ENR 1.7 ALTIMETER SETTING PROCEDURES
1.7.1 Introduction
1.1 The procedures herein describe the method intended for use in providing adequate vertical separation between aircraft and adequate terrain clearance during all phases of a flight. This method is based on the following principles.
a) during flight, when at or below a fixed altitude called the transition altitude (TA), an aircraft is flown at altitudes determined from an altimeter set at sea level pressure (QNH) and its vertical position is expressed in terms of altitudes;
b) during flight above the TA an aircraft is flown along surfaces of constant atmospheric pressure based on an altimeter setting of 1013,2 hPa (QNE) and throughout this phase of a flight the vertical position of an aircraft is expressed in terms of flight level (FL);
c) the change in reference from altitude to flight levels, and vice versa, is made, when climbing through the TA and, when descending through the transition level (TL);
d) during the approach to land, terrain clearance may be determined by using the QNH altimeter setting (giving altitude).
System Of Flight Levels
1.2 Flight level zero shall be located at the atmospheric pressure level of 1013,2 hPa. Consecutive flight levels shall be separated by a pressure interval corresponding to at least 500′ (152,4m) in the Standard Atmosphere.
|
FLIGHT LEVEL NUMBER |
HEIGHT STANDARD ATMOSPHERE FEET METERS |
FLIGHT LEVEL NUMBER |
HEIGHT IN STANDARD ATMOSPHERE FEET METERS |
||
|
10 |
1 000 |
300 |
050 |
5 000 |
1 500 |
|
15 |
1 500 |
450 |
… |
…… |
…… |
|
20 |
2 000 |
600 |
100 |
10 000 |
3 050 |
|
25 |
2 500 |
750 |
… |
…… |
…… |
|
30 |
3 000 |
900 |
150 |
15 000 |
4 550 |
|
35 |
3 500 |
1 050 |
… |
…… |
…… |
|
40 |
4 000 |
1 200 |
200 |
20 000 |
6 100 |
|
45 |
4 500 |
1 350 |
… |
…… |
…… |
|
50 |
5 000 |
1 500 |
500 |
50 000 |
15 250 |
1.3 Flight levels shall be numbered according to the following table which indicates the corresponding height in the Standard Atmosphere in feet:-
Transition Altitude (TA)
1.4 A transition altitude is specified for each aerodrome in the Virtual AIP for the bigger airfields.
1.5 The TA for all points of departure and arrival within 25 nautical miles of any aerodrome are shown on each particular aerodrome page in the VAIP.
1.6 In VMC flights departing from, or arriving at points beyond 25 nautical miles from any of the aerodromes listed shall observe the height of 2000ft above the ground or water as the TA.
1.7 In IMC flights departing from, or arriving at points beyond 25 nautical miles from any of the aerodromes listed shall observe the lowest safe cruising altitude as the TA.
Transition Levels (TL)
1.8 The change in reference from “flight level”, used while en-route, to “altitude” used in the vicinity of an aerodrome, is made at a horizontal transition place located above the transition altitude which is called the “transition level”.
1.9 Transition levels will be adjusted when barometric pressure changes beyond specified limits so that the TL will never be less than 1000ft above the TA.
1.10 The ATSU at aerodromes will provide the current transition level for their aerodrome and points within 25 nautical miles of their aerodrome in the approach and landing instructions.
1.11 VMC flights intending to land at points beyond 25 nautical miles from any of the aerodromes listed shall observe the height of 3000 ft above the ground or water as the TL.
1.12 In IMC, flights intending to land at points beyond 25 nautical miles from any of the aerodromes listed shall observe the flight level 500ft above the lowest safe altitude as the TL.
Application Of Procedure
Take-Off And Climb
1.13 A QNH altimeter setting will be made available to aircraft in the routine take-off and climb clearances.
1.14 Before take-off at least one altimeter in the aircraft shall be set to QNH and the vertical positioning of the aircraft during climb shall be reference to altitude until reaching the TA.
1.15 On reaching the TA at least one altimeter in the aircraft shall be set to 1013,2 hPa (29,92 in) and thereafter the vertical positioning of the aircraft shall be referred to in flight levels (FL).
Note: On reaching the TA pilots will re-set their altimeters to 1013,2 hPa without requesting ATC permission to do so, nor is it necessary to advise ATC that the change has been made.
En Route
1.16 Vertical separation during en-route flight shall be assessed in terms of flight levels.
1.17 The vertical position of an aircraft shall normally be expressed in terms of flight levels both in air reports and air traffic service messages.
Approach And Landing
1.18 A QNH altimeter setting shall be made available in the routine approach and landing clearances.
1.19 The vertical positioning of aircraft during approach shall be controlled with reference to flight levels until reaching the TL, except as provided for in the following paragraph.
1.20 Vertical positioning of aircraft above the TL may be by reference to altitude (QNH) or heights (QFE); provided that, after the descent to land is commenced, level flight above the TA is not indicated or anticipated.
1.21 This exception is intended to apply primarily to jet aircraft for which an uninterrupted descent from a high altitude is desirable.
1.22 On reaching the TL, pilots will reset their altimeters to the QNH without requesting ATC permission to do so, it is also not necessary to advise ATC that the change has been made.
Missed Approach
1.23 The relevant parts of the foregoing procedures shall apply in the event of a missed approach.
Procedures Applicable To Operators (Including Pilots)
1.24 The levels at which the en-route stages of an IFR flight are to be conducted shall be specified in the flight plan in terms of Flight Levels. Stages conducted in the vicinity of an aerodrome shall be stated as altitudes if below the TA and in Flight Levels if above the TA.
1.25 There is no requirement for VFR flight to state its intended Flight Level/Altitude in a flight plan. However, where a level is stated it shall be:-
a) In terms of Flight Levels if the flight is to be conducted at or above 1500′ above the surface; or
b) In terms of Flight Levels or Altitude (by day only) if the flight is to be conducted below 1500′ above the surface.
1.26 The flight level, or levels, selected for a flight should:-
a) In IMC, ensure adequate terrain clearance, and
b) For IFR flights, satisfy ATC clearance, and
c) For all IFR and night flights and for VFR flights at or above 1500′ above the surface by day be compatible with the application of the Semi-circular Rule.
Responsibility For Determining The Current Transition Level
1.27 APP is responsible for determining and providing to arriving aircraft the current TL for their CTR/TMA. This level will also apply as the TL for any arriving aircraft landing within 25nm of that unit.
1.28 At a manned aerodrome which is not in a CTR the TWR or is responsible for determining the TL for their aerodrome and for any arriving aircraft landing within 25nm of the aerodrome.
1.29 APP (or TWR) must at all times be on the alert for changes in the QNH which will necessitate a change in the current TL accordingly without delay.
Determination Of The Current Transition Level
1.30 Transition Levels shall be determined with reference to the requirements as per local instructions.
1.31 In the table below, the current QNH must be applied to the table relevant to the station. The flight level indicated against the pressure range within which the current QNH falls, shall be the current TL.
1.32 This table ensures at least 1000′ vertical separation between an aircraft at TA and one at TL.
QNH Pressures At Which Transition Level Shall Be Altered
Table to determine TLs (TO BE AMENDED)
QNH IN HECTOPASCALS
959 TO 977
978 TO 995
996 TO 1013
1014 TO 1032
1033 TO 1050
1051 TO ABOVE