AIM

8/15/19

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24

En Route Procedures

6. Use of RNAV Distance in lieu of DME

Distance. 

Substitution of RNAV computed distance

to or from a NAVAID in place of DME distance is
permitted when holding. However, the actual holding
location and pattern flown will be further from the
NAVAID than designed due to the lack of slant range
in the position solution (see FIG 5

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3

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7). This may

result in a slight difference between RNAV distance
readout in reference to the NAVAID and the DME

readout, especially at higher altitudes. When used
solely for DME substitution, the difference between
RNAV distance to/from a fix and DME slant range
distance can be considered negligible and no pilot
action is required.

REFERENCE

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AIM Paragraph 1

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2

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3, Use of Suitable Area Navigation (RNAV) Systems

on Conventional Procedures and Routes

FIG 5

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3

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7

Difference Between DME Distance From NAVAID & RNAV Computed Distance From NAVAID

7. Use of RNAV Guidance and Holding.

RNAV systems, including multi

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sensor Flight

Management Systems (FMS) and stand

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alone GPS

receivers, may be used to furnish lateral guidance
when executing a hold. The manner in which holding
is implemented in an RNAV system varies widely
between aircraft and RNAV system manufacturers.
Holding pattern data may be extracted from the
RNAV database for published holds or may be
manually entered for ad

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hoc ATC

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assigned holds.

Pilots are expected to be familiar with the capabilities
and limitations of the specific RNAV system used for
holding.

(a)

All holding, including holding defined on

an RNAV or RNP procedure, is based on the
conventional NAVAID holding design criteria,
including the holding protected airspace construc-
tion. There are differences between the holding entry
and flight track assumed in conventional holding
pattern design and the entry and track that may be
flown when RNAV guidance is used to execute
holding. Individually, these differences may not
affect the ability of the aircraft to remain within
holding pattern protected airspace. However, cumu-

latively, they can result in deviations sufficient to
result in excursions up to limits of the holding pattern
protected airspace, and in some circumstances
beyond protected airspace. The following difference
and considerations apply when an RNAV system
furnishes the lateral guidance used to fly a holding
pattern:

(1)

Many systems use ground track angle

instead of heading to select the entry method. While
the holding pattern design allows a 5 degree
tolerance, this may result in an unexpected entry
when the winds induce a large drift angle.

(2)

The holding protected airspace is based

on the assumption that the aircraft will fly

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over the

holding fix upon initial entry. RNAV systems may
execute a “fly

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by” turn when approaching the

holding fix prior to entry. A “fly

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by” turn during a

direct entry from the holding pattern side of holding
course may result in excursions beyond protected
airspace, especially as the intercept angle and ground
speed increase.

(3)

During holding, RNAV systems furnish

lateral steering guidance using either a constant bank
or constant radius to achieve the desired inbound and