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are now capable of direct flight over long distances
with increasing precision. Furthermore, RNAV
(RNP) instrument approach procedures are now
capable of precision curved flight tracks. [Figure A13] The availability of RNAV equipment has reached
all facets of commercial, corporate, and general aviation. Airborne navigation databases have played a
large role in this progress.
Although database providers have implemented a standard for airborne navigation databases, pilots must
understand that RNAV is an evolving technology.
Information published on current aeronautical charts
must be used in cases where discrepancies or uncertainties exist with a navigation database. There are many
variables relating to database, manufacturer, and user
limitations that must be considered when operating with
any RNAV equipment. Manufacturer documentation,
aeronautical charts, and FAA publications are the pilot’s
best source of information regarding these capabilities
and limitations.
Figure A-13. Example of an RNAV (RNP) RF Leg Segment and Associated FMS Control Display Unit.
SETOC
FONVI
JUBOL
WIRSO
LEGEND
RNP 2 = RNP Value of 2.00 NM
2 RNP = 2 Times the RNP Value (2 x RNP)
2 x RNP
2 x RNP
RNP Segment
Width (4 x RNP)
RF Leg (Constant
Radius Arc)
Course Centerline
(RF Flight Track)
Arc Ending Point
(Segment Terminating Fix)
Next
Segment
Radius 1.5 NM
(Example)
Arc Center Point
(Arc Center Fix)
Previous
Segment
Arc Initial Point
(Segment Initial Fix)
RNP 0.11
(Example)
RNP 0.11
RNP 0.11
4 RNP
2 RNP
2 RNP
P V
LE
c Ce
nter
nter Fix
Poin
x)
ck)
A-15
2 RNP 2 RNP
ROC
RNP navigation enables the geometry of instrument approach procedure design to be very
flexible, and allows the incorporation of radius-to-fix (RF) legs enabling the FMS/autopilot to
follow curved flight tracks. The constant radius arc RF leg defines a constant radius turn between
two database fixes, lines tangent to the arc, and a center fix. While the arc initial point, arc ending
point, and arc center point are available as database fixes, implementation of this leg type may
not require the arc center point to be available as a fix.
A-16
B-1
At higher altitudes, protected airspace helps to maintain
separation between aircraft. At lower altitudes, protected
airspace also provides separation from terrain or
obstructions. But, what does it mean to be established
on course? How wide is the protected airspace of a particular route? How can you tell from the cockpit whether
your aircraft is nearing the limits of protected airspace?
The intent of this appendix is to answer these questions
and explain the general limits of protected airspace by
means of typical instrument indications.
Some pilots assume that flying to the tolerances set out
in the FAA Instrument Practical Test Standards (PTS)
(http://www.faa.gov/education_research/testing/airmen/test_standards/) will keep them within protected
airspace. As a result, it is important to observe the last
sentence of the following note in the PTS:
“The tolerances stated in this standard are intended to be
used as a measurement of the applicant's ability to operate in the instrument environment. They provide guidance for examiners to use in judging the applicant's
qualifications. The regulations governing the tolerances
for operation under Instrument Flight Rules (IFR) are
established in 14 CFR Part 91.”
The in-flight presentation of course data can vary widely
based upon the selection and distance from a
Navigational Aid (NAVAID) or airfield. Consequently,
you need to understand that in some cases, flying to the
same standards required during your instrument rating
flight test does not necessarily ensure that your aircraft
will remain within protected airspace during IFR operations or that your aircraft will be in a position from
which descent to a landing can be made using normal
maneuvers.
For example, the PTS requires tracking a selected
course, radial, or bearing within 3/4 of full-scale deflection (FSD) of the course deviation indicator (CDI).
Since very high frequency omnidirectional ranges
(VORs) use angular cross track deviation, the 3/4 scale
deflection equates to 7.5 degrees, and means that the aircraft could be as much as 6.7 NM from the centerline
when 51 NM from the VOR station. A VOR receiver is
acceptable for IFR use if it indicates within four degrees
of the reference when checked at a VOR test facility. If
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Instrument Procedures Handbook (IPH)仪表程序手册下(170)
