All About ILS Approach
The Instrument Landing System (ILS) is a precision approach and landing aid system that provides pilots with vertical and horizontal guidance during the final stages of an approach. It consists of several components that work together to facilitate accurate navigation and safe landings.
The ILS approach is of paramount importance in aviation, especially in challenging weather conditions or at airports with limited visibility. It ensures pilots have reliable guidance to maintain the correct glide path and alignment with the runway, reducing the risk of accidents and enhancing overall safety.
Ils Approach Categories
The Instrument Landing System (ILS) approach categories categorize aircraft based on their approach speed and the minimums required for an ILS approach. These categories are defined to ensure that pilots have the necessary equipment, training, and visibility to safely conduct ILS approaches. There are four ILS approach categories, from Category I to Category III, with subcategories within some of them:
- Category I (CAT I):
- Decision Height (DH): 200 feet (or higher) above the threshold.
- Runway Visual Range (RVR): 1,800 feet or more.
- Approach Speed: Less than 90 knots.
- Autopilot Not Required.
- Category II (CAT II):
- DH: Between 100 and 200 feet above the threshold.
- RVR: Between 1,200 and 1,800 feet.
- Approach Speed: 90 knots or more.
- Autopilot May Be Required.
- Category II Enhanced (CAT II-E):
- DH: Between 100 and 200 feet above the threshold.
- RVR: Between 1,200 and 1,800 feet.
- Approach Speed: 140 knots or more.
- Autopilot May Be Required.
- Aircraft equipped with enhanced ILS systems.
- Category III (CAT III):
- DH: Less than 100 feet above the threshold.
- RVR: Less than 1,200 feet.
- Autopilot and Autothrottle Required.
- May have subcategories:
- Category III A (CAT IIIA): DH less than 100 feet, RVR less than 700 feet.
- Category III B (CAT IIIB): DH less than 50 feet, RVR less than 700 feet.
- Category III C (CAT IIIC): No DH and no RVR minimums. Allows for "zero-zero" landings.
The specific requirements and equipment needed for each category can vary based on the aircraft type, manufacturer, and airline procedures. Pilots must be appropriately trained and certified to conduct ILS approaches in their respective categories, and the aircraft must be equipped with the necessary avionics and systems to support these approaches.
Category III approaches, especially CAT III C, are the most advanced and allow for landings in extremely low visibility conditions. These approaches are typically used at major international airports and are part of the advanced equipment and training needed for airlines to operate in such environments.
How to interpret an approach plate
Interpreting an approach plate, which is a critical skill for instrument-rated pilots, involves understanding the various symbols, numbers, and information presented on the chart. Here's a step-by-step guide on how to interpret an approach plate:
- Title and Identification:
- Identify the airport and runway for which the approach plate is intended. Note the ILS frequency or other navigation aids relevant to the approach.
- Topographic Information:
- Study the topographic information to get a sense of the airport's layout, nearby terrain, and any significant landmarks. This will help you understand the geographical context of the approach.
- Procedure Information:
- Determine the type of approach (ILS, LOC, or a combination) and the final approach course. Pay attention to any specific instructions for the approach, including headings, altitudes, and restrictions.
- Profile View:
- Review the side view of the approach, which depicts the descent profile from the initial approach fix (IAF) to the runway. Key elements to look for include:
- Altitudes: The chart will show step-down altitudes at specific locations on the approach. These indicate the minimum altitudes you should maintain at each point.
- Glideslope Intercept: Identify the location where you intercept the glide slope, typically depicted with a lightning bolt symbol.
- Decision Altitude (DA) or Decision Height (DH): This is the altitude or height at which you must decide whether to continue the approach or execute a missed approach. It's a crucial reference point for decision-making.
- Visual Descent Point (VDP): If applicable, this is the point along the approach path where you should have visual contact with the runway environment. It aids in determining if you can continue the approach.
- Review the minimums section to find the decision altitude (DA) or decision height (DH) and visibility requirements. These are the critical criteria for initiating a landing or a missed approach.
- Radio Frequencies:
- Identify the relevant radio frequencies, including the ILS frequency, localizer frequency, marker beacon frequencies, and air traffic control communication frequencies.
- Missed Approach Procedure:
- Study the missed approach procedure for the approach. Note the initial climb heading, the altitude to which you should climb, and the subsequent actions to be taken. This information is essential if you need to abandon the approach and go around.
- Final Approach Fix (FAF):
- Find the location of the final approach fix, usually indicated with a crossing altitude and a distance from the runway threshold. The FAF is where the final segment of the approach begins.
- Airport Information:
- Review any airport-related information, including the layout of runways, taxiways, and relevant taxi instructions. Ensure you're familiar with the airport's geography.
- Communication and Navigation Aids:
- Verify the communication frequencies and navigation aids used during the approach, such as VORs, NDBs, and marker beacons.
- Additional Notes and Cautions:
- Carefully read any notes and cautions provided on the approach plate. This may include information on terrain obstacles, special procedures, or other considerations for the approach.
Remember that interpreting an approach plate is a dynamic process that requires attention to detail, especially regarding altitudes, headings, and the decision altitude/height. Before flying an ILS or any instrument approach, pilots should thoroughly review the approach plate, understand the key elements, and be prepared to execute the approach procedures precisely, particularly in low-visibility conditions.
How the ILS Approach Works
The ILS system consists of three primary components: the localizer, glide slope, and marker beacons. Each component plays a crucial role in providing pilots with the necessary guidance for a smooth and accurate landing.
The localizer and glide slope signals are transmitted by ground-based transmitters and received by antennas on the aircraft. Pilots use these signals to maintain the correct lateral and vertical course alignment throughout the approach and landing phase.
ILS approach charts are essential resources that outline the necessary procedures and information for pilots to execute a successful ILS approach. Pilots carefully study these charts to ensure they follow the correct path and adhere to any specific guidelines or considerations provided.
- Components of ILS:
- Localizer (LOC): The localizer is a ground-based radio transmitter located at the far end of the runway. It emits a narrow radio beam that provides lateral guidance for the aircraft. The localizer beam is aligned with the extended centerline of the runway, helping the pilot maintain the correct course to the runway.
- Glideslope (GS): The glideslope transmitter is typically located near the runway and emits a vertical radio beam that guides the aircraft's descent path. The glideslope provides vertical guidance, ensuring the aircraft maintains the proper rate of descent to reach the runway's touchdown zone.
- Marker Beacons: Marker beacons are ground-based radio beacons that provide distance information to the aircraft. They are typically located along the approach path and indicate specific distances from the runway. There are three types of marker beacons: Outer Marker (OM), Middle Marker (MM), and Inner Marker (IM).
- Receiver and Instruments: The aircraft is equipped with an ILS receiver and related instruments in the cockpit. The ILS receiver receives signals from both the localizer and glideslope transmitters. These signals are processed and displayed on instruments, such as the Course Deviation Indicator (CDI) for lateral guidance and the Vertical Speed Indicator (VSI) for vertical guidance.
- Establishing the ILS Approach:
- Before initiating an ILS approach, the pilot must receive clearance from air traffic control (ATC) to use the ILS. ATC will provide the necessary instructions and clearances.
- The pilot selects the appropriate ILS frequency and course (localizer) on the navigation radios.
- As the aircraft approaches the ILS intercept point, the pilot tunes in to the glideslope frequency to receive vertical guidance.
- Following the ILS Guidance:
- Lateral Guidance (Localizer): The CDI on the aircraft's instrument panel displays the aircraft's lateral position relative to the localizer course. The pilot adjusts the aircraft's heading to keep the CDI centered, ensuring alignment with the runway.
- Vertical Guidance (Glideslope): The VSI or vertical speed indicator provides information on whether the aircraft is above, below, or on the glideslope. The pilot adjusts the aircraft's pitch attitude and power to maintain the desired rate of descent along the glideslope.
- Marker Beacon and Decision Altitude/Height:
- As the aircraft descends on the glideslope, it may pass over marker beacons. Each marker beacon emits a distinctive signal that is received in the cockpit, indicating specific distances from the runway.
- At a predetermined point along the approach path, the pilot reaches the decision altitude (for precision approach) or decision height (for precision approach with radio altimeter). At this point, the pilot makes a critical decision to either continue the approach to land or execute a missed approach if visual contact with the runway and necessary visual references are not established.
- Landing or Missed Approach:
- If the aircraft has the required visual references in sight and the runway environment is visible, the pilot proceeds with the landing.
- If the pilot does not have the required visual references by the decision altitude/height, a missed approach procedure is initiated, and the aircraft climbs away from the runway to a safe altitude.
More information about ILS Approach
- FAA Instrument Flying Handbook (Chapter 16):
- The FAA's Instrument Flying Handbook contains detailed information on instrument approaches, including ILS approaches. Chapter 16, titled "Approaches," provides comprehensive coverage of ILS procedures, components, and techniques.
- FAA Instrument Flying Handbook - Chapter 16
- Jeppesen Instrument/Commercial Manual:
- Jeppesen's Instrument/Commercial Manual is a widely used resource by pilots in their instrument and commercial flight training. It covers ILS approaches and other advanced aviation topics in-depth.
- Jeppesen Instrument/Commercial Manual
- AOPA's IFR Insights: ILS Approaches:
- The Aircraft Owners and Pilots Association (AOPA) offers informative articles and insights into ILS approaches, explaining the procedures and providing tips for successful ILS flying.
- AOPA's IFR Insights on ILS Approaches
- YouTube Tutorials and Videos:
- YouTube has a wealth of video tutorials and flight demonstrations related to ILS approaches. Search for videos that provide step-by-step guidance on ILS procedures, cockpit views of ILS landings, and tips from experienced pilots.
- Flight Training Organizations and Schools:
- Many flight training organizations and flight schools offer comprehensive training materials and courses on ILS approaches as part of their instrument and commercial pilot training programs. Contact a local flight school or training center for resources and training options.
- Aviation Forums and Communities:
- Online aviation forums and communities, such as those on websites like Pilots of America (POA) and Reddit's r/flying, often have discussions, questions, and shared experiences related to ILS approaches. You can learn from the experiences of other pilots.
- Aviation Books:
- Consider reading aviation books that focus on instrument flying and ILS approaches. Titles like "Instrument Flying Handbook" by the FAA and "The Instrument Flight Manual" by William K. Kershner are valuable resources.
- Aircraft Manufacturer's Documentation:
- Aircraft manufacturers often provide specific guidance on operating their aircraft during ILS approaches in the aircraft's pilot operating handbook (POH) or flight manual. These documents can provide insights into aircraft-specific procedures.