Instrument Approaches and Holding

Each segment has a defined purpose, protected area and start and end point. Some segments may begin at a specified point when a physical fix is unavailable.

Primary and secondary areas

Full minimum obstacle clearance is applied across the primary area. In each secondary area it reduces laterally to zero at the outer edge. The aircraft remains protected only when it flies the published tracks, levels, speeds and timing.

The arrival segment connects en-route flight with the IAF. A STAR provides the standard transition, while a published arrival route may connect another fix or facility to the procedure.

Arrival protection

The protected width reduces from the en-route value to the initial-approach value. Convergence is limited to 30 degrees on each side of the route axis. If the route is at least 46 km, 25 NM, long, convergence begins 46 km, 25 NM, before the IAF. On a shorter route it begins at the route start.

MSA and TAA

A minimum sector altitude or terminal arrival altitude provides at least 300 m, 1,000 ft, obstacle clearance within 46 km, 25 NM, of the associated navigation aid, IAF or IF. A TAA is used with a PBN approach and commonly uses a T or Y arrangement with three IAFs around the IF. Where published, the TAA replaces the 25 NM MSA for that arrival.

The initial segment manoeuvres the aircraft from the IAF to the IF. The intermediate segment then stabilises track, speed and configuration before final approach.

Initial segment limits

Track guidance normally leads to the IF. The maximum interception angle is 90 degrees for a precision approach and 120 degrees for a non-precision approach. Full MOC in the primary area is at least 300 m, 1,000 ft, reducing to zero at the secondary-area outer edge.

Reversal procedures

If suitable IAF or IF geometry is unavailable, the procedure may use a 45 degree and 225 degree procedure turn, an 80 degree and 260 degree procedure turn, a base turn or a racetrack. The published direction and timing must be followed because the protected area is specific. A procedure-turn area does not permit a racetrack or hold unless the chart says so.

Racetrack

From overhead the fix, turn 180 degrees onto the outbound track, fly the published one, two or three minutes, then turn 180 degrees in the same direction to intercept the inbound track. A DME distance or intersecting radial may replace time.

Intermediate segment

Descent should be as shallow as practical while the aircraft is configured for final approach. MOC reduces from 300 m, 984 ft, at the beginning to 150 m, 492 ft, at the end. The segment ends at the FAF for an NPA or at the FAP for an approach with a glide path. If no FAF exists, the inbound track becomes the final segment.

The final segment provides alignment and descent. The type depends on whether the operation supplies lateral guidance only or both lateral and vertical guidance.

2D and 3D operations

Terminal procedure families

NPA with and without a FAF

With a FAF, the final segment ends at the MAPt. The optimum FAF distance is 9.3 km, 5 NM, from threshold, and the maximum is normally 19 km, 10 NM. A stepdown fix can produce two OCA/H values, with the lower value used only when that fix is positively identified. Without a FAF, a facility near the aerodrome may serve as both IAF and MAPt. Descent to MDA/H begins only after the aircraft is established inbound.

Visual segment surface

The visual segment surface, or VSS, is a PANS-OPS surface between the approach minimum and the runway threshold. It identifies obstacles that may affect execution of the visual segment after an instrument approach, except a circling approach.

Precision final approach

The precision final segment begins at the FAP, where the intermediate altitude intercepts the nominal glide path. For a 3 degree path this normally occurs 6 to 19 km, 3 to 10 NM, from threshold, at 300 to 900 m, 1,000 to 3,000 ft, above runway elevation. An outer marker or DME fix verifies the glide-path and altimeter relationship. Do not descend below its crossing altitude before crossing it.

A stable final approach avoids abrupt level-offs and late configuration changes. CDFA gives a continuous descent on an NPA while respecting every published altitude.

Continuous descent final approach

CDFA may use VNAV guidance or a manually calculated descent rate. It is flown without level-offs to a point about 15 m, 50 ft, above threshold where flare should begin for the aircraft type. The path must pass at or above every stepdown-fix altitude. Advisory VNAV does not cancel a published restriction.

Stabilised approach

A stabilised approach reaches the required landing configuration, speed, lateral path and descent profile early enough for small corrections. If the approach is not stable by the operator's gate, or the required visual reference is absent at the applicable minimum, go around.

The procedure designer establishes obstacle clearance. The operator converts that design value into an operational minimum by adding any required margin or applying a higher system or operational limit.

Definitions

Reference datum by approach

Type A and Type B

Type A has an MDA/H or DA/H at or above 75 m, 250 ft. Type B has a DH below 75 m, 250 ft. Category I has DH at least 60 m, 200 ft, with visibility at least 800 m or RVR at least 550 m. Category II has DH below 60 m but at least 30 m, 100 ft, and RVR at least 300 m. Category III has DH below 30 m, 100 ft, or no DH, and RVR below 300 m or no RVR limit.

How an operational minimum is formed

The margin above OCA/H can reflect aircraft approach speed and height loss, altimeter system, aerodrome and terrain characteristics, aircraft performance and equipment, meteorological reporting, operating category and crew qualification. A published or approved lower limit overrides a smaller calculated value.

One missed approach is published for each instrument approach. It begins at the defined MAPt or decision point and protects the climb until another approach, hold or en-route phase can begin.

When it starts

For PA or APV, do not initiate below DA/H. For an NPA, begin at the specified MAPt and not below MDA/H. The MAPt may be the intersection of an electronic glide path with DA/H, a fix or facility, or a specified distance from the FAF. If the MAPt is reached without the required visual reference, act immediately.

Standard construction

The normal minimum missed-approach climb gradient is 2.5 percent.

Turning missed approach

A turn is published only when terrain or another factor requires it. The protected area uses the final missed-approach speed for the category. Fly the published sequence before navigating elsewhere, unless ATC issues a safe alternative clearance.

Circling is the visual phase after an instrument approach that positions the aircraft to land on a runway not suitably aligned for a straight-in approach.

The circling area

Protection is built by drawing arcs from runway thresholds and joining them with tangents. The radius is category-dependent and accounts for the permitted circling speed, a 46 km/h, 25 kt, wind throughout the turn, and an average bank of 20 degrees or 3 degrees per second, whichever requires less bank. A promulgated sector may be excluded from the OCA/H calculation when its obstacle lies outside the final and missed-approach areas.

Descent below MDA/H

1. The required visual reference has been established and can be maintained.
2. The landing threshold is in sight.
3. Required obstacle clearance can be maintained.
4. The aircraft is positioned to make a landing using normal manoeuvres.

Loss of visual reference

Apply the missed approach for the instrument procedure. Make an initial climbing turn towards the landing runway and over the aerodrome, then establish on the published missed-approach track. The exact path depends on where visual reference was lost, but the climb towards the aerodrome keeps the aircraft within the circling protection while the published track is regained.

A standard hold has right turns. The inbound track leads to the fix, the outbound leg is flown on the holding side, and the protected area includes entry and wind-correction allowances.

How to fly the pattern

Make each turn with 25 degrees bank or 3 degrees per second, whichever requires less bank. Correct heading and timing for known wind during both entry and established holding. Start outbound timing over or abeam the fix, whichever occurs later. If abeam cannot be determined, start when the outbound turn is complete.

Time and distance

Outbound still-air time is one minute at or below 4,250 m, 14,000 ft, and one and one-half minutes above that level. If DME defines the outbound leg, turn when the limiting distance is reached. A limiting radial may require an earlier inbound turn. Advise ATC promptly if the aircraft cannot remain within normal holding conditions.

A hold followed by an initial approach designed above 230 kt may be published at that higher speed. The 280 kt or Mach 0.8 turbulence value is used only after ATC clearance unless the publication already permits it. The 170 kt value is only for a hold restricted to Categories A and B.

Minimum holding level

The published level provides at least 300 m, 984 ft, obstacle clearance and is rounded up to the next 50 m or 100 ft. Over high or mountainous terrain, total clearance may be increased to 600 m, 1,969 ft. A protected holding area may be surrounded by a 5 NM buffer where MOC tapers from full at the inner boundary to zero at the outer boundary.

Entry depends on arrival heading relative to the three sectors. A five-degree flexibility zone exists on either side of each sector boundary.

VOR and VOR/DME restrictions

For a VOR intersection, entry is limited to the radials forming that intersection. For a VOR/DME fix, the entry track may be the VOR radial, the DME arc, or a published entry radial to a fix at the outbound end. A DME-arc entry is published only when an operational difficulty makes the other entries impracticable.

DME distance and limiting radial

When DME defines outbound length, the outbound leg ends at the limiting DME distance. If a limiting radial is reached first, follow it until initiating the inbound turn. The turn must start no later than the limiting DME distance.

RNAV VOR/DME procedure details

A VOR/DME RNAV arrival and approach uses one indicated reference facility containing collocated VOR and DME equipment and is an NPA. Bali uses the term flight management computer for the multi-sensor RNAV system. Arrival flight technical tolerance is 3.7 km, 2.0 NM, until 46 km, 25 NM, from the IAF, then 1.9 km, 1.0 NM. Final-approach MOC in the primary area is 75 m, 246 ft. The FAF is a fly-by waypoint, the threshold and MAPt are flyover waypoints, and the earliest missed track splays 15 degrees either side until SOC. A missed-approach holding fix, MAHF, marks the end of the missed segment at or after the point where the minimum climb reaches the altitude required for en-route flight or holding.

Simultaneous operations increase runway capacity. The four basic modes differ in whether approaches are independent or dependent, departures are simultaneous, or arrivals and departures are segregated.

Independent approaches, NOZ and NTZ

The normal operating zone extends either side of each final approach course and contains an aircraft operating normally. For Mode 1, only the inner half of each NOZ is relevant. The no transgression zone is the protected corridor centred between extended runway centre lines. It is at least 610 m wide. Any penetration demands immediate controller intervention to protect the aircraft on the adjacent approach.

Monitoring and intercept

Parallel approaches are radar monitored on dedicated frequencies. Only straight-in approaches are used, and track reversal is not permitted. A high side and low side provide 300 m, 1,000 ft, vertical separation until both aircraft are established. For dependent approaches the final intercept angle is no more than 30 degrees, with at least 1 NM of straight and level flight before localiser intercept and at least 2 NM established before glide-path intercept.

Spacing and diverging tracks

Simultaneous missed-approach and departure tracks should diverge by at least 30 degrees. If a controller cannot provide the required surveillance, parallel operations are suspended and single-runway operation resumes.

If the centre-line distance is less than the spacing required by wake-turbulence criteria, the parallel runways are treated as a single runway for departing-aircraft separation. A simultaneous dependent parallel-departure mode is therefore not used.