1. Introduction
Radar guided approaches continue to be available at some airports. These may be approaches to runways that have no other instrument letdown procedures, or back-up approaches in the event of unserviceable navaids.
There are two types of radar approaches: precision and non-precision. Since the only airborne equipment required is a functioning radio transceiver, the type of approach is only dependent on the type of ground radar used.
The precision approach is called Precision Radar Approach, also known as Precision Approach Radar (PAR) approach. A PAR approach is one in which accurate navigation guidance in azimuth and elevation is given by the radar controller.
Older systems use two separate antennas, one scanning the vertical plane and one scanning horizontally, modern systems use a single antenna.
Only the final approach area is covered and the range is usually limited to 10 NM, azimuth to 20° and elevation to 7°. Because of this, it can only be used for the runway for which it has been installed and calibrated.
PAR is typically a military system and is therefore mostly found at military airports or combined military/civil airports.
Normally a PAR unit is combined with a collocated Surveillance Radar Element (SRE).
The military use the term “Ground Controlled Approach” (GCA) for such a combination, while the correct ICAO term is “Precision Approach Radar System” (PARS).
At some airports, PAR may be used to monitor ILS or other approaches, but of course only if the final approach track as well as the ILS glide path, or VOR or NDB approach angle, coincide.
The non-precision approach is called Surveillance Radar Approach (SRA), also known as SRE approach or Aerodrome Surveillance Radar (ASR) approach.
An SRE approach is one in which a normal TMA radar facility is used to provide azimuth guidance to the pilot on final. Although specifically certified for this purpose, an SRE approach is less precise than a PAR approach, and higher limits apply.
One SRE installation can be used for several or all runways at one or more airport(s).
The ROM provides a summary of PAR and SRE approach procedures for in-flight use.
2. SRE Approach Segments (ICAO)
The initial approach segment begins at the IAF, defined as the position at which radar contact with the aircraft for the purpose of executing a radar approach is established, and ends at the IF. In this segment, radar vectoring is provided along predetermined tracks or on a tactical basis.
The intermediate segment begins at the IF, the point where the initial approach track intersects the intermediate approach track. The maximum angle between initial and intermediate tracks is 90°.
Because the intermediate segment is intended to prepare the aircraft speed and configuration for entry into the final approach segment, the gradient should be flat. However, where needed a maximum gradient of 5% (2.8°) may be used.
The intermediate track will normally be in-line with the final approach track, but may differ from the final approach track up to 30°, where needed.
The optimum length of this segment is 5 NM, maximum 15 NM. In case of airspace restrictions, this may have to be reduced to 1.5 NM, depending on the angular difference between the initial and intermediate tracks.
The intermediate track intersects the final approach track at the FAF.
The final approach segment begins at the FAF, which is a radar fix on the final approach track, and ends at the MAPt or the runway threshold, whichever occurs last.
The minimum length is 3 NM, maximum 6 NM, depending on the approach angle.
For straight-in approaches, the final approach track coincides with the extended runway centre line. For Circling approaches, the final approach track will cross the Circling area or intercept the down wind leg of the Circling pattern.
An SRE approach is normally not possible when the distance between the radar antenna and either the FAF or MAPt is more than 20 NM, see Figure 1.
3. PAR Approach Segments (ICAO)
The initial and intermediate segments are normally based on the use of SRE, see before, except that there is no IF defined at the end of the initial SRE segment.
The last part of the SRE intermediate segment, normally in-line with the final approach track, will bring the aircraft into a combined PAR intermediate and final approach area along the extended runway centre line, maximum length 15 NM.
The PAR intermediate segment transforms into the final approach segment at the point where the aircraft intercepts the final descent path, identical to FAP for ILS.
This point of descent shall be within 2 NM of the PAR coverage.
In absence of an SRE, charted VOR or NDB guidance may have to be used to bring the aircraft within PAR coverage.
4. Recommendations for Radar Approaches
- The approach should be flown stabilised. This allows for small and accurate corrections to the flight path from established stable reference values. Refer to the AOM non-precision flight techniques.
- All instructions should be followed without delay.
- An alternative course of action, to adopt in case of radar failure, must be planned in advance: the approach could either be continued using non-radar facilities, or completed visually.
- The approach should be monitored by all available radio navaids. This will not only aid in enhancing situational awareness and terrain avoidance, but will also assist the pilot in anticipating required configuration changes before establishing on final approach.
- When planning a Circling procedure after a radar approach, inform ATC of your aircraft category: this allows ATC to provide the correct Circling OCA/H.
5. General ICAO SRE and PAR Procedures
- The aircraft will be advised of the nominal glide path angle and, on request, the approximate rate of descent to be maintained on final.
- Unless published, the aircraft will be advised of the COM failure procedure.
- The aircraft will be advised of its position at least once before commencing final approach, as well as of the type of approach and the runway to be used. These are standard initial approach radar procedures, not only applicable for SRE / PAR final approaches.
- All headings, altitudes and altimeter settings shall be acknowledged until advised not to acknowledge further transmissions.
- The aircraft is given explicit heading instructions to correct for centre line deviations.
- The aircraft is informed of glide path deviations (PAR), or advisory altitudes or heights (SRE), and is expected to adjust the aircraft’s rate of descent accordingly to regain the correct profile.
- On final approach, the aircraft will be reminded to check that wheels are down and locked.
- Landing clearance, or any alternative clearance, is normally passed to the aircraft before 2 NM from touchdown.
The aircraft shall be directed, stating the reason, to execute a missed approach:
- When it appears to the controller that the aircraft is dangerously positioned on final; or
- For reasons involving traffic conflicts; or
- If no landing clearance has been received by the SRE or PAR controller from the TWR before a distance of 2 NM, or such other distance as agreed with TWR, from touchdown; or
- When instructed by TWR.
The aircraft shall be advised, stating the reason, to consider executing a missed approach:
- When the aircraft reaches a position from which it appears to the controller that a successful approach cannot be completed; or
- If the aircraft is not visible on the radar display for any significant interval during the last 2 NM of the approach; or
- If the position of the aircraft is in doubt during any part of final approach.
The pilot should assume a COM failure to exist when radio contact is lost for five (5) seconds when on final for a PAR approach, or when within 4 NM from touchdown on an SRE approach that terminates less than 2 NM from touchdown.
Unless ATC has previously issued a specific radar or COM failure procedure, the pilot is cleared to fly any published approach when radar has failed or communication has been lost. If possible, remain in VMC.
6. The Surveillance Radar Approach
During an SRE approach, the radar controller provides distances from touchdown, azimuth instructions and advisory altitude, or height, information so as to enable the aircraft to carry out the approach.
CAUTION: In certain countries controllers may assume that aircraft use a QFE setting on final and they will consequently provide advisory heights instead of altitudes.
The pilot shall be informed at regular intervals of the aircraft’s position in relation to the extended runway centre line. Heading corrections shall be given to bring the aircraft back on the extended centre line in accordance with the PAR approach technique.
In case of azimuth deviations, the pilot is expected to follow the explicit instructions of the controller without delay.
At or before the start of the final approach, the pilot will be informed of the point at which the SRE approach will be terminated. This is, whichever is the earliest:
- Normally at a distance of 2 NM from touchdown; or
- Before the aircraft enters an area of continuous radar clutter; or
- When the pilot reports that a visual approach can be made.
The pilot will be advised when he is approaching the point at which descent should begin. Just before reaching that point, he will be informed of the straight in or Circling OCA/H and instructed to commence descent and check applicable minima.
Pre-computed altitudes, or heights, through which the aircraft should be passing shall normally be passed every 1 NM at the same time as the distance.
These altitudes, or heights, assume 50 ft height at the threshold and are rounded off to 100 ft increments up to 2 NM from the threshold, thereafter to 10 ft.
ICAO recommends States to use an approach angle of 2.8° (5%): 300 ft/NM.
Distance from touchdown shall normally be transmitted at intervals of 1 NM until the aircraft reaches a distance of 4 NM from touchdown. Thereafter, distance information should be transmitted at more frequent intervals, although not at the expense of azimuth information.
NOTE: In certain countries the controller will inform the pilot when to start final descent, while subsequent advisory altitudes, or heights, at each mile will only be provided if requested by the pilot before starting the approach.
However, any step-down fixes on final will always be given, because these are mandatory values, given for reasons of obstacle clearance, not as “advisory” altitudes or heights.
If the accuracy of the radar system permits and when approved by the appropriate ATS authority, SRE approaches may be continued to the threshold of the runway, or to a prescribed point that is less than 2 NM from touchdown. In this case:
- Distance and altitude information shall be given at each half NM.
- The aircraft will be advised that no further acknowledgement of transmissions is required when within 4 NM of touchdown.
- While the aircraft is within a distance of 4 NM from touchdown, transmissions should not be interrupted for more than five (5) seconds.
- The radar controller should not be responsible for any duties other than those directly connected with a particular approach.
7. Communications Example SRE Approach
In the following example it is assumed that the aircraft has been vectored to intercept the final approach track at 8 NM from touchdown at 2200 ft QNH and that the touchdown elevation is 300 ft.
| Controller | Aircraft |
|---|---|
| FCG 123, this will be a surveillance radar approach to runway 27, terminating at 1 mile from touch down. Obstacle clearance altitude 400 ft. Maintain 2200 ft. Check your minima. | Maintain 2200 ft, runway 27, FCG 123. |
| FCG 123, turn right heading 275, final approach, report runway in sight. | Heading 275, FCG 123. |
| FCG 123, approaching 6 miles from touchdown, commence descent now to maintain a 3° glide path. | FCG 123 descending. |
| FCG 123, check wheels down and locked. | FCG 123. |
| FCG 123, 5½ miles from touchdown, altitude should be 2000 ft. | FCG 123. |
| FCG 123, going right of track, turn left heading 270. | Heading 270, FCG 123. |
| FCG 123, 5 miles from touchdown, altitude should be 1900 ft. | FCG 123. |
| FCG 123, closing slowly from the right, 4½ miles from touchdown, altitude should be 1700 ft. | FCG 123. |
| FCG 123, cleared to land, wind calm. | Cleared to land, FCG 123. |
| FCG 123, 4 miles from touchdown … altitude should be 1600 ft … do not acknowledge further transmissions. 3½ miles from touchdown … altitude should be 1400 ft. On track … turn right heading 272 … 3 miles from touchdown … altitude should be 1300 ft. 2½ miles from touchdown … altitude should be 1100 ft. 2 miles from touchdown … altitude should be 900 ft. On track … heading is good … 1½ miles from touchdown … altitude should be 800 ft. On track … 1 mile from touchdown … approach completed. |
8. The Precision Radar Approach
During a PAR approach, the controller provides information on position relative to the extended runway centre line and glide slope, and instructions on corrective actions.
When the aircraft is transferred to the PAR controller, normally not less than 1 (one) NM from interception of the glide path, a radio check shall be made on the discrete frequency to be used for the approach. The pilot will then be advised that no further acknowledgement of transmission is required.
Interruption of transmission should not occur for more than five (5) seconds during final approach.
The aircraft shall be informed at regular intervals of its position in relation to the extended runway centre line. Heading corrections shall be given to bring the aircraft back on the extended centre line: the pilot should not take corrective action unless specifically instructed to do so.
The aircraft shall be informed when it is approaching the point of interception of the glide path and, just before interception, it shall be instructed to begin its descent and to check the applicable minima.
Thereafter, the aircraft shall be informed at regular intervals of its position in relation to the glide path. Deviations from the glide path shall be given, together with instructions to adjust the rate of descent if corrective action does not appear to be sufficient.
Contrary to azimuth deviations, the pilot is expected to take corrective action regarding glide path deviations on the basis of information given by the controller, even though not specifically instructed to do so. Before the aircraft reaches a point 2 NM from touchdown, or a greater distance as necessary for faster aircraft, a certain degree of tolerance will be allowed with regard to deviations from the glide path: elevation information will not specify the actual number of metres or feet above or below the glide path unless this is required to emphasise the rate of change or the extent of the displacement.
Thereafter, any deviations from the glide path will be given to the aircraft, preferably in terms of specific distances, metres or feet, above or below the glide path.
The use of emphasis in the manner in which the information is transmitted should normally be sufficient to expedite action by the pilot when necessary, e.g. “STILL 60 feet too low”.
Distance from touchdown shall be transmitted at intervals of 1 NM until the aircraft reaches a distance of 4 NM from touchdown. Thereafter, distance information should be transmitted at more frequent intervals, although not at the expense of azimuth and elevation information and guidance.
Should the elevation element fail during final approach, the radar controller will inform the aircraft immediately. If possible, the controller shall change to an SRE approach, informing the aircraft of the revised OCA/H. Alternatively; instructions should be given for a missed approach.
A precision radar approach is terminated when the aircraft reaches the point at which the glide path intersects with the OCA/H, or when the aircraft reports VMC. Nevertheless, advisory information is in some cases given, without notification, until the aircraft is over the threshold or has reached a specified distance from it.
When the controller can see, via the elevation element, that the aircraft may be initiating a missed approach, he will take the following action:
- When there is sufficient time for a reply, aircraft is more than 2 NM from touchdown, the controller will transmit the aircraft’s height above the glide path and ask if the pilot intends to make a MISAP. Upon confirmation by the pilot, the controller shall pass MISAP instructions.
- When there is not sufficient time for a reply, aircraft is less than 2 NM from touchdown, the precision approach shall be continued, emphasising the aircraft’s displacement, and terminated at the normal termination point. If it is apparent that the aircraft is making a MISAP, either before or after the normal termination point, the controller shall pass MISAP instructions.
9. Communications Example PAR Approach
In the following example it is assumed that the aircraft has been radar vectored into PAR coverage and has been identified to the PAR controller by radar transfer. It is based on a published 3° glide path to runway 27.
| Controller | Aircraft |
|---|---|
| FCG 123, —— (name) Precision, report heading and altitude. | Maintaining 3000 ft, heading 240, FCG 123. |
| FCG 123, position 6 miles east of ——- (airport), turn right heading 260, descend to 2500 ft, QNH 1014. | Heading 260, descend 2500 ft, QNH 1014, FCG 123. |
| FCG 123, closing from the right, turn right heading 270. | Right heading 270, FCG 123. |
| FCG 123, approaching glide path, heading is good. | FCG 123. |
| FCG 123, how do you read? | Read you 5, FCG 123. |
| FCG 123, do not acknowledge further transmissions, on track, approaching glide path … check your minima … commence descent now at 500 ft per minute … I say again 500 ft per minute … check wheels down and locked … on glide path, 5 miles from touchdown … turn right 5 degrees, new heading 275, I say again 275 … 4 miles from touchdown, slightly below glide path … below glide path 100 ft, adjust rate of descent … 50 ft below glide path, turn left heading 270, 3 miles from touchdown … coming back to the glide path … on glide path … 2½ miles from touchdown … FCG 123, cleared to land (by TWR) … on glide path … heading 270 is good, slightly above glide path … 2 miles from touch down … coming back to the glide path … on glide path, 1¾ miles from touchdown … turn right 2 degrees, new heading 272 … 1½ miles from touchdown … on glide path, 1¼ miles from touchdown, rate of descent is good, on glide path 1 mile from touchdown … ¾ of a mile from touchdown, on glide path … on centre line … ½ mile from touchdown, on glide path, ¼ mile from touchdown, approach completed. |
NOTE:
- The controller may request the pilot to provide him with the applicable minima before starting final approach, instead of only advising “check your minima”.
- He will advise the pilot upon reaching the given DA.
- Information beyond this particular DA is then of an advisory nature only.
- In order to avoid blocking the PAR frequency too long, the pilot should contact TWR as soon as possible after termination of the approach. This may be after landing.