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Alternate Missed Approach Procedures

Alternate Missed Approach Procedures



Missed Approach Procedure coding is accomplished as an integral part of the Approach Procedure Coding and is provided for each approach procedure contained in the Navigation database. Specific coding is incorporated to facilitate the identification of where the Missed Approach Coding starts within any given approach procedure.

If a navaid used on a missed approach procedure is out of service, the entire procedure would become unavailable. Alternate missed approach procedures are a way to get around the failure of one navaid rendering the entire procedure useless even though the primary navaid is still available.

For example, if the missed approach for an ILS is based on flying to a VOR and that VOR is out of service, it would render the ILS unusable even though the localizer and glide slope are functioning.

When ATC clears an aircraft for an approach, it authorizes the aircraft to fly the approach and the missed approach procedure without further clearance. Ground-based approaches – ILS, VOR, DME, or NDB approaches are designed so the missed approach is based on a different navaid than the primary approach navaid. This requires that whatever ground stations make up the missed approach procedure are available. These procedures are only for approaches based on ground-based navaids. GPS approaches do not require alternate missed procedures.

So, the FAA has developed alternate missed approach procedures for most ground-based procedures. The alternate procedure may be based on navaids not used in the approach procedure or the primary missed approach.

As per ARINC, only one missed approach can be coded with one approach procedure in the Navigation database.

Figure1 below illustrates an Approach Procedure with a Primary Missed Approach and an Alternate Missed Approach.

Figure 1 – NOTAM & ATIS – Alternate missed approach in use

When the Alternate missed approach procedure is implemented by NOTAM, it becomes a mandatory part of the procedure. The NOTAM will specify both the textual instructions and any additional equipment requirements necessary to complete the procedure. The alternate missed approach holding fix is shown in a separate graphic on the plan view of the approach plate.

The alternate missed approach instructions are not published on the IAP’s chart to avoid confusion, only the primary missed approach flight path is shown. The holding pattern, however, will be on the chart.

ATC may clear the aircraft for the alternate procedure when necessary. ATC will read it to the crew if an alternate procedure is required. When the alternate missed approach is issued prior to beginning the approach, the pilot must either accept it, request a different full approach procedure or coordinate alternatives with ATC if the aircraft is not equipped to fly the alternate missed approach.

The crew may have to suspend the primary missed approach track and manually enter the alternate fixes. However, If the crew is aware that an airport is using an alternate missed approach procedure either by NOTAM and/or ATIS, the crew can manually enter the alternate missed approach procedure into the FMS ahead of time (Figure 2). This will allow the crew to enter the alternate missed approach procedure in advance, and let the FMS fly it, so the crew doesn’t need to manually fly the procedure.

Figure 2 – Primary Missed Approach and Alternate Missed Approach on FMS

 

Sunaina Wanchoo, Technical Support Engineer - The Hub, supports Honeywell Flight Management System for Honeywell Aerospace Technical Support. She can be reached via email at sunaina.wanchoo@Honeywell.com.