ENR 1.7 ALTIMETER SETTING PROCEDURES

1. INTRODUCTION

1.1. The altimeter setting procedures in use generally conform to those contained in PANS-OPS ICAO Doc 8168-OPS/611 Volume III, section 2, and only differences are stated.

1.2. Transition Altitude (TA) is given on the instrument approach charts.

1.3. QNH reports and temperature information for use in determining adequate terrain clearance are provided in the Operational Flight Information Service (OFIS) broadcasts and are available on request from the Air Traffic Services Units (ATSUs).

1.4. QNH values are given in Hectopascal (hPa) and rounded down to the nearest whole hPa.

2. BASIC ALTIMETER SETTING PROCEDURES

2.1 General

2.1.1 System of flight levels

2.1.1.1. FL zero is located at the atmospheric pressure level of 1013.25 hPa (29.92 IN inches Hg). Consecutive FLs are separated by a pressure interval corresponding to 500 FT in the Standard Atmosphere.

2.1.1.2. Flight levels shall be numbered according to Table 4.7.

2.1.2. Transition Altitude (TA)

2.1.2.1. Muscat FIR Transition Altitude (TA) is common and specified as 13000 FT.

2.1.2.2. Transition Altitude (TA) is published in Aeronautical Information Publications and shown on the instrument approach charts.

2.1.3 Transition level (TLTRL)

2.1.3.1. Muscat FIR Transition level (TLTRL) is common and specified as FL 150.

2.1.4 References to vertical position

2.1.4.1. The Vertical positioning of aircraft operating at or below the TA shall be expressed in terms of Altitude (ALT).

2.1.4.2. The Vertical positioning of aircraft operating at or above the TLTRL is expressed in terms of Flight Levels (FL).

2.1.4.3. Vertical positioning of aircraft while passing through the Transition Layer, shall be expressed in terms of:

a) altitude when descending and,

b) flight levels when climbing.

2.1.5 The terminology TA/TLTRL applies during:

a) climb;

b) en-route flight; and

c) approach and landing

Note.— This does not preclude a pilot using a QFE setting for terrain clearance purposes during the final approach to the runway.

2.2 Take-off and climb.

2.2.1 A QNH altimeter setting is made available to aircraft in taxi clearance prior to take-off.

2.2.2 During climb, all references in A/G communication to vertical position shall be in terms of:

a) FL when at or above TA; or

b) ALTs when at or below TA.

2.2.3 The altimeter subscale setting shall be changed from QNH to 1013.25 (ISA) on leaving or passing the TA.

2.3 Enroute

2.3.1 Vertical separation enroute is assessed in terms of:

a) ALT, when at and below the TA; and

b) FL, when at and above the TLTRL.

Note: Transition Level for Muscat FIR is fixed at FL150. Transition Altitude for the Muscat FIR is fixed at 13000 FT. Highest usable cruising altitude 13000 FT. Lowest usable cruising level FL150. ACFT at or below the TA arriving at or departing from controlled airfields are to change from regional to airfield QNH or vice versa at 50 NM or on entering or leaving controlled airspace.

2.3.2 Terrain clearance

2.3.2.1 Terrain clearance shall be assessed on the basis of the latest Regional QNH obtainable from ATC.

2.4 Approach and landing

2.4.1 A QNH altimeter setting shall be made available to aircraft in approach clearance and in clearance to enter the traffic circuit.

2.4.2 A QFE altimeter settings are clearly identified by ATS for AD ELEV and THR ELEV if 7 FT or more below AD ELEV and are available in approach and landing clearances on request.

2.4.3 Vertical positioning of aircraft during approach is controlled by reference to:

a) FL, until reaching the TLTRL; and

b) ALT, when below the TLTRL.

Note: This does not preclude a pilot using either:

a) QNH setting from top of descent when cleared for uninterrupted descent to a level below TLTRL; or

b) QFE setting for terrain clearance purposes during final approach to the runway.

2.5 Missed approach

2.5.1 The relevant parts parts of 2.1.4, 2.2, “Take-off and climb” and 2.4, “Approach and landing” shall be applied in the event of a missed approach.

3. ALTIMETER SETTING REGIONS (ASR).

3.1. For terrain clearance purposes, a Regional QNH, i.e., the lowest forecast MSL pressure value, valid for a period of 3 hours and amended as necessary by actual reports, is available from ATSUs.

3.2. The Muscat FIR is divided into three altimeter setting regions. As depicted on ENR 1.7-3 they are designated as

a) ASR Muscat between 25N and 20N,

b) ASR Dhofar South of 20N and

c) ASR Mussandam North of 25N

4. PROCEDURES APPLICABLE TO OPERATORS (Including Pilots).

4.1 Flight planning

4.1.1 The levels at which a flight is to be conducted shall be specified in a flight plan in terms of :

a) Flight Levels (FL) if the flight is to be conducted at or above the Transition Level (TLTRL) (or the lowest usable flight level, if applicable); and

b) Altitudes (ALTs) if the flight is to be conducted in the vicinity of an aerodrome and at or below the Transition Altitude (TA).

4.1.2 The altitudes or flight levels selected for flight should:

a) ensure adequate terrain clearance at all points along of the entire route; and

b) be compatible with the table of cruising levels as shown on page ENR 1.7-1. satisfy ATC requirements; and

c) be compatible with the table of cruising levels as shown in Table 4.2

4.2 Table of cruising levels

4.2.1 The cruising levels to be observed when so required are as follows:

a) In areas where, on the basis regional air navigation agreement and in accordance with conditions specified therein, a vertical separation minimum (VSM) of 300 m (1000 ft) is applied between FL290 and FL 410 inclusive.


Table of Cruising Levels
From 000° to 179°						From 180° to 359°
IFR Flights			VFR Flights			IFR Flights			VFR Flights
FL	Altitude		FL	Altitude		FL	Altitude		FL	Altitude
FL	Metres	Feet	FL	Metres	Feet	FL	Metres	Feet	FL	Metres	Feet
	300 900 1500 2150 2750 3350 3950	1000 3000 5000 7000 9000 11000 13000		450 1050 1700 2300 2900 3500 -	1500 3500 5500 7500 9500 11500 -		600 1200 1850 2450 3050 3650 -	2000 4000 6000 8000 10000 12000 -		750 1350 2000 2600 3200 3800 -	2500 4500 6500 8500 10500 12500 -
150 170 190 210 230 250 270 290 330 370 410 450 490 etc.	4550 5200 5800 6400 7000 7600 8250 8850 10050 11300 12500 13700 14950 etc.	15000 17000 19000 21000 23000 25000 27000 29000 33000 37000 41000 45000 49000 etc.	Class A Airspace No VFR flights above ALT 11500 FT			160 180 200 220 240 260 280 300 320 340 360 380 400 430 470 510 etc.	4900 5500 6100 6700 7300 7900 8550 9150 9750 10350 10950 11600 12200 13100 14350 15550 etc.	16000 18000 20000 22000 24000 26000 28000 30000 32000 34000 36000 38000 40000 43000 47000 51000 etc.	Class A Airspace No VFR flights above ALT 12500 FT

ALTIMETER SETTING REGIONS