA 192-96 have been met.

This review showed that the documentation and process for GPS and
GPS/WAAS Class C sensor approvals is somewhat complicated. Generally,
the documentation is thorough, but in some cases is difficult to
interpret and difficult to cross-reference. There are efforts underway
to account for some of the difficulties related to use of the
documentation. First, TSO-C129 is being updated (TSO-C129B) to refer to
the newer requirements of RTCA DO-229. Second, a checklist for approval
of GPS/WAAS equipment is under development.

# 1. INTRODUCTION

Navigation using the Global Positioning System (GPS) is becoming more
common in the aviation community. Advancements to GPS including the Wide
Area Augmentation Systems (WAAS) will make the use of GPS even more
attractive to airlines and pilots; it potentially will allow the use of
GPS/WAAS as the primary means of navigation. Manufacturers of new
aircraft are incorporating GPS navigation sensors into their flight
management systems. Owners of existing aircraft are either installing
stand-alone GPS systems or are incorporating GPS sensors into integrated
navigation or flight management systems. A similar trend is expected in
the future for GPS/WAAS equipment. The Federal Aviation Administration
(FAA) is tasked with the problem of satisfying the demands of airlines
and pilots to update their aircraft while maintaining a level of safety
over the various types of GPS equipment and GPS installations.

The goal of this project is to evaluate the human factors and operations
issues associated with the integration of Class C GPS sensors and Class
Beta GPS/WAAS sensors into navigation systems in low-end transport
category aircraft. Low-end transport category aircraft typically refers
to older aircraft flown in part 121 or part 135 operations that do not
have "glass cockpits" and were manufactured prior to the development of
GPS. FAA Aircraft Certification Offices (ACOs) are responsible for
technical standard order (TSO) authorization of GPS and GPS/WAAS
equipment and for the first-time approval of GPS and GPS/WAAS
installations. The approval of GPS or GPS/WAAS sensor installations in
low-end transport aircraft is different from the approval of both
stand-alone GPS systems (GPS Class A or GPS/WAAS Class Gamma) and GPS
sensors in flight management systems of newer glass cockpit aircraft
(GPS Class C or GPS/WAAS Class Beta). With stand-alone equipment, the
equipment TSO authorization requirements cover all aspects of the
equipment, including both human factors and operations issues. The
navigation sensor and user interface are contained in the same unit and
can be evaluated independently from the installation (although each
installation must also be approved for airworthiness). With the newer
glass cockpit aircraft, the GPS sensor equipment may be evaluated
through a TSO authorization. Then the installation is either evaluated
as a part of a flight management system in the original type certificate
of an aircraft or the sensor is easily integrated into a flight
management system that has already been evaluated for human factors and
operations and requires little, if any, changes to the user interface.

In incorporating sensors into navigation systems in low-end transport
category aircraft, performance of the GPS and GPS/WAAS sensor equipment
may receive TSO approval, but evaluation of the user interface of the
integrated system is not specified (though it is implied) in the
equipment approval documentation and may be more complicated than the
evaluation of stand-alone or glass cockpit systems. The incorporation of
GPS or GPS/WAAS sensors may constitute a major change in the avionics on
the flight deck. Careful consideration must be given to human factors
and operations issues for each installation, since each installation is
likely to be unique.

Another issue related to the installation of GPS and GPS/WAAS sensors is
the accuracy of the equipment. GPS systems indicate accuracy using
horizontal integrity level (HIL) and GPS/WAAS systems indicate accuracy
using horizontal protection level (HPL) for GPS/WAAS systems. Another
way of indicating accuracy is through estimated position uncertainty
(EPU) and required navigation performance (RNP). In the future, aircraft
that demonstrate navigation accuracy better than certain RNP values may
be permitted to fly special procedures or airspace associated with
various RNP criteria. Many of the human factors and operations
requirements to meet RNP criteria are the same as those for GPS and
GPS/WAAS. However, there are a few differences or additional criteria
described in chapter 6 that will affect installation requirements for
GPS and GPS/WAAS equipment.

Documentation is available that describes equipment approval
requirements and airworthiness approval requirements for GPS sensors and
associated navigation or flight management systems. Documentation also
is available for approval of GPS/WAAS equipment, though the acceptance
of this documentation by the FAA (through a TSO) is in draft form. Draft
documentation is available describing RNP criteria. The first task of
this project was to review and compare the documentation available on
equipment approval, installation approval, and RNP criteria to identify
human factors and operations issues associated with the installation of
GPS and GPS/WAAS equipment. This paper describes the results of the
document review.

There are seven main sections in this document. These include:

2.  System description of both GPS and GPS/WAAS.

3.  Approval process for GPS and GPS/WAAS equipment.

4.  GPS and GPS/WAAS equipment classifications.

5.  Description of required navigation performance (RNP).

6.  Summary of each of five approval documents --- 1) TSO-C129A, 2) RTCA
    DO-208, 3) RTCA DO-229, 4) AC 20-130A, and 5) RTCA 192-96.

7.  Comparison of the approval requirements from the five documents
    presented in table form and a discussion of the major differences
    between human factors and operations issues in GPS and GPS/WAAS, as
    well as the impact of RNP criteria on these installations.

8.  Recommendations for further work to assist ACOs in the approval of
    GPS and GPS/WAAS sensor installations in low-end transport category
    aircraft.

# 2. SYSTEM DESCRIPTION

This section describes both GPS and the GPS/WAAS. Sources for the
information in this section include Adler and Ruelos (1993), Department
of Transportation (DOT) and Department of Defense (1993), Joint DOD/DOT
Task Force on GPS (1993), RTCA, Inc. (1996), and DeCleene (1996).

## 2.1 Global Positioning System

The Navstar GPS is a satellite-based radionavigation system jointly
managed by the Department of Defense (DOD) and the DOT. GPS was
originally developed as a military system. It is subject to limitations
imposed by the DOD for national security reasons. However, the DOD and
the DOT have undertaken a cooperative effort to make GPS available for
use as an integral part of the civil radionavigation system.

GPS consists of three functional segments: space, control, and user. The
space segment is a constellation of 24 satellites. The satellites orbit
the earth at an altitude of about 10,900 nautical miles with four
satellites in each of six different orbital planes. This constellation
guarantees that at least four satellites will be greater than 5 degrees
above the horizon with respect to the user anywhere in the world, at any
time.

The control segment controls satellite operations. A master control
station (MCS) is located at Falcon Air Force Base in Colorado. A
worldwide network of five signal monitoring stations and three uplink
ground antennas complete the control segment. Monitor stations collect
and send GPS navigation signal data to the MCS for evaluation and
determination of required corrections. Corrections to satellite atomic
clocks or orbital parameters are relayed to the satellites from the
ground antennas. Other satellite subsystems including power, thermal
balance, and attitude are also monitored by the MCS.

The user segment is the GPS receiver that receives data from the
satellite to compute position. GPS compares the time it takes to receive
radio signals from each satellite to compute position. Data from four
satellites are needed to solve an equation with four unknowns ---
latitude, longitude, altitude, and time. The time computation is
required due to receiver clock error.

Accuracy and integrity are important GPS performance characteristics.
Accuracy refers to the degree of conformity of a GPS position estimate
to the true position. The service provided to civil users is called the
Standard Position Service (SPS). The DOD employs a process called
selective availability to degrade the accuracy of the GPS signal for
SPS, the U.S. guarantees an SPS horizontal accuracy of 100 meters 95
percent of the time and 300 meters 99.99 percent of the time. Altitude
(above WGS-84 ellipsoid) can be determined to within 140 meters 95
percent of the time.

GPS accuracy is much greater than any other en route navigation system.
However, GPS accuracy is not sufficient for precision approach and
departure (and would not be even if selective availability was turned
off). The type of augmentation to GPS known as differential GPS can
provide lateral and vertical accuracy of around 5 to 10 meters and may
be developed to allow for precision approach and departure. Currently,
the Coast Guard operates a differential GPS system for maritime use.
WAAS is one type of system that provides differential GPS corrections,
yielding the accuracy, integrity, continuity, and availability for en
route navigation through precision approach operation.

Integrity refers to the ability of the system to provide timely warnings
to users when GPS data should not be used. Users must remain aware of
the integrity of the GPS data. Since four satellites are required for
GPS navigation, users must know if they are not receiving four
satellites or if a satellite is not operating within tolerance.

There are several ways a user can monitor the integrity of the GPS data.
One method is known as receiver autonomous integrity monitoring (RAIM).
Using RAIM, the receiver monitors its own integrity and alerts the user
if integrity is lost. However, RAIM requires five operational satellites
with good geometry and is not always available. A second method is
automatic monitoring through the use of other navigation sources or
perhaps through the use of differential ground stations such as those
provided by WAAS. For IFR use, the FAA currently requires automatic
integrity monitoring --- either RAIM or RAIM equivalent (through the use
of other navigation sources or differential techniques such as WAAS).

Because of the potential for loss of integrity with the GPS system, the
FAA does not allow operators to use GPS as the primary means of
navigation except in certain circumstances (oceanic and remote areas).
An alternate navigation system approved for the route to be flown must
be installed and operational on the aircraft. In the airspace where GPS
may be used as the primary means of navigation, the FAA requires that
operators use a ground prediction program that predicts the availability
of satellites over the proposed route at the proposed time, excludes any
satellites that are unusable, and predicts whether navigation integrity
and continuity can be maintained throughout the flight.

## 2.2 DGPS Wide Area Augmentation System

Differential techniques may be applied to GPS to achieve substantial
improvements in position accuracy and to provide integrity information.
Differential GPS (DGPS) uses information obtained from a land-based
receiver at a surveyed site to determine and transmit corrections to
users. DGPS systems have three basic components: 1) a land-based
receiver that monitors and collects satellite data and compares the data
with known survey position data, 2) a method of transmitting corrections
determined at the site (or at a central control station) to users, and
3) user equipment that has hardware and software necessary to receive
and apply the corrections to information received from GPS satellites.

There are several methods of transmitting DGPS data to users. Data can
be transmitted over a small geographic area or over a broad geographic
area. DGPS systems that transmit data over a fairly small area are known
as local area augmentation systems (LAAS). LAAS data will

be transmitted from a ground-based site (such as an airport). DGPS
systems that transmit over a broad area are referred to as wide area
augmentation systems (WAAS). WAAS broadcasts will be transmitted via
satellite to cover an area that is nearly hemispheric. The accuracy of
DGPS systems is dependent on a number of factors, including the distance
from the user to the reference site.

A WAAS is being developed for use in the U.S. National Airspace System
(NAS). This WAAS uses ground stations to calculate GPS integrity and
correction data and then uses geostationary satellites to broadcast GPS
integrity and correction data to GPS/WAAS receivers. The WAAS is made up
of an integrity and reference monitoring network, processing facilities,
geostationary satellites, and control facilities. Reference stations and
integrity monitors are data collection sites dispersed throughout the
U.S. that use GPS/WAAS ranging receivers to collect data from the GPS
and from the WAAS satellites. The reference stations forward the data to
central data processing sites that determine differential corrections,
ionospheric delay information, GPS/WAAS accuracy, and error bounds for
monitored satellites. The central processing sites also generate
navigation messages for the geostationary satellites and WAAS messages.
The information from the central data sites are broadcast to users from
the geostationary satellites.

The operational goal of WAAS is to augment the integrity and accuracy of
GPS so that GPS/WAAS can replace the existing radionavigation
infrastructure in the U.S. NAS. WAAS augments GPS to obtain the required
accuracy for precision approaches and provides integrity, continuity,
and availability of service that is not available with GPS without
augmentation.

# 3. APPROVAL OF GPS AND GPS/WAAS SENSOR EQUIPMENT AND INSTALLATION

The process for obtaining approval to install and use GPS or GPS/WAAS
equipment in low-end transport category aircraft is relatively
complicated. The Code of Federal Regulations (CFRs) are the only
regulatory documents that the equipment and installation must meet, but
consistent with that code, operators must obtain airworthiness approval
from the FAA in order to install and operate GPS or GPS/WAAS equipment.
A process has been developed to provide manufacturers and operators with
information needed to help obtain airworthiness approval. This process
involves the use of voluntary guidelines in different forms. The
guidelines are stated so that they provide a means, but not the only
means, for obtaining airworthiness approval. This system allows the FAA
and industry to publish standards for equipment that, even though they
are voluntary, are usually followed because they shorten the time and
ease the workload required for approval. Manufacturers or operators are
permitted to choose alternate methods rather than meet the published
standards to verify airworthiness. However, this is likely to entail
more effort and take more time to receive FAA approval than is required
if the published standards are followed.

The first voluntary step for GPS or GPS/WAAS equipment is authorization
of the equipment in accordance with a TSO. With GPS equipment, TSO-C129
provides the minimum operational performance standards required for a
GPS system or sensor to be identified with a TSO-C129 Class marking.
This equipment authorization provides potential buyers of GPS equipment
with the knowledge that the equipment has been designed and manufactured
in accordance with the industry standard. In addition, buyers may find
that FAA airworthiness approval of equipment (for supplemental
navigation) with TSO-C129 authorization proceeds more smoothly and
quickly than approval of equipment without TSO authorization. TSOs
generally do not contain the actual guidelines for developing and
testing the equipment. Rather, they reference industry and FAA developed
standards such as RTCA Minimum Operational Performance Standards (MOPS),
RTCA software development procedures, and RTCA environmental testing
procedures. With GPS these documents include RTCA DO-208, DO-178B, and
DO-160C. Where the FAA has identified exceptions to the industry
standard (e.g., RTCA) documents, the TSO standard lists these
exceptions. This is the case with TSO-C129 for GPS equipment.

Currently, there is no published TSO for the approval of GPS/WAAS
equipment. However, the TSO is in draft form and an RTCA document
(DO-229) with MOPS for GPS/WAAS has been published. The draft TSO
(TSO-WAAS) references RTCA DO-229. It is expected that TSO-WAAS will
establish a standard for GPS/WAAS equipment to be approved for primary
means navigation.

After the manufacturer has obtained TSO authorization, the installation
approval process begins. The FAA (usually the ACO) may allow
installation of equipment that does not meet the TSO or meets the TSO
with deviations. In this situation, the manufacturer or operator is
required to show that the equipment meets the equivalent of the
requirements called out in the TSO. The next step in the approval
process is airworthiness approval of the equipment and installation by
the FAA. A means of obtaining airworthiness approval may be described in
an FAA document such as an advisory circular (AC). While there are no
ACs specific to GPS or GPS/WAAS sensors (AC 20-138 is specific to GPS
equipment but it applies only to stand-alone equipment, not to Class C
GPS sensors), there is an AC (AC 20-130A) that describes guidelines for
obtaining airworthiness approval of navigation or flight management
systems integrating multiple navigation sensors. This document applies
to GPS sensors but not to GPS/WAAS sensors. The AC calls out performance
requirements, testing (bench tests, ground tests, and flight tests)
requirements, and data evaluation requirements. The airworthiness
approval may be completed by different FAA offices depending on the
complexity of the equipment and installation. With first time approvals
of GPS equipment intended for IFR use, an ACO is required to perform the
airworthiness approval.

For both the equipment approval and the installation airworthiness
approval, manufacturers and operators will be required to provide the
FAA with data showing that they have met the performance standards
called out in the various documents. This data will include information
such as wiring diagrams and environmental test results. The FAA may also
choose to inspect and test the equipment according to the procedures
called out in the standards.

Unfortunately the standards used in the approval process for GPS
equipment are subject to different interpretations. Some of the
documentation is written in a manner that makes it difficult to
understand and apply. Individuals at different ACOs as well as
manufacturers and operators may interpret the information differently.
With GPS/WAAS equipment, all of the needed information is not yet
available. In addition, there are slight differences in the requirements
in the various standards. There are also differences in the requirements
for GPS equipment and GPS/WAAS equipment. Another problem is the
distinction between TSO approval of equipment and approval of
installation. While TSOs do not include installation requirements, they
may (as in the case of TSO-C129) contain requirements that the
manufacturer show that the equipment interface properly with installed
equipment such as an FMS. ACO engineers are then unsure how to approve
equipment independent of the installation. A GPS sensor authorized to
TSO-C129 on one aircraft may not meet the same standards when installed
on another aircraft. These TSO requirements to ensure installed
equipment performance also are slightly different than the requirements
listed in ACs intended to include installation requirements. It is the
goal of this project to compare the requirements of the various
documents for GPS sensor installations.

Another level of approval that manufacturers may desire is approval of
equipment to specific RNP criteria. The RNP concept, benefits of
approval, and approval requirements are described in chapter 5.

# 4. GPS AND GPS/WAAS TSO EQUIPMENT CLASSIFICATION

The FAA has created a classification of different types GPS and GPS/WAAS
equipment. The classification consists of a functional class and an
operational class. For example, a GPS receiver in functional Class A and
operational Class 1 is referred to as a Class A(1) receiver. TSO-C129
describes the classes for GPS approval. RTCA DO-229 describes the
classification for GPS/WAAS equipment. TSO-WAAS (draft) adopts the
classification specified in RTCA DO-229 except that it does not yet
recognize operational Classes 3 and 4 (that allow the use of GPS/WAAS
for precision approach). Table 1 displays the different functional and
operational classes for GPS and table 2 displays the functional and
operational classes for GPS/WAAS equipment.

**Table 1. GPS TSO-C129 Equipment Classification**

  ---------------- -----------------------------------------------------------
  TSO-C129         
  Classification   
  of GPS Equipment 

  Functional Class 

  A                GPS sensor data and navigation capability (stand-alone
                   receiver).

  B                GPS sensor data to an integrated navigation system (i.e.,
                   FMS, multisensor, navigation system, etc.).

  C                GPS sensor data to integrated navigation system (as in
                   Class B) which provide enhanced guidance to an autopilot,
                   or flight director, to reduce flight technical errors.

  Operational      
  Class            

  1                Uses RAIM for integrity monitoring and approved for use in
                   oceanic, en route, terminal, and nonprecision approach
                   operations.

  2                Uses RAIM for integrity monitoring and approved for use in
                   oceanic, en route, and terminal operations.

  3                Uses an integrated navigation system that provides
                   integrity equivalent to RAIM and approved for use in
                   oceanic, en route, terminal, and nonprecision approach (not
                   applicable to Class A equipment).

  4                Uses an integrated navigation system that provides
                   integrity equivalent to RAIM and approved for use in
                   oceanic, en route, and terminal operations (not applicable
                   to Class A equipment).
  ---------------- -----------------------------------------------------------

**Table 2. GPS/WAAS RTCA DO-229 Equipment Classification (continued)**

  ---------------- -----------------------------------------------------------
  RTCA DO-229      
  Classification   
  of GPS/WAAS      
  Equipment        

  Functional Class 

  Beta             GPS/WAAS sensor data to an integrated navigation system.
                   Provides integrity in the absence of WAAS using FDE.

  Gamma            GPS/WAAS sensor and a navigation function to provide path
                   deviations relative to a selected path (stand-alone).
                   Provides integrity in the absence of WAAS using FDE.
                   Includes database, display outputs, and pilot controls.

  Delta            GPS/WAAS sensor and a navigation function to provide path
                   deviations relative to a selected path. Does not provide a
                   database or direct pilot controls. Applicable only to Class
                   4 for precision approach, providing an ILS replacement.

  Operational      
  Class            

  1                Supports oceanic and domestic en route and terminal
                   operation. Must check WAAS-reported integrity status of GPS
                   satellites, but not required to apply differential
                   corrections.

  2                Supports oceanic and domestic en route, terminal,
                   nonprecision approach, and departure operation. In
                   nonprecision approach mode, must apply long-term and fast
                   WAAS differential corrections.

  3                Supports oceanic and domestic en route, terminal,
                   nonprecision approach, precision approach, and departure
                   operation. In precision approach mode, must apply
                   long-term, fast, and ionospheric corrections.

  4                Supports precision approach operation. Intended as
                   replacement to ILS, applicable only to Class Delta.
                   (Delta-4 equipment is likely to also meet requirements for
                   Beta-1,-2, or -3).
  ---------------- -----------------------------------------------------------

# 5. REQUIRED NAVIGATION PERFORMANCE

Required navigation performance (RNP) is another important concept in
the approval of GPS and GPS/WAAS equipment. RNP was defined by ICAO
(Doc. 9650) as a statement of navigation performance accuracy,
integrity, continuity, and availability necessary for operations within
a defined airspace. RTCA in RTCA 192-96, draft, has modified this
concept slightly in its definition of RNP RNAV: "A statement of the
navigation performance accuracy necessary for operation within a defined
airspace. Note that there are additional requirements, beyond accuracy,
applied to a particular RNP type." The RNP RNAV minimum aviation system
performance standard (MASPS) (RTCA 192-96, draft) defines the additional
requirements beyond accuracy.

Accuracy, integrity, continuity, and availability are currently included
in GPS and GPS/WAAS approvals through requirements that differ slightly
from those described for RNP RNAV approvals in RTCA 192-96. For example,
TSO-C129 lists required position fixing error, CDI centering, flight
technical error (FTE), and requirements for RAIM or other types of
integrity monitoring. The concept of RNP (and RNP RNAV) was developed as
a means of describing navigation requirements without identifying a
specific sensor or navigation technology.

A draft of MASPS standards for RNP for area navigation (RNAV) (RTCA
192-96) has been written specifying performance standards for area
navigation equipment to meet in order to operate in RNP RNAV designated
airspace or using RNP RNAV designated procedures. It is believed that
equipment meeting RNP criteria will allow users to benefit from
approvals to operate in desirable airspace or using desirable
procedures. RNP RNAV criteria are specified using RNP RNAV types that
indicate the accuracy and integrity of the equipment. Better equipment
accuracy and integrity will allow equipment to meet more stringent
criteria (e.g., RNP-1 RNAV for 1 nautical mile versus RNP-4 RNAV for 4
nautical miles) and operate using more RNP routes and procedures. While
the FAA has not yet adopted the RNP RNAV standards, manufacturers may
want to develop GPS/WAAS equipment that meet the standards specified in
RTCA 192-96 to ensure accuracy and integrity that will allow purchasers
to take advantage of future RNP routes and procedures. Because
manufacturers obtaining approvals of GPS and GPS/WAAS sensors may also
want approvals of their equipment to various RNP RNAV types, this
document has reviewed human factors and operations issues associated
with RNP RNAV requirements (as described in RTCA 192-96) as they compare
to the requirements of GPS and GPS/WAAS equipment requirements.

# 6. GPS, GPS/WAAS, AND RNAV EQUIPMENT AND INSTALLATION APPROVAL DOCUMENTS

The existing requirements for GPS and GPS/WAAS equipment and
installation approval were reviewed in order to identify and compare
human factors and operations issues. Five requirements documents and
three supporting documents were reviewed. A summary of each of the five
requirements documents and a description of the three supporting
documents follows.

## 6.1 RTCA DO-208 - Minimum Operational Performance Standards for Airborne Supplemental Navigation Equipment Using Global Positioning System (GPS) (RTCA, 1991)

RTCA DO-208 is a combined industry and government document that contains
minimum operational performance standards for airborne supplemental
navigation equipment (2D and 3D) using GPS. It contains most of the
requirements for approval of GPS equipment for IFR use called out by
TSO-C129. The requirements cover equipment performance including user
interface issues. Though the document discusses integrated and
multisensor systems, the document does not specify different
requirements for Class C (sensor only) equipment versus Class A
(stand-alone systems) equipment.

## 6.2 TSO-C129A - Airborne Supplemental Navigation Equipment Using the Global Positioning System (GPS) (FAA, 1992)

TSO C129A prescribes the minimum performance standard that
"supplemental" area navigation equipment using GPS must meet to be
identified as TSO-C129A approved. In general, TSO-C129A references the
minimum performance standards of Section 2 of RTCA DO-208 as
requirements for approval of GPS equipment. TSO-C129A defines the
different equipment classes (as described previously) and lists
exceptions to the RTCA DO-208 document for each of the equipment
classes. Since this project deals specifically with GPS sensor (Class
C(1) and C(3)) equipment, the section describing exceptions to RTCA
DO-208 for Class C() equipment was reviewed for integration with the
RTCA DO-208 requirements to identify the complete list of requirements
for GPS Class C(1) and C(3) equipment.

While RTCA DO-208 does not make a distinction in requirements for Class
C equipment, TSO-C129A does. TSO-C129A exempts Class C equipment from
some requirements. Generally, requirements dealing specifically with
user interface issues such as data entry and information display are
exempted by TSO-C129A, presumably because Class C equipment are sensors
only and do not include user interface components. However, TSO-C129A
does state that the integrated navigation systems that use Class C
sensors may have to meet the requirements listed. That is, TSO-C129A
exempts Class C equipment from many of the user interface requirements
while at the same time implying that the equivalent of the requirements
must be met when integrating the sensors with other equipment.
Unfortunately, the actual installation requirements and the factors that
determine the user interface requirements of integrated navigation
systems are not specifically stated.

One example of this problem is the statement in TSO-C129A that the
requirements of RTCA DO-208 paragraph 2.2.1.13 (Integrity alarm for GPS
receivers) do not apply to Class C3 and Class C4 equipment. While Class
C3 and C4 equipment is not required to use RAIM for integrity
monitoring, an equivalent method must be used. The statement in
paragraph 2.2.1.13.1 --- "*Regardless of the method used to ensure
integrity, the integrity system shall meet the general specifications
given in Table 2-1"* should probably apply to all systems, regardless of
the method of ensuring integrity. The annunciation of integrity alarm
(2.2.1.13.2) is also important regardless of the method of ensuring
integrity, however, TSO-C129A exempts GPS Class C3 and C4 equipment from
these requirements.

Another example of a difficulty involved in interpreting TSO-C129A is
the reference to equivalence of requirements in the section "Exceptions
to RTCA DO-208 for Class A( ) equipment" for Class C equipment. When the
reader turns to the referenced section, the wording often lists
requirements specific to Class A1 equipment. It is assumed that Class C1
equipment must meet the equivalent of the requirement for Class A1
equipment and that Class C2 must meet the equivalents of Class A2, etc.;
however, this is not clearly stated in the document. In addition, this
reference adds an additional translation of information (page turning
and cross-referencing within TSO-C129A and between TSO-C129A and RTCA
DO-208).

## 6.3 RTCA DO-229 - Minimum Operational Performance Standards for Global Positioning System/Wide Area Augmentation System Airborne Equipment (RTCA, 1996)

RTCA DO-229 is a combined industry and government document that provides
minimum operational performance standards for GPS/WAAS. It is similar to
the RTCA DO-208 document except that it applies to GPS/WAAS equipment
rather than GPS equipment. The draft FAA Order TSO-WAAS references RTCA
DO-229 as an acceptable means for approval of GPS/WAAS equipment as
TSO-C129A does for GPS equipment. TSO-WAAS states that the standards in
RTCA DO-229 should be used as the standards for approval of GPS/WAAS
equipment.

RTCA DO-229 does make a distinction in requirements for Class Beta( ),
Gamma( ), and Delta(4) equipment. The requirements for Class Beta( )
equipment generally deal with accuracy and functionality and do not
include user interface requirements. The document does, however, state
the following:

> "*There are a number of integration issues associated with the
> installation of Class Beta equipment (such as compatibility with the
> navigation computer). Compatibility will have to be established for
> each navigation computer; the appropriate standards for determining
> that compatibility are not included in this standard . . . Class Beta
> equipment, together with the navigation computer, database, controls,
> and display will provide equivalent performance to Class Gamma and
> Delta equipment*"

Therefore, while RTCA DO-229 does not provide requirements for the human
factors and operations issues associated with the integrated navigation
system user interface for GPS/WAAS Class Beta equipment, it does suggest
that the installed sensor and integrated navigation system should meet
the same criteria as listed for Class Gamma and Delta equipment. As with
GPS equipment, the document does not specifically list requirements or
factors influencing the evaluation of user interface of GPS/WAAS Class
Beta sensors in integrated navigation systems. It does imply, however,
the human factors and operations requirements in section 2.2 for Class
Gamma equipment should be applicable to integrated navigation system
using Class Beta sensors.

A few other sections of RTCA DO-229 should also be helpful in evaluating
Class Beta integrated navigation systems. Section 2.5 covers test
methods and procedures, and section 2.5.10.2 provides procedures for
human factors bench tests. The human factors bench tests cover equipment
usability, display brightness and readability, audible alarms, and
controls.

## 6.4 AC 20-130A - Airworthiness Approval of Navigation or Flight Management Systems Integrating Multiple Navigation Sensors (FAA, 1996)

AC 20-130A establishes an acceptable means of obtaining airworthiness
approval of multisensor navigation of flight management system
integrating data from multiple navigation sources for use as a
navigation system. Since RTCA DO-208 and RTCA DO-229 deal with approval
of the GPS or GPS/WAAS equipment only, the documents do not require
evaluation of the installation and integration (though they do list
installed equipment requirements). AC 20-130A provides installation and
integration requirements for navigation and flight management systems
integrating multiple navigation sensors including GPS, Omega/VLF,
Loran-C, VOR/DME, Multiple DME, or INS/IRU sensors. AC 20-130A states
that it does not apply to systems incorporating GPS/WAAS sensors.

AC 20-130A lists requirements for GPS Class C equipment including a
requirement that the GPS sensor be approved in accordance with an
applicable TSO (e.g., TSO-C129A) and requirements dealing with human
factors and operations aspects of the user interface. This document
describes a method for obtaining airworthiness approval of a GPS sensor
in an integrated navigation or flight management system. It provides a
list of airworthiness criteria for first time and follow-on IFR or VFR
approval. Since this project deals specifically with ACO approval of
Class C GPS equipment in low-end transport category aircraft, the
section on first time IFR approvals was reviewed. Both the airworthiness
requirements and the approval process evaluations (bench test, data
evaluation, ground test, and flight test) were reviewed. AC 20-130A
covers human factors, operations, accuracy, and reliability of the
installed equipment.

## 6.5 RTCA Paper No. 192-96/SC 181-061 Minimum Aviation Performance System Standards: Required Navigation Performance for Area Navigation Draft 8 (RTCA, 1996)

The final requirements document reviewed was RTCA 192-96. RTCA 192-96 is
a draft MASPS for area navigation systems operating in an RNP RNAV
environment. Of interest is whether approvals of multisensor systems
which incorporate GPS Class C or GPS/WAAS Class Beta equipment to be
used in RNP RNAV environments will have additional or differing human
factors and operations issues than approvals that do not include use of
GPS or GPS/WAAS in RNP environments. RTCA 192-96 describes RNP and
related concepts and defines RNP RNAV and RNP-x RNAV types. Information
is provided on user interface requirements including human factors
issues and operational capabilities. Appendix E of RTCA 192-96 describes
RNP RNAV assessment criteria for existing aircraft. This section is
useful in the application of GPS sensors into integrated navigation
systems of low-end transport category aircraft. Appendix E lists
additional requirements for existing systems to meet the MASPS for RNP
RNAV.

## 6.6 Supporting Documents

Three supporting documents were reviewed:

1)  "FAA Human Factors and Operations Checklist for Stand-Alone GPS
    Receivers (TSO-C129A1)" (Huntley, et al., 1995),

2)  "A Review of Principles and Guidelines for the Design of Controls
    and Displays for Stand-Alone GPS and Loran Receivers" (McAnulty,
    1994), and

3)  *Global Positioning System, A Guide for the Approval of GPS Receiver
    Installation and Operation* (Wright, 1996).

The "Human Factors and Operations Checklist for Stand-Alone GPS
Receivers" provides a human factors and operations evaluation tool for
stand-alone GPS receivers. It includes both a bench test and a flight
test. This document includes the requirements of TSO-C129, RTCA DO-208,
and AC 20-138 (the stand-alone GPS receiver equivalent of AC 20-130A).
It also includes human factors guidelines from other FAA, military, and
industry documents. This document uses an evaluation (rather than a
guideline) approach, providing evaluators with scenarios to follow and
evaluation considerations for each scenario. While it is not a required
document for approval, it is a valuable tool for ensuring that GPS
stand-alone equipment meets [at least]{.underline} the human factors
requirements of TSO-C129 and AC 20-138. Many of the same procedures and
requirements should be applicable to an integrated navigation system
with a GPS sensor installation.

McAnulty (1994) discusses some aspects of automation and GPS and
describes GPS interfaces. This document lists the relevant human factors
guidance from RTCA DO- 208 and discusses the literature available for
design guidance. It provides more of a design (rather than evaluation)
guideline approach to the design of controls and displays. It includes
detailed information about the selection, design, and arrangement of
controls and displays.

The GPS installation and approval guide (Wright, 1996) lists the
requirements of flight standard district office aviation safety
inspectors for approving GPS installation and operation. This document
provides checklists for the various phases of this approval process.
Items in the checklist include guidance on all the aspects of the
approval process, not just human factors and operations issues. This
document covers field airworthiness approvals only; therefore, it may
not consider all the issues that are involved in a first-time approval.
As is the case with the human factors and operations checklist, the
guide is not a required document, but it provides a valuable tool for
aviation safety inspectors to ensure that a new system meets all of the
various installation and operation requirements documents.

# 7. HUMAN FACTORS AND OPERATIONS ISSUES, SIMILARITIES AND DIFFERENCES WITH GPS VERSUS GPS/WAAS EQUIPMENT

## 7.1 Comparison Tables of Human Factors, Operations, and Accuracy Issues for GPS and GPS/WAAS Requirements Documents

Table 3 lists the requirements for GPS and GPS/WAAS called out by the
documents reviewed. The number and the title of the guideline is
presented in the table. If the intent of the requirement was similar
across the different documents, they are written in the same row. Also,
the requirements were grouped into three separate areas: 1) traditional
human factors requirements, 2) user interface functional
characteristics, and 3) system integrity, annunciations, alerts, and
accuracy. Within these groups, an attempt was made to organize the items
so that related issues are close together. Therefore, differences
between the documents can be seen by noting the blank areas (or holes)
in the tables.

Only requirements determined to be directly related to human factors
issues, operational issues (i.e., the functions of the equipment that
are apparent to the pilot --- functions that may be selected, output
that may be viewed), or accuracy issues, are included. Examples of
requirements that are not covered include maintenance requirements, fire
resistance, signal processing characteristics, equipment performance in
environmental conditions, and automatic satellite selection.
Requirements that were questionable as to whether they should be
considered human factors or operations issues (e.g., display update
rate, lateral maneuver anticipation) were included.

The table is organized with the three documents that apply to GPS
(TSO-C129, RTCA DO-208, and AC 20-130A) on the left, then the document
that applies to GPS/WAAS (RTCA DO-229), and finally the document that
applies to RNAV approvals (RTCA 192-96) on the right. There currently is
no GPS/WAAS document that deals specifically with installation
airworthiness approval.

Column one lists the combined requirements of RTCA DO-208 and TSO-C129A.
This column lists requirements called out in RTCA DO-208 with cells
coded to indicate TSO-C129A exceptions to the requirements. Cells that
are grayed are items that TSO-C129A states do not apply to Class C
equipment. Cells that have an asterisk (\*) are items that TSO-C129A
states a change to the existing requirement in RTCA DO-208 or states
that an equivalent capability must be provided by the Class C equipment.
There are some requirements that one paragraph of TSO-C129 stated Class
C equipment was exempt from (shaded) and a different paragraph of
TSO-C129 stated a change to or equivalent capability requirement (\*)
for Class C equipment. It is assumed that these items (with shading and
an asterisk) should be considered requirements.

Column two lists the requirements of RTCA DO-208 that are not
specifically sensor equipment requirements but should be met by the
integrated navigation system once the equipment is installed.

Column three lists the requirements of AC 20-130A for GPS sensors used
under IFR, first time installation approval. In the cases where a
requirement is described twice in the document (for example, some
requirements are described as an airworthiness requirement, a bench test
item, and a flight test item), only the first mention of the item in the
document is noted.

Column four lists RTCA DO-229 requirements from section 2.1 that include
requirements applicable to Beta, Gamma, and Delta equipment for en
route, terminal, nonprecision approach, and precision approach modes and
the requirements called out in sections 3.1 and 3.2 covering installed
equipment performance for Class Beta equipment. In the case where a
requirement of the same title is slightly different for different
operations, the numbers for each listing are noted, then the title of
the requirement.

Column five covers requirements called out in RTCA DO-229 that are not
listed as requirements of Class Beta sensors, however, the document
states that the integrated navigation equipment should meet the
equivalent of these requirements. They include requirements from
sections 2.2 that are applicable to Gamma equipment for en route,
terminal, nonprecision approach, and precision approach modes and
requirements from section 3.3 covering installed equipment performance
for Class Gamma equipment for all operating modes. Where a section lists
several related requirements, only the number of the main heading or
first requirement is listed. This column also includes vertical
navigation (VNAV) requirements from Appendix F of RTCA DO-229 which are
subject to change since RTCA Special Committee 181 is developing VNAV
criteria in support of evolving RNP concepts.

Column six covers requirements described in the MASPS for RNP RNAV (RTCA
192-96). These include both original equipment requirements and existing
equipment requirements as described in Appendix E of RTCA 192-96.

Table 4 presents the same information in summary form (without exact
titles, section numbers, or the reference to be implied for actual
requirements) so that it is easy to see which of the documents cover
various aspects of the system or installation. The differences between
GPS and GPS/WAAS requirements are also easily noted in table 4.

+-----------+----------+--------+---------+--------------+---+------------+
| **Table   |          |        |         |              |   |            |
| 3. Human  |          |        |         |              |   |            |
| Factors,  |          |        |         |              |   |            |
| Op        |          |        |         |              |   |            |
| erations, |          |        |         |              |   |            |
| Accuracy  |          |        |         |              |   |            |
| Req       |          |        |         |              |   |            |
| uirements |          |        |         |              |   |            |
| /Issues** |          |        |         |              |   |            |
+===========+==========+========+=========+==============+===+============+
| GPS Class |          |        | G       |              | R |            |
| C         |          |        | PS/WAAS |              | N |            |
|           |          |        | Class   |              | P |            |
|           |          |        | Beta    |              | R |            |
|           |          |        |         |              | N |            |
|           |          |        |         |              | A |            |
|           |          |        |         |              | V |            |
+-----------+----------+--------+---------+--------------+---+------------+
| Required  | Required | Requi  | R       | Required     |   | Required   |
| of sensor | (        | rement | equired | (implied) of |   | by RTCA    |
| by        | implied) | of     | of      | integrated   |   | 192-96 for |
| TSO-C129  | of       | inte   | sensor  | navigation   |   | operation  |
| A and/or  | in       | grated | by RTCA | system by    |   | in RNP     |
| RTCA      | tegrated | navi   | DO 229  | RTCA DO 229  |   | RNAV       |
| DO-208    | na       | gation | (in     | (Class Gamma |   | airspace   |
|           | vigation | system | cluding | equivalent)  |   | (there may |
| Shaded =  | system   | by AC  | in      |              |   | be some    |
| exempt by | by RTCA  | 2      | stalled |              |   | d          |
| TSO       | DO-208   | 0-130A | eq      |              |   | ifferences |
|           | (i       |        | uipment |              |   | in         |
| \* =      | nstalled |        | requir  |              |   | re         |
| changed   | e        |        | ements) |              |   | quirements |
| by TSO    | quipment |        |         |              |   | depending  |
|           | perf     |        |         |              |   | on the     |
|           | ormance) |        |         |              |   | level of   |
|           |          |        |         |              |   | RNP RNAV   |
|           |          |        |         |              |   | airspace   |
|           |          |        |         |              |   | desired)   |
+-----------+----------+--------+---------+--------------+---+------------+
| Tr        |          |        |         |              |   |            |
| aditional |          |        |         |              |   |            |
| Human     |          |        |         |              |   |            |
| Factors   |          |        |         |              |   |            |
| Req       |          |        |         |              |   |            |
| uirements |          |        |         |              |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
| 2.1.4     | 3.1.1.1  | 9b(8)  | 3.1.1.1 | 2.2.1.1.1    |   | 3.4.2      |
| Operation | Acces    | System | Access  | Controls     |   | Displays   |
| of        | sibility | co     | ibility |              |   | and        |
| c         |          | ntrols |         | 2.2.1.1.1.1  |   | controls   |
| ontrols\* |          |        |         | Operation    |   |            |
|           |          |        |         |              |   |            |
| 2.1.5     |          |        |         | 3.3.1.1.3    |   |            |
| Acce      |          |        |         | Operation of |   |            |
| ssibility |          |        |         | controls     |   |            |
| of        |          |        |         |              |   |            |
| c         |          |        |         | 3.3.1.3.2.5  |   |            |
| ontrols\* |          |        |         | Controls     |   |            |
|           |          |        |         | ac           |   |            |
|           |          |        |         | cessibility, |   |            |
|           |          |        |         | usability,   |   |            |
|           |          |        |         | visibility   |   |            |
|           |          |        |         |              |   |            |
|           |          |        |         | 3.3.1.1.4    |   |            |
|           |          |        |         | A            |   |            |
|           |          |        |         | ccessibility |   |            |
|           |          |        |         | of controls  |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           |          |        |         | 3.3.1.1.5    |   | 1.2.4.1    |
|           |          |        |         | Arrangement  |   | Controls,  |
|           |          |        |         | of controls  |   | displays,  |
|           |          |        |         |              |   | and system |
|           |          |        |         |              |   | alerting   |
+-----------+----------+--------+---------+--------------+---+------------+
| 2.1.8     |          | 9b(8)  |         | 2.2.1.1.1.2  |   |            |
| Contro    |          | System |         | Control      |   |            |
| l/display |          | co     |         | labels       |   |            |
| re        |          | ntrols |         |              |   |            |
| adability |          | (rea   |         |              |   |            |
|           |          | dable) |         |              |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           | 3.1.4    | 9b(8)  | 3.1.1.3 |              |   | 3.4.2      |
|           | Ina      | System | Inad    |              |   | Displays   |
|           | dvertent | co     | vertent |              |   | and        |
|           | turnoff  | ntrols | turnoff |              |   | controls   |
+-----------+----------+--------+---------+--------------+---+------------+
| 2.1.7     |          |        |         | 3.3.1.1.2    |   |            |
| Contro    |          |        |         | Con          |   |            |
| l/display |          |        |         | trol/display |   |            |
| c         |          |        |         | capability   |   |            |
| apability |          |        |         |              |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
| 2.1.8     | 3.1.2    | 9b(3)  |         | 2.2.1.1.3.1  |   | 3.4.2      |
| Contro    | Display  | Lo     |         | Brightness,  |   | Displays   |
| l/display | vi       | cation |         | contrast,    |   | and        |
| re        | sibility | of     |         | and color    |   | controls   |
| adability |          | system |         |              |   |            |
|           |          | di     |         | 2.2.1.1.3.2  |   |            |
|           |          | splays |         | Angle of     |   |            |
|           |          |        |         | regard       |   |            |
|           |          |        |         |              |   |            |
|           |          |        |         | 3.3.1.1.     |   |            |
|           |          |        |         | 1/3.3.3.1.1/ |   |            |
|           |          |        |         | 3.3.4.1.1    |   |            |
|           |          |        |         | Display      |   |            |
|           |          |        |         | visibility   |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           |          | 9c(1)( |         | 3.3.1.3.1.1  |   |            |
|           |          | ii)(B) |         | Cockpit      |   |            |
|           |          | C      |         | layout of    |   |            |
|           |          | ockpit |         | installed    |   |            |
|           |          | layout |         | equipment    |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           |          |        |         | 3.3.1.2.2    |   |            |
|           |          |        |         | Data entry   |   |            |
|           |          |        |         | capability   |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           |          |        |         | 2.2.1.1.2/   |   |            |
|           |          |        |         | 3.3.3.3.2.1  |   |            |
|           |          |        |         | Equipment    |   |            |
|           |          |        |         | operating    |   |            |
|           |          |        |         | procedures   |   |            |
|           |          |        |         | (time        |   |            |
|           |          |        |         | critical     |   |            |
|           |          |        |         | functions)   |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           |          | 9c(1)( |         | 3.3.1.3.2.6  |   | 1.2.4.1    |
|           |          | iv)(J) |         | Crew         |   | Controls,  |
|           |          | Crew   |         | workload     |   | displays,  |
|           |          | wo     |         |              |   | and system |
|           |          | rkload |         |              |   | alerting   |
|           |          |        |         |              |   |            |
|           |          |        |         |              |   | 3.4.1      |
|           |          |        |         |              |   | General    |
+-----------+----------+--------+---------+--------------+---+------------+
|           |          |        |         | 2.2.1.1.3.3  |   |            |
|           |          |        |         | Symbology    |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           |          |        |         | 2.2.1.1.3.4  |   |            |
|           |          |        |         | A            |   |            |
|           |          |        |         | lphanumerics |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           |          |        |         | 2.2.1.1.5    |   |            |
|           |          |        |         | Set of       |   |            |
|           |          |        |         | standard     |   |            |
|           |          |        |         | a            |   |            |
|           |          |        |         | bbreviations |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           |          |        |         | 2.2.1.1.5    |   |            |
|           |          |        |         | Set of       |   |            |
|           |          |        |         | standard     |   |            |
|           |          |        |         | a            |   |            |
|           |          |        |         | bbreviations |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
| User      |          |        |         |              |   |            |
| Interface |          |        |         |              |   |            |
| F         |          |        |         |              |   |            |
| unctional |          |        |         |              |   |            |
| Charac    |          |        |         |              |   |            |
| teristics |          |        |         |              |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           |          | 9c(1)( |         | 3.3.1.3.2.3  |   |            |
|           |          | iv)(D) |         | Steering     |   |            |
|           |          | St     |         | response     |   |            |
|           |          | eering |         |              |   |            |
|           |          | re     |         |              |   |            |
|           |          | sponse |         |              |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
| 2.1.2     |          | 9c(1)( |         | 3.3.2.3.2.1  |   |            |
| General   |          | iv)(B) |         | Equipment    |   |            |
| pe        |          | Fu     |         | operation    |   |            |
| rformance |          | nction |         |              |   |            |
|           |          | of     |         |              |   |            |
|           |          | con    |         |              |   |            |
|           |          | nected |         |              |   |            |
|           |          | equ    |         |              |   |            |
|           |          | ipment |         |              |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
| 2.1.10    | 3.2.1.3  |        |         | 2.2.1.3.10   |   | 3.5.5.1    |
| Maneuver  | Lateral  |        |         | Waypoint     |   | Flight     |
| antic     | maneuver |        |         | sequencing   |   | progress   |
| ipation\* | anti     |        |         |              |   |            |
|           | cipation |        |         | 3.3.2.3.2.4  |   |            |
|           |          |        |         | Lateral      |   |            |
|           |          |        |         | maneuver     |   |            |
|           |          |        |         | anticipation |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           | 3.2.1.6  |        |         | F.2.3.2      |   |            |
|           | Vertical |        |         | Vertical     |   |            |
|           | maneuver |        |         | maneuver     |   |            |
|           | anti     |        |         | anticipation |   |            |
|           | cipation |        |         |              |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           | 3.2.1.7  |        |         | F.2.3.3.     |   |            |
|           | A        |        |         | Automatic    |   |            |
|           | utomatic |        |         | altitude     |   |            |
|           | altitude |        |         | change       |   |            |
|           | change   |        |         |              |   |            |
|           | (notif   |        |         |              |   |            |
|           | ication) |        |         |              |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           | 3.2.1.4  |        |         | 3.3.2.3.2.5/ |   |            |
|           | A        |        |         | 3.3.3.3.2.4  |   |            |
|           | utomatic |        |         |              |   |            |
|           | lateral  |        |         | Automatic    |   |            |
|           | change   |        |         | lateral      |   |            |
|           | (annu    |        |         | change       |   |            |
|           | nciation |        |         |              |   |            |
|           | of       |        |         |              |   |            |
|           | i        |        |         |              |   |            |
|           | mpending |        |         |              |   |            |
|           | waypoint |        |         |              |   |            |
|           | c        |        |         |              |   |            |
|           | rossing) |        |         |              |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           |          | 9c(1)( |         | 3.3.1.3.2.7/ |   |            |
|           |          | iv)(L) |         | 3.3.4.3.2.3  |   |            |
|           |          | Cont   |         |              |   |            |
|           |          | inuity |         | Continuity   |   |            |
|           |          | of     |         | of           |   |            |
|           |          | data   |         | navigation   |   |            |
|           |          | during |         | data         |   |            |
|           |          | ma     |         |              |   |            |
|           |          | neuver |         |              |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
| 2.1.11    |          |        | 2.1     | 2.2.2.4.4    |   |            |
| Update    |          |        | .2.6.1/ | Displayed    |   |            |
| rate      |          |        | 2.      | data update  |   |            |
| (d        |          |        | 1.4.6.1 | rate         |   |            |
| isplay)\* |          |        | P       |              |   |            |
|           |          |        | osition |              |   |            |
|           |          |        | output  |              |   |            |
|           |          |        | update  |              |   |            |
|           |          |        | rate    |              |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
| 2.2.1.8   |          |        | 2       | 2.2.1.4./    |   | 3.5.5.2    |
| Position  |          |        | .1.2.6/ | 2.2.2.4/2.2. |   | Navigation |
| display\* |          |        | 2.1.4.6 | 3.4/2.2.4.4/ |   | data       |
|           |          |        | P       |              |   |            |
|           |          |        | osition | Navigation   |   |            |
|           |          |        | output  | displays     |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           |          |        |         | 2.2.1.1.3.6  |   |            |
|           |          |        |         | Default      |   |            |
|           |          |        |         | navigation   |   |            |
|           |          |        |         | display page |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
|           |          |        |         | 2.2.1.4.     |   |            |
|           |          |        |         | 1/2.2.3.4.1/ |   |            |
|           |          |        |         | 2.2.4.4.1    |   |            |
|           |          |        |         | Primary      |   |            |
|           |          |        |         | navigation   |   |            |
|           |          |        |         | display      |   |            |
+-----------+----------+--------+---------+--------------+---+------------+
| 2.3.1.2   | 3.2.1.2  |        |         | 2.2.4.4.5    |   |            |
| Vertical  | Vertical |        |         | Non-numeric  |   |            |
| path      | path     |        |         | vertical     |   |            |
| deviation | d        |        |         | path         |   |            |
|           | eviation |        |         | deviation    |   |            |
|           | display  |        |         | display      |   |            |
|           |          |        |         |              |   |            |
|           |          |        |         | 3.3.4.2.2    |   |            |
|           |          |        |         | Vertical     |   |            |
|           |          |        |         | path         |   |            |
|           |          |        |         | deviation    |   |            |
|           |          |        |         | display      |   |            |
+-----------+----------+--------+---------+--------------+---+------------+

**Table 3. Human Factors, Operations, Accuracy Requirements/Issues**

+-----------+----------+--------+---------+--------------+------------+
| GPS Class |          |        | G       |              | RNP RNAV   |
| C         |          |        | PS/WAAS |              |            |
|           |          |        | Class   |              |            |
|           |          |        | Beta    |              |            |
+-----------+----------+--------+---------+--------------+------------+
| Required  | Required | Requi  | R       | Required     | Required   |
| of sensor | (        | rement | equired | (implied) of | by RTCA    |
| by        | implied) | of     | of      | integrated   | 192-96 for |
| TSO-C129  | of       | inte   | sensor  | navigation   | operation  |
| A and/or  | in       | grated | by RTCA | system by    | in RNP     |
| RTCA      | tegrated | navi   | DO 229  | RTCA DO 229  | RNAV       |
| DO-208    | na       | gation | (in     | (Class Gamma | airspace   |
|           | vigation | system | cluding | equivalent)  | (there may |
| Shaded =  | system   | by AC  | in      |              | be some    |
| exempt by | by RTCA  | 2      | stalled |              | d          |
| TSO       | DO-208   | 0-130A | eq      |              | ifferences |
|           | (i       |        | uipment |              | in         |
| \* =      | nstalled |        | requir  |              | re         |
| changed   | e        |        | ements) |              | quirements |
| by TSO    | quipment |        |         |              | depending  |
|           | perf     |        |         |              | on the     |
|           | ormance) |        |         |              | level of   |
|           |          |        |         |              | RNP RNAV   |
|           |          |        |         |              | airspace   |
|           |          |        |         |              | desired)   |
+-----------+----------+--------+---------+--------------+------------+
| 2.3.1.3   |          |        |         | F.2.3.1      |            |
| Vertical  |          |        |         | Vertical     |            |
| profile   |          |        |         | profile      |            |
+-----------+----------+--------+---------+--------------+------------+
| 2.2.1.1.1 | 3.2.1.1  |        |         | 2.2.2.4.3    | 3.5.5.1    |
| Numeric   | Cro      |        |         | /2.2.3.4     | Flight     |
| display   | ss-track |        |         | .3/2.2.3.4.3 | progress   |
| in        | d        |        |         | Numeric      |            |
| formation | eviation |        |         | cross track  |            |
|           | display  |        |         | deviation    |            |
+-----------+----------+--------+---------+--------------+------------+
| 2.2.1.1.2 | 3.2.1.1  |        |         | 3.3.1.2.1    | 3.5.5.1    |
| No        | Cro      |        |         | Cross track  | Flight     |
| n-numeric | ss-track |        |         | deviation    | progress   |
| display   | d        |        |         | display      |            |
| in        | eviation |        |         |              |            |
| formation | display  |        |         | 2.2.1.4.2    |            |
|           |          |        |         | /2.2.2.4/    |            |
|           |          |        |         | 2.2.3.4.2    |            |
|           |          |        |         | Non-numeric  |            |
|           |          |        |         | di           |            |
|           |          |        |         | splay/output |            |
|           |          |        |         | char         |            |
|           |          |        |         | acteristics, |            |
|           |          |        |         | Non-numeric  |            |
|           |          |        |         | cross-track  |            |
|           |          |        |         | deviation    |            |
|           |          |        |         |              |            |
|           |          |        |         | 2.2.4.4.5    |            |
|           |          |        |         | Non-numeric  |            |
|           |          |        |         | vertical     |            |
|           |          |        |         | deviation    |            |
+-----------+----------+--------+---------+--------------+------------+
| 2.2.1.2   |          |        |         | 2.2.1.4/2.2  | 3.5.5.1    |
| Waypoint  |          |        |         | .3.4/2.2.4.4 | Flight     |
| distance  |          |        |         |              | progresss  |
| display\* |          |        |         | Navigation   |            |
|           |          |        |         |              | 3.5.5.2    |
|           |          |        |         | Display      | Navigation |
|           |          |        |         |              | data       |
|           |          |        |         | Active       |            |
|           |          |        |         | waypoint     | 3.4.2      |
|           |          |        |         | distance     | Displays   |
|           |          |        |         | display      | and        |
|           |          |        |         |              | controls   |
|           |          |        |         | Active       |            |
|           |          |        |         | waypoint     |            |
|           |          |        |         | bearig       |            |
|           |          |        |         | display      |            |
|           |          |        |         |              |            |
|           |          |        |         | Desired      |            |
|           |          |        |         | track        |            |
|           |          |        |         | displays     |            |
|           |          |        |         |              |            |
|           |          |        |         | Waypoint     |            |
|           |          |        |         | dist         |            |
|           |          |        |         | ance/bearing |            |
|           |          |        |         | display      |            |
|           |          |        |         |              |            |
|           |          |        |         | Horizontal   |            |
|           |          |        |         | protection   |            |
|           |          |        |         | level        |            |
|           |          |        |         |              |            |
|           |          |        |         | Missed       |            |
|           |          |        |         | approach     |            |
|           |          |        |         | waypoint     |            |
|           |          |        |         | bearing      |            |
|           |          |        |         | display      |            |
|           |          |        |         |              |            |
|           |          |        |         | 3.3.1.3.2.4  |            |
|           |          |        |         | Displayed    |            |
|           |          |        |         | GPS/WAAS     |            |
|           |          |        |         | navigation   |            |
|           |          |        |         | parameters   |            |
+-----------+----------+--------+---------+--------------+------------+
| 2.2.1.3   |          |        |         | 2.2.1.4.6    |            |
| TO-FROM   |          |        |         | Display of   |            |
| ind       |          |        |         | TO or FROM   |            |
| ication\* |          |        |         | operation    |            |
+-----------+----------+--------+---------+--------------+------------+
|           |          |        |         | 2.2.1.1.3.5  | 3.8        |
|           |          |        |         | Moving map   | Enhanced   |
|           |          |        |         |              | navigation |
|           |          |        |         |              | display    |
|           |          |        |         |              | interface  |
+-----------+----------+--------+---------+--------------+------------+

**Table 3. Human Factors, Operations, Accuracy Requirements/Issues**

+-----------+----------+--------+---------+--------------+------------+
| GPS Class |          |        | G       |              | RNP RNAV   |
| C         |          |        | PS/WAAS |              |            |
|           |          |        | Class   |              |            |
|           |          |        | Beta    |              |            |
+-----------+----------+--------+---------+--------------+------------+
| Required  | Required | Requi  | R       | Required     | Required   |
| of sensor | (        | rement | equired | (implied) of | by RTCA    |
| by        | implied) | of     | of      | integrated   | 192-96 for |
| TSO-C129  | of       | inte   | sensor  | navigation   | operation  |
| A and/or  | in       | grated | by RTCA | system by    | in RNP     |
| RTCA      | tegrated | navi   | DO 229  | RTCA DO 229  | RNAV       |
| DO-208    | na       | gation | (in     | (Class Gamma | airspace   |
|           | vigation | system | cluding | equivalent)  | (there may |
| Shaded =  | system   | by AC  | in      |              | be some    |
| exempt by | by RTCA  | 2      | stalled |              | d          |
| TSO       | DO-208   | 0-130A | eq      |              | ifferences |
|           | (i       |        | uipment |              | in         |
| \* =      | nstalled |        | requir  |              | re         |
| changed   | e        |        | ements) |              | quirements |
| by TSO    | quipment |        |         |              | depending  |
|           | perf     |        |         |              | on the     |
|           | ormance) |        |         |              | level of   |
|           |          |        |         |              | RNP RNAV   |
|           |          |        |         |              | airspace   |
|           |          |        |         |              | desired)   |
+-----------+----------+--------+---------+--------------+------------+
| 2.2.1.4   |          |        |         | 2.2          | 3.5.1.1.   |
| Flight    |          |        |         | .1.2/2.2.3.2 | General    |
| path      |          |        |         | / 2.2.4.2    | flight     |
| se        |          |        |         | Path         | planning   |
| lection\* |          |        |         | selection    |            |
|           |          |        |         |              |            |
|           |          |        |         | > Flight     |            |
|           |          |        |         | > plan       |            |
|           |          |        |         | > selection  |            |
|           |          |        |         | >            |            |
|           |          |        |         | > Flight     |            |
|           |          |        |         | > plan       |            |
|           |          |        |         | > activation |            |
|           |          |        |         | >            |            |
|           |          |        |         | > Approach   |            |
|           |          |        |         | > selection  |            |
|           |          |        |         | >            |            |
|           |          |        |         | > Missed     |            |
|           |          |        |         | > approach   |            |
|           |          |        |         | > sequencing |            |
|           |          |        |         | >            |            |
|           |          |        |         | > T          |            |
|           |          |        |         | O-TO/TO-FROM |            |
|           |          |        |         | >            |            |
|           |          |        |         | > To         |            |
|           |          |        |         | > operation  |            |
|           |          |        |         | >            |            |
|           |          |        |         | > From       |            |
|           |          |        |         | > operation  |            |
+-----------+----------+--------+---------+--------------+------------+
| (a)       |          |        |         | 2.2.1.2.2    | 3.5.2.1.1  |
| (3)(xxii) |          |        |         | Flight plan  | General    |
| Flight    |          |        |         | review       | flight     |
| plan      |          |        |         |              | planning   |
| c         |          |        |         |              |            |
| apability |          |        |         |              |            |
+-----------+----------+--------+---------+--------------+------------+
| 2.2.1.5   | 3.2.1.8  |        |         | 3.3.2.2.2    | 3.5.2.1.1  |
| Waypoint  | Display  |        |         | Waypoint     | General    |
| entry     | of       |        |         | input and    | flight     |
|           | selected |        |         | display      | planning   |
| 2.2.1.9   | waypoint |        |         |              |            |
| Input     |          |        |         |              |            |
| data      |          |        |         |              |            |
| obse      |          |        |         |              |            |
| rvation\* |          |        |         |              |            |
| (Flight   |          |        |         |              |            |
| plan)     |          |        |         |              |            |
+-----------+----------+--------+---------+--------------+------------+
| 2.2.1.6   |          |        |         | 2.2.1.2.5    | 3.5.2.1.2  |
| Waypoint  |          |        |         | User-defined | Us         |
| storage\* |          |        |         | waypoints    | er-defined |
|           |          |        |         |              | fixes      |
+-----------+----------+--------+---------+--------------+------------+
| 2.3.1.1   |          |        |         | F.2.2 Flight |            |
| Waypoint  |          |        |         | plan -       |            |
| altitude  |          |        |         | waypoint     |            |
|           |          |        |         | altitude     |            |
+-----------+----------+--------+---------+--------------+------------+
|           |          |        |         | 2.2.2        | 3.5.2.1.3  |
|           |          |        |         | .6.1/2.2.3.6 | Selection  |
|           |          |        |         | .1/2.2.4.6.1 | of RNP     |
|           |          |        |         | Caution      | RNAV type  |
|           |          |        |         | associated   |            |
|           |          |        |         | with loss of |            |
|           |          |        |         | integrity    |            |
|           |          |        |         | monitoring   |            |
+-----------+----------+--------+---------+--------------+------------+

**Table 3. Human Factors, Operations, Accuracy Requirements/Issues**

+-----------+----------+--------+---------+--------------+------------+
| GPS Class |          |        | G       |              | RNP RNAV   |
| C         |          |        | PS/WAAS |              |            |
|           |          |        | Class   |              |            |
|           |          |        | Beta    |              |            |
+-----------+----------+--------+---------+--------------+------------+
| Required  | Required | Requi  | R       | Required     | Required   |
| of sensor | (        | rement | equired | (implied) of | by RTCA    |
| by        | implied) | of     | of      | integrated   | 192-96 for |
| TSO-C129  | of       | inte   | sensor  | navigation   | operation  |
| A and/or  | in       | grated | by RTCA | system by    | in RNP     |
| RTCA      | tegrated | navi   | DO 229  | RTCA DO 229  | RNAV       |
| DO-208    | na       | gation | (in     | (Class Gamma | airspace   |
|           | vigation | system | cluding | equivalent)  | (there may |
| Shaded =  | system   | by AC  | in      |              | be some    |
| exempt by | by RTCA  | 2      | stalled |              | d          |
| TSO       | DO-208   | 0-130A | eq      |              | ifferences |
|           | (i       |        | uipment |              | in         |
| \* =      | nstalled |        | requir  |              | re         |
| changed   | e        |        | ements) |              | quirements |
| by TSO    | quipment |        |         |              | depending  |
|           | perf     |        |         |              | on the     |
|           | ormance) |        |         |              | level of   |
|           |          |        |         |              | RNP RNAV   |
|           |          |        |         |              | airspace   |
|           |          |        |         |              | desired)   |
+-----------+----------+--------+---------+--------------+------------+
| 2.2.1.7   |          |        |         | > 2.2.1.3.10 | 3.5.2.1.4  |
| Waypoint  |          |        |         | > Waypoint   | Fix        |
| or leg    |          |        |         | > sequencing | sequencing |
| seq       |          |        |         | > 2.2.1.3.11 |            |
| uencing\* |          |        |         | > T          |            |
|           |          |        |         | O-TO/TO-FROM |            |
+-----------+----------+--------+---------+--------------+------------+
|           | 3.2.1.5  |        |         | 2.2.1.3.4    | 3.5.2.2.1  |
|           | D        |        |         | Direct-to    | Direct-to  |
|           | irect-to |        |         |              |            |
|           | function |        |         | 3.3.2.3.2.6  |            |
|           |          |        |         | Direct-to    |            |
|           |          |        |         | function     |            |
+-----------+----------+--------+---------+--------------+------------+
|           |          |        |         | 2.2.1.3/2.2  | 3.5.2.2.2  |
|           |          |        |         | .3.3/2.2.4.3 | Us         |
|           |          |        |         | Path         | er-defined |
|           |          |        |         | definition   | Cours      |
|           |          |        |         |              | e-to-a-fix |
|           |          |        |         | Fixed        |            |
|           |          |        |         | waypoint to  |            |
|           |          |        |         | a fixed      |            |
|           |          |        |         | waypoint     |            |
|           |          |        |         |              |            |
|           |          |        |         | Constant     |            |
|           |          |        |         | radius to a  |            |
|           |          |        |         | fix          |            |
|           |          |        |         |              |            |
|           |          |        |         | Course to a  |            |
|           |          |        |         | fix waypoint |            |
|           |          |        |         |              |            |
|           |          |        |         | From leg     |            |
|           |          |        |         |              |            |
|           |          |        |         | Approach     |            |
|           |          |        |         | path         |            |
|           |          |        |         | definition   |            |
|           |          |        |         |              |            |
|           |          |        |         | Missed       |            |
|           |          |        |         | approach     |            |
|           |          |        |         | path         |            |
|           |          |        |         | definition   |            |
|           |          |        |         |              |            |
|           |          |        |         | Departure    |            |
|           |          |        |         | path         |            |
|           |          |        |         | definition   |            |
+-----------+----------+--------+---------+--------------+------------+
|           |          |        |         | 2.2.1.3.7    | 3.5.4 Path |
|           |          |        |         | Fly-by turns | steering   |
|           |          |        |         |              |            |
|           |          |        |         | 2.2.1.3.8    |            |
|           |          |        |         | Fly over     |            |
|           |          |        |         | turns        |            |
|           |          |        |         |              |            |
|           |          |        |         | 2.2.1.3.9    |            |
|           |          |        |         | Fixed radius |            |
|           |          |        |         | turns        |            |
|           |          |        |         |              |            |
|           |          |        |         | 2.2.1.3.11   |            |
|           |          |        |         | T            |            |
|           |          |        |         | O-TO/TO-FROM |            |
|           |          |        |         |              |            |
|           |          |        |         | 3.3.1.3.2.8  |            |
|           |          |        |         | Fly-by turn  |            |
|           |          |        |         | performance  |            |
+-----------+----------+--------+---------+--------------+------------+
|           |          |        |         | 2.2.1.3.12   | 3.5.2.2.3  |
|           |          |        |         | Holding      | Holding    |
|           |          |        |         | patterns/    |            |
|           |          |        |         | procedure    |            |
|           |          |        |         | turns        |            |
+-----------+----------+--------+---------+--------------+------------+
|           |          |        |         |              | 3.5.2.2.4  |
|           |          |        |         |              | Parallel   |
|           |          |        |         |              | offsets    |
+-----------+----------+--------+---------+--------------+------------+
|           |          |        |         |              | 3.5.3      |
|           |          |        |         |              | Navigation |
|           |          |        |         |              | aid        |
|           |          |        |         |              | selection  |
+-----------+----------+--------+---------+--------------+------------+
|           |          | 9c(1)( |         | 2.2.2.7/2.2  | 3.5.5.3    |
|           |          | iv)(A) |         | .3.7/2.2.4.7 | Navigation |
|           |          |        |         | Mode         | modes and  |
|           |          | Ope    |         | switching    | p          |
|           |          | rating |         | requirements | erformance |
|           |          | modes  |         |              |            |
+-----------+----------+--------+---------+--------------+------------+
|           |          | 9c(1)( |         |              |            |
|           |          | iv)(N) |         |              |            |
|           |          |        |         |              |            |
|           |          | Ope    |         |              |            |
|           |          | ration |         |              |            |
|           |          | during |         |              |            |
|           |          | appr   |         |              |            |
|           |          | oaches |         |              |            |
+-----------+----------+--------+---------+--------------+------------+
|           |          |        |         | 3.3.3.3.2.5  |            |
|           |          |        |         | Missed       |            |
|           |          |        |         | approach     |            |
+-----------+----------+--------+---------+--------------+------------+
|           |          | 9b(9)  |         | 2.2.1.5      | 3.6        |
|           |          | Navi   |         | Database     | Navigation |
|           |          | gation |         | requirements | database   |
|           |          | da     |         |              | re         |
|           |          | tabase |         |              | quirements |
+-----------+----------+--------+---------+--------------+------------+

**Table 3. Human Factors, Operations, Accuracy Requirements/Issues**

+-----------+----------+--------+---------+--------------+------------+
| GPS Class |          |        | G       |              | RNP RNAV   |
| C         |          |        | PS/WAAS |              |            |
|           |          |        | Class   |              |            |
|           |          |        | Beta    |              |            |
+-----------+----------+--------+---------+--------------+------------+
| Required  | Required | Requi  | R       | Required     | Required   |
| of sensor | (        | rement | equired | (implied) of | by RTCA    |
| by        | implied) | of     | of      | integrated   | 192-96 for |
| TSO-C129  | of       | inte   | sensor  | navigation   | operation  |
| A and/or  | in       | grated | by RTCA | system by    | in RNP     |
| RTCA      | tegrated | navi   | DO 229  | RTCA DO 229  | RNAV       |
| DO-208    | na       | gation | (in     | (Class Gamma | airspace   |
|           | vigation | system | cluding | equivalent)  | (there may |
| Shaded =  | system   | by AC  | in      |              | be some    |
| exempt by | by RTCA  | 2      | stalled |              | d          |
| TSO       | DO-208   | 0-130A | eq      |              | ifferences |
|           | (i       |        | uipment |              | in         |
| \* =      | nstalled |        | requir  |              | re         |
| changed   | e        |        | ements) |              | quirements |
| by TSO    | quipment |        |         |              | depending  |
|           | perf     |        |         |              | on the     |
|           | ormance) |        |         |              | level of   |
|           |          |        |         |              | RNP RNAV   |
|           |          |        |         |              | airspace   |
|           |          |        |         |              | desired)   |
+-----------+----------+--------+---------+--------------+------------+
| System    |          |        |         |              |            |
| I         |          |        |         |              |            |
| ntegrity, |          |        |         |              |            |
| Annun     |          |        |         |              |            |
| ciations, |          |        |         |              |            |
| and       |          |        |         |              |            |
| Alerts    |          |        |         |              |            |
+-----------+----------+--------+---------+--------------+------------+
| 2.2.1.10  |          |        |         | 3.3.1.3.2.2  |            |
| Failu     |          |        |         | Failure      |            |
| re/status |          |        |         | modes/a      |            |
| indi      |          |        |         | nnunciations |            |
| cations\* |          |        |         |              |            |
+-----------+----------+--------+---------+--------------+------------+
| 2         |          |        | 2       | 2.2          | 3.5.6      |
| .2.1.13.1 |          |        | .1.1.13 | .1.6/2.2.2.6 | Alerting   |
| General   |          |        | Alerts/ | / 2.2.3.6 /  |            |
| integrity |          |        | outputs | 2.2.4.6      |            |
| requi     |          |        |         |              |            |
| rements\* |          |        | 2       | > Alerts     |            |
|           |          |        | .1.4.10 | >            |            |
| 2         |          |        | A       | > Caution    |            |
| .2.1.13.2 |          |        | lerts/o | > associated |            |
| Ann       |          |        | utputs/ | > with loss  |            |
| unciation |          |        | inputs  | > of         |            |
| of        |          |        |         | > integrity  |            |
| integrity |          |        | > Pro   | > monitoring |            |
| alarm\*   |          |        | tection | > Caution    |            |
|           |          |        | > level | > associated |            |
| 2         |          |        | >       | > with loss  |            |
| .2.1.13.3 |          |        | > Nav   | > of         |            |
| RAIM      |          |        | igation | > navigation |            |
| impleme   |          |        | > alert | >            |            |
| ntation\* |          |        | >       | > Mode       |            |
|           |          |        | > Pr    | > switching  |            |
|           |          |        | ecision | >            |            |
|           |          |        | > a     | requirements |            |
|           |          |        | pproach |              |            |
|           |          |        | > mode  |              |            |
+-----------+----------+--------+---------+--------------+------------+
|           |          | 9c(1)  |         | 2.2.1.1.4    |            |
|           |          | (i)(D) |         | A            |            |
|           |          | An     |         | nnunciations |            |
|           |          | alysis |         |              |            |
|           |          | of     |         | Annunciators |            |
|           |          | f      |         | Messages     |            |
|           |          | ailure |         |              |            |
|           |          | modes  |         |              |            |
|           |          | and    |         |              |            |
|           |          | a      |         |              |            |
|           |          | nnunci |         |              |            |
|           |          | ations |         |              |            |
+-----------+----------+--------+---------+--------------+------------+
|           |          |        | 2.1.1.5 |              | 2.2        |
|           |          |        | Sa      |              | C          |
|           |          |        | tellite |              | ontainment |
|           |          |        | in      |              | integrity  |
|           |          |        | tegrity |              |            |
|           |          |        | status  |              | 2.3        |
|           |          |        |         |              | C          |
|           |          |        | 2.1.2   |              | ontainment |
|           |          |        | .2.2/2. |              | continuity |
|           |          |        | 1.4.2.2 |              |            |
|           |          |        | In      |              |            |
|           |          |        | tegrity |              |            |
|           |          |        | mon     |              |            |
|           |          |        | itoring |              |            |
|           |          |        |         |              |            |
|           |          |        | 2.1.    |              |            |
|           |          |        | 2.2.2.1 |              |            |
|           |          |        | WAAS-p  |              |            |
|           |          |        | rovided |              |            |
|           |          |        | in      |              |            |
|           |          |        | tegrity |              |            |
|           |          |        | mon     |              |            |
|           |          |        | itoring |              |            |
|           |          |        |         |              |            |
|           |          |        | 2.1.    |              |            |
|           |          |        | 2.2.2.2 |              |            |
|           |          |        | FDE     |              |            |
|           |          |        | p       |              |            |
|           |          |        | rovided |              |            |
|           |          |        | in      |              |            |
|           |          |        | tegrity |              |            |
|           |          |        | mon     |              |            |
|           |          |        | itoring |              |            |
+-----------+----------+--------+---------+--------------+------------+
|           |          |        |         | 2.2.1.4.8    | 3.5.5.3    |
|           |          |        |         | Horizontal   | Navigation |
|           |          |        |         | protection   | modes and  |
|           |          |        |         | level        | p          |
|           |          |        |         |              | erformance |
|           |          |        |         |              | (estimate  |
|           |          |        |         |              | of         |
|           |          |        |         |              | position   |
|           |          |        |         |              | un         |
|           |          |        |         |              | certainty) |
+-----------+----------+--------+---------+--------------+------------+

+----------------------------------+--------+--------+--------+--------+
| **Table 4. Summary of            |        |        |        |        |
| Requirements**                   |        |        |        |        |
+==================================+========+========+========+========+
|                                  | *      |        | **GPS/ | *      |
|                                  | *GPS** |        | WAAS** | *RNP** |
+----------------------------------+--------+--------+--------+--------+
|                                  | **TS   | **AC   | **RTCA | **RTCA |
|                                  | O-C129 | 20-    | DO     | 19     |
|                                  | & RTCA | 130A** | -229** | 2-96** |
|                                  | DO     |        |        |        |
|                                  | -208** |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Traditional Human Factors        |        |        |        |        |
| Requirements                     |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Controls                         |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Operations                       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Accessibility                    |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Arrangement                      |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Labels/Readability               |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Inadvertent turnoff              |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Control/display capability       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Displays                         |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Visibility/Location              |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Brightness, contrast, and color  |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Alphanumerics                    |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Data entry capability            |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Equipment operating procedures   |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Crew workload                    |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Standard abbreviations           |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| User Interface Functional        |        |        |        |        |
| Characteristics                  |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Steering response                |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Equipment operation/performance  |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Maneuver anticipation            |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Lateral                          |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Vertical                         |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Altitude change notification     |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Lateral change notification      |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Continuity of data during        |        |        |        |        |
| maneuver                         |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Data update rate                 |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Position display/output          |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Displayed GPS/WAAS navigation    |        |        |        |        |
| parameters                       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Default navigation display page  |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Primary navigation display       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Horizontal deviation display     |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Vertical path deviation display  |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Vertical profile                 |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Numeric cross-track deviation    |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Non-numeric cross-track          |        |        |        |        |
| deviation                        |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Navigation display/flight        |        |        |        |        |
| progress/nav data                |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
|                                  |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > (Active) waypoint distance     |        |        |        |        |
| > display                        |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Active waypoint bearing        |        |        |        |        |
| > display                        |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Desired track                  |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Waypoint distance/bearing      |        |        |        |        |
| > display                        |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Horizontal protection          |        |        |        |        |
| > level/Estimate of position     |        |        |        |        |
| > uncertainty                    |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Missed approach waypoint       |        |        |        |        |
| > distance/bearing display       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| TO-FROM indication               |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Moving map/Enhanced guidance     |        |        |        |        |
| display                          |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Flight plan/path selection       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Flight plan activation         |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Approach selection               |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Missed approach sequencing     |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > TO-TO/TO-FROM                  |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > TO operation                   |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > FROM operation                 |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Flight plan review               |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Waypoint entry and display       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| User-defined waypoints           |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Waypoint altitude                |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Selection of RNP RNAV            |        |        |        |        |
| type/Selection of HPL            |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Waypoint, fix, or leg sequencing |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Direct-to operation              |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Other path definition functions  |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Fixed waypoint to a fixed      |        |        |        |        |
| > waypoint                       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Constant radius to a fix       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Course to a fix waypoint       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > FROM leg                       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Approach path definition       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Missed approach path           |        |        |        |        |
| > definition                     |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Departure path definition      |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Turns/path steering              |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Fly-by turns                   |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Fly over turns                 |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Fixed radius turns             |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > TO-TO/TO-FROM                  |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Holding patterns procedure turns |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Parallel offsets                 |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
|                                  |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
|                                  |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
|                                  |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Navigation aid selection         |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Operating modes and switching    |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Approach operation               |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Missed approach                |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Database requirements            |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| System Integrity, Annunciations, |        |        |        |        |
| Alerts, and Accuracy             |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Failure/status annunciations     |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Integrity requirements and       |        |        |        |        |
| alerts                           |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Loss of navigation, navigation |        |        |        |        |
| > alert                          |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > RAIM Implementation            |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Protection level               |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Loss of integrity monitoring   |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Precision approach mode        |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > Mode switching requirements    |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Human factors of annunciations,  |        |        |        |        |
| messages                         |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Satellite integrity status       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Integrity monitoring             |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > WAAS integrity monitoring      |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| > FDE integrity monitoring       |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+
| Horizontal protection            |        |        |        |        |
| level/Estimate of position       |        |        |        |        |
| uncertainty                      |        |        |        |        |
+----------------------------------+--------+--------+--------+--------+

## 7.2 Differences in Approval Requirements Between GPS and GPS/WAAS

A review of the comparison tables presented above shows that there are a
number of similar guidelines in the GPS and GPS/WAAS requirements. There
are, however, a few holes in the tables that indicate areas of
differences between the requirements for the two systems. In addition,
close inspection of the requirements reveals some differences.

### 7.2.1 Traditional Human Factors Issues 

The first section of tables 3 (page 21) and 4 (page 27) present the
requirements for traditional human factors issues. A number of the
requirements are similar across the documents. While the wording and
organization may be different, the intent of the requirements are mostly
the same. It can be seen from the table that RTCA DO-229 provides a few
more specific human factors guidelines on traditional human factors
issues such as controls, displays, and workload than are provided by the
other documents. This can also be seen in comparing the information
provided for each guideline from the documents. For example:

> *RTCA DO 208*
>
> *2.1.4 [Operation of Controls]{.underline}*
>
> *Controls intended for use during flight shall be designed to minimize
> errors and, when operated in all possible combinations and sequences,
> shall result in a condition whose presence or continuation would not
> be detrimental to the continued performance of the equipment.
> **Controls shall be designed to maximize operational suitability and
> minimize pilot workload. Reliance on pilot memory for operational
> procedures shall be minimized (added by TSO-C129).***
>
> *AC 20-130A*
>
> *9b(8) [System Controls]{.underline}*
>
> *All displays, controls, and annunciators must be readily readable
> under all normal cockpit conditions and expected ambient light
> conditions (total darkness to bright reflected sunlight). Night
> lighting provisions must be compatible with other cockpit lighting.
> All displays and controls must be arranged to facilitate equipment
> usage. Controls that are normally adjusted in flight shall be readily
> accessible and properly labeled as to their function. System controls
> and displays shall be designed to maximize operational suitability and
> minimize pilot workload. System controls shall be arranged to provide
> adequate protection against inadvertent system turnoff. Reliance on
> pilot memory for operational procedures shall be minimized.*
>
> *RTCA DO 229*
>
> *2.2.1.1.1.1 [Operation]{.underline}*
>
> *Controls that are normally adjusted in flight shall be accessible
> without interfering with the visibility of critical displays. Controls
> shall provide clear tactile or visual feedback when operated. The
> controls shall be movable without excessive effort, and detents shall
> be well defined. Spacing and physical size of the controls shall be
> sufficient to avoid inadvertent activation. Controls shall be operable
> with the use of only one hand.*
>
> *3.3.1.1.3 [Operation of Controls]{.underline}*
>
> *Controls intended for use during flight shall be designed to minimize
> errors and, when operated in all possible combinations and sequences,
> shall result in a condition whose presence or continuation would not
> be detrimental to the continued performance of the equipment. Controls
> shall be designed to maximize operational suitability and minimize
> pilot workload. The amount of force required to activate knobs/buttons
> shall be acceptable, feedback to the pilot should be adequate, and
> risk of inadvertent activation or deactivation should be minimized.
> Knob shape and size should not interfere with equipment use and should
> help distinguish controls. Reliance on pilot memory for operational
> procedures shall be minimized. The control/display shall be operable
> with the use of only one hand. A quick-reference card summarizing the
> user interface to the GPS/WAAS equipment should be provided. Examples
> of the information expected to be included on such a reference card
> can be found in Section 4 of this document.*

This difference (more complete and specific guidelines in RTCA DO 229)
does not appear to be specifically related to the implementation of
WAAS. That is, the traditional human factors information provided in
RTCA DO-229 should be applicable to any GPS sensor installation.

Another observation that can be made from reviewing the above example is
that there is a great deal of redundancy in the requirements both
between and within the documents. Redundancy within a document probably
could be lessened through document organization. Redundancy is to be
expected between documents and would not be a problem if all of the
documents stated the same thing. However, since there are minor
differences, individuals evaluating systems may have to read several
documents to make sure that all issues are covered. It does appear that
the requirements provided in RTCA DO-229 include all of the requirements
of the other documents (and more) so that a system that meets the human
factors criteria of RTCA DO-229 should at least meet the requirements of
the other documents.

One final observation on the presentation of traditional human factors
items in these documents is that the information is highly subjective.
The outcome of the evaluation will be dependent on the evaluator. RTCA
DO-229 has made some effort to reduce the subjective nature of the task
by providing procedures and checklists for human factors bench tests.
These checklists are based on the FAA Human Factors and Operations
Checklist for Standalone GPS Receivers previously discussed. RTCA DO-229
has also provided a few quantitative measures such as minimum character
size and recommended minimum times and numbers of actions for various
equipment functions are provided by RTCA DO-229. Minimum button or knob
size and separation is not included. It is understandable that there is
resistance to providing information that may limit future development of
better products, however, the information may be presented in a way that
indicates that it is reference information for the evaluator and not
necessarily a requirement.

### 7.2.2 User Interface Functional Characteristics. 

The second section of the tables (pages 22 to 26 for table 3 and page 27
to 29 for table 4) presents user interface functional characteristics.
These requirements specify system operation, display characteristics,
and pilot controllable functions. In comparing the requirements of the
documents, it is clear that RTCA DO-229 for GPS/WAAS has more detailed
requirements for the functional characteristics of the equipment and the
user interface than does RTCA DO-208 for GPS. Some of the differences
between the sets of documents include:

1.  RTCA DO-229 lists specifically what data must be displayed
    continuously and what data must be displayed continuously or on a
    default navigation page that can be accessed with a single action in
    two seconds or less.

2.  RTCA DO-229 requires that equipment have both TO-TO and TO-FROM
    operational capability while RTCA DO-208 and TSO-C129 do not have
    this requirement.

3.  RTCA DO-229 also specifies the presentation of the following data
    that is not specifically required by RTCA DO-208 and TSO-C129
    including:

    a.  Active waypoint bearing display

    b.  Desired track

    c.  Horizontal protection level

    d.  Missed approach waypoint distance display

    e.  Missed approach waypoint bearing display

    f.  Non-numeric vertical deviation

4.  RTCA DO-229 specifies in greater detail the functionality and
    interface required for flight path definition and selection.

5.  Some of the quantitative requirements in terms of display
    resolution, accuracy, linearity, and deflection requirements are
    slightly different between the two documents.

6.  TSO-C129 does not require approach mode selection and sequencing for
    Class C equipment, though it is expected that this is an error in
    the document since TSO-C129 does describe an addition of approach
    mode selection and sequencing to the RTCA requirements for Class A
    equipment (section (a)(3)(xii)).

The presentation of horizontal protection level with GPS/WAAS is due to
the new concepts of integrity and accuracy that are being implemented
with GPS/WAAS equipment (described in more detail in the following
section). A few of the other differences are due to the expected (though
it is not allowed in the current draft of TSO-WAAS) use of GPS/WAAS for
precision approach, whereas GPS may only be approved for nonprecision
approach. Most of the differences between the interface functional
requirements for GPS versus GPS/WAAS do not appear to be due to
fundamental differences between the GPS and GPS/WAAS equipment. Many of
the differences may simply be due to the natural progression of
knowledge of the systems between the time of production of the GPS
information and the GPS/WAAS information. In general, equipment that
meets the Minimum Operational Performance Standards of GPS/WAAS
equipment should more than meet the requirements of GPS equipment.

Manufacturers of GPS/WAAS equipment may be interested in manufacturing
equipment that will meet the requirements of both TSO-C129 and TSO-WAAS
since the full implementation of the WAAS network may not be complete
for some time. Users could then use GPS only when WAAS systems were
unavailable and use GPS/WAAS when WAAS was available. The intent of the
WAAS MOPS was to create requirements to replace TSO-C129 so that systems
that meet the requirements of the WAAS TSO can be used to fly both GPS
and GPS/WAAS operations so that manufacturers need to reference only the
WAAS MOPS for both types of operations (DeCleene, 1996).

### 7.2.3 System Integrity, Annunciations, and Alerts

The final section of table 3 (page 26) and table 4 (page 29) covers
system integrity, annunciations, alerts, and accuracy. This is one area
where differences between the two system approval requirements are
expected since GPS/WAAS provides a completely different method of
ensuring navigation integrity than is provided by GPS alone.
Annunciations and alert requirements associated with integrity
monitoring and navigation failure are slightly different. GPS/WAAS
equipment is expected provide better accuracy and better integrity
monitoring and, therefore, is expected to be approvable as providing the
"primary means" of navigation. Because of this, more stringent
requirements on accuracy and integrity are imposed on GPS/WAAS
equipment.

The requirements from the documents indicate that there are differences
between GPS and GPS/WAAS in these areas. The techniques used to measure
accuracy and integrity are different for GPS and GPS/WAAS. The GPS/WAAS
approval documentation introduces a new measure of accuracy called
pseudorange error (versus position fixing error for GPS). The concept of
horizontal and vertical protection levels also are introduced and must
be used in integrity checking for GPS/WAAS.

The requirements for Class C sensors list the form that alerts and
annunciators must take by requiring equivalence to Class A equipment.
The requirements do not list the form of the information (or output of
the sensor) to be passed to the equipment providing the alerts. The
requirements in RTCA DO-229 list specifically the information that Class
Beta sensors must output to be used in alerts. RTCA DO-229 specifies the
form of the alerts and annunciators of Class Beta sensors through the
requirement that installed Class Beta sensors have performance
equivalent to Class Gamma and Delta equipment.

There are other differences in the requirements of GPS versus GPS/WAAS
equipment than the means of measuring accuracy and integrity. These
differences are in the form of the presentation of alerts. The main
difference between the alert presentation requirements for GPS versus
GPS/WAAS equipment is that the GPS approval requires alerts on the
primary navigation display in more situations than are required for
GPS/WAAS approval. Also the GPS requirements state removal or flagging
of potentially incorrect navigation data on the display. The GPS/WAAS
requirements recommend, however, that the navigation data continue to be
displayed in these situations. Finally, there appear to be differences
in the requirements for annunciations at the time of mode switching
(changes to the display or system that occur in conjunction with changes
in phase of flight).

Additionally, there are differences between the requirements for GPS and
GPS/WAAS dealing with system integrity, annunciations, and alerts. As
discussed above, it is the intention of the WAAS MOPS to replace the GPS
requirements so that systems that meet the WAAS requirements may also be
used for GPS operations when the WAAS is not operational.

The human factors aspects of the annunciator design should be similar
for GPS and GPS/WAAS, though RTCA DO-229 is the only document that
provides a complete description of what factors to evaluate to ensure
good human factors design of annunciators.

## 7.3 Impact of RNP on the Approval of GPS and GPS/WAAS Sensors

Many of the same approval requirements for GPS and GPS/WAAS equipment
are listed in the RNP RNAV MASPS. Table 4 shows that the RNP MASPS
requirements are slightly more detailed than the GPS requirements and
slightly less detailed than the GPS/WAAS requirements. The issues
described in section 7.2.1 apply also to the traditional human factors
issues associated with RNP approvals. Many of the requirements are the
same though they may be worded slightly differently. There are no
fundamental differences for systems to be used as RNP RNAV equipment
versus GPS or GPS/WAAS equipment in terms of traditional human factors
issues.

There are a few user interface functionality requirements that are
unique to RNP RNAV approvals. These include 1) selection of RNP RNAV
type, 2) navigation aid selection, 3) estimate of position uncertainty
(and alerts associated with required RNP type) 4) parallel offsets and
parallel offset status alerting, and 5) capability to fly published RNP
RNAV holding procedures. The differences between the RNP requirements
and the GPS and GPS/WAAS requirements are generally due to the use of
the RNP concept for accuracy and integrity and due to the more general
applicability of the RNP document to all RNAV equipment rather than only
GPS or GPS/WAAS equipment. Of these five differences, the first three
are met by equivalent means in the WAAS MOPS, including selection of HAL
and display of HPL.

With the exception of the requirements for parallel offsets and the
capability to fly published RNP RNAV holds as described in the RTCA
192-96, equipment that meets the human factors and operations
requirements of RTCA DO-229 for GPS/WAAS should meet the requirements of
RNP equipment. Equipment certified to TSO-C129 rather than TSO-WAAS will
have to be evaluated more carefully to ensure that all of the additional
requirements of RTCA 192-96 have been met.

# 8. CONCLUSIONS

Aircraft certification specialists face a daunting task in the approval
of GPS and GPS/WAAS sensors in low-end transport category aircraft. The
documentation available does not clearly separate sensor equipment and
integrated navigation system requirements. For GPS systems, evaluation
requires that specialists either modify RTCA DO-208 with the information
listed in TSO-C129 or flip back and forth between the documents (and
within the TSO-C129 document). The presentation of information in
TSO-C129 is often difficult to interpret for the installation of sensors
since the document states that the sensors are exempt from several
requirements yet it also states changes to those requirements or
equivalent performance requirements. There are also, potentially, a few
errors in TSO-C129 (for example, omission of a portion of a table on
page 27, omission of pressure/barometric altitude input information)
that exacerbate the problem of interpreting the information. These types
of problems also inevitably lead to misunderstandings with
manufacturers.

For GPS/WAAS equipment installations, the information provided in RTCA
DO-229 is more complete and there (currently) are few exceptions to the
document specified in TSO-WAAS. However, there are some ambiguous
requirements in this document as well, especially in the distinction
between sensor equipment approval and integrated navigation equipment
installation requirements. There are several sections of the document
with redundant information and readers may have difficulty determining
which sections actually apply to a given situation or may find
themselves reading the same requirements in different places. For
example, some of the Class Gamma installed equipment requirements are
the same as Class Gamma general requirements, though the organization
and wording may be slightly different. The same is true for the Class
Gamma equipment test procedures and the installed equipment test
procedures. There are a few differences between requirements of GPS and
GPS/WAAS equipment that appear to be due to the recency of information
for the GPS/WAAS document. For this reason, certification specialists
reviewing GPS equipment may choose to supplement the GPS requirements
with the more complete and more recent applicable information in the
GPS/WAAS document.

Navigation equipment manufacturers interested in ensuring that GPS or
GPS/WAAS equipment meets RNP RNAV standards that may be imposed for
certain airways and procedures face another approval document. RTCA
192-96 is in draft form and there is currently no draft FAA document
supporting the MASPS for RNP RNAV. With the exception of the
requirements for parallel offsets and the capability to fly published
RNP RNAV holds as described in the RTCA 192-96, many of the human
factors and operations requirements in this document are the same as
those for GPS/WAAS and equipment meeting GPS/WAAS requirements should
also meet RNP RNAV requirements.

This review showed that there were a few problems with the documentation
and process for GPS and GPS/WAAS Class C sensor approvals. Generally,
the documentation is thorough, but in some cases is difficult to
interpret and cross-reference. There are efforts underway to account for
some of the problems discussed. First, TSO-C129 is being updated
(TSO-C129B) to refer to the newer requirements of RTCA DO-229. Second, a
checklist for approval of GPS/WAAS equipment is under development.

# REFERENCES

Adler, E.L. and Ruelos, C.H. 1993. GPS - Global Positioning System,
Using the Global Positioning System for Navigation on Boeing Airplanes.
*Airliner*. October-December.

DeCleene, B. 1996. Personal communication.

Department of Transportation and Department of Defense 1993*. 1992
Federal Radio-navigation Plan*. DOT-VNTSC-RSPA-92-2/DOD-4650.5.
Washington, DC.

Federal Aviation Administration. 1992. Technical Standard Order,
TSO-C129a, Airborne Supplemental Navigation Equipment Using the Global
Positioning System GPS). Washington, DC.

Federal Aviation Administration. 1994. Advisory Circular, AC 120-CNS
Draft 4 Rev 1, Criteria for Approval of Required Navigation Performance
(RNP) for Air Carrier Operations. Washington, DC.

Federal Aviation Administration. 1996. Advisory Circular, AC 20-130A,
Airworthiness Approval of Navigation or Flight Management Systems
Integrating Multiple Navigation Sensors. Washington, DC.

Huntley, M.S., J.W. Turner, C.S. Donovan, and E. Madigan. 1995. *FAA
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Secretaries of Defense and Transportation. Washington, DC: Joint DOD/DOT
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McAnulty, M.D. 1994. *A Review of Principles and Guidelines for the
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RTCA. 1991. RTCA/DO208, *Minimum Operational Performance Standards for
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RTCA, Inc. 1996. *Minimum Operational Performance Standards for Global
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Wright, M.C. 1996. *Global Positioning System: A Guide for the Approval
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