(3) All TA voice messages (aural traffic advisories) below 400 ft AGL while descending and below 600 ft AGL while climbing, and
(4) All RAs below 1100 ft AGL while climbing and below 900 ft AGL while descending, to allow automatic sensitivity level selection when close to the ground, and to determine that individual targets are on the ground.
(5) Also provide information to indicate when the radio altitude information is invalid.
c. Aircraft configuration. Use discrete information from flaps, slat, landing gear, and/or other aircraft configuration sensors to ensure that TCAS II appropriately inhibits CLIMB and INCREASE CLIMB RAs to the airplane performance limits as described in paragraph 2-16 and 2-17.
d. Aircraft identification. Provide discrete information to the Mode S transponder for the unique aircraft Mode S identification code and its maximum airspeed capability.
e. Attitude. Aircraft pitch and roll attitude may be provided to assist with stabilization of the directional antenna function to assure surveillance and to ensure TA display data remain unaffected by aircraft normal maneuvers. If attitude information is used by TCAS II, provide information to indicate when the attitude data are invalid.
f. Heading. Aircraft heading may be provided for the TA display reference presentation. Information must also be provided to indicate when the heading data are invalid.
g. System failure display. Provide an indication to indicate when RAs are not possible due to failure of the TCAS II equipment or any of its sensors or displays.
h. Altitude alerter data. You may provide the current clearance altitude from the altitude alerter to enable TCAS II to select RAs that are more consistent with the aircraft’s altitude clearance once the immediate collision threat has been resolved.
NOTE: Altitude alert functionality is optional per RTCA/DO-185A and RTCA/DO-185B. Not all TSO-C119( ) TCAS II units will have this option available.
i. Mode S Transponder Gillham altitude input requirements. The Gillham format uses 11 discrete wires that, depending on which wires are turned off or on, represent an altitude value. The Gillham format is sometimes called a blind encoder, as error detection and/or correction on the wires is not conducted. For this reason, ARINC 718, Mark 3 Air Traffic Control Transponder (ATCRBS/MODE S), dated December 1989, states: “Pins have been reserved to permit the direct application of Gillham code data to the transponder. This practice is not encouraged because of concerns that a “stuck bit” in the coded input could be the cause of serious errors in TCAS II resolution advisories.” This is a failure mode peculiar to t he Gillham code against which protection is virtually impossible. If Gillham coded altitude use cannot be 19
avoided for the TCAS II installations, two sources of altitude information must be connected to the transponder and their values compared. All transponder altitude comparator failures must be annunciated.
j. Hybrid surveillance failure annunciations (TSO-C119d units only). For aircraft equipped with centralized alert and warning system and or an onboard maintenance system, consideration should be given to integrating the hybrid surveillance alerting functionality into the system so as to alert the crew with an appropriate failure annunciation. Refer to section 2-21 for more information.
2-19. Verifying and Validating TCAS II Software . It is required for the first installation of a manufacturer’s TCAS II equipment to verify and validate TCAS II software using the procedures outlined below. Also, apply these procedures to subsequent software changes to a manufacturer’s TCAS II equipment. A manufacturer may provide a design that partitions the software, which affects RAs from other software such as that necessary for the traffic display.
The TCAS II manufacturer may not use the minor change authority of the TSO system to change any software not partitioned from the software that affects RAs.
a. Verification and validation of TCAS II software represents a unique challenge.
Collision avoidance algorithms, commonly called “the CAS logic,” are specified in detail in a formal statechart representation in the CAS requirements specification (CRS) in RTCA/DO-185A, Volume II and RTCA/DO-185B, Volume II. In addition, Attachment A of Volume II provides a software design specification in pseudocode that meets these requirements.
This detail is required because the coordination algorithms in the CAS logic assume that the software implemented by all manufacturers will have exactly the same CAS logic. However, the surveillance software necessary to establish and maintain the relative tracks of nearby transponder-equipped aircraft and the software necessary to provide the interface with the Mode S transponder and with other aircraft sensors and displays, must be developed by the manufacturer of the TCAS II equipment. This hybrid approach to the specification of the software requirements means that the application of the software criteria in RTCA/DO-178B, Software Considerations in Airborne Systems and Equipment Certifications, dated December 1, 1992, for the detailed CAS requirements and the pseudocode software design have been satisfied by the FAA and our contractors, while the remaining requirements of RTCA/DO-178B are the responsibility of the manufacturer.
b. If software is used for the display of TCAS II RAs or in the operation of the Mode S transponder data link, the verification and validation of this software must be done to Level B requirements, as defined in RTCA/DO-178B. Also, apply these procedures when the TCAS II manufacturer develops the software requirements for the TCAS II processor associated with functions other than surveillance or the CAS logic. With the software design specified in RTCA/DO-185A, Volume II or RTCA/DO-185B, Volume II, the manufacturer of the TCAS II processor should conduct code walk-throughs and develop and perform module tests and module integration tests to verify that the specified software design was implemented correctly. This includes the surveillance software necessary to establish and maintain the relative tracks of nearby transponder-equipped aircraft.
c. The functional tests required by TSO-C119b and TSO-C119c/TSO-C119d, as described in RTCA/DO-185A, Volume I and RTCA/DO-185B, Volume I respectively, do not provide complete testing for the TCAS II processor software. However, coverage analysis performed on the CAS test suite, described in Volume I, demonstrated that each column of every transition table and macro, and each identity transition in the CAS requirements specification in RTCA/DO-185A, Volume II or RTCA/DO-185B, Volume II is tested by the CAS test suite.
Thus, the CAS test suite provides more than full decision coverage (but not full condition coverage) as defined in RTCA/DO-178B. TCAS II manufacturers must develop additional functional tests that correspond to the detailed requirements that they develop for the TCAS II processor. The potential consequences of software errors in the TCAS II processor or resolution display require the manufacturer to provide a structural coverage analysis showing single condition test coverage of all instructions at the source code that can affect the generation and display of RAs. These tests may be a combination of module tests, module integration tests and functional tests.
d. Equipment produced under a TSO has obtained FAA concurrence that the software for the equipment was produced in accordance with RTCA/DO-178B for a particular software level. Subsequent installations of the same TCAS II equipment on other aircraft types do not require any additional verification if the software and the interface is not changed.
2-20. Testing for Failures System Safety Analysis. Unannunciated failures of the TCAS II equipment, its associated transponder, or sensors or displays that could generate an incorrect RA, must be improbable. This can be accomplished using the methods described in AC 25.1309-1A, System Design and Analysis. We expect that a functional hazard assessment (FHA), a failure modes and effects analysis (FMEA), and a quantitative probability analysis of the TCAS II equipment, Mode S transponder, displays, and sensors (including altitude information sources) will be necessary to establish that a false RA is improbable. Specifically, show that the probability of an incorrect RA without a failure annunciation is on the order of 1.0 x 10-4 per flight hour in the terminal environment and 1.0 x 10-5 per flight hour in the enroute environment.
The frequency of encounters where another aircraft could present a potential threat depends on the density of aircraft in the airspace. In terminal airspace, the frequency may be assumed to be once every 10 hours and, in enroute airspace, it may be once every 200 hours. You may establish different frequencies based on operational data. Provide these analyses for the first installation of TCAS II equipment on a new model aircraft. For subsequent installations of the same equipment in other aircraft, you may use some of the same analyses paying particular attention to the differences in the altitude sensors that are used.
NOTE: Develop software involved in generating RAs to RTCA/DO178B, Level B standards.
2-21. Maintenance Considerations for Hybrid Surveillance Functionality (TSO-C119d only).
a. RTCA/DO-300A section 2.2.10, Monitoring Requirements, provides a means for annunciation or recording of failures of own-ship latitude, longitude and/or ground speed inputs.
Note that a failure of any of these inputs will not cause TCAS to fail, but it will disable the hybrid surveillance functionality.
b. To ensure that hidden failures are not resident in airborne TCAS II units for long periods of time, failures of hybrid surveillance must be annunciated to the flight crew or the continued airworthiness must be assessed during periodic scheduled maintenance tasks. Periodic reliability reporting for the hybrid surveillance functionality is also required. Depending on the level of avionics integration in the aircraft, different methods can be used to ensure the continued airworthiness of the hybrid surveillance such as:
(1) For those aircraft equipped with an engine indicating and crew alerting (EICAS) system (or other similar annunciation system) integrate the failure information into the warning system such that a failure of hybrid surveillance is annunciated to the flight crew.
(2) For aircraft equipped with an onboard maintenance computer interfaced with TCAS, add a scheduled maintenance task to the aircraft’s maintenance program to check for presence of any existing or past failures of hybrid surveillance. Take corrective action as specified by the TCAS manufacturer.
(3) For aircraft without a centralized warning system and/or an onboard maintenance computer, add a scheduled maintenance task to the aircraft’s maintenance program to check for presence of any existing or past failures of hybrid surveillance and to ensure hybrid surveillance is functional. Take corrective action as specified by the TCAS manufacturer.
(4) If a scheduled maintenance task is employed, the installer must establish the initial frequency of the task in conjunction with the manufacturer of the TCAS equipment but on a frequency not to exceed two calendar years between tasks. Normal maintenance escalation procedures could later be used to extend the maintenance frequency when adequate justification to do so is provided to the cognizant ACO. Coordinate any such extension request with the ACO prior to implementation of changes.
c. Operators of TCAS equipment with hybrid surveillance are required to report hybrid surveillance maintenance history to the TCAS manufacturer periodically but not to exceed 18 calendar months between reports.
Chapter 3. Test and Evaluation (Initial Approval).
3-1. General. Test the first installation of a manufacturer’s TCAS II or Mode S transponder system. This will verify the design and installation performs its intended function under the expected operating conditions, and that there are no adverse interactions between the TCAS II Mode S transponder and existing aircraft systems. The test will also show that other aircraft equipment has not been adversely affected.
3-2. Create a Test Plan. Provide a test plan that includes adequate testing to perform this verification. This test plan will generally require a combination of ground tests, basic flight tests, and flight tests involving planned encounters with another TCAS II equipped aircraft. You can use an aircraft other than a transport category aircraft for either the TCAS II installation or for the air-to-air cooperative flights. The rest of this chapter lists and explains the minimum elements of the test plan.
3-3. Basic Ground Tests.
a. Bearing accuracy. Demonstrate the bearing estimation accuracy of the TCAS II system as installed in the aircraft. Measure the bearing accuracy using a calibrated antenna range that allows precise echo controlled, far field, angle-of-arrival measurements at or slightly above zero degrees elevation and over 360 degrees in azimuth. The bearing accuracy may also be measured using a fixed transponder location while rotating the test aircraft on a compass rose while measuring the bearing angles at 30-degree intervals. Alternately, the airplane is fixed and the transponder may be moved (refer to Appendix B for cautionary note on testing). Manual readout of the bearing estimate may be done directly from a plan position display on the traffic advisory display. Alternatively, the bearing estimates may be automatically recorded or read from a special test display. A maximum error of ±15 degrees in azimuth is acceptable; however, larger errors are acceptable in the area of the tail (for example, within ±45 degrees of the tail) when that area is not visible from the cockpit. In this case, aircraft structure may interfere with the signal path.
b. Sensor failures. Evaluate simulated failures of the aircraft sensors integrated with TCAS II to determine that the resulting system failure state agrees with the predicted results.
These tests should be part of the ground test plan.
c. Electromagnetic interference (EMI). Survey the flight deck EMI to determine that the TCAS II equipment is not a source of objectionable conducted or radiated interference to previously installed systems or equipment, and that operation of the TCAS II equipment is not adversely affected by conducted or radiated interference from previously installed systems and equipment. Pay attention for possible interference with TCAS II equipment from weather radar, particularly if operating in the C-band.
d. Evaluate the general arrangement and operation of controls, displays, circuit breakers, annunciators, and placards of the TCAS II system. Conduct a human factors evaluation of the controls, displays and annunciators. Evaluate the TCAS controls and the controls of installed 23
systems that interact with TCAS (for example, transponders) to determine that they are designed and located to prevent inadvertent actuation. Evaluate TCAS displays and annunciations to determine that they support flight crew awareness of TCAS status changes which could result from TCAS mode selections, intentional pilot actuation of other installed systems, or inadvertent pilot actions with TCAS or other installed systems. Evaluate TCAS displays to ensure all information is, at a minimum, legible, unambiguous, and attention-getting (as applicable). In particular, where transponder functions are integrated with other system controls, ensure that unintended transponder mode switching, especially switching to STANDBY or OFF, is not possible. Pay close attention to line select keys, touch screens or cursor controlled trackballs as these can be susceptible to unintended mode selection resulting from their location in the flight deck (for example proximity to a foot rest or adjacent to a temporary stowage area).
e. Evaluate the TCAS II self-test features and failure mode displays and annunciators.
f. Verify that the pressure altitude source and radio altimeter are properly interfaced with the TCAS II equipment.
g. Verify that the windshear and the ground proximity warning system/terrain awareness warning system (GPWS/TAWS) warnings and TCAS II voice alerts are compatible. Also, verify that windshear or GPWS/TAWS warnings can be clearly understood and that TCAS II is automatically switched to the TA Only mode when TCAS II and windshear voice or GPWS/TAWS announcements simultaneously occur. The alert priorities should be windshear, GPWS/TAWS and then TCAS II.
h. Verify the performance of TCAS II traffic display by observing any available area traffic.
i. Evaluate the TCAS II system installation for satisfactory identification, accessibility, and visibility during both day and night conditions.
j. Determine that any configuration of discretes associated with the TCAS II logic, including inhibits of climb RAs, operate properly. (Changes in logic or function with aircraft configuration, altitude, or speed.)
k. Verify that the ICAO 24-bit aircraft address and maximum airspeed are correct.
Additionally, verify that other features, which may be optional, such as extended squitter, aircraft identification reporting or other data link uses also function correctly. Verify that the transponder and data sources meet the requirements of the failure condition classifications associated with the features. For example, an unannunciated failure of the transponder extended squitter resulting in erroneous information being transmitted is at least a major failure condition.
l. If connected, verify that the altitude alerter is providing correct data to TCAS and that the TCAS II V7.0 or V7.1 logic, as applicable, correctly weakens or strengthens the displayed RA using the altitude alerter input.
m. Verify that the air/ground inputs are connected properly.
NOTE 1: CAUTION - When the aircraft is on the ground, the Mode S transponder must be inhibited from replying to any Mode A, Mode C, Mode A/C/S all-call interrogations and Mode S-only all-call interrogations.
NOTE 2: This inhibit is usually accomplished via an appropriate transponder pin connected through the weight-on-wheels switch, but it might also be accomplished through some other automatic means (for example, velocity/altitude algorithm, etc.). The inhibit means must be verified during ground testing.
NOTE 3: While on the ground, the transponder normally should stop output of acquisition squitters (short squits), and should continue output of extended squitters (known as long squits or ADS-B) in the surface format, and it should reply to any discretely-addressed aircraft interrogations. This too should be verified during ground testing. The exact conditions for transmission of acquisition squitter are specified in DO-181E section paragraph 2.2.18.2.6, Acquisition Squitter Protocols.
3-4. Basic Flight Tests.
a. During all phases of flight, determine if there is any mutual interference with any other aircraft system. Have all installed systems, including the weather radar, operating during the flight test.
b. Evaluate TCAS II aural messages for acceptable volume and intelligibility during both low and high cockpit noise levels (idle descent at low speed and high power at maximum operating limit speed Vmo) with headset covering outboard ear only (when appropriate) and without headsets. In the case of 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. If the TCAS II TEST is used to simulate voice announcements, ensure that the audio level is not changed by use of the TEST function.
c. Demonstrate that traffic information remains valid and usable when the aircraft is pitched ±15 degrees and rolled approximately 30 degrees during normal maneuvers by observing area traffic in the traffic advisory display.
d. Evaluate the effective surveillance range of the traffic display, including target azimuth reasonableness and track stability. Use of targets of opportunity or a non-transport category (low speed) aircraft as a target for these tests is permissible.
e. Determine that any configuration discretes (changes in logic or function with aircraft configuration, altitude, or speed) associated with the TCAS II logic, including inhibits of climb RAs, operate properly unless previously demonstrated during ground tests.
f. Perform the additional flight tests in RTCA/DO-185A or RTCA/DO-185B, paragraph
3.4.4 as applicable, unless previously accomplished under TSO-C119b or TSO-C119c/TSO C119d respectively.
g. Evaluate TCAS II for noninterference during coupled autopilot and flight director (FD) approaches to the lowest minimums approved for the aircraft.
h. Before any cooperative flight tests at any altitude involving the TCAS II-equipped aircraft and another aircraft, fly both aircraft in close formation to ensure matched altimetry readouts. These checks should be flown at the speeds and altitudes to be used for the tests.
i. Evaluate all selectable modes of the TCAS II to determine that they perform their intended function and that the operating mode is clearly and uniquely annunciated.
j. Re-evaluate any previously installed aircraft systems that required changes as a result of the TCAS II installation. (For example, electronic flight instrument system (EFIS), FD, PFD, navigation displays (ND), IVSI, interface etc.)
k. When hybrid surveillance functionality is included, perform the flight tests in RTCA/DO-300 or DO-300A, MOPS for Traffic Alert and Collision Avoidance System II (TCAS II) Hybrid surveillance, dated December 13, 2006 and dated Mar 20, 2013 respectively, paragraph 3, as appropriate unless previously accomplished under TSO-C119c or TSO-C119d.
3-5. Planned Encounter Flight Tests. The objective of these flight tests is to demonstrate adequate TCAS II surveillance and to verify smooth, predictable TCAS II performance. First establish the appropriate safety rules, static system leak test (if necessitated by having opened the system), and altimeter correlation between the encounter aircraft and the TCAS aircraft. The following encounters between the TCAS II aircraft and a dedicated intruder aircraft should be flown to assure that the TCAS II aircraft system performs its intended function by generating TAs and RAs and is consistent with RTCA/DO-185A or RTCA/DO-185B as applicable, and RTCA/DO-300 or RTCA/DO-300A as appropriate. The intruder aircraft must be equipped with a previously approved transponder installation capable of Mode A, Mode C, and for those tests necessary, Mode S, TCAS II and ADS-B Mode S Extended Squitter if appropriate. These tests are also intended to expose the installed TCAS II system to a reasonable number of carefully controlled encounters that are likely to occur in service. This matrix covers the envelope of encounter speeds, altitudes, and geometries that have in the past identified flaws in surveillance, logic, and antenna mechanization that were not detected earlier by bench tests. Fly the following encounters:
a. Intruder overtaking TCAS II aircraft (from the aft quadrants).
b. Head-on.
(1) Low and high closure speeds.
(2) Above climb limit, TCAS II to TCAS II.
(3) TCAS II against Mode C with TCAS II above intruder and above climb limit (intent is to force TCAS II aircraft to descend.)
(4) At 3000 feet over calm water to evaluate multipath protection.
c. Converging.
(1) Crossing (intruder above TCAS II, descending or vice versa.)
(2) Evaluate the TA-only mode during planned encounters.
(3) Evaluate a mix of intruder transponder modes (A, C, S and S with extended squitter) but primary emphasis should be on TCAS II-to-TCAS II coordination, and on Mode C replies from the intruder aircraft.
(4) Evaluate a mix of encounters with TCAS II both above and below the intruder.
(5) If a flight test is necessary to ensure compatibility with other designs, verify correct air-to-air coordination between the test TCAS II and another manufacturer’s previously approved equipment (refer to paragraph 2-15).
(6) Evaluate the effect of electrical transients (bus transfer) during encounters. The TCAS II should not experience adverse effects. No false TAs or RAs should be generated as a result of electrical transients. Normal TCAS II functions and displays should be restored within approximately three seconds.
3-6. Mode S Transponder Tests.
a. This guidance doesn’t cover Mode S Extended Squitter or Mode S Elementary/Enhanced surveillance.
b. The tests described in these paragraphs may be used to obtain the certification of a stand-alone Mode S transponder installation (an installation without TCAS II). These tests should also be used to evaluate a Mode S transponder installed as part of a TCAS II installation.
The tests primarily verify the installed antenna(s) are compatible with the Mode S transponder and provide an adequate response to ground radar interrogations during normal aircraft maneuvers.
c. Additionally, these tests demonstrate that the Mode S transponder functions properly as installed and does not interfere with other aircraft electronic equipment. The need for a detailed flight test is reduced when the Mode S transponder and antenna installation are identical 27
or similar to that of previously approved ATCRBS transponder installation. If a previously installed and certified transponder is being upgraded, all of the guidance in this section is not necessarily required to approve the upgrade. A careful examination of the proposed transponder upgrade should be accomplished to determine which of the tests specified in this section are necessary and appropriate. Typical testing associated with the initial installation and certification of a new transponder may not be necessary when upgrading a previously approved transponder. For example, if a software upgrade is being considered which would add extended squitter functionality to a transponder in a previously approved installation, detailed flights would not be required if appropriate ground testing adequately evaluates the added functionality.
NOTE 1: CAUTION! When conducting flight testing of the transponder or TCAS system, you must prevent being a source of interference to ATC or other TCAS aircraft operating in the area.
For example, using a fixed transponder to simulate an intruder aircraft can cause data to be transmitted which produce false targets for the ground ATC surveillance systems or airborne TCAS aircraft.
These false indications of “intruder aircraft” could result in unnecessary ATC communications and possibly in TCAS induced aircraft maneuvers. Therefore, conduct such testing in coordination with ATC.
NOTE 2: The conduct of this test requires cooperation with ATC radar controllers. Coordination with ATC is important before the flight test for any necessary approval of the flight and agreement with the flight test procedures. During the flight test, communication will be required with the controller monitoring the aircraft and reporting transponder performance data.
d. If the Mode S transponder uses a top mounted antenna in addition to a bottom mounted antenna installed at, or near, the same location used by a previously approved ATCRBS transponder antenna, conduct a comprehensive ground test and evaluation in accordance with Appendix B and perform a functional flight test. The transponder code, altitude reporting and “IDENT” features of the transponder should be exercised during normal maneuvering. There should be no objectionable behavior observed by the ATC controller.
e. If a Mode S transponder is installed in an aircraft which does not have a previously approved ATCRBS transponder installation, or that uses a bottom mounted antenna location which differs significantly from that used by a previously approved ATCRBS transponder antenna, conduct the following ground and flight tests:
NOTE: References to the radar facility are references to the radar that provides the data used by the ATC controller(s) during the flight test for monitoring the aircraft and reporting transponder performance data. These are not references to the ATC facility with the radar displays used by the controllers.
(1) Conduct ground tests and evaluations per Appendix B.
(2) Climb and Distance Coverage. Begin at a distance of at least 10 nautical miles (NM) from, and an altitude of 2000 to 3000 feet above the radar facility and using a transponder code assigned by ATC, fly on a heading that will pass the aircraft over the radar facility. At a distance of 5 to 10 NM beyond the radar facility, fly the aircraft at its normal maximum climb attitude to within 90 percent of the certificated altitude for the aircraft, maintaining the aircraft heading within 5 degrees of the track from the radar facility. After reaching the maximum altitude for which the aircraft is certificated, fly level at the maximum altitude to 160 NM for turbojet and some turboprop powered airplanes (or 80 NM for most other aircraft) from the radar facility. (Distance from the radar facility is a function of the airplane’s maximum certificated altitude.) Communicate with the ATC controller for evidence of transponder dropout. During the flight, check the “IDENT” mode of the ATC transponder to assure that it is performing its intended function. There should be no unexpected dropouts (no return for two or more sweeps).
Uncontrollable ringing that hinders use of the ground radar is unsatisfactory.
(3) Long Range Reception. At 90 percent of maximum certificated altitude, perform left and right 360-degree turns, at bank angles of 8 to 10 degrees. The aircraft should be at least 160 (or 80) NM from the radar facility. During these turns, request that the ATC controller monitor the radar displays. There should be no dropouts (no return for two or more sweeps).
(4) High Angle Reception. Perform two 360-degree turns, one to the right and one to the left, at bank angles of 8 to 10 degrees with the airplane at a distance of 50 to 70 NM from the radar facility and at an altitude of at least 35,000 feet or within 90 percent of the maximum altitude for which the aircraft is certificated. There should be no dropouts (no return for two or more sweeps). Switch the transponder to a new code assigned by the ATC controller. The aircraft secondary return on the ATC controller’s radar display should indicate a Mode A code change.
(5) High Altitude Cruise. Within 90 percent of the aircraft’s maximum certificated altitude or its maximum operating altitude beginning at a point 160 (or 80) NM from the radar facility, fly on a course that will pass over the radar facility. The ATC controller should report no unexpected transponder dropout or “ring around.”
(6) Surveillance Approach. Beginning at or above 90 percent of the certificated maximum altitude for the aircraft, perform a letdown and approach to a runway of an airport served by Airport Surveillance Radar (ASR) having an ATCRBS facility. Make the approach at the maximum normal rate of descent. Normal approach and landing configuration for the aircraft should continue down to an altitude of 200 feet or less above the ground radar antenna elevation. Not more than one dropout should occur for any 10 sweeps during final approach.
Uncontrolled ringing that hinders use of the ground radar is unsatisfactory.
(7) Holding and Orbiting Patterns.
(a) At an altitude of 2000 feet above the radar antenna or minimum obstruction clearance altitude (whichever is greater) with landing flaps and gear extended, fly left and right 29
360-degree turns approximately 10 miles from the radar facility. There should be no signal dropouts.
(b) At an altitude of 2000 feet above the radar antenna or minimum obstruction clearance altitude (whichever is greater), fly 45 degree sectors of left and right 10 mile orbital patterns around a radar facility with gear and landing flaps extended. There should be no signal dropouts.
(8) Altitude Reporting. Conduct a functional test of the altitude encoder by comparison with ATC displayed altitudes. Verify correspondence at several altitudes between ATC readings and the Captain’s altimeter, when set at or corrected to 29.92 inches of mercury (or equivalent).