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Understanding Instrument Approach Procedure Charts

Overview of Instrument Approach Procedure Charts

• Instrument approach procedure charts can be confusing for first-time users, but they contain essential information for navigation.

• The VOR chart for runway 34 at Carroll County Airport in Maryland serves as a basic example to explore the components of these charts.

Sections of an Approach Chart

• Each instrument approach plate is divided into six sections: margin identification, briefing strip, plan view, profile view, airport sketch, and landing minimums.

Margin Identification

• The margin identifier includes the city and state (Westminster, Maryland), a numbering system identifier, and the responsible organization (FAA).

• The last update date is represented by two digits for the year followed by the number of days into that year; this specific chart was updated on the 140th day of 2021.

• The procedure title indicates it’s a VOR approach to runway 34; not all approaches target specific runways.

• Additional identifiers include the airport name (Carroll County Airport) and its corresponding codes (DMW and KDNW).

• Dates of effectiveness are noted; this particular procedure is valid from June 17 to July 15, 2021. Updates occur every 28 days.

Briefing Strip Details

Procedural Information

• The top stack contains procedural information such as primary navigation type (VOR) with its frequency (117.9) and military channel (126).

• Inbound approach course is specified as 358 degrees magnetic; runway landing distance available is noted as 5100 feet with touchdown zone elevation at 788 feet. Airport elevation is slightly higher at 789 feet.

Middle Stack Information

• Procedure notes may include symbols indicating equipment requirements or exceptions; however, this specific chart has minimal notes present. Symbols like upside-down triangles indicate various procedures or requirements.

• A missed approach textual description provides critical instructions: "climbing left turn to 2900 direct to EMI VORTAC and hold." This description appears multiple times on the chart for clarity.

Communications Information

• Communication frequencies relevant for the approach include weather on 121.25 MHz and Potomac Approach on 125.52 MHz; GCO allows ground communication with ATC via frequency listed above (122.7 MHz).

Plan View Insights

Top-down View Features

Approach Procedures and Minimum Safe Altitudes

Overview of Approach Segments

• The approach includes a Morse identifier and channel 126 for military use, featuring basic segments depicted in a racetrack pattern.

• The solid line racetrack indicates a hold in lieu of procedure turn, contrasting with traditional holds which would be shown as dotted or dashed lines.

• The final approach segment leads directly from the Westminster VOR to the runway, with a graphical representation of the missed approach segment showing a left turn back to the VOR.

Minimum Safe Altitudes (MSA)

• MSAs provide emergency clearance over obstructions, typically offering 1,000 feet above all obstacles within a sector; crucial for instrument approaches when communication with air traffic control is lost.

• Specific MSAs are assigned based on direction: 3,400 feet to the north/west and 2,600 feet to the south/east of the Westminster VOR.

Profile View vs. Plan View

• The profile view presents vertical approach paths side-on compared to the top-down plan view; both show identical segments including holds and missed approaches.

• A graphical depiction illustrates sequential steps for executing a missed approach: initiating a left climbing turn up to 2,900 feet before proceeding direct to the Westminster VOR.

Airport Sketch Details

• An airport sketch resembles an airport diagram but lacks detailed taxiway identifiers; it includes runway dimensions and elevation data along with lighting information such as PAPI lights.

• A time and distance table may indicate how long it takes to travel from final approach fix to missed approach point at various ground speeds (e.g., 4 minutes and 20 seconds at 90 knots).

Landing Minimum Requirements

• The landing minimum section outlines altitude and visibility requirements for approaches, differentiating between straight-in and circling landings based on aircraft categories related to speed.

Understanding Minimum Descent Altitude and Approach Procedures

Relationship Between Elevation Figures

• The height above the threshold is 692 feet, while the minimum sea level (MSL) reading from the altimeter is 1480 feet. This indicates that 692 feet represents the height above ground level.

• By adding the touchdown zone elevation of 788 feet to the height above threshold (692 feet), we arrive at a minimum descent altitude of 1480 feet. This calculation helps clarify how these figures interrelate.

• If there’s confusion regarding these numbers, one can deduce relationships by simple addition or subtraction between them to understand their significance better.

Visibility Requirements for Different Aircraft Categories

• For Category C aircraft, while maintaining a minimum descent altitude of 1480 feet MSL, visibility requirements increase from one mile to two miles. Faster aircraft necessitate better visibility conditions for safe landing approaches.