Altimeter setting methodology[PDF]
- 1 Introduction
- 2 Tune altimeter
- 3 Transition altitude and transition level
- 4 Use of altimeter setting
- 5 See also
- 6 Reference
- 7 Author
One of the main instruments of the aircraft is the altimeter.
Depending on the aircraft equipment, the pressure altimeter will only accept a sub-setting:
- in hecto Pascal (hPa)
- in inches of Mercury (in Hg)
Example of an altimeter showing one or both units:
- red arrow = setting display in inHg
- blue = setting display in hPa
- green = tune button
Most altimeters in hectopascal do not show any decimals. In that case, select the nearest value.
This altimeter should be set only with:
- Local QNH pressure
- Local QFE pressure
- Standard pressure 1013hPa or 29,92 inHg
A pilot will receive QNH information from the Air Traffic Controller when:
- aircraft is cleared to descend to an altitude below the Transition Level (TL),
- during initial approach clearance (for IFR only)
- when cleared to enter the control zone (CTR) or the traffic circuit (mainly for VFR)
- sometimes as part of a taxi clearance
- pilot requests it
- the QNH changes.
Transition altitude and transition level
In order to put in the altimeter settings, it is important to know the transition altitude and transition level in controlled areas.
You must know that:
- TA is published on charts in controlled areas
- TA is given in ATIS of controlled areas ( Ground, Tower, Approach positions)
- TA is the maximum altitude where the altimeter setting is at local QNH
- TA can be identical in one or more countries, but TA can also be different in each airport of a country
- TA is defined for a TMA where it is published
You must know that:
- TRL is sometimes published on charts in controlled areas
- TRL is sometimes calculated by ATC for its controlled area in function of TA and local QNH
- TRL is given in ATIS of controlled areas (Ground, Tower, Approach positions)
- TRL is the minimum flight level where the altimeter setting is at 1013 hPa (or 29.92 inHg)
- TRL is the first usable IFR level above the transition altitude
The transition layer is the gap between the transition altitude and the transition level.
Use of altimeter setting
This chapter is showing practical information for VFR or IFR pilots to correctly set their altimeter settings in time during their flight.
During climbing - from ground to cruise flight level
You will find the different steps to set the altimeter for departing aircraft:
- On ground, the pilot shall set its altimeter at airfield QNH given by the airfield ATIS or given by ATC.
- On ground, the pilot must take transition altitude and transition flight level values from charts or from the airfield ATIS ( Pilot could ask ATC in service to get this information)
- After take-off, the pilot shall monitor its altitude and compare it to transition altitude
- At the time where the actual aircraft altitude is greater than the transition altitude, the pilot without any ATC advice must set all his altimeter settings to 1013 hPa or 29.92 inHg.
- Then, the pilot verifies that he will cross the transition flight level to make sure that he never stabilizes in the transition layer.
During descent – from cruise flight level to airfield circuit/landing
You will find the different steps to set the altimeter for arriving aircraft:
- When flying above transition level, the pilot shall already have set altimeter settings to 1013 hPA or 29.92 inHg.
- When entering into a controlled area, the pilot must take transition level, transition altitude and local nearby QNH values (or airfield destination QNH) from airfield ATIS, from ATC in service or from charts.
- When descending, the pilot shall monitor his current flight level and compare it to the transition level
- At the time where actual aircraft flight level is lower than transition flight level, the pilot without any ATC advise must set all his altimeter settings to local, destination or nearby airfield QNH.
- Then, the pilot verifies that he will cross the transition altitude to make sure that he never stabilizes in the transition layer.
- ICAO documentation Annex 2 - Rules of the Air - 10th Edition July 2005
- VID 150259 - Creation
- VID 150259 - Wiki integration
- VID 450012 - Update
DATE OF SUBMISSION
- 00:17, 14 May 2021
- This documentation is copyrighted as part of the intellectual property of the International Virtual Aviation Organisation.
- The content of this documentation is intended for aviation simulation only and must not be used for real aviation operations.