3-1 CHAPTER 3. AIRBORNE RADAR APPROACHES
3.1 Applicability. This chapter applies to helicopter ARA procedures for offshore landing sites conducted under instrument flight rules (IFR). The procedure criteria in this chapter applies to airborne weather radar with ground mapping mode that has a demonstrated navigational capability acceptable to the Administrator for ARA operations.
3.2 Helicopter Requirements.
3.2.1 Airborne Radar.
3.2.1.1 Suitable for Use as Primary Instrument Operation Aid. The airborne weather radar systems that have proved suitable for use as primary instrument operation aids are short-range pulse radars, manufactured and approved for the purpose of weather avoidance rather than navigation. Minimum system components for procedures based on airborne radar only (with or without beacon capability) are as follows:
1. As a minimum, ARA systems must meet the airworthiness requirements of Technical Standard Order (TSO)-C63, Airborne Weather Radar Equipment, or TSO-C102, Airborne Radar Approach and Beacon Systems for Helicopters.
2. Stabilized 120- degree/60-degree sector scanning antenna with scan rates of no less than 12/min and 24/min respectively.
3. Adjustable light display.
4. Alphanumeric display for selected ranges and azimuth markers; however, alphanumeric display for selected ranges is not required when:
• A positive means for determining selected scale is available, and
• The radar operator is appropriately trained.
5. The indicated range error should not exceed ±0.2 NM for display ranges of 5 NM or less.
6. The lowest selectable range display should be at least 2.5 NM with a range mark display of 0.5 NM to meet the authorized landing minimums.
Equipment that provides a lowest range display of 5 NM with a range mark display of 1 NM may be used, but a ¼ NM penalty is imposed on established visibility minimums.
7. Tilt control ±15 degrees.
8. Test pattern.
9. Primary mode (beacon mode may be necessary for cluster approach).
10. Fault monitor or self-test.
11. An operational course bearing cursor that provides course guidance is required to fly cluster operations below obstacles.
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12. With zero pitch and roll signals applied to the antenna scanner representing level flight attitude, the indicator update strobe line should indicate the antenna beam center to within ±3 degrees at any scan angle.
3.2.2 Radio Altimeter.
3.2.2.1 TSO Requirement. The radio altimeter must meet the requirements of TSO-C87, Airborne Low-Ra nge Radio Altimeter.
Note: A radio altimeter must be installed and operational before descent to the radio altitude (RA) minimum descent height (MDH) is authorized.
3.2.3 Offshore Heliport Facilities. W hen required to ensure positive identification of targets, a radar transponder beacon should be evaluated during the approval process.
3.3 Airworthiness.
3.3.1 Installation Requirements. Installation of an ARA system for IFR use is a major change in type design, and the provisions of 14 CFR part 21, § 21.97 and part 43, §§ 43.5 and 43.7 apply. The following are requirements for system installation:
1. System controls and data displays must be conveniently accessible and visible to radar operators at their duty stations. The system controls should be protected against inadvertent operation.
2. Electrical power for the system should be obtained from a bus that provides maximum reliability for electrical power without jeopardizing other essential or emergency loads.
3. The ARA system should not be a source of objectionable electromagnetic interference and must not be adversely affected by electromagnetic interference from other helicopter equipment.
4. Any probable malfunction of the ARA system should not adversely affect the normal operation of other systems or equipment installed in the helicopter.
5. System performance should not be adversely affected by helicopter attitude, altitude, or main rotor revolutions per minute (rpm) normally encountered in flight operations.
3.4 Maintenance.
3.4.1 Title 14 CFR Part 135. Part 135 operators must maintain their aircraft under part 135 requirements and their approved maintenance program. Airborne radar, radio altimeter, and Global Positioning System (GPS) maintenance must be performed for this equipment installed in the aircraft.
3.4.2 Title 14 CFR Part 91. Part 91 operators must maintain their aircraft under part 91 operating procedures. Airborne radar, radio altimeter, and GPS maintenance must be performed for this equipment installed in the aircraft. Operators under part 91 using
3-3 ARAs who do not have an approved maintenance program should establish procedures to annually inspect and test the ARA equipment. These procedures should include methods for analyzing malfunctions and defects to determine whether established inspections and tests reasonably assure the equipment is maintaining its accuracy. In addition to the equipment manufacturer’s recommendations and Supplemental Type Certification (STC), the following test and inspections should be included:
3.4.2.1 Visual Inspection. A visual inspection to determine the condition and security of the equipment mounting, electrical wiring and connectors, radome, antennas and cables, wave guide and couplings, indicator mounts, knobs, etc.
3.4.2.2 Functional Test. A functional test of the airborne radar ground mapping mode, radio altimeter, and navigation system to determine operating condition. Tests should be performed in accordance with appropriate manufacturer’s procedures.
3.4.2.3 Other Tests/Inspections (as appropriate). Other appropriate tests and inspections are used to determine whether the complete system is operating properly.
Note: The inspection and test procedures will be approved by the Flight Standards office issuing the ARA authorization before the operator conducts any IFR ARA procedure in instrument meteorological conditions (IMC).
3.5 Flight Standards Office Approval. Each operator’s maintenance program must be approved by the Flight Standards office issuing the ARA authorization before any IFR ARA procedures may be conducted. A certificated air carrier submits a written request with the proposed chart through the responsible Flight Standards office Principal Operations Inspector (POI). The responsible Flight Standards office ensures that a particular radar and GPS meet minimum requirements, the flightcrew training requirements are met, and helicopter and avionics maintenance requirements are adequate. The Flight Standards office should request support from the FOG representative, if required. Each operator’s maintenance or inspection program must be approved by the Flight Standards office issuing the ARA authorization before any ARA operations in IMC may be conducted.
3.6 Procedure Development Criteria.
3.6.1 Sample ARA. The certificated air carrier or operator submits the operation request including the proposed chart to the principal inspector (PI) of the responsible Flight Standards office. The PI should notify the FPAG for operational coordination within their specified area of operation. For operations outside of the responsible Flight Standards office’s operational area, the FPAG should coordinate with the controlling air traffic facility and Flight Standards office (if required) for the intended operational area.
Instrument operation chart examples are in Appendix B, Figure B-3, Sample ARA Chart for Single Platform, and Figure B-4, Sample ARA Chart for Platform Cluster. The
3-4 following note is charted in the plan view of the operation: “Special Authorization. WX RADAR in ground mapping mode required.”
3.6.1.1 Procedure Identification. The procedure is identified as “ARA” with the name of the cluster or rig (e.g., “WINTR 120”). If the operation requires beacon capability, the operation will be annotated “Beacon Required.” A note specifying the platform containing the beacon is printed on the plan view of the chart (e.g., “Beacon on Platform 1”). (See Appendix B, Figure B-4.)
3.6.1.2 Procedure Construction. For ARA procedures, obstructions 50 ft or higher above the surface are considered obstacles. Where landing sites or operation targets are less than 100 ft above the surface, all obstacles within 50 ft of the site’s height must be charted. An ARA procedure to an offshore site has two areas: the intermediate area, and the final operation area. Missed approach airspace is contained within the two areas (see Figure 3-1, Single Approach Target Area, and Figure 3-2, Cluster Approach Target Area). Determine whether the operation is for a single landing site or for a cluster of landing sites. Identify the final approach area and connect it to the en route structure by an overlying intermediate area that is used for transition. The procedure must also contain the onshore navigation facility, the route designation, and the location of the destination site or landing site cluster. The ARA chart contains a table to determine the time required to fly an outbound 4 NM leg for a teardrop procedure turn. Sample ARA charts are contained in Appendix B, F igures B-3 and B-4.
3.6.1.3 Single Approach Target Procedure Construction. This procedure provides for an into-the-wind final descent to the landing site from any direction, depending on the surface wind reported in the approach target area and the operating procedures selected by the flightcrew (see Figure 3-1).
1. In termediate Approach Fix (IF). The IF is located on the en route course centerline not less than 10 NM or more than 20 NM from the approach target.
2. Obstacle Clearance. The Required Obstruction Clearance (ROC) for the intermediate approach area is 500 ft above the highest known obstacle in the intermediate approach area until arrival at the Final Approach Point (FAP) inbound. The lowest charted minimum altitude is 600 ft mean sea level (MSL) and is charted as follows: “600′ MSL or no lower than the barometric MDA adjusted for RASS.” This note is required to assure that the FAP altitude is no lower than the minimum descent altitude (MDA) adjusted for the Remote Altimeter Setting Source (RASS).
3. Intermediate Approach Area. The intermediate approach area is centered on a straight course between the IF and the operation target. The intermediate approach area is bounded by an arc having a 7 NM radius centered on the approach target. Straight lines drawn tangent to the arc
3-5 extend the area to the en route boundaries at the IF. The intermediate approach area overlies and includes the entire final approach area.
3.6.2 Final Approach Area. T he final approach area is the area contained within a circle with a 4 NM radius centered on the approach target.
Figure 3-1. Single Approach Target Area
3.6.2.1 Sing le Approach Target Landing Minimums.
3.6.2.1.1 Rad io Altimeter. The RA is the higher of RA 200 ft or 50 ft above the landing site. The RA MDA visibility is ¾ sm.
3.6.2.1.2 Barom etric MDA. The barometric MDA minimums are computed by adding 250 ft to the highest obstacle in the final approach area, and this value is rounded up to the next 20-ft increment. In Figure 3-1, the highest obstacle in the final approach area is a 120-ft oil derrick. A ROC of 250 ft is added to the MSL height of this derrick. The MDA is rounded up to 380 ft MSL. An adjustment is made for the RASS when the source is more than 5 NM from the landing site. The barometric MDA visibility is ½ sm.
3.6.3 Cluster Approach Target Procedure Construction. This procedure provides for an into-the-wind final descent to the cluster area from any direction, depending on the
3-6 surface wind reported in the cluster area, and the procedure selected by the flightcrew. A plan view for a cluster instrument approach target area is shown in Figure 3-2.
3.6.3.1 IF. The IF is located on the en route course centerline not less than 10 NM and/or more than 20 NM from the nearest landing site or approach target in the cluster.
3.6.3.2 ROC. The ROC for the intermediate operation segment is 500 ft above the highest known obstacle in the intermediate operation area. The lowest intermediate altitude is 700 ft MSL and is charted as follows: “700′ MSL or no lower than the barometric MDA adjusted for RASS.” This note is required to assure that the FAP altitude is no lower than the MDA adjusted for the RASS.
3.6.3.3 Intermediate Approach Area. The intermediate approach area is bounded by arcs whose radii are centered on each outlying landing site or approach target in the cluster. Each radius is 7 NM. Straight lines drawn tangent to arcs at the lateral extremities of this area extend the area to the en route boundaries at the IF. The intermediate approach area overlays and includes the entire final approach area.
3.6.4 FAP. T he FAP can be any point on the arcs defining the limits of the final approach area.
The FAP is a point inbound to the landing site or approach target at 4 NM on the radar display.
3.6.4.1 Fina l Approach Area. The final approach area is bounded by arcs whose radii are centered on each outlying landing site or approach target in the cluster. Each radius is 4 NM.
3.6.5 Cluster Approach Target Landing Minimums (see Figure 3-2).
3.6.5.1 Radio Altimeter. The RA is the highest of the following: 200 ft RA, 50 ft RA above the landing site elevation, or 100 ft RA above the highest obstruction located within a cluster if a course bearing cursor is not used. The RA MDA visibility minimum is ¾ sm.
3.6.5.2 Barometric MDA. The barometric MDA minimums are computed by adding a ROC of 250 ft to the highest obstacle in the final approach area, and this is rounded up to the next 20-ft increment. In Figure 3-2, the highest obstacle in the final operation area is a 166-ft oil derrick. A ROC of 250 ft is added to this value. The MDA is rounded up to 420 ft MSL.
Note: The barometric MDA visibility is ½ sm or ¾ sm.
• If the lowest descent altitude is above obstructions, the lowest visibility is ½ sm.
• If the lowest descent altitude is below obstructions, the lowest visibility is ¾ sm.
3.6.5.3 Proceeding Visually. After visual reference with the landing site or approach target is established, the pilot proceeds visually to the landing site. Chart the following note: "PROCEED VISUALLY TO THE LANDING SITE."
3.6.5.4 Chart Note. Chart the following note for a RASS for the single and cluster operation target operations using barometric MDAs: ¿Altimeter source more than 5 NM but less than 75 NM, increase MDA 5' for each mile over 5 NM from operation target."
Figure 3-2. Cluster Approach Target Area Plan View NOT TO SCALE Minimum Descent Altitude (MDA) Add 250 ft to the Highest Obstacle in the Final Approach Area. Round Up to the Next 20 ft Increment.
7 NM Example:
7 NM Obstacle Height = 166 ft MSL ROC = +250 ft (166 ft) MDA = 416 ft MSL Round To: 420 ft MSL Final Nearest Platform in Cluster More Than 20 NM from Not Less Than 10 NM or Approach 4 NM Area Intermediate Area Landing Site (FAP- At Any Point on (Includes Final Approach Area (Approach Target) Radii and Tangent Lines into the Wind) Intermediate * Fix (IF) Landing Sites Maintain MEA Until Crossing the IF
3.7 Missed Approach Segment.
3.7.1 Missed Approach Construction. The missed approach is constructed for the single and cluster procedures in the same way. The missed approach begins at the missed approach point (MAP) and ends at an appropriate point or fix where intermediate approach or en route obstacle clearance is provided.
3.7.1.1 MAP. The MAP is no closer to the approach target than the minimum authorized visibility for landing, as observed on the radar display.
3.7.1.2 Missed Approach Area. The missed approach area is the clear zone left or right of the final approach course, 1.5 NM long and 2.0 NM wide (see Figure 3-3, Clear Zone and Clear Sector).
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3.7.1.3 Recording the Missed Approach. Chart the following missed approach:
“Climbing turn into the clear zone, then climbing turn to the MEA direct to the IF, or as directed by ATC.”
3.7.2 Missed Approach Holding. Chart the following holding instructions: “Hold over the intermediate fix on the inbound course, 1 minute legs, maintain the MEA or as directed by ATC.”
Figure 3-3. Clear Zone and Clear Sector
3.8 Op erational Requirements.
3.8.1 Approved Weather Observation and Reporting Requirements. Refer to FAA Order 8900.1, Volume 3, Chapter 18, Section 7, Part H Helicopter Terminal Instrument Procedures and Airport Authorizations and Limitations.
3.8.2 Offshore Environment Operation. Operators approved to conduct IFR operation in the offshore environment in accordance with parts 91, 91K, and 135 for the appropriate operational approval (e.g., Letter of Authorization (LOA), management specification (MSpec), or operations specification (OpSpec)) may comply with the requirements by any one of the following methods or one with an equivalent level of safety (ELOS) approved by the Administrator:
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1. One station: The operation coordinates must be within 10 NM of an approved weather reporting station.
2. Two stations: The operation coordinates must be within an observed area defined by the location of two approved weather reporting stations.
a. In the Gulf of America as defined in Figure 3-4 and excluding the Mississippi Delta bounded area in Figure 3-5:
• The observation area centerline is established by the actual bearing between the two stations; the actual distance between the two stations is not to exceed 80 NM. The centerline must continue on either side of each weather station by 10 NM.
• The lateral width of the observed area may not be greater than 40 NM on either side of the established centerline.
• The resultant maximum observation area is a rectangle 100 NM by 80 NM.
Figure 3-4. Gulf of America Expanded Weather Box Boundary
Figure
3-5. Excluded Area for Gulf of America Expanded Weather Box Boundary Corner Latitude Longitude NW 30 25'34.82"N 89 43'53.27"W NE 30 21'42.70"N 87 52'19.31"W SW 28 50'26.73"N 89 47'41.13"W SE 28 47'17.53"N 87 56'59.98"W
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b. In all other areas:
• The observation area centerline is established by the actual bearing between the two stations; the actual distance between the two stations is not to exceed 40 NM. The centerline must continue on either side of each weather station by 10 NM.
• The lateral width of the observed area may not be greater than 40 NM on either side of the established centerline.
• The resultant maximum observation area is a rectangle 60 NM by 80 NM.
3.8.3 Parts 91 and 135 Operators—Authorized Areas of En Route Operations, Limitations, and Provisions.
1. Operators conducting IFR operations in areas authorized by OpSpec B050, Authorized Areas of En Route Operations, Limitations, and Provisions, will comply with the requirements of the OpSpec.
2. Part 91 operations within oceanic airspace are covered in LOA H104, Helicopter Offshore Instrument Operations: Offshore Standard Approach Procedure (OSAP), Airborne Radar Approach (ARA), and Helicopter En Route Descent Area (HEDA) Operations, and the applicable International Civil Aviation Organization (ICAO) Annex.
3.9 Course Guidance.
3.9.1 Use of Radar. T he radar operator interprets radar returns on the cockpit display and vectors the helicopter clear of observed targets to the MAP. The nature of offshore operations is such that numerous permanent or transient targets may be displayed on radar. For ARA procedures, obstructions 50 ft or higher above the surface are considered obstacles. Where landing sites are less than 100 ft above the surface, all obstacles within 50 ft of the landing site’s height are charted. Those obstacles depicted within the final approach area on the ARA chart will include known height; however, those objects not shown on the chart must be considered moving obstacles of unknown height that radar provides means of lateral rather than vertical clearance on final approach. Before final approach, vertical clearance over surface obstacles is ensured by adherence to specified minimum altitudes. Missed approach obstacle avoidance is provided by an immediate climbing turn to a clear zone.
3.10 Planning.
3.10.1 ARA P ro cedure. Operational experience has shown that an ARA procedure to a single landing site is a relatively uncomplicated operation. However, operations to and from a landing site cluster increase the potential for operator error. This can be reduced by careful evaluation of the procedure during the approval process, adequate training by the operator, proper approach planning, and use of aids such as a course bearing cursor to supplement basic airborne radar.
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3.10.2 T arget Identification . Prompt and positive identification of the landing site solely by the use of ground mapping mode can be difficult when returns from moving targets confuse the pattern of the targets depicted in a cluster area. Where identification of a cluster cannot be ensured in ground mapping mode and approved air navigation facilities are unavailable to resolve target ambiguity, the approving authority should, as an option, consider whether to require installation of a radar beacon.
3.10.3 Approach Planning. To ensure obstacle-free flightpaths on final and missed approach, it is necessary to thoroughly scan and evaluate these areas before the operation is initiated.
3.10.4 Overshooting the MAP. Range errors caused by the time required for target update, possible equipment malfunctions, equipment accuracy, and crew reaction time may cause the MAP to be closer to the landing site than the desired MAP. While turning during the missed approach, airborne radar cannot be relied upon to provide lateral obstacle avoidance. Therefore, it is imperative that crews be trained to execute an immediate climbing turn toward a clear zone at the MAP. To ensure obstacle clearance, it is necessary to initiate the missed approach at the designated MAP. Otherwise, the flightpath could transgress an area that does not provide missed approach obstacle clearance.
3.10.5 Use of Course Bearing Cursor. A final approach flown by maintaining the operation target on the course bearing cursor increases the probability that the helicopter will be on the final approach course upon arrival at the designated MAP.
3.10.6 Flexibility. An offshore ARA requires procedural flexibility to provide options for the crew in planning the approach. The approach must provide a transition from an en route fix to a downwind position before beginning the final approach. This requires a provision in the approach for selection of a FAP that accounts for variations in wind conditions. On a cluster operation, where the close proximity of other targets does not permit sufficient lateral clearance for an ARA directly to the landing site, the operation can be made to a more suitable operation target located on the perimeter of the cluster and proceed visually to the landing site. Selection of an approach target depends upon existing wind conditions that in turn determine the location of the FAP, landing site selection, and missed approach clear zone. An approved ARA operation will provide an into-the-wind final descent to a cluster perimeter or to a single landing site from any direction.
3.11 Sy stem Limitations and Procedural Consideration.
3.11.1 B lind Flightpath Segments. If the FAP is not established directly downwind and the final approach course is not directly upwind, a homing approach will result. A homing approach can result in blind flightpath segments. This means that, with wind speeds as low as 0.3 of the airspeed, segments of the flightpath may not be visible to the radar operator when using a 40-degree sweep angle. When using a 120-degree sweep angle, a wind speed of 0.9 of the airspeed may cause blind flightpath segments. Homing
3-12 approaches can occur whenever the wind speed-to-airspeed ratio is greater than or equal to:
sweep anglesin = 2
3.11.1.1 No-Wind Condit ions. In a no-wind condition, a target return 1 NM to the left or right of the 0-degree azimuth mark will disappear from the radar display at the following ranges as the distance to the target decreases:
Table 3-1. No Wind Sweep Angle Range 120 degrees 0.58 NM 80 degrees 1.19 NM 60 degrees 1.73 NM 40 degrees 2.75 NM
3.11.1.1 Cross-Wind Conditions. When a wind causes a 10-degree crab, or in a 10-degree offset approach, a target 1 NM to the side of the 0-degree azimuth mark away from the crab or offset will disappear at the following ranges:
Table 3-2. Cross Wind Sweep Angle Range 120 degrees 0.84 NM 80 degrees 1.73 NM 60 degrees 2.75 NM 40 degrees 5.67 NM Note: Lateral obstacle clearance is accomplished by radar and therefore it is important that the FAP is clearly established.
3.12 Missed Approach Area.
3.12.1 Clear Zone. The clear zone in Figure 3-3 is designed to protect the missed approach. The dimensions of this figure are based on a helicopter being on track at the MAP with a ground speed of 70 knots and a climb gradient of no less than 304 ft/NM (355 ft/min).