ENR 1.7  Altimeter Setting Procedures

1   GENERAL

The altimeter setting procedures in use generally conform to Part III of ICAO Doc 8168, Volume I.

1.1   Transition Altitude

A common transition altitude of 4 500 FT is applicable in Brussels FIR.

Transition Layer (MIL only)

The transition layer is the airspace between the transition altitude and the transition level.

To ensure minimum standard radar separation between uncontrolled flights at or below 4 500 FT and controlled flights above the transition altitude, a transition layer of minimum 1 000 ft and maximum 1 499 FT will be taken into account to determine the transition level. Within the transition layer no minimum vertical radar separation with uncontrolled flights is provided.

Transition Level (MIL only)

The transition level is the lowest flight level available for use above the transition altitude. The following parameters are used to calculate the transition level:

  • Transition altitude (TA): 4 500 FT;
  • Transition layer (Tlay): 1 000 FT;
  • Standard QNH: 1013.2 HPA;
  • FT / HPA: 26.7;
  • Transition level (TL);
  • Regional QNH (Reg QNH).

TL = [TA + Tlay + ((1013.2 - Reg QNH) x 26.7)] / 100 and rounded up to the first VFR or IFR flight level (whichever comes first). The calculation has to be correct to 0.0001 before rounding up to FL. This formula results in the value of the transition level in relation to the regional QNH taking into account a transition layer of minimum 1 000 ft and maximum 1 499 FT. This formula is primarily intended for precise calculations to be used in systems. A quick reference table is published below.

Regional QNHTransition Level
921 - 93880
939 - 95775
958 - 97570
976 - 99465
995 - 101360
1014 - 103155
1032 - 105050
1051 - 106945
107040
Corresponding Flight Level for a specific QNH value
QNH950 - 954.9955 - 974.9975 - 989.9990 - 1009.91010 - 1024.91025 - 1044.91045 - 1055
ALT
5002520151050-5
1000302520151050
15003530252015105
200040353025201510
250045403530252015
300050454035302520
350055504540353025
400060555045403530
450065605550454035
500070656055504540
550075706560555045
600080757065605550
650085807570656055
700090858075706560
750095908580757065
8000100959085807570
85001051009590858075
900011010510095908580
9500115110105100959085
100001201151101051009590

Note: An aerodrome QNH setting is a setting of which the source is located at or less than 5 NM from the landing threshold.

2   PROCEDURES

2.1   Take-off and Climb

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

Vertical positioning of aircraft during climb is expressed in terms of altitude until reaching the transition altitude above which vertical positioning is expressed in terms of flight level.

2.2   Approach and Landing
General

A QNH altimeter setting and the transition level are made available in approach clearance and in clearance to enter the traffic circuit.

Vertical positioning of aircraft during approach is controlled by reference to flight levels until reaching the transition level below which vertical positioning is controlled by reference to altitude.

When flying outside controlled airspace at or below 4 500 FT AMSL, the altimeter should be set to the QNH of the aerodrome of destination as soon as entering the controlled airspace associated with it (TMA or CTR as the case may be).

A QFE altimeter setting is only given on request and shall only be used for terrain clearance during final approach. The reference datum of the QFE altimeter setting is either:

  1. the threshold elevation:
    • for instrument runways (SRA or NDB approaches), if the threshold elevation is 7 FT or more below the aerodrome elevation;
    • for precision approach runways (ILS);
  2. the aerodrome elevation.
Missed Approach Procedure for Military Pilots

In the event of a missed approach, pilots shall use the QNH unless otherwise instructed by the control tower. If the missed approach procedure requires a climb above the transition altitude, pilots shall follow the relevant altimeter setting procedures given in § 1.3 above.

Note 1: Military pilots shall comply with the civilian instructions when flying within airspace controlled by civil authorities.

Note 2: An aerodrome QNH setting is a setting of which the source is located at or less than 5 NM from the landing threshold.

2.3   En-route

The cruising level at which a flight or a portion of a flight is to be conducted shall be expressed in terms of flight level when operated above the transition altitude.

When flying in a controlled airspace associated with an aerodrome (TMA or CTR) at or below the transition altitude, the aerodrome QNH value given by the relevant control unit shall be used for the altimeter setting.

When flying outside controlled airspace at or below 4 500 FT AMSL, the altimeter shall be set to the regional QNH given on pilot's request by Brussels FIC, Semmerzake ATCC or by any ATC unit. The regional QNH is the lowest of the QNH values for the following stations: EBAW, EBBE, EBBR, EBCI, EBCV, EBFS, EBBL, EBFN, EBLG, ELLX, EBOS, EBSH and EBSP.

VFR flights conducted at or below 3 000 FT AGL do not have to maintain a semi-circular cruising level and consequently are not compelled to use any particular altimeter setting. However, they are advised:

  • to take into consideration, for terrain and obstacle clearance purpose, either the regional QNH or the QNH value relevant to the area overflown (EBBR, ELLX, EBOS and EBSP) obtainable from Brussels FIC or Semmerzake ATCC;
  • to take note that high speed low level military flights, having a flight visibility less than 5 KM, are mandatory conducted under IFR and are therefore maintaining semi-circular IFR cruising altitudes based on the regional QNH.

3   TABLE OF CRUISING LEVELS

Magnetic track
From 000 degrees to 179 degreesFrom 180 degrees to 359 degrees
IFR flightsVFR flightsIFR flightsVFR flights
FLALTFLALTFLALTFLALT
MFTMFTMFTMFT
103001 000---206002 000---
309003 000351 0503 500401 2004 000451 3504 500
501 5005 000551 7005 5006065
70752 3007 5008085
9095100105
110115120125
130135140145
150155160165
170175180185
190200
210220
230240
250260
270280
290300
310320
330340
350360
370380
390400
410430
450470
490510
etc.etc.