2-7 contains system safety assessment standards for the TCAS II system design.
2.2.8 Caution/Warning Lights.
2.2.8.1 You may install discrete caution and/or warning lights that are separate from the traffic display. The purpose of these additional indicators is to annunciate the presence of potentially threatening intruder aircraft at times when the pilot’s attention may be diverted from the primary TCAS display. You can use two different discrete TCAS II annunciators:
2.2.8.1.1 A discrete amber (or yellow) caution annunciator, which indicates the presence of a TCAS II TA. Installation of this discrete caution annunciator is optional. When installed, it must be in each pilot’s primary field of view and be inhibited below 400 feet above ground level (AGL).
2.2.8.1.2 A discrete red warning annunciator that indicates the presence of a TCAS II RA. This red warning must be in each pilot’s primary field of view and be inhibited below 900 feet AGL. An IVSI with a lighted red arc or an alphanumeric message on the electronic attitude display indicator (EADI) is acceptable instead of this discrete warning annunciator.
2.2.8.2 Because of the number of TCAS II advisories expected in service, you should not interface the basic aircraft master caution and warning system with TCAS II caution/warning alerts provided for intruder and threat aircraft. Overuse of the primary aircraft caution and warning system tends to reduce its effectiveness in annunciating non-TCAS II system failures.
2.2.8.3 Discrete visual alerts should remain on until the pilot cancels them or until TCAS II no longer considers the aircraft an intruder or a threat.
2.2.9 Aural Alert Requirements.
2.2.9.1 Annunciate each TCAS II aural alert by a dedicated voice message over a cockpit speaker at a volume adequate for clear understanding at high cockpit noise levels, but not excessively loud at low noise levels. The evaluation includes the case where a flight crew member is wearing a headset, covering the outboard ear when appropriate. In turbo-prop aircraft where the aircrew utilizes headsets via the aircraft audio distribution panel, the aural messages should hold the same acceptable volume and intelligibility during both low and high cockpit noise levels.
2.2.9.2 Annunciate TCAS II TAs by the voice message “TRAFFIC, TRAFFIC” stated once for each TA.
2.2.9.3 Annunciate TCAS II RAs by the following voice messages, as appropriate:
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2.2.9.3.1 “CLIMB, CLIMB”-- climb at the rate depicted by the green (fly to) arc or line on the IVSI or other suitable indicator.
2.2.9.3.2 “DESCEND, DESCEND”-- descend at the rate depicted by the green (fly to) arc or line on the IVSI or other suitable indicator.
2.2.9.3.3 “MONITOR VERTICAL SPEED”-- ensure that vertical speed is out of the illuminated IVSI red arc or line, or other suitable indication.
2.2.9.3.4 “ADJUST VERTICAL SPEED, ADJUST”-- modify the vertical speed to a value within the illuminated green arc or line, or outside the prohibited area on other suitable indications. Only V7.0 TCAS II units provide this aural.
2.2.9.3.5 ”LEVEL OFF, LEVEL OFF” -- reduce vertical speed to zero feet per minute. A green arc or line will be illuminated beginning at zero feet per minute. The system can issue this as the initial RA or as a subsequent RA.
Only V7.1 TCAS II units provide this aural.
2.2.9.3.6 “CLEAR OF CONFLICT”-- range is increasing, and separation is adequate; expeditiously return to the applicable clearance, unless ATC directs otherwise.
2.2.9.3.7 “CLIMB, CROSSING CLIMB, CLIMB, CROSSING CLIMB”-- climb at the rate depicted by the green (fly to) arc or line on the IVSI or other suitable indicator. The aircraft will best achieve safe separation by climbing through the threat’s flight path.
2.2.9.3.8 “DESCEND, CROSSING DESCEND, DESCEND, CROSSING DESCEND”--descend at the rate depicted by the green (fly to) arc or line on the IVSI or other suitable indicator. The aircraft will best achieve safe separation by descending through the threat’s flight path.
2.2.9.3.9 “MAINTAIN VERTICAL SPEED, MAINTAIN”-- maintain the existing climb or descent rate as depicted by the green (fly to) arc or line on the IVSI or other suitable indicator. The aircraft will best achieve safe separation by not altering the existing vertical speed.
2.2.9.3.10 “MAINTAIN VERTICAL SPEED, CROSSING MAINTAIN”-- maintain the existing climb or descent rate as depicted by the green (fly to) arc or line on the IVSI or other suitable indicator. The aircraft will best achieve safe separation by not altering the existing vertical speed and climbing or descending through the threat’s flight path.
2.2.9.4 The TCAS II must provide the following voice messages to annunciate enhanced TCAS II maneuvers when the initial RA does not provide sufficient vertical separation. The tone and inflection must connote increased urgency.
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2.2.9.4.1 “INCREASE CLIMB, INCREASE CLIMB”--climb at the rate depicted by the green (fly to) arc or line on the IVSI or other suitable indicator.
Received after “CLIMB” advisory, and indicates the aircraft needs to climb faster to achieve safe vertical separation from a maneuvering threat aircraft.
2.2.9.4.2 “INCREASE DESCENT, INCREASE DESCENT”--descend at the rate depicted by the green (fly to) arc or line on the IVSI or other suitable indicator. Received after “DESCEND” advisory, and indicates the aircraft needs to descend faster to achieve safe vertical separation from a maneuvering threat aircraft.
2.2.9.4.3 “CLIMB - CLIMB NOW, CLIMB - CLIMB NOW”--climb at the rate depicted by the green (fly to) arc or line on the IVSI or other suitable indicator. Received after a “DESCEND” RA and indicates the aircraft needs to reverse its vertical direction to achieve safe vertical separation from a maneuvering threat aircraft.
2.2.9.4.4 “DESCEND - DESCEND NOW, DESCEND - DESCEND NOW”--- descend at the rate depicted by the green (fly to) arc or line on the IVSI or other suitable indicator. Received after a “CLIMB” RA and indicates the aircraft needs to reverse its vertical direction to achieve safe vertical separation from a maneuvering threat aircraft.
2.2.9.4.5 The system must inhibit all TCAS II aural alerts below 400 ft AGL while descending and below 600 ft AGL while climbing.
2.2.9.4.6 The system must aurally annunciate both increases and decreases in the threat level.
2.2.9.4.7 In general, we will evaluate other messages that are clear and unambiguous on an individual basis. Do not use messages that contain negatives (for example, “DON’T CLIMB”).
2.2.10 Failures, TCAS and Transponder. 14 CFR Sections 25.1302, 25.1309(c), and 25.1322 contain requirements for flight crew alerting. For purposes of compliance with Sec.
25.1322(b) with regard to a TCAS II and or Mode S transponder system, accident experience has shown that loss of TCAS II or Mode S transponder functionality requires flight crew awareness and may require subsequent flight crew response. This response includes checking for proper TCAS II system settings and operation as well as Mode S transponder settings and operation. Therefore, for new installations of TCAS II and/or transponders, to meet Sec. 25.1322 requirements for the TCAS II installation, the following failures must be annunciated in yellow/amber in the pilots’ primary field of view, and are recommended to be interfaced with the aircraft’s master caution and warning system to provide alerts for:
2.2.10.1 A transponder failure.
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2.2.10.2 Transponder in the standby mode.
2.2.10.3 A TCAS II failure.
2.2.10.4 TCAS II in the standby mode.
Note 1: Guidance for compliance with 14 CFR Sections 25.1302, and 25.1322 is contained in AC 25.1302-1, Installed Systems and Equipment for Use by the Flightcrew and AC 25.1322-1, Flightcrew Alerting.
Note 2: For the purposes of this subsection, a new installation is considered to be: 1) Installation of a Mode S transponder in an aircraft that does not currently have one fitted; 2) Installation of a TCAS II system in an aircraft that does not currently have one fitted or 3) A new aircraft, i.e. one that has not received a type certificate.
2.3 Airworthiness Considerations.
2.3.1 Certification Program. This AC will guide your installation of TCAS II V7.0 or V7.1 systems and Mode S transponder systems. TCAS II system installations include the TCAS, the Mode S system, antennas, control panel and display components. Mode S transponder installations include the Mode S transponder, antennas, and control panel.
These components are all certified initially as a single installed system with a defined configuration. Any change to the defined configuration requires either a new Initial Approval or a Follow-On Approval. The system displays information and provides advisories in a number of formats. The degree of system integration to perform these functions is extensive and as a result, you must direct your program toward airworthiness approval through the type certification or supplemental type certification process.
2.3.2 Certification plan. Develop a comprehensive certification plan. Include how you’ll comply with the applicable certification requirements, and list the substantiating data and necessary tests in your plan. Include a system description and an estimated time schedule. A well-developed certification plan will be of significant value both to you (the applicant) and the appropriate FAA certification office.
2.3.3 Equipment Compatibility Requirements.
2.3.3.1 Make an evaluation to show that the TCAS II system communicates with other manufacturers’ approved TCAS II systems. Include a TCAS II to TCAS II coordination demonstration, or equivalent, with at least one other manufacturer’s approved TCAS II system in your evaluation. If you can show for a specific design that communication link failures are no more hazardous than encountering a Mode C intruder, then these tests are not necessary. Also, after completing mature bench tests, future certification experience may show that these tests are no longer necessary. Submit evidence to show that you performed TCAS/transponder interoperability bench tests using the same TCAS/transponder pairing (the same part
2-11 numbers) as the installation seeking certification. You can satisfy interoperability bench tests by either of the following:
2.3.3.2 Conduct the following RTCA/DO-185A or RTCA/DO-185B tests as applicable, using the actual TCAS unit and Mode S transponder seeking certification:
2.4.2.2.3.1 2.4.2.2.3.2, 2.4.2.2.4.1, 2.4.2.2.4.2.1, 2.4.2.2.4.2.3, 2.4.2.2.4.2.5, 2.4.2.2.4.2.6, 2.4.2.2.4.2.7, 2.4.2.2.4.2.8, and, 2.4.2.2.5.
2.3.3.3 Conduct the following tests in RTCA/DO-181E as applicable, Minimum Operational Performance Standards for Air Traffic Control Radar Beacon System/Mode Select (ATCRBS/Mode S) Airborne Equipment, using the actual TCAS unit and Mode S transponder seeking certification:
Procedure 30, Procedure 31 a-d, Procedure 32a-c and d (1 & 2), Procedure 34, Procedure 36 a and c, and, Procedure 37 a and b.
2.3.3.4 In addition, conduct the following RTCA/DO-181E tests as applicable, using a TCAS simulator coupled with the actual Mode S transponder:
Procedure 31e, Procedure 32d (3-16), Procedure 33, Procedure 35, Procedure 36b,
2-12 Procedure 37c and, Procedure 38.
Note: These equipment compatibility requirements are only necessary for the initial approval.
2.3.4 Aircraft Performance Considerations. Use paragraphs 2.3.4 through 2.3.5 and Table 1 of this AC to help you evaluate the need to inhibit TCAS II CLIMB and/or INCREASE CLIMB RAs resulting from inadequate aircraft climb performance. The collision avoidance maneuvers the TCAS II commands as RAs assume an aircraft’s ability to safely achieve them. If it’s likely the required response to CLIMB and INCREASE CLIMB RAs are beyond the performance capability of the aircraft, then TCAS II must know beforehand so it can change strategy and issue an alternative RA. The aircraft interface and discrete settings relative to altitude and/or aircraft configuration must provide these performance limits to TCAS II. However, carefully consider the need to inhibit TCAS II CLIMB or INCREASE CLIMB RAs since the alternative RAs may not provide the optimum solution to the encounter. Inhibiting these RAs will increase the likelihood of TCAS II:
2.3.4.1 Issuing crossing maneuvers (crossing through an intruder’s altitude), thus increasing the probability that an RA may be thwarted by the intruder maneuvering,
2.3.4.2 Causing an increase in DESCEND RAs at low altitude, and
2.3.4.3 Providing no RAs if below the descend inhibit altitude of 1200 feet AGL during takeoff and 1000 feet AGL on approach.
2.3.5 Evaluating Aircraft Performance. The configuration interface may need switches or sensors, besides the basic airplane flap position switches, to prevent unnecessary TCAS II inhibits. For example, if you need to inhibit CLIMB RAs for the maximum takeoff flap setting only, and no switch exists to sense that position, install an additional switch instead of simply using one that may exist at lesser flap angle settings.
2.3.5.1 Because TCAS II can only accept a limited number of inputs related to airplane performance, it’s not possible to automatically inhibit CLIMB and INCREASE CLIMB RAs in all cases where it may be appropriate to inhibit such RAs. In these cases, TCAS II may command maneuvers that may significantly reduce stall margins or result in stall warnings.
Conditions where this may occur include bank angles greater than 15 degrees, weight/altitude/temperature combinations outside the envelope shown in Table 1, initial speeds below those shown in Table 1, one engine inoperative, leaving the aircraft configuration fixed for climb RAs on landing transition to go-around, and abnormal configurations such as landing gear not retractable. Provide information concerning this aspect of TCAS in the airplane flight manual (AFM) or airplane flight manual supplement (AFMS) so that flight crews may take appropriate action.
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2.3.5.2 Aircraft configuration, true airspeed available during initial climb (to safely trade for climb rate if needed), and the initial airspeed margin from the current stall speed all significantly affect an aircraft’s low altitude climb capability during takeoff, approach, or landing.
2.3.5.2.1 Table 1, Conditions 1 through 3 apply to the takeoff and initial climb configuration analysis.
2.3.5.2.2 Table 1, Conditions 4 through 6 apply to the approach flap configuration analysis when operating in the terminal area with the flaps set at less than the landing flaps.
2.3.5.2.3 Table 1, Conditions 7 through 9 apply to the landing flight regime analysis. To be consistent with normal operation, indicate in the AFM or AFMS that when a climb RA occurs with the aircraft in the landing configuration, the pilot should initiate the normal go-around procedure when complying with the TCAS II RA. Therefore, you can assume that the flaps are retracted from the landing position to the go-around position when evaluating Table 1, Conditions 7 through 9.
2.3.5.3 To prevent very unlikely combinations of events, such as weight/altitude/temperature limiting conditions, in conjunction with low airspeed, high drag configurations, and unusual encounter geometries causing climb inhibits when the aircraft’s performance is more than adequate, Table 1 places the entry and exit conditions and RAs into two classes of encounters.
2.3.5.3.1 Maneuvers A and B represent reasonably severe combinations of entry conditions and RAs, and restricts the exit conditions to an airspeed of
1.2VS1 (or 1.13VSR1 for those airplanes that use reference stall speed (VSR) in lieu of stalling speed (VS)).
2.3.5.3.2 Maneuver C represents reasonably worst-case combinations of entry conditions and RAs, and this very unlikely event may require flying near stall warning conditions through the recovery.
2.3.5.3.3 Airspeeds between 1.2VS1 (or 1.13VSR1 for those airplanes that use reference stall speed (VSR) in lieu of stalling speed (VS)) and stall warning represent a range of usable airspeeds that the flight crew can trade for climb performance (the same as current wind shear recovery procedures recommend) for evaluation of this low probability event. The altitude/temperature envelope represents a range of values that exist at busy airports in the continental United States. Operations outside this envelope may require special crew procedures if the normal AFM weight, altitude, temperature, and configuration limitations are not sufficiently compensating, such as operation at Mexico City.
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2.3.5.4 For those airplanes that may routinely operate at low climb airspeeds during the clean configuration, enroute phase of flight, such as propeller commuter airplanes, consider providing a discrete to the TCAS II based on airspeed. Such an input, derived from a TCAS II interface system, would provide for CLIMB or INCREASE CLIMB RA inhibits when the airplane is in the clean configuration and operating below a certain airspeed. We consider such a scheme appropriate instead of an across-the-board inhibit for the clean configuration regardless of flight regime (which does not provide the best overall level of safety for other configurations).
2.3.5.5 Excess power (propeller-driven) or excess thrust (turbojet) and true airspeed (that may be available to safely trade for climb rate) are also significant factors in aircraft’s climb capability when operating at or near maximum approved operating altitude. The system should not inhibit climb RAs if the aircraft has adequate performance available or because it may exceed its maximum certificated altitude by several hundred feet during an RA. Table 1, Conditions 10 and 11, shows configurations that you should evaluate in this flight regime. If the aircraft has approval for significant alternative configurations, (such as spare engine pod and gear down operation,) then the initial airspeed you use for the analysis should be appropriate for them. In the analysis of the aircraft’s ability to accelerate and return to the initial speed and altitude following the RA, an undershoot of approximately 200 feet is permissible.
2.3.5.6 In icing conditions, the aircraft limited performance weights are lower, and sometimes the operating speeds are higher, to account for icing system bleeds and residual ice drag on the unprotected surfaces. Therefore, the capability to perform the TCAS II maneuvers remains essentially unchanged, eliminating the need to provide additional RA inhibits under these circumstances. However, if a particular aircraft design shows marginal capability to operate in the icing environment, consider additional RA inhibits enabled by icing system activation.
2.3.5.7 If Table 1, Maneuver A causes operation at airspeeds below the minimum, then inhibit the CLIMB RA. If Table 1, Maneuver B or C causes operation at airspeeds below the minimum, then inhibit the INCREASE CLIMB RA. However, early recovery of 1 to 2 seconds is of little or no consequence on the collision avoidance maneuver and the system will achieve a higher overall level of safety if it does not provide inhibits under these circumstances, as this AC has previously discussed in paragraph
2.3.4.
2-15 Table 1. Maneuvers
CONDITION FLIGHT REGIME WEIGHT
ALTITUDE,
TEMPERATUR E1 THRUST FLAPS GEAR INITIAL AIRSPEED2 MINIMUM AIRSPEED2 MANEUVER3 1 Takeoff Part 25 climb limit Maximum rated takeoff All takeoff Up V2+204 1.2VS15 thru RA A 2 Takeoff Part 25 climb limit Maximum rated takeoff All takeoff Up V2+204 1.2VS15 thru RA B 3 Takeoff Part 25 Climb limit Maximum rated takeoff All takeoff Up AFM allengine takeoff speed6 15° bank to stall warning7 thru recovery C 4 Approach Part 25 Climb limit Spin up to max go-around thrust during maneuver from thrust for level flight Less than landing Up 1.6VS1 1.2VS15 thru RA A 5 Approach Part 25 Climb limit Spin up to max go-around thrust during maneuver from thrust for level flight Less than landing Up 1.6VS1 1.2VS15 thru RA B 6 Approach Part 25 Climb limit Spin up to max go-around thrust during maneuver from thrust for level flight Less than landing Up, or down to up Min.
maneuver speed from training procedures 15° bank to stall warning7 thru recovery C
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CONDITION FLIGHT REGIME WEIGHT
ALTITUDE,
TEMPERATUR E1 THRUST FLAPS GEAR INITIAL AIRSPEED2 MINIMUM AIRSPEED2 MANEUVER3 7 Landing, Transition to Go-Around at RA Part 25 Climb limit Spin up to max go-around thrust during maneuver from thrust required for 3° glideslope Transition from landing flap to goaround flap Down to up VREF + 10 1.2VS15 thru RA A 8 Landing, Transition to Go-Around at RA Part 25 Climb limit Spin up to max go-around thrust during maneuver from thrust required for 3° glideslope Transition from landing flap to goaround flap Down to up VREF + 10 1.2VS15 thru RA B 9 Landing, Transition to Go-Around at RA Part 25 climb limit Spin up to max go-around thrust during maneuver from thrust required for 3° glideslope Transition from landing flap to goaround flap Down to up VREF + airspeed addition from training procedures 15° bank to stall warning7 thru recovery C 10 En Route Critical Wt/Alt giving 0.3g to buffet onset Thrust for level flight increased to max continuous, if required Up Up Long-range cruise Higher of
1.2VS5 if defined or buffet onset A 11 En Route Critical Wt/Alt giving 0.3g to buffet onset Thrust for level flight increased to max continuous, if required Up Up Long-range cruise Higher of
1.2VS5 if defined or buffet onset B
2-17 Notes:
1. Weight = Lesser of climb limit or structural; Airport Pressure Altitude = sea level to 5300 ft; Temperature = ISA ± 50 °F; Evaluate conditions 1 through 3 700 ft above airport; evaluate conditions 4 - 9 1700 ft above airport.
2. For those airplanes that use reference stall speed (VSR) in lieu of stalling speed (VS), replace 1.2 VS1 with 1.13 VSR1, 1.2VS with
1.13VSR and 1.6 VS1 with 1.5 VSR1.
3. Maneuvers:
a. Maneuver A evaluates the TCAS II CLIMB RA. From the initial steady-state condition, after a 3-second pilot-reaction time delay, rotate the aircraft at 1.25 g to attain +1500 feet per minute climb. Hold until the total duration of the RA of 25 seconds has elapsed. Recover to attain the initial trim airspeed.
b. Maneuver B evaluates the TCAS II INCREASE CLIMB RA following a CLIMB RA. From the initial steady-state condition, after a 3-second pilot-reaction time delay, rotate the aircraft at 1.25 g to attain +1500 feet per minute climb. Hold until 15 seconds has elapsed from when the CLIMB RA was issued. Then, after a 1-second pilot reaction time-delay to the INCREASE CLIMB RA, rotate the aircraft again at 1.25 g to attain +2500 feet per minute climb and hold until the total duration of the RA of 25 seconds has elapsed. Recover to attain the initial trim airspeed.
c. Maneuver C evaluates a maximum duration TCAS II INCREASE CLIMB RA following a minimum duration CLIMB RA.
From the initial steady-state condition, after a 3-second pilot-reaction time delay, rotate the aircraft at 1.25 g targeting +1500 feet per minute climb until 6 seconds has elapsed from when the the system issued the CLIMB RA. Then, after a 1-second pilot-reaction time delay to the INCREASE CLIMB RA, rotate the aircraft again at 1.25 g to attain +2500 feet per minute climb and hold until the total duration of the RA of 25 seconds has elapsed. Recover to attain the initial trim airspeed.
4. VY + 10 for nontransport category aircraft without a defined V2.
5. For those airplanes where the power-on stalling speed is significantly lower than the power-off stalling speed, use 1.1VS or
1.08VSR for those airplanes that use reference stall speed (VSR) in lieu of stalling speed (VS).
6. VY for nontransport category aircraft without a defined V2
7. For those airplanes where the power-on stalling speed is significantly lower than the power-off stalling speed, use VS1 or 0.94VSR1 for those airplanes that use reference stall speed (VSR) in lieu of stalling speed (VS).
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2.3.5.8 A summary of the system inhibits (limitations) programmed into the TCAS II computer is given in Table 2 below.
Table 2 System Inhibits
INHIBIT PARAMETERS Increase Descent RA Inhibited below 1650 ft AGL while climbing and inhibited below 1450 ft AGL while descending.
Descend RA Inhibited below 1200 ft AGL while climbing and inhibited below 1000 ft AGL while descending.
TA Voice Messages Inhibited below 400 ft AGL while descending and inhibited below 600 ft AGL while climbing.
RAs Inhibited below 1100 ft AGL while climbing, and inhibited below 900 ft AGL while descending. (TCAS automatically reverts to TA only).
Self-Test Can be inhibited when airborne.
Advisory Priority Automatically reverts to TA only when higher priority advisories (such as GPWS/TAWS and windshear) occur.
Climb RA Can be inhibited, based upon aircraft performance capability.
Increase Climb RA Can be inhibited, based upon aircraft performance capability.
2.3.6 How Aircraft Systems Should Interface with TCAS II.
2.3.6.1 Pressure altitude information.
The pressure altitude data must be from the most accurate source available in the aircraft and it must be the same data the associated Mode S transponder transmits. The accuracy of the altitude data must be at least that specified in RTCA/DO-185A or RTCA/DO-185B, paragraph 3.2.8 as applicable. You must show that the resolution of the altimetry source is compatible with TCAS II. The altitude source with the finest compatible resolution must be used. When available, the resolution should be in increments of 10 feet or less. Also provide information to indicate when the pressure altitude information is invalid.
2.3.6.2 Radio altitude information.
2.3.6.2.1 Provide radio altitude information to the TCAS II to inhibit: