ILS approaches

Separate alignment, descent and fix information

The localizer supplies lateral alignment to the runway; the glideslope supplies vertical descent guidance on the front-course ILS. The published procedure also identifies fixes using markers, DME or other authorized means. Approach and runway lighting support the visual transition. Having a localizer needle does not prove a usable glideslope, valid fix identification or available landing lights.

Tuning the charted localizer frequency normally pairs the associated glideslope channel in ILS equipment. Select and identify the received facility, then verify correct receiver/source, signal status and sensible indications for the charted position. ILS identification is a Morse identifier beginning with I. Use actual decoded received identification or listen as appropriate; a stored airport label alone does not prove the signal. Maintenance or an outage can leave misleading indications. Do not use an approach NOTAMed out of service simply because identification or needles appear.

The localizer course is fixed by the transmitter, not moved by turning an OBS knob. Set the charted front course as appropriate for the installation’s HSI, flight director and autopilot. Understand its sensing and flags from the supplement. A GPS final-leg depiction does not authorize replacing required localizer guidance. The basic initial-rating operation here is a conventional Category I ILS, with minima from the actual chart and capability.

AIM 1-1-9: ILS components, pairing, identification and sensing · AIM 1-1-11: maintenance identification and out-of-service procedures · ACS II.B.K2a, printed page 6: VOR/DME/ILS navigation equipment (ILS scope here)

Respect coverage and suspect unusual indications

Normal localizer service covers 18 NM within 10° of the front course and 10 NM between 10° and 35°, within its specified altitude band. The current AIM describes that band from 1,000 feet above the highest terrain along the course to 4,500 feet above the antenna elevation. A charted expanded service volume may support more; ATC has specified radar-monitored provisions beyond the standard volume. Do not invent your own long-range intercept from a moving-map needle.

The normal glideslope is usually usable to 10 NM unless expanded coverage is certified. False paths and reverse sensing can occur well above the published path. An apparently centered needle at an unexpected high altitude is not proof of the correct glideslope. Plan to intercept the valid path from below at the charted/assigned altitude and proper final course, following aircraft-specific capture procedures. Cross-check charted fix/altitude geometry and monitor actual descent.

On a localizer back course, false glideslope indications may appear even without a warning flag. Disregard them unless a glideslope is specifically provided by the published procedure. Fly a back-course approach only when published and authorized; sensing depends on the installation. Vehicles and aircraft near ILS antennas can distort guidance. Critical-area protection is conditional and is not guaranteed at a nontowered airport or in all good-weather operations. Monitor a coupled approach and be ready to intervene.

AIM 1-1-9: localizer/glideslope volumes, false paths and critical-area interference · IFH Chapter 9, printed 9-40: ILS false courses and reflections

Brief a usable ILS and its alternatives

Confirm the exact current ILS procedure, assigned transition, frequencies/identifier, required equipment, final course, intercept altitude, fixes, applicable category, DA and visibility, missed route/gradient and current NOTAMs. Read chart notes and the current TPP inoperative-components information. A light outage can change visibility; an equipment requirement can affect whether a particular line is available. Use only the adjustment authorized for that procedure and operation.

ILS Category I/II/III describes an ILS operational category, not the aircraft approach-category A/B/C speed band. The charted ILS DA may be higher than common textbook examples. Do not assume “200 and one-half” everywhere. Higher-category minima, unavailable altimeter sources, chart notes and actual aircraft approval can change the usable operation. Special CAT II/III, autoland and low-visibility authorizations are outside this initial-rating lesson.

Confirm how the required fixes are identified. A middle marker is no longer generally required. An outer marker can have an authorized substitute such as charted DME/fixes, radar or suitable RNAV fix identification. That does not mean any GPS distance can be treated as the marker. When marker equipment is used, recognize its actual light/audio indications: the outer marker is blue with dashes, the middle marker amber with alternating dots/dashes, and the inner marker white with dots. Current AIM recommends the receiver’s low sensitivity for proper marker reception. Verify power, audio/indicator checks and any sensitivity control using the actual installation documentation; a lamp/audio test proves its test circuit, not receipt of the correct fix. A middle marker is not generally required; use the charted required marker or authorized substitute. Brief the separate LOC line, stepdowns/MAP and MDA only if it is a usable planned alternative; its minimum is not the ILS DA.

AIM 1-1-9: markers/substitutes, ILS minima and inoperative components · AIM 5-4-5: equipment and altimeter notes · AIM 5-4-7: aircraft speed category · 14 CFR §91.175(b), (k): minimums and authorized fix substitution

Make capture a verified sequence

Retain the assigned altitude on vectors/unpublished routing until established on the appropriate published segment unless ATC instructs otherwise. Follow each restriction. An approach clearance is not permission to intercept a glideslope early and descend through an outside-final crossing restriction. Current AIM guidance requires compliance with restrictions outside the precision final approach point (PFAF), even when following vertical guidance.

Prepare the source, course and modes using the actual AFM/POH/supplement. Establish a manageable lateral intercept, verify localizer capture/track, and remain at the authorized glideslope-intercept altitude until the valid path is reached. Whether a mode is armed or active and the conditions for capture vary by installation; confirm annunciations and aircraft response. A source auto-switch or a GPS-to-LOC change should be expected, checked and understood before the busy segment.

Intercept the valid glideslope from below rather than chasing a high indication downward. At the published final interception, begin the planned stable descent and confirm altitude, fix and mode agreement. LOC-only stepdowns in the final segment do not apply to an approved ILS DA descent on its valid glideslope; preceding restrictions still apply. If too high, fast, poorly positioned or unable to capture safely, advise ATC and obtain vectors or fly an appropriate missed instead of forcing capture.

14 CFR §91.175(i): altitude until established · AIM 5-4-5: outside-final restrictions versus approved vertical final · AIM 1-1-9: glideslope interception and false-course cautions · ACS VI.B.S4/S6, printed page 15–16

Use a planned rate, then monitor the path

Determine an initial descent rate from the charted angle and anticipated groundspeed, not indicated airspeed alone. For an invented 3.0° path, descent gradient is approximately 318 ft/NM. At 90 knots groundspeed (1.5 NM/min), that is about 477 ft/min; at 120 knots (2 NM/min), about 636 ft/min. The familiar groundspeed-times-five estimate is only an approximation. Use a charted rate table or a suitable calculation for the actual angle.

These rates help establish the descent as guidance begins; they are not universal pitch/power settings. Use aircraft-specific configuration, approach speed and power guidance. Adjust to follow the valid glideslope while monitoring attitude, airspeed, altitude, vertical rate, lateral trend and distance. Wind changes alter the required rate. Use small anticipatory corrections because localizer/glideslope indications become more sensitive nearer the runway.

Complete the relevant landing checklist and configure in time to meet trained stabilized criteria. Excess speed, late drag changes, large needle deviations or an excessive descent rate demand a decision before DA. Following the glideslope does not prove the aircraft is stable or landing performance adequate. An MFD supports position/drift awareness but must not replace the scan or signal checks. Stay on the valid path; flying below it can jeopardize obstacle clearance.

IPH Chapter 4, printed 4-37: stable approach and required descent rates · AC 120-108A §3.4, printed 3-3–3-4: angle/gradient/rate arithmetic · AIM 1-1-9: below-glidepath and threshold-crossing cautions · ACS VI.B.K4/S11–S12, printed 15–16

Decide at DA and preserve a normal visual path

DA is the published MSL altitude for the decision; DH is a height reference where specified. Use the actual chart and altimeter/minimums equipment required for that operation. Ordinary natural-vision continuation requires all three §91.175 conditions: position continuously allowing a normal descent and normal maneuvers, required flight visibility, and a distinctly visible identifiable listed runway reference.

If they are absent at DA/DH, immediately initiate the missed. Do not level at DA, wait for a better view, or continue down the glideslope searching. A DA procedure anticipates the prompt transition to climb; it is different from the no-dip MDA floor on a LOC approach. Seeing approach lights alone permits descent only to 100 feet above TDZE unless red terminating or side-row bars are also identifiable. A runway glimpse cannot rescue inadequate visibility or abnormal geometry.

With all conditions met, transition smoothly to a stable visual path, normal aiming point and normal touchdown-zone landing. Maintain control and instrument cross-check during the change in visual attention. ILS indications below the authorized minimum are not an unconditional instrument path to touchdown; charted threshold-crossing height is a planning reference for the antenna geometry, not a promise about main-wheel height. Cross-check usable visual slope guidance and actual runway/obstacle situation. Go around if stability or required conditions are lost.

14 CFR §91.175(c)–(e): visual descent/landing and missed · AIM 1-1-9: glidepath below DH and antenna/TCH limitations · AIM 5-4-21: missed procedure limitations · ACS VI.B.S13–S15, printed page 16

Plan a failure before it occurs

An inoperative localizer makes the ILS approach unavailable. An inoperative glideslope can leave a published LOC operation, but that requires usable LOC equipment, its own restrictions/MDA/MAP, adequate weather and a prepared supported operation. Do not continue using ILS DA with a failed glideslope. Before final, a change may be manageable after rebriefing and confirming the applicable clearance; after a late failure, a missed is often the safe response. It is never authority to ignore a stepdown or descend below a newly applicable MDA.

Recognize flags, abnormal rate/altitude geometry, intermittent signals and differences between expected path and actual response. Evaluate available independent information. A coupled aircraft can follow a disturbed signal, and “autopilot on” does not repair a failed source. Use the installation’s failure/disconnect/manual-flight procedure and maintain control. Do not troubleshoot by prolonged heads-down reprogramming near minimums.

Inform ATC promptly when workload permits, state the malfunction and remaining capability, and advise unable if the assigned operation no longer fits. Use §91.187 and current reporting guidance. Plan another supported approach or diversion; a different chart to the same failed localizer may not solve the problem. If the failure occurs below DA or after visual transition, use the aircraft go-around and the appropriate below-minimums missed considerations, rather than assuming normal missed protection automatically applies.

AIM 1-1-9: inoperative LOC/GS and signal distortion · AIM 1-1-13: reports of navigation malfunctions · 14 CFR §91.187: IFR equipment malfunction reporting · AIM 5-4-21: below-minimums missed limitations

Verify modes for the climb as well as the descent

Know the installation’s go-around switch, flight-director behavior, autopilot limitations/disconnects, lateral source and missed-navigation sequencing. Some systems require specific source changes, activation or acknowledgement; others perform them automatically. A button labeled go-around is not proof of a commanded climb or a correctly flown missed. Check active modes and aircraft pitch/performance while controlling it.

Brief initial power/pitch/configuration from the actual AFM/POH, climb track, turn/altitude restrictions, gradient and missed hold. Apply the manufacturer’s sequence, establish required performance, verify a positive climb and complete the checklist. There is no generic gear/flap-retraction order or power setting for all single-engine airplanes. If a published or ATC-assigned climb cannot be met, advise before starting the approach when known.

At the missed, retain the specified lateral path and restrictions. A go-around before the normal MAP can begin the climb but does not authorize an early missed turn; maximum altitude restrictions remain. A circling or late/below-DA go-around needs position-specific planning. Review Missed approaches and rehearse the actual panel with an instructor.

AIM 5-4-21: missed track, gradient and timing limitations · AIM 5-5-5: pilot/controller missed responsibilities · ACS VI.C, printed page 17: manufacturer-based missed handling

Keep the decision ahead of the workload

Make the approach brief and equipment/mode preparation before workload peaks. Organize chart/checklists, minima reminders and radio frequencies. Read back clearance restrictions, clarify uncertain instructions and advise unable early. Maintain phase-appropriate two-way communications and obtain landing clearance where required; an ILS clearance alone is not a landing clearance.

Use SRM or CRM to protect the scan. The flying pilot controls and monitors; another qualified crewmember can confirm source, altitude, deviations and decision calls. In single-pilot flight, avoid combining runway search, mode programming and checklist reading at DA. Use concise calls and defer nonessential tasks. Weather deterioration, runway wind, lighting outages and fuel can change the plan; brief what would make a repeat worthwhile and when to divert.

A stable descent to DA and an early prepared missed require less improvisation than attempting to salvage an approach. If ATC changes the runway/procedure, complete a usable new brief and source/fix/minima check before accepting an operation the aircraft cannot safely perform. Request time or vectors if needed.

AIM 5-4-6: clearance and approach responsibilities · AIM 5-4-21: missed planning · ACS VI.B.R6 and S2/S4/S6/S17, printed 15–16

Explore an ILS from entry to the next clearance

With a current chart and the actual supplement, describe the assigned entry, tune/identify/status/source checks, fix substitutions, altitude gates, localizer/glideslope capture, initial descent rate, configuration/checklist, adjusted DA/visibility and complete missed. Change the weather, lights or glideslope status and explain what operation remains. Identify active/armed modes on the actual system during ground training where appropriate.

Practice explaining a late source flag, uncaptured mode, unstable intercept and no-reference DA decision. Name who flies, monitors and communicates. These tolerances are evaluation standards, not permission to violate a clearance, cross below a restriction or continue an unstable approach. This ground lesson prepares the selected ILS flight task; it cannot demonstrate capture, control, checklist use or landing proficiency.

ACS VI.B.S1–S17, printed 15–16 · ACS Appendix 3, printed page 34: approved vertical guidance to DA

FLIGHT SCENARIO

What would change your plan?