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(to determine altimeter serviceability).
VFR ALTIMETERS
With an accurate QNH set, a VFR altimeter(s) should read site elevation to within 100FT
(110FT at test sites above 3,300FT) to be accepted as serviceable by the pilot. If an
aircraft fitted with two VFR altimeters continues to fly with one altimeter reading
100FT (110FT) or more in error, the faulty altimeter must be placarded unserviceable
and the error noted in the maintenance release.
VFR altimeters are not permitted for aeroplane operations above FL200. VFR flights
operating above FL200 must be equipped with an altimeter calibrated to IFR standards.
ACCURATE QNH AND SITE ELEVATION
A QNH can be considered accurate if it is provided by ATIS, tower or an automatic
remote-reporting aerodrome sensor. Area or forecast QNH must not be used for the
test.
Site elevation must be derived from aerodrome survey data published by Airservices or
supplied by the aerodrome owner.
ALTIMETER SETTING RULES
GENERAL
Heights measured from a QNH or Area QNH datum must be expressed in full, eg
3,000FT as “THREE THOUSAND” and 1,800FT as”ONE THOUSAND EIGHT HUNDRED”,
adding, if necessary , “ON… (QNH)”.
Expressions of height measured from the 1013.2HPA datum must always include the
words “FLIGHT LEVEL”.
Flights cruising at or below the transition altitude must change the Area QNH altimeter
setting when advised of a change by ATS. Pilots of aircraft not using radio must use
the QNH setting obtained by setting the altimeter to aerodrome elevation before
take-off.
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GENERAL
SECTION
ALTIMETER SETTING PROCEDURES
TRANSITION LAYER, ALTITUDE AND LEVEL
The system of altimetry used in Australia makes use of a transition layer between the
transition altitude which is always 10,000FT and the transition level of FL110 to
separate aircraft using QNH from those using 1013.2 HPa as a datum.
For cruising at or below the transition altitude, the altimeter reference must be Area
QNH.
For cruising at and above the transition level, the Standard Pressure altimeter setting
of 1013.2 HPa must be used.
The positions to change between QNH and 1013.2 HPa are shown in the diagram
on the next page.
QNH is available from ATS. When departing an aerodrome within a CTR, Area QNH,
for applicable aircraft, may not be provided until communication is established with
the Area Control Service or Flight Service. Cruising within the transition layer is not
permitted.
AREA QNH
Area QNH is a forecast value which is valid for a period of 3 hours and normally
applies throughout an Area QNH Zone (AQZ). Area QNH Zones will be subdivided,
if necessary, to meet the following standards:
• Area QNH forecasts are to be within +/- 5 HPa of the actual QNH at any low-level
point (below 1,000 FT AMSL) within or on, the boundary of the appropriate area
during the period of validity of the forecasts.
• Area QNH must not differ from an adjoining Area QNH by more than 5 HPa.
LOCAL QNH
Local QNH, whether provided by ATS, AWS or Aerodrome Forecast (TAF) or by using
the altimeter subscale to indicate airfield elevation AMSL, is used as shown in the
diagram on the next page.
LIMITATIONS
To retain a minimum buffer of 1,000FT above the transition altitude, FL110 will not be
available for cruising when the Area QNH is less than 1013.2 HPa. With a progressive
decrease in the value of the Area QNH, FL115 and FL120 will not be available when
the Area QNH is below 997 HPa and 980HPa respectively. At the oceanic limits of
Australian FIRs, a pilot may fly a level different from those set out in the tables of
cruising levels due to area QNH conflicting with the standard pressure setting.
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GENERAL
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ALTIMETER SETTING PROCEDURES
TRANSITION LAYER
10000
8000
6000
4000
2000
FL125 NOT AVAILABLE WHEN AREA QNH IS BELOW 963 HPA
FL12O NOT AVAILABLE WHEN AREA QNH IS BELOW 980 HPA
FL115 NOT AVAILABLE WHEN AREA QNH IS BELOW 997 HPA
FL110 NOT AVAILABLE WHEN AREA QNH IS BELOW 1013 HPA
ALTIMETRY
FL110
ALTITUDE
LEVEL
Set 1013.2
Set Local QNH or, if not available, Area QNH
Set Area QNH just prior to top of climb Set Local QNH (if available)
ALTITUDES - All operations on QNH or Area QNH
Set Local QNH if known, otherwise aerodrome elevation
MSL
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DIAGRAM
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VFR Flight Guide(55)
