AC 20412 DATE 2/19/81 ADVI$ORY CIRCULAR
DEPARTMENT OF TRANSPORTATION Federal Aviation Administration Washington, D.C.
FARGUIDANCE MATERIAL & bject : AIRWORIVINESS AND OPERATIONAL, APPRX??& OF AIRBORNE SYSTEMS '1cD
BE USED IN LIEU OF A GROUND PROXIMITY WARNING SYSTEM(S) (GPWS) 1 PURPOSE. This advisory circular wovides information and guidance I regarding the airmrthiness and operational approval of airborne equipment/system(s) in accordance with Federal Aviation Regulations (FAR) § 135.153, paragraphs (b) and (c).
2 . RELATEDREADINGMATERIAL.
a, Advisory Circular 25-6, Ground Proximity Warninq Systems (GPWS).
Copies may be obtained from the U.S. Department of Transportation, Publications Section (M-443.1), Washington, D.C. 20590.
b -Radio Technical Corrkssion for Aeronautics (.RICA) Document No. D&160, "Ek~vironmental mnditions and Test Procedures for Airborne Electronic/Electrical Equipment and Instruments (current issue)," and RICA Document No. DO-161A, "Minimum Performance Standards - Airborne Ground Proximity Warning Systems/ dated May 27, 1976. Copies of these documents may be obtained from the RICA Secretariat, Suite 655, 1717-H Street, N.W., Washington, D.C. 20006.
c. Technical Standard Order (TSO), TSO-C92a, Ground Proximity Warning Gliae Slope Deviation Alerting Equipment. Copies may be obtained from the 'Federal Aviation Administration, Systems Branch (AWS-130), mm 334, 800 Independence Avenue, S.W.I Washington, D.C. 20591.
3 BACKGROUND. Section 135.153(b) allows the use of alternate equipment in lieu of a Ground Proximity Warning System (GPWS) for certain turbojet operations conducted under FAR Part 135. Section 135.153(b) also requires that the use of any such system must be approved by the Director, Flight Standards Service.‘ Since the Flight Standards LService has reorganized at the Washington level, that approval should now come from the Office of Airmrthiness and/or the Office of Flight Operations.
Initiated by: AbE-13O AFO-210
AC 20- 112 z/19/81 4 GENERAL GUIDELINES The equipment/system to be used in lieu of a GPWS should perform the same basic functions as the GPWS which is to mnvey warnings of excessive closure rates with the terrain and excessive deviations below a glide slopz, 5 AIRWX?I'HINESS CONSIDERATIONS. The airborne equipnent/systems, tiich may be under consideration in lieu of a GPWS, should use the same basic performance standards described in RKA mcment No. lXH61A referenced in paragra@ 3, as modified by this ar3visory circular, and permitted by $j 135.153, paragrraphs (b) and (c).
a. Equipent/System Considerations. 'Ihe mrds "equipment/system" as used herein includes all of the components, subsystems, or units necessary to perform its intended function. For example, the equipent/system could include cockpit controls, display, computing unit, aural warning unit, etc.
The equipment/system need not include the associated sensors for which other performance standards are applicable (e.g., radio altimeter).
(1) Location of Display and Controls. Displays and controls . should be visible to and usable by each pilot tiile seated at his duty station if the equipment is to be operated by the pilots.
(2) Control(s) Considerations. -
(i) Controls Fklich are not normally adjusted in flight need not be readily accessible to the flightcrew.
(ii) Controls should be arranged to wovide adequate protection against inadvertent turnoff.
(iii) The operation of controls intended for use during flight, _ in all possible combinations and sequences, should not result in a condition whose presence or continuation muld be detrimental to the continued performance of the equipnent/system.
(3) Failure Protection. Any plrobable failure of the equipent/system should not derogate the normal operation of equipment connected to it nor should normal operation result in failure or degraded performance of interfaced equipment. Likewise, the failure of interfaced equipent should not render the equipent/system inoperative.
(4) Failure Monitoring and/or Self-Test. Failure mornitoring and/or a self-test should be used to provide a psitive indication of status or cr>nditions.
(5) Unwanted/False Warnings. ?he equipTlent/system should be designed to minimize unwanted or false warnings.
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(6) Environmental Conditions. !Ihe equipment/system should be . . . capable of performing its mtended function over the environmental ranges expected to be encountered in actual operation.
(7) Aircraft Electrical Power Source. The equipnent/system should be installed so that it receives electrical power from a bus that provides maximum reliability of operation without jeopardizing essential or emergency loads assigned to that bus.
b Demonstration of Performancea An applicant for approval of the * equip-n&/system installation should show that performance can be demonstrated by a combination of ground and flight evaluations:
(1) Ground Evaluation. After installation, an operational/functional check should be performed to demonstrate mpatibility betwen the equipnent/system and the aircraft electrical/electronic systems, al.1 normal operating functions are exercised, and any emergency/failure anditions expected maybe observti.
(2) Flight Evaluation. The equipent should be flight ev&luated to determine that the-and installation criteria are met. All nw>des of operation should be functionally checked and verified. Airplane Flight Manual procedures should be evaluated, including abnormal and emergency procedures if applicable.
c. Airplane Flight Manual. The Airplane Fliqht Manual should mntain the following information (see S 135.153, paragraphs (c)(l) and (2) for reqirements):
(1) Normal wocedures for operating the equipent.
(2) Equipment operating limitations.
(3) Emergency/abnormal operating procedures.
d 0 Aimrthiness Approval. - Applications for approval will be . coordinated with the Office of Airmrthiness.
6 uied OPERATIONAL CONSIDERATIONS. Section 135.153(b) requires that a system in lieu of a GFWS be capable of conveying warnings of excessive closure rates with terrain, and any deviations below glide slope by visual and aural means. Those requirements are basic. It is anticipated that the equipnent/system submitted for approval for use under S 135.153(b) may also combine several other functions within the stiitted systems (e.g., aural .
callouts of altitude below 1000 feet, landing-gear-not-down warnings, etc.). Consideration of these other warnings and indications is important but the basic requirements of S 135.153(b) should not be cwnpromised. The operational evaluation of a system should determine that it will reliably and consistently perform the minimum basic functions. Factors to consider Par 5 3
AC 20-112 2/l9/81 vary in accordance with the equipment/system under review but should include the following concepts:
a. Flightcrew Information. The equipent/system should prrovide the flightcrew with audible and visual information which will alert the flightcrew to take the proper action to prevent inadvertent collision with the terrain caused by: unintentional close prroximity to ground, excessive closure rates to terrain, negative climb rate after takeoff, and excessive downward deviation from an Instrment Landing System Glide Slope.
(1) Aural&sual Information. Distinctive aural and/or visual informationshould be provided to warn of each condition in paragraph 7.a.
The aural warning should consist of mrds or sounds to wand the attention of the flightcrew to the situation in time to avoid inadvertent collision with the terrain. The equipment/system should be designed to minimize distracting audible signals where no threat to inadvertent ground hazard exists. The visual warning should be distinctive under all normal lighting conditions and mmensurate with other cockpit warnings. .M Aural/visual warning methods should be mpatible with the user's flight procedures.
(2) Deactivation Capability. Means to deactivate the warning . . indications may be provided for fllghtcrew use in planned abnormal and emergency conditions.
(3) Glide Slope Alert. An alert should be given at least by the time the aircraft is 1.5 dots below glide slope. A system that gives an alert tien an aircraft is less than 1.5 dots below a glide slope is not acceptable. Where a decision height is used as a parameter@ the glide slope alert may be inhibited tien below decision height.
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(i) If glide slope alerting is deactivated, it should be automatically reactivated for the next approach.
(ii) !%e glide slope deviation alert should consist of the aural annunciation "Glide Slope" (or other acceptable annunciation). An aural warn ing related to dltitude should take prrecedence Over this alert.
b Flight Sumnary Report. A review of a surmnary of any flight experience that could vovide data on the operational reliability and accuracy should be conducted. Pilot amen& should be reviewed, if available.
c. Inflight Evaluation. An inflight evaluation of the equipent/ system should be anducted to observe performance of the equipment in the " four ties mentioned in paragraph 7 .a. Such an evaluation should include observation of the system at other than optimum conditions (i.e., rough terrain on final approach, performance during circling approaches, etc.).
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d. Operations Manual Evaluation. The operational evaluation should . include a review of proposed @era s Manual revisions emapassing equipnent/system description and operation. Proposed revisions to the Minimum Fquipent List should also be considered, if approplriate. - 7 l DISCUSSION.
a. Requests for approval of an equipent/system should be sent directly to the appropriate regional office for evaluation.
b. Approval of the equipment/systems are granted by letter, from the Office of Airwxthiness and the Office of Flight @errat ions, based on the
- region's evaluation report and recommendations.
(Jbseph A. Pontecorvo "Acting Director of Airworthiness Director of Flight Operations Par 6