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suitable navigation information from “one GNSS; or two DMEs; or one VOR/DME; or one IRS”.
RNP AR approaches need to have a clear, unobstruct- ed GNSS signal from the satellites when conducting an approach such as along the ridgeline of mountains in Palm Springs, CA. It is also worth noting that RNP AR approaches do not use or require WAAS. This also means that the lateral distance remains linear from the FAP (yes, Final Approach Point, not Final Approach Fix) to the MAP unlike the angular guidance provided by an LPV WAAS approach.
RF = Radius to a Fix
The curved portions of the approach are referred to as Radius-to-a-Fix legs (RF). In addition to the obvious curved lines, RF legs can be identified on the plan view of the ap- proach charts by the lack of the magnetic course printed on the chart. The profile view identifies the curved path by “LT Arc” or RT Arc” for left turning arc or right turning arc respectively.
Speed Limits
To keep the airplane within the required lateral distance, there may be speed limits. Posted speed limits, such as “Max 210 KIAS” may be printed on the plan view next to an intersection. The manufacturer may establish additional restrictions (e.g. the CL-650 must be fully configured by the Intermediate Fix (IF) on the approach,” and the FAA imposes a maximum airspeed from the FAP to the DA of 140 knots for a CAT C category airplane.
Flying the Approach
Let’s use the Rockwell Collins Pro Line 21 on the CL-650 for demonstration purposes.
When cleared for the approach, proceed directly to the cleared fix, select Approach and VNAV Modes on the Flight Control Panel (FCP), and remember to verify that the appropriate modes were accepted on the Flight Mode Annunciator (FMA). Set a lower altitude in the altitude selector to the FAP altitude or MDA to ensure the aircraft continues on the descent path for the approach. When the Flight Mode Annunciator captures the VGP (Vertical Glide Path), the approach will no longer recognize or capture altitudes in the altitude selector or altitude alerting device. You may now set the missed approach altitude in the alti- tude selector to prepare for a missed approach.
Lastly, confirm that the message on the Primary Flight Display (PFD) switches from “RNP AR ARM” to RNP AR APPR” and verify that the RNP APPR CDI Scale indicates “0.3 nm” prior to crossing the final approach point (FAP).
Now you can pretty much just sit back and watch the magic happen. The airplane will fly curved paths around cities, mountains, or airspace while descending via an FMS-generated glide path down to a decision altitude.
Tolerances
The maximum allowed lateral deviation is two dots, and vertically one dot. The one dot vertical is 75 feet. An amber deviation alert is displayed for deviations beyond the above limits.
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July 2023 / TWIN & TURBINE • 5