Appendix A A-12 A.6.21 Horizontal Miss Distance (HMD). The horizontal range between two aircraft at the CPA.
A.6.22 Hybrid Surveillance (HS). Combined use of active and passive surveillance to update an ACAS track.
A.6.23 Initial Type Certificate (TC)/Supplemental Type Certificate (STC) (as related to ACAS).
The first FAA ACAS airworthiness approval in accordance with a TC or an STC of any one or combination of the following components: an ACAS processor (computer), a directional antenna, and/or a Mode S transponder.
A.6.24 Intruder. A n aircraft that has satisfied the ACAS TA generation criteria.
A.6.25 Maintenance Review Board (MRB). An FAA board responsible for establishing maintenance requirements for a specific aircraft type. MRB requirements are usually formulated in conjunction with information provided by the manufacturer and prospective operators through industry working groups. Responsible Flight Standards offices apply MRB requirements in reviewing and approving the maintenance program of an air carrier.
A.6.26 Master Minimum Equipment List (MMEL). An FAA document listing stipulation that may provide authorization for the continuation of flight beyond a terminal point with certain inoperative equipment. AED develops MMELs in conjunction with an FOEB established for each aircraft type. FAA MMELs serve as the basis for an operator to develop specific MELs applicable to its particular aircraft and operational requirements.
A.6.27 Mode A. ATCRBS S SR equipment or mode of operation that replies to interrogations with a 4-digit transponder code with 4,096 possible codes (non-altitude reporting).
A.6.28 Mode C. ATCRBS SS R equipment or mode of operation that replies to interrogations with aircraft pressure altitude information.
A.6.29 Mode S. Mode Select (S), SS R equipment, or mode of operation that replies to interrogations with transponder code, aircraft pressure altitude information, a discrete address, and other aircraft information.
A.6.30 Multiple Threat Encounter. An e ncounter involving two or more threats against own-ship being processed simultaneously by the ACAS.
A.6.31 National Airspace System (NAS). The common network of U.S. airspace; air navigation facilities; equipment and services; airports or landing areas; aeronautical charts, information, and services; rules, regulations, and procedures; technical information, human resources, and material; and system components shared jointly with the military.
A.6.32 National Simulator Program (NSP). Program consisting of simulator evaluation specialists responsible for evaluating FSTDs to aid the POI in approving use of a specific FSTD in a training program.
Appendix A A-13 A.6.33 Other Traffic. A n aircraft that is more than 6 nautical miles (NM) laterally or more than 1,200 feet vertically from own-ship.
A.6.34 Passive Surveillance. The use of ADS-B Out pos ition messages to update the ACAS track of other aircraft.
A.6.35 Pressure Altitude. The height above a Standard Datum Plane (SDP), a theoretical level where the weight of the atmosphere is 29.92 inches of mercury (inHg)/1013.25 millibars (mb). Aircraft transponders transmit and ACAS uses pressure altitude so that ACAS can function correctly with relative altitude between aircraft regardless of the barometric scale setting of the altimeter. When an aircraft is below Flight Level (FL) 180, ATC automation corrects the pressure altitude received from the transponder for nonstandard pressure to display the estimated indicated altitude of the aircraft to the controller.
A.6.36 Principal Inspector (PI). Refers to one of the following three FAA inspectors who is selected as primary for an air carrier:
A.6.36.1 Prin cipal Avionics Inspector (PAI). The FAA inspector responsible for overseeing all avionics issues relative to a specific operator, including input on training programs, OpSpecs, MEL requests, etc.
A.6.36.2 Principal Maintenance Inspector (PMI). The FAA inspector responsible for overseeing all maintenance issues relative to a specific operator, including input on training programs, OpSpecs, MEL requests, etc.
A.6.36.3 Principal Operations Inspector (POI). The FAA inspector responsible for overseeing all operational issues relative to a specific operator, including training programs, OpSpecs approval, MEL approval requests, etc.
A.6.37 Proximate Traffic. Tr affic shown on the traffic display that is within 6 NM laterally and 1,200 feet vertically of own-ship that does not meet the threshold for a TA or an RA.
A.6.38 Relative Altitude. The d ifference in altitude between own-ship and another aircraft. The value is positive when the other aircraft is higher and negative when the other aircraft is lower.
A.6.39 Resolution Advisory (RA). Aura l voice and display information provided by ACAS II to a flightcrew, advising that a particular maneuver should or should not be performed to attain or maintain minimum safe vertical separation from a threat aircraft.
A.6.39.1 Altitud e Crossing RA. An RA that directs a flightcrew to cross through the altitude of a threat aircraft to achieve safe vertical separation.
A.6.39.2 Coordinated Crossing RA. Initial RA coordinated between aircraft operating ACAS II and that direct the aircraft to cross in altitude.
Appendix A A-14 A.6.39.3 Corrective RA. An RA that advises the flightcrew to either deviate from current vertical speed, such as climb when the aircraft is level, or to maintain an existing climb or descent rate.
A.6.39.4 Increase Rate RA. An RA that is issued after an initial climb or descend RA that indicates additional climb or descent rate is required to achieve safe vertical separation. An increase rate RA requires a climb or descent rate of 2,500 fpm.
A.6.39.5 Initial RA. First RA generated during an encounter.
A.6.39.6 Preventive RA. An RA that requires a flightcrew to avoid certain deviations from current vertical rate, such as a do not climb RA when the aircraft is level.
A.6.39.7 Reversal RA. An RA that indicates a change in the direction previously generated by ACAS II and that is required to achieve safe vertical separation
(e.g., an initial descend RA that reverses to a climb RA).
A.6.39.8 Subsequent RA. A modified RA generated during an encounter after the initial RA but before a “Clear of Conflict” annunciation. Subsequent RAs may be weakened, strengthened, or reversed.
A.6.39.9 Weakened RA. An initial corrective RA that changes to an RA calling for a return to level flight because ACAS II has determined that safe vertical separation is projected (e.g., a climb RA weakens to a do-not-descend advisory once the desired vertical separation has been achieved).
A.6.40 Sense. A direction that an RA may take (either cli mb or descend) relative to the existing flight path of own-ship.
A.6.41 Significant ACAS Events. Si gnificant ACAS events are those that meet any one of the following guidelines:
A.6.41.1 Altitu de Excursion. There is an altitude excursion of more than 1,000 feet from an assigned level altitude.
A.6.41.2 Coordinated Crossing RA. ACAS II generates a coordinated crossing RA.
A.6.41.3 Descent RA. ACAS II generates a descent RA when own-ship is below 1,000 feet AGL.
A.6.41.4 Performance. ACAS is suspected of not performing as designed.
A.6.41.5 Reversal RA. ACAS II generates a reversal RA.
A.6.41.6 Loss of Standard Air Traffic Control (ATC) Separation. There is a loss of standard ATC separation resulting from compliance with an ACAS II-generated RA.
Appendix A A-15 A.6.42 Squitter. Spontaneous transmission generated by Mode S transponders a nd ADS-B transmitters.
A.6.43 Standard Datum Plane ( SDP). A theoretical level where the weight of the atmosphere is
29.92 inHg/1013.25 mb.
A.6.44 Supplemental Type Certificate (STC). An FAA certificate attesting to the fact that modification to the respective aircraft, engines, or other components meet 14 CFR airworthiness requirements.
A.6.45 Tau ( τ). Greek symbol representing the time to CPA.
A.6.46 Traffic Alert and Collision Avoidance System (TCAS) I and II. See ACAS I and ACAS II.
A.6.47 TCAS Operational Performance Assessment (TOPA). Program to characterize and assess the performance of ACAS in the U.S. NAS and, when appropriate, make recommendations to improve operational performance.
A.6.48 Threat. An aircraft that has satisfied the ACAS II RA generation criteria.
A.6.49 Track. Estimated position and velocity of a single aircraft based on correlated surveillance data reports.
A.6.50 Traffic. Ai rcraft with an operating transponder capable of being tracked and displayed by an aircraft operating ACAS.
A.6.51 Traffic Advisory (TA). Aural voice and display information provided by ACAS to a flightcrew, identifying the location of nearby traffic that meets certain minimum separation criteria.
A.6.52 Type Certificate (TC). An FAA certificate attesting to the fact that the respective aircraft, engines, or other components meet 14 CFR airworthiness requirements.
A.6.53 Vertical Miss Distance (VM D). The relative altitude between own-ship and displayed aircraft at CPA.
Appendix B B-1 APPENDIX B. SAMPLE ACAS GROUND AND FLIGHT TRAINING PROGRAM B.1 Introduction. This appendix provides a set of training standards for ACAS flightcrew training. The information contained in this appendix related to Traffic Advisories (TA) is also applicable to ACAS I users. Training standards are divided into areas of instruction required for ground training (academics) and the performance objectives for the maneuvers required in flight training.
B.2 ACAS II Ground Training. ACAS II ground training should cover, in general terms, ACAS II theory to the extent appropriate to ensure proper operational use. Aircrews should understand basic concepts of ACAS II logic, Closest Point of Approach (CPA), time to CPA (represented by the Greek symbol tau (τ)), and altitude separation thresholds for the issuance of Resolution Advisories (RA), as well as the relationship between displayed traffic information and issuance of TAs and RAs. The ground training program should address the following:
B.2.1 T heories of Operation .
B.2.1.1 Objective. Demonstrate knowledge of how ACAS II functions.
B.2.1.2 Criteria. The pilot must demonstrate an understanding of the following functions:
1. S urveillance:
a. ACAS II interrogates other aircraft operating a transponder within a nominal range of 14 nautical miles (NM).
b. ACAS II surveillance range will be reduced in geographic areas with a large number of ground interrogators and/or aircraft operating ACAS II. A minimum surveillance range of 4.5 NM is guaranteed for airborne ACAS II aircraft.
2. C ollision Avoidance:
a. TAs can be generated against any aircraft operating a transponder even if the aircraft is non-altitude reporting (and own-ship is below 15,500 feet pressure altitude).
b. RAs can be generated only in the vertical plane and only against aircraft that are reporting altitude.
c. RAs generated against a threat aircraft operating ACAS II are coordinated to ensure complementary RAs are generated.
d. Failure to respond to an RA deprives own-ship of the collision protection provided by its ACAS II. In encounters where both aircraft are operating TA/RA mode, failure to respond to an RA by one aircraft restricts the RA maneuvers available to the other ACAS II-equipped aircraft.
Appendix B B-2 B.2.2 Advisory Thresholds.
B.2.2.1 Objective. Demonstrate knowledge of the criteria for issuing TAs and RAs.
B.2.2.2 Criteria. The pilot should be able to demonstrate an understanding of the methodology used by ACAS II to generate TAs and RAs and the general criteria for the issuance of these advisories, including the following:
1. ACAS II advisories are typically based on time to CPA. The separation standards provided by Air Traffic Control (ATC) are different from ACAS TA and RA thresholds.
2. In encounters with a slow closure rate, ACAS II advisories will be generated based on distance.
3. The timing of TA and RA generation varies with altitude. The threshold for TA and RA is longer at higher altitudes:
a. TAs generally occur 8 to 15 seconds prior to an RA.
b. RAs generally occur from 15 to 35 seconds before the projected CPA.
c. RAs are chosen to provide the desired Vertical Miss Distance (VMD) at CPA. As a result, RAs may generate a climb or descent through the altitude of the threat aircraft.
B.2.3 ACAS II Limitations.
B.2.3.1 Objective. To verify the pilot is aware of the limitations of ACAS II.
B.2.3.2 Criteria. The pilot should demonstrate a knowledge and understanding of the ACAS II limitations, including the following:
1. ACAS II may neither track nor display aircraft that are not operating a transponder, including transponders that have failed.
2. ACAS II will automatically fail if the input from the barometric altimeter, radio altimeter, or transponder is lost.
3. In some installations, the loss of information from other onboard systems, such as an Inertial Reference System (IRS) or Attitude and Heading Reference System (AHRS), may result in an ACAS II failure. Individual operators should ensure their flightcrews are aware of what types of aircraft system failures will result in an ACAS II failure.
4. Some aircraft within 380 feet Above Ground Level (AGL) (nominal value) will not be displayed. If ACAS II can determine that an aircraft below this altitude is airborne, it will display it.
5. ACAS II may not display all proximate aircraft operating a transponder in areas of high-density traffic.
Appendix B B-3
6. Because of design limitations, the bearing displayed by ACAS II is not sufficiently accurate to support the initiation of horizontal maneuvers based solely on the traffic display.
7. Because of design limitations, TCAS II may neither display nor generate an advisory against aircraft with a vertical speed of more than 10,000 feet per minute (fpm).
8. A stall warning, Terrain Awareness and Warning System (TAWS) “Pull Up” alert, or windshear warning takes precedence over a TA or an RA. When either a stall warning, TAWS “Pull Up” alert, or windshear warning is active, TA and RA aural annunciations will be inhibited, and ACAS II will automatically switch to the TA-ONLY mode of operation.
ACAS II will remain in TA-ONLY mode for 10 seconds after the TAWS “Pull Up” alert or windshear warning is removed.
B.2.4 ACAS II Inhibits.
B.2.4.1 Objective. To verify the pilot is aware of the conditions that certain functions of ACAS II are inhibited.
B.2.4.2 Criteria. The pilot should demonstrate a knowledge and understanding of the various ACAS II inhibits, including the following:
1. Increase descent RAs are inhibited below 1,450 feet AGL.
2. Descend RAs are inhibited below 1,100 feet AGL.
3. All RAs are inhibited below 1,000 feet AGL.
4. All ACAS II aural annunciations are inhibited below 500 feet AGL.
5. The altitudes and configurations that inhibit climb and increase climb RAs. ACAS II can still generate climb and increase climb RAs when operating at the maximum altitude or certified ceiling. Responses to climb RAs while operating at the maximum altitude or certified ceiling are expected to be complied with in the normal manner.
Note: In some aircraft types, climb or increase climb RAs are never inhibited.
B.2.5 Operating Procedures.
B.2.5.1 Pilot Knowledge. The pilot should demonstrate the knowledge required to operate ACAS II and interpret the information presented by ACAS II.
B.2.5.2 Training Topics. This training should address the following topics:
Appendix B B-4 B.2.5.2.1 Use o f Controls.
1. Objective. To verify the pilot can properly operate all ACAS II and display controls.
2. Criteria. The pilot should demonstrate the proper use of controls, including the following:
a. Aircraft configuration required to initiate a self-t est.
b. Steps required to initiate a self-test.
c. Recognizing when the self-test was successful and when it was unsuccessful. When the self-test is unsuccessful, recognizing the reason for the failure and, if possible, correcting the problem.
d. Recommended usage of traffic display range selection. Low ranges are used in the terminal area, and the higher display ranges are used in the en route environment and in the transition between the terminal and en route environment.
e. If available, recommended usage of the above/below mode selector.
Above mode should be used during climb, and below mode should be used during descent.
f. Recognition that the configuration of the traffic display (i.e., range and Above/Below selection) does not affect the ACAS II surveillance volume.
g. Selection of appropriate ranges on the traffic display to increase situational awareness of close-in traffic when an advisory is generated.
h. If available, proper selection of the display of absolute or relative altitude and the limitations of using the absolute display option if a barometric correction is not provided to ACAS II.
i. Proper configuration to display the appropriate ACAS II information without eliminating the display of other needed information.
j. Selection of various ACAS II and transponder operating modes.
B.2.5.2.2 Display I nte rpretation.
1. Objective. To verify a pilot understands the meaning of all information that can be displayed by ACAS II.
2. Criteria. The pilot should demonstrate the ability to properly interpret information displayed by ACAS II, including the following:
a. Other traffic (i. e., traffic within the selected display range that is not proximate traffic, a TA, or an RA).
b. Proximate traffic (i.e., traffic that is within 6 NM and 1,200 feet).
c. Non-altitude reporting aircraft.
Appendix B B-5
d. ADS-B Only TA-ONLY (AOTO) traffic.
e. No-bearing TAs and RAs.
f. Off-scale TAs and RAs. The selected range should be changed to ensure that all available information on the intruder or threat aircraft is displayed.
g. TAs. The minimum available display range that allows the traffic to be displayed should be selected to provide the maximum display resolution.
h. RAs (traffic display). The minimum available display range of the traffic display that allows the traffic to be displayed should be selected to provide the maximum display resolution.
i. RAs. Pilots should demonstrate knowledge of the meaning of the red and green areas, or the meaning of pitch or flight path angle cues displayed on Primary Flight Displays (PFD), RA displays, Head-Up Displays (HUD), etc. For displays using red and green areas, demonstrate knowledge of when the green areas will and will not be displayed.
j. If appropriate, awareness that navigation displays oriented Track-Up may require a pilot to make a mental adjustment for drift angle when assessing the bearing of proximate traffic.
k. ACAS II symbology differences when incorporated with ADS-B In.
B.2.5.2.3 Use of the TA-ONLY Mode.
1. Objective. To verify that a pilot understands the appropriate times to select the TA-ONLY mode of operation and the limitations associated with using this mode.
2. Criteria. The pilot should demonstrate the following:
a. Knowledge of the standard operating procedures for the use of TA-ONLY mode.
b. Reasons for using TA-ONLY mode and situations where the use of TA-ONLY may be desirable.
c. The TA aural annunciation is inhibited below 500 feet AGL. As a result, TAs generated below may not be noticed unless the TA display is included in the routine instrument scan.
B.2.5.2.4 Crew Coordination.
1. Objective. To verify pilots adequately brief other crewmembers on how ACAS advisories will be handled. This portion of the training may be combined with other training, such as Crew Resource Management (CRM).
Appendix B B-6
2. Criteria. Pilots should demonstrate during their preflight briefing the procedures that will be used in responding to TAs and RAs, including the following:
a. Division of duties between the Pilot Flying (PF) and Pilot Monitoring (PM), including a clear definition of who will fly the aircraft during a response to an RA;
b. Expected callouts;
c. Conditions where an RA may not be complied with and who will make this decision; and
d. Communications with ATC.
Note: The operator should specify the conditions under which an RA need not be complied with.
B.2.5.2.5 Reporting Requirements.
1. Objective. To verify the pilot is aware of the requirements for reporting RAs to the controller and other authorities.
2. Criteria. The pilot should demonstrate the following:
a. The use of the standard phraseology in this AC, and
b. Where information can be obtained regarding the need for making written reports when an RA is generated.
B.3 ACAS II Maneuver Training. The scenarios included in the maneuver training should include initial RAs that require a change in vertical speed (corrective RA); initial RAs not requiring a change in vertical speed; maintain rate RAs; altitude crossing RAs; increase rate RAs; reversal RAs; weakened RAs; RAs generated while the aircraft is at a maximum altitude; and multiple threat encounters. The scenarios should also include demonstrations of the consequences of not responding to RAs, slow or late responses, and maneuvering opposite to the direction called for by the displayed RA as follows:
B.3.1 TA Responses.
B.3.1.1 Objective. To verify the pilot properly interprets and responds to TAs.
B.3.1.2 Criteria. The pilot should demonstrate:
1. Proper division of responsibilities between the PF and PM. The PF should continue to fly the airplane and be prepared to respond to any RA that might follow. The PM should provide updates on the traffic location shown on the ACAS II traffic display and use this information to help visually acquire the intruder.
2. Proper interpretation of the displayed information. Both pilots confirm that the aircraft they have visually acquired is the aircraft that has caused the
Appendix B B-7 TA to be issued. Use should be made of all information shown on the display, note being taken of the bearing and range of the intruder (amber circle), whether it is above or below (data tag), and its vertical speed direction (trend arrow).
3. All available information is used to assist in visual acquisition.
4. Unnecessary requests for traffic information are not made following TAs.
5. No maneuvers are made based solely on the information shown on the ACAS II display.
6. When visual acquisition is attained, right-of-way rules are used to maintain or attain safe separation. Unnecessary maneuvers are not initiated. The limitations of making maneuvers based solely on visual acquisition are understood.
B.3.2 RA Responses.
B.3.2.1 Objective. To verify the pilot properly interprets and responds to RAs.
B.3.2.2 Criteria. The pilot should demonstrate the following:
1. Proper division of responsibilities between the PF and PM. The PF should respond to the RA with the correct flight path management techniques, including manual flight operations or effective use of the autoflight system (when ACAS II mode is available). The PM should provide updates on the traffic location, check the traffic display, and monitor the response to the RA. Proper CRM should be used. If standard operating procedures require the Pilot in Command (PIC) to fly all RAs, transfer of aircraft control should be demonstrated.
2. Proper interpretation of the displayed information. The pilot recognizes any threat aircraft causing an RA (red square on the traffic display) and responds appropriately.
3. For RAs requiring a change in vertical speed, initiation of a response in the proper direction is made within 5 seconds of the RA being displayed.
The change in vertical speed is accomplished with an acceleration of approximately 0.25 g to obtain the required vertical rate. ATC is notified of the RA response without delay after initiating the maneuver using the standard phraseology.
4. Recognition of, and the proper response to, modifications to the initially displayed RA.
a. For increase rate RAs, the vertical speed is increased within
2.5 seconds of the RA being displayed. The change in vertical speed is accomplished with an acceleration of approximately 0.35 g.
Appendix B B-8
b. For reversal RAs, the maneuver is initiated within 2.5 seconds of the RA being displayed. The change in vertical speed is accomplished with an acceleration of approximately 0.35 g.
c. For weakened RAs, the vertical speed is modified to initiate a return toward level flight within 2.5 seconds of the RA being displayed. The change in vertical speed is accomplished with an acceleration of approximately 0.25 g.
d. For RAs that strengthen, the maneuver to comply with the revised RA is initiated within 2.5 seconds of the RA being displayed. The change in vertical speed is accomplished with an acceleration of approximately 0.25 g.
5. Recognition of altitude crossing encounters and the proper response to these RAs.
a. For RAs that do not require a change in vertical speed, that the vertical speed needle or pitch angle remains outside the red area on the RA display.
b. For maintain rate RAs, that the vertical speed is not reduced. Pilots should recognize that a maintain rate RA may result in crossing the altitude of the threat aircraft.
c. That if a justified decision is made to not comply with an RA, the resulting vertical rate is not in a direction opposite to the sense of the displayed RA.
d. That the deviation from the current clearance is minimized by leveling the aircraft when the RA weakens, and when “Clear of Conflict” is annunciated, executing a prompt return to the current clearance; and notifying ATC using the standard phraseology as soon as permitted by flightcrew workload after resuming the current clearance.
e. That, when possible, an ATC clearance or instruction is complied with while responding to an RA (e.g., if the aircraft can level at the assigned altitude while responding to a reduce climb or reduce descent RA, it should be done).
f. That when simultaneous conflicting instructions to maneuver are received from ATC and an RA, the RA is complied with, and ATC is notified using the standard phraseology as soon as permitted by flightcrew workload.
g. Awareness that ACAS II is designed to cope with a multiple threat encounter, and that ACAS II can optimize separation by climbing or descending toward one of them (e.g., ACAS II only considers aircraft that it considers a threat when generating an RA. As such, it is possible for ACAS II to generate an RA against one threat that results in a maneuver toward another aircraft that is not classified as a threat. If