© Advisory US Department of Transportation Circular Federal Aviation Administration Subject: Installation of Terrain Awareness and Date: 6/14/00 AC No: 23-18 Warning System (TAWS) Approved Initiated By: ACE-100 Change:
for Part 23 Airplanes
1. PURPOSE 3
2. RELATED REGULATIONS AND DOCUMENTS 3 A. AIRWORTHINESS REGULATIONS 3 B. OPERATING REGULATIONS 4
c. AC, ORDERS, TSO, AND RELATED DOCUMENTS 4 D. INDUSTRY DOCUMENTS 6 E. OTHER DOCUMENT 6
3. DEFINITIONS 6
4. BACKGROUND 9 A. REGULATIONS 9 B. TSO-C151A 10
c. NEED FOR GUIDANCE 11
5. DISCUSSION 11 A. REGULATORY BASIS 11
6. SYSTEM DESCRIPTION 12 A. CLASS A TAWS EQUIPMENT AS DEFINED IN TSO-C151A 12 B. CLASS B TAWS EQUIPMENT, AS DEFINED IN TSO-C15U 12
7. AIRWORTHINESS CONSIDERATIONS 14 A. INITIAL INSTALLATION 14 B. FOLLOW-ON INSTALLATIONS 14 c PROJECT SPECIFIC CERTIFICATION PLAN 15 D. SYSTEM SAFETY ASSESSMENT 16 E. SOFTWARE 17 F. POSITION SOURCES 17 G. TERRAIN DATABASE 19 H. DISPLAY PRESENTATION 19
i. ALERTS 22
j . ALERT PRIORITIZATION K. SYSTEM INHIBIT L. FLIGHT DATA RECORDER M. SYSTEMS EVALUATIONS N. GROUND TEST REQUIREMENTS
o. FLIGHT-TEST REQUIREMENTS
p. AFMORAFMS 22 25 25 26 26 26 30
6/14/00 AC-23-18
1. PURPOSE. This advisory circular (AC) establishes an acceptable means, but not the only means, of obtaining Federal Aviation Administration's (FAA) airworthiness approval for the installation of a TAWS that has been approved under Technical Standard Order (TSO)-C151a, Terrain Awareness and Warning System, in a Part 23 airplane. The FAA's TSO process is a means for obtaining FAA design and performance approval for an appliance, system, or product;
however, the TSO does not provide installation approval. This AC serves to provide guidance for designing an acceptable installation for a TAWS that complies with TSO-C151a. The guidance provided is specific to installations of these systems on airplanes certificated under Title 14 of the Code of Federal Regulations (14 CFR) Part 23 [commonly referred to as Part 23 of the Federal Aviation Regulations (FAR)]. It describes the airworthiness considerations for such installations as they apply to the unique features of the TAWS and the interface of the TAWS with other systems on the airplane.
Equipment that does not meet the minimum performance standards specified in TSO-C 151a shall not be identified as TAWS equipment. Applicants that are not required to install TAWS and choose to install the system may deviate from the guidelines in this AC as necessary, provided the level of safety for the airplane's existing certification basis is not degraded.
Like all advisory material, this AC is not mandatory and does not constitute a regulation. It is issued for guidance purposes and to outline a method of compliance with applicable airworthiness requirements.
Because the method of compliance presented in this AC is not mandatory, the terms "shall" and "must" used in this AC apply only to an applicant who chooses to follow this particular method and prescribed standards of TSO-C 15 la.
2. RELATED REGULATIONS AND DOCUMENTS.
a. Airworthiness Regulations. These acceptable means of compliance refer to the applicable sections of 14 CFR Part 23. The corresponding paragraphs of the former Civil Air Regulations (CAR) are shown in parenthesis for airplanes certificated under CAR.
§ 23.771 (3.381) Pilot compartment.
§ 23.773 (3.382) Pilot compartment view.
§ 23.777 (3.3841) Cockpit controls.
§ 23.1301 (3.651 Equipment: Function and installation.
and 3.652) § 23.1303 (3.655(a)) Flight and navigation instruments.
§ 23.1309 Equipment, systems, and installations.
§ 23.1311 Electronic display instrument systems.
§ 23.1321 (3.661 Arrangement and visibility.
and 3.662) § 23.1322 Warning, caution, and advisory lights.
§ 23.1331 (3.668) Instruments using a power source.
§ 23.1351 (3.681, Electrical Systems and Equipment: General.
3.682, and 3.685) § 23.1353 (3.683) Storage battery design and installation.
§ 23.1357 (3.690, Circuit protective devices.
3.691, and 3.692) §23.1359 Electrical system fire protection.
§ 23.1361 (3.688 and 3.689) Master switch arrangement.
§ 23.1365 (3.693) §23.1367(3.694 and 3.695) §23.1381 (3.696 and 3.697) Electric cables and equipment.
Switches.
Instrument lights.
§ 23.1383 (3.698 and 3.699) Taxi and landing lights.
§ 23.1431 (3.721) § 23.1459 §23.1501 (3.735 and 3.737) §23.1529 § 23.1541 (3.755) §23.1543(3.756) § 23.1545 (3.757) § 23.1559 (3.770) § 23.1581 (3.777) § 23.1583 (3.761 and 3.778) Electronic equipment.
Flight recorders.
Operating Limitations and Information: General.
Instructions for Continued Airworthiness.
Markings and Placards: General.
Instrument markings: General.
Airspeed indicator.
Operating limitations placard.
Airplane Flight Manual and Approved Manual Material:
General.
Operating limitations.
b. Operating Regulations. More specifics on these regulations are provided in paragraph 5.
§ 91.223 Terrain awareness and warning system § 121.354 Terrain awareness and warning system § 121.360 Ground proximity warning—glide slope deviation alerting system § 135.153 Ground proximity warning system § 135.154 Terrain awareness and warning system
c. AC, Orders, TSO, and Related Documents. Later revisions are acceptable. The following publications may be obtained free of charge from the U.S. Department of Transportation, Subsequent Distribution Office, Ardmore East Business Center, 3341 Q 75th Avenue, Landover, MD 20785:
AC 20-115B AC 20-136 AC 21 -16D Radio Technical Commission for Aeronautics (RTCA), Inc.,RTCA/DO-178B Protection of Aircraft Electrical/Electronic Systems Against the Indirect Effects of Lightning RTCA Document DO-160D
AC 23-15 AC23.1311-1A AC23.1309-1C AC 20-112 AC20-130A AC 20-138 AC 90-45A FAA Order 8110.4B FAA Order 8260.3B TSO-C67 TSO-C92c TSO-C106 TSO-C113 TSO-C 115b TSO-C 117a TSO-C 129a Small Airplane Certification Compliance Program Installation of Electronic Displays in Part 23 Airplanes Equipment, Systems, and Installations in Part 23 Airplanes Airworthiness and Operational Approval of Airborne Systems to be Used in Lieu of Ground Proximity Warning System Airworthiness Approval of Navigation or Flight Management Systems Integrating Multiple Navigation Sensors Airworthiness Approval of Global Positioning System (GPS) Navigation Equipment for Use as a VFR and IFR Supplemental Navigation System Approval of Area Navigation Systems for Use in the U.S. National Airspace System Type Certification United States Standard for Terminal Instrument Procedures (TERPS) Aitiinetei, Pressure Autuatcu, ociisitrvc iypc Airborne Radar Altimeter Equipment Airborne Ground Proximity Warning Equipment Air Data Computer Airborne Multipurpose Electronic Displays Airborne Area Navigation Equipment Using Multi-Sensor Inputs Airborne Windshear Warning and Escape Guidance Systems for Transport Airplanes Airborne Supplemental Navigation Equipment Using the Global Positioning System (GPS)
TSO-C 145 Airborne Navigation Sensors Using the Global Positioning System (GPS) Augmented by the Wide Area Augmentation System (WAAS) TSO-C 151a Terrain Awareness and Warning System The FAA technical reports listed below can be obtained from the National Technical Information Service in Springfield, Virginia 22161.
DOT/FAA/CT-96/1 Human Factors Design Guide DOT/FAA/AAR-95/3 FAA Aircraft Certification Human Factors and Operations Checklist for Standalone GPS Receivers
d. Industry documents. Obtain RTCA, Inc. documents listed below from RTCA, Inc., 1140 Connecticut Avenue NW, Suite 1020, Washington, D.C. 20036-4001.
RTCA/DO-160D, Environmental Conditions and Test Procedures for Airborne Equipment RTCA/DO-161A, Minimum Performance Standards - Airborne Ground Proximity Warning Equipment RTCA/DO-178B, Software Considerations in Airborne Systems and Equipment Certification RTCA/DO-200, Preparation, Verification and Distribution of User-Selectable Navigation Data Bases RTCA/DO-200A, Standards for Processing Aeronautical Data RTCA/DO-208, Minimum Operational Performance Standards for Airborne Supplemental Navigation Equipment Using Global Positioning System (GPS)
e. Other document.
The FAA and Industry Guide to Product Certification, January 25, 1999. Available on internet:
http://av-info.faa.gov/dst/CPIGUIDE.pdf
3. DEFINITIONS.
a. Alert: A visual, aural, or tactile stimulus presented to either attract attention or convey information regarding system status or condition, or both.
b. Aural Alert: A discrete sound, tone, or verbal statement used to annunciate a condition, situation, or event.
c. Caution Alert: An alert requiring immediate flightcrew awareness. Subsequent corrective action normally will be necessary.
d. Class A TAWS Equipment: A class of equipment that is defined in TSO-C 15 la. Asa minimum, it will provide alerts for the following circumstances:
Reduced required terrain clearance.
Imminent terrain impact.
Premature descent.
Excessive rates of descent.
Excessive closure rate to terrain.
Negative climb rate or altitude loss after take-off.
Flight into terrain when not in landing configuration.
Excessive downward deviation from an ELS glideslope.
Descent of the airplane to 500 feet above the terrain or nearest runway elevation (voice callout "Five Hundred") during a non-precision approach.
Class A TAWS installations must provide a terrain awareness display that shows either the surrounding terrain or obstacles relative to the airplane, or both. See paragraph 5 to determine which operating rules and aircraft configurations require Class A TAWS equipment.
e. Class B TAWS Equipment: A class of equipment that is defined in TSO CI 5 la. Asa minimum, it will provide alerts forihe following circumstances:
Reduced required terrain clearance.
Imminent terrain impact.
Premature descent.
Excessive rates of descent.
Negative climb rate or altitude loss after take-off.
Descent of the airplane to 500 feet above the terrain or nearest runway elevation (voice callout "Five Hundred") during a non-precision approach.
Class B TAWS installation may provide a terrain awareness display that shows either the surrounding terrain or obstacles relative to the airplane, or both. See paragraph 5 to determine which operating rules and aircraft configurations require Class B TAWS equipment.
f. Controlled Flight Into Terrain (CFIT): An accident or incident in which the airplane, under the flightcrew's control, is inadvertently flown into terrain, obstacles, or water without either sufficient or timely flightcrew awareness to prevent the event, or both.
g. Corrected Altitude: A computed aircraft altitude designed to help ensure optimal operation of the TAWS function through all phases of flight and atmospheric conditions. Corrected altitude can be
computed using pressure altitude, GPS altitude, radio altitude, terrain and runway elevation, etc. data to reduce or eliminate errors potentially induced in corrected barometric altitude by temperature extremes, non-standard altitude conditions, and altimeter miss-sets.
h. Failure: The inability of the equipment or any sub-part of that equipment to perform within previously specified limits.
i. False Alert: A warning or caution that occurs when the design terrain warning or caution threshold of the system is not exceeded.
j. Forward Looking Terrain Avoidance (FLTA): The FLTA function looks ahead of the airplane along and below the airplane's lateral and vertical flight path and provides suitable alerts if a potential CFIT threat exists.
k. Hazard: A state or set of conditions that, together with other conditions in the environment, could lead to an accident.
1. Hazardously Misleading Information (HMI): An incorrect depiction of the terrain threat relative to the airplane during an alert condition (excluding source data).
m. Imminent Terrain Impact: An alert when the airplane is currently below the elevation of a terrain cell along the airplane's lateral projected flight path and it is based upon the vertical projected flight path. The equipment predicts that the terrain clearance will be less than the value given in the RTC column of TSO-C151a, Table 3.1.
n. Nuisance Aiert: An inappropriate alert, occurring during normal safe procedures, that occurs as a result of a design performance limitation of TAWS.
o. Obstacle: A structure that may be in the flight path of the airplane. The obstacle database generally contains the catalog of obstacles of 100 feet or greater in height located within North America and portions of the Caribbean. Caution and warning visual and audio alerts are provided when a conflict with the obstacle is detected.
p. Premature Descent Alert (PDA): A function of the TAWS that uses the airplane's current position and flight path information, as determined from a suitable navigation source and airport database, to determine if the airplane is hazardously below the normal (typically 3 degree) approach path for the nearest runway as defined by the alerting algorithm.
q. Required Terrain Clearance (RTC): The minimum requirements for obstacle or terrain clearance as defined by United States Standard for Terminal Instrument Procedures (TERPS), FAA Order 8260.3B, and the Aeronautical Information Manual (AIM). The TAWS required RTC by phase of flight is shown in TSO-C151a, Table 3.1.
r. Terrain Awareness and Warning System (TAWS): A system that provides the flightcrew with sufficient information and alerting to detect a potentially hazardous terrain situation and so the flightcrew may take effective action to prevent a CFIT event.
s. Terrain Awareness Display: A display of the surrounding terrain or obstacle(s) relative to the airplane.
t. Terrain Database: Terrain or obstacle information stored within a TAWS.
u. Time-shared Display: A display that shows terrain information, plus additional information from other systems [for example, an Electric Flight Instrument System/Navigation Display/Multi-Function Display (EFIS/ND/MFD)].
v. Visual Alert: The use of projected or displayed information to present a condition, situation, or event to the flightcrew.
w. Warning Alert: An alert for a detected terrain threat that requires immediate flightcrew action.
4. BACKGROUND.
a. Regulations. Beginning in the early 1970's, a number of studies looked at the occurrence of "controlled flight into terrain" (CFIT) accidents, where a properly functioning airplane under the control of a fully qualified and certificated crew is flown into terrain (or water or obstacles) with no apparent awareness on the part of the crew.
Findings from these studies indicated that man}' such accidents could have been avoided if a warning device called a ground proximity warning system (GPWS) had been used. As a result of these studies and recommendations from the National Transportation Safety Board (NTSB), in 1974 the FAA required all Part 121 certificate holders (that is, those operating large turbine-powered airplanes) and some Part 135 certificate holders (that is, those operating large turbojet airplanes) to install TSO approved GPWS equipment (§§ 121.360 and 135.153) (39 FR 44439, December 18, 1974).
In 1978, the FAA extended the GPWS requirement to Part 135 certificate holders operating smaller airplanes: turbojet-powered airplanes with 10 or more passenger seats. These operators were required to install TSO-approved GPWS equipment or alternative ground proximity advisory systems that provide routine altitude callouts whether or not there is any imminent danger (§ 135.153) (43 FR 28176, June 29, 1978). This requirement was considered necessary because of the complexity, size, speed, and flight performance characteristics of these airplanes. The GPWS equipment was considered essential in helping the pilots of these airplanes to regain altitude quickly and avoid what could have been a CFIT accident.
Installation of GPWS's or alternative FAA-approved advisory systems was not required on turbopropeller powered (turboprop) airplanes operated under Part 135 because, at that time, the general consensus was that the performance characteristics of turboprop airplanes made them less susceptible to CFIT accidents. For example, it was thought that turboprop airplanes had a greater ability to respond
quickly in situations where altitude control was inadvertently neglected, as compared to turbojet airplanes. However, later studies, including investigations by the NTSB, analyzed CFIT accidents involving turboprop airplanes and found that many of these accidents could have been avoided if GPWS equipment had been used.
Some of these studies also compared the effectiveness of the alternative ground proximity advisory system to the GPWS. GPWS was found to be superior in that it would warn only when necessary, provide maximum warning time with minimal unwanted alarms, and use command-type warnings.
Based on these reports and NTSB recommendations, in 1992 the FAA amended § 135.153 to require GPWS equipment on all turbine-powered airplanes with 10 or more passenger seats (57 FR 9944, March 20, 1992).
After these rules were issued, advances in terrain mapping technology permitted the development of a new type of ground proximity warning system that provides greater situational awareness for flightcrews. The FAA has approved certain installations of this type of equipment, known as the enhanced ground proximity warning system (EGPWS). However, in the proposed final rule, the FAA is using the broader term "terrain awareness and warning system" (TAWS) because the FAA expects that a variety of systems may be developed in the near future that would meet the improved standards contained in the proposed final rule.
The TAWS improves on existing GPWS systems by providing the flightcrew much earlier aural and visual warning of impending terrain, forward looking capability, and continued operation in the landing configuration. These improvements provide more time for theflightcrew to make smoother and gradual corrective action.
In 1998, the FAA issued Notice No. 98-11, Terrain Awareness and Warning System (63 FR 45628, August 26, 1998), proposing that all turbine-powered U.S.-registered airplanes type certificated to have six or more passenger seats (exclusive of pilot and copilot seating), be equipped with an FAA-approved terrain awareness and warning system. On March 23, 2000, the FAA issued Amendments 91-263, 121 273, and 135-75 (65 FR 16736, March 29, 2000) with an effective date of March 29, 2001. These amendments amended the operating rules to require that all U.S. registered turbine-powered airplanes with six or more passenger seats (exclusive of pilot and copilot seating) be equipped with an FAA approved TAWS. See paragraph 5 for more details.
b. TSO-C151a. On November 29, 1999, the FAA issued TSO-C 15la and canceled TSO-C151. The FAA took this action to clarify and correct certain paragraphs and tables that appeared in TSO-C 151. The FAA has determined that the changes to TSO-C 151 a are of a clarifying and corrective nature, and that these changes do not alter the original intent of the airworthiness requirements of the paragraphs or tables being changed. TSO-C 151a prescribes the minimum design standards that a TAWS must meet to be identified with the TSO-C 15la marking. The TAWS described in the TSO is representative of the "next generation" GPWS. In addition to the standards and test procedures required for the FLTA functions, the TAWS incorporates the standards and test procedures for basic GPWS equipment (as defined in 10
TSO-C92c and in RTCA DO-161A). For further in-depth information concerning the TAWS' capabilities, refer to TSO-C 15la.
c. Need for Guidance. The FAA's TSO process is a means of obtaining FAA design and performance approval for an appliance, system, or product. However, the TSO does not provide procedures for installation approval or procedures for design or implementation of an installation. With future rulemaking and heightened interest by manufacturers and operators to equip Part 23 airplanes with TAWS systems that are compliant with TSO-C 151 a, the FAA has recognized the need to establish guidance material for the design and test requirements for the installation of such systems. This AC has been developed as the means for providing such guidance for Part 23 airplanes. This AC describes the airworthiness considerations for designing a TAWS installation. The airworthiness considerations discussed apply only to the interface of the TAWS with other aircraft systems.
5, DISCUSSION.
a. Regulatory Basis. New requirements under 14 CFR Parts 91, 121, and 135 require the installation of the TAWS. Specifically:
(1) § 91.223 states that no person may operate a turbine-powered U.S.-registered airplane configured with six or more passenger seats, excluding any pilot seat, unless that airplane is equipped with an approved terrain awareness and warning system that meets the requirements of Class B equipment of TSO-C151. This section does not apply to: (a) Parachuting operations when conducted entirely within a 50 nautical mile radius of the airport from which such local flight operations began, (b) Fire fighting operations, and (c) Flight operations when incident to the aerial application of chemicals and other substances.
(2) § 121.354 states that no person may operate a turbine-powered airplane unless that airplane is equipped with an approved terrain awareness and warning system, including a terrain awareness display, that meets the requirements for Class A equipment of TSO-C151.
(3) § 135.154 states that no person may operate a turbine-powered U.S.-registered airplane configured with six to nine passenger seats, excluding any pilot seat, unless that airplane is equipped with an approved terrain awareness and warning system that meets the requirements of Class B equipment of TSO-C151. It also states that no person may operate a turbine-powered U.S.-registered airplane configured with 10 or more passenger seats, excluding any pilot seat, unless that airplane is equipped with a terrain awareness and warning system that meets the provisions of Class A equipment ofTSO-C151.
(4) Part 121 and 135 regulations also mandate that GPWS be replaced with a TAWS approved under TSO-C151.
(5) For the compliance schedule, §§ 121.360 and 135.153 have an expiration date of March 29, 2005, for the use of current GPWS systems. U.S. registered airplanes manufactured after March 29, 2002, must be equipped with TAWS. Turbine-powered airplanes manufactured on or before March 29, 2002, must be equipped with TAWS by March 29, 2005.
6. SYSTEM DESCRIPTION. TAWS is intended to provide flightcrews with aural and visual alert aids aimed at preventing a CFIT accident through increased terrain awareness.
a. Class A TAWS equipment as defined in TSO-C151a.
(1) Class A TAWS equipment provides three principal alerting functions. These are:
(a) FLTA function, which includes:
• Reduced required terrain clearance.
• Imminent terrain impact.
(b) PDA function.
(c) Basic GPWS functions, as defined in TSO-C15 la and RTCA DO-161 A, which include:
• Excessive rates of descent.
. Excessive closure rate to terrain.
• Negative climb rate or altitude loss after take-off.
• Flight into terrain when not in landing configuration.
• Excessive downward deviation from and ILS glideslope.
• Descent of the airplane to 500 feet above the terrain or nearest runway elevation (voice callout "Five Hundred").
(2) The Class A TAWS system will require a display. The terrain display and terrainthreat alerting are made possible by the TAWS' acceptance of a variety of input parameters.
Color displays are not required; monochromatic displays have been allowed and will continue to be allowed. These parameters are used in conjunction with a terrain and airport database(s) that reside within the TAWS computer. The Class A TAWS places an airplane symbol on a digital terrain map and applies terrain display algorithms. Terrain mapping information may be provided on either a weather radar (WXR) display, Electronic Flight Instrument System (EFIS) display, or other compatible display screens. Aircraft position information is provided by either the Flight Management Computer (FMC), Global Positioning System (GPS), or other source of positional information that meets the requirements specified in paragraph 7.f. of this AC.
(3) The Class A TAWS for operations under Part 135 (turbine-powered U.S.-registered airplane configured with 10 or more passenger seats, excluding any pilot seat) will be required to incorporate either an integral (internal) GPS or interface with an independent approved GPS for horizontal position information.
b. Class B TAWS equipment, as defined in TSO-C151a.
(1) Class B TAWS equipment provides three principal alerting functions. These are: