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Curved Approaches
by Ed Verville
Have you ever looked at an approach plate and won- dered what was up with the curved lines on the plan view? These approaches actually allow you to fly an instrument approach with a curved path
and also provide a glide path down to a Decision Altitude (DA). We have made amazing strides with GPS approaches. The first approaches provided lateral guidance down to a Minimum Descent Altitude (MDA). Sometime later, manu- facturers created approaches with vertical guidance using baro-aiding. The next leap occurred in the United States when the Satellite Based Augmentation System (SBAS) and the Wide Area Augmentation System (WAAS) provided vertical guidance. WAAS approaches provide approach minimums down as low as ILS CAT I minimums, 200-foot DH and 1800 RVR.
AR = Authorization Required
The “AR” in the notes section indicates that special air- craft and aircrew authorization is required. Pilots need to attend specialized training, much like you would for an ILS CAT II authorization. The training will include flying at least two approaches in a full-motion simulator, both as pilot flying and as pilot monitoring, for a multi-pilot crew. The approaches will include normal approaches and being vectored off the approach for re-sequencing. You will also need to perform a published missed approach and com- plete a landing out of an approach. You will subsequently
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(RNP AR)
need to request authorization from the FAA, which will be granted in the form of a Letter of Authorization or Operations Specifications.
The airplane also needs to be certified for RNP AR ap- proaches. The Bombardier Challenger CL-650 with the Pro Line 21 is approved for approaches with an RNP as low as 0.3. This 0.3 is the minimum lateral approach sensitivity. It indicates that a full-scale deflection of the CDI from about the Final Approach Point (FAP) to the Missed Approach Point (MAP) will be about 1/3 of a mile. The approach minimums will actually be based on the sensitivity of the approach capability. Boeing’s 777 is certified for RNP AR approaches down to minimums of 0.12. The lower RNP minimums will provide lower approach minimums.
RNP = Required Navigation Performance
RNP defines performance-based navigation to operate between two points in space or in a block of airspace. In addition to the RNP lateral sensitivity requirement, the approaches also require specific equipment just like when flying a CAT II Approach or flying in RVSM airspace.
Required Equipment
An interesting observation from an RNP AR “required equipment list” indicates that “two GNSS sensors must be available to commence the approach” and “one GNSS sen- sor is required to continue the approach.” This differs from the Flight Management System limitations that require