1. CGS Ground School Airmanship Altimetry
© Crown copyright No part of this presentation may be reproduced without the permission of the issuing authority. The views expressed in this presentation do not necessarily reflect the views or policy of the MOD.

2. Definitions
Elevation - the vertical distance of an object above mean sea level.
Airfield elevation is therefore the vertical distance of the airfield above mean sea level.
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING
Elevation

3. Definitions
QFE - the observed air pressure at airfield elevation, corrected for temperature.
When QFE is set on the altimeter sub-scale the altimeter will indicate the vertical distance above the airfield. This vertical distance is called height.
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING
Height

4. Definitions
QNH - the observed pressure at airfield elevation, corrected for temperature and reduced to mean sea level.
When QNH is set on the altimeter sub-scale the altimeter will indicate the vertical distance above mean sea level. This vertical distance is called altitude.
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING
Altitude

5. Cross country flying using QNH
A major flight safety problem can occur when flying cross-country from a region of high pressure to a region of low pressure if the departure airfield QNH is used throughout the flight. L
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING H

6. Cross country flying using QNH
On reaching the low pressure area (980 hPa), although the altimeter would read 2000 ft, the aircraft would actually be at only 600 ft!
If an aircraft was to take off in an area of high pressure (1026 hPa) and climb to 2000 ft (pressure 960 hPa) and then fly towards an area of low pressure (980 hPa).
This can be remembered using the saying "High to Low - down you go".
Even though the aircraft was being flown at an indicated height of 2000 ft (pressure of 960 hPa) the aircraft would descend as the flight progressed into the low pressure area.
To overcome this problem, when flying cross-country, the regional pressure setting for each region passed through should be used.
2000ft
(960 hPa)
2000ft
(914 hPa)
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING
1000ft
(993 hPa)
1000ft
(947 hPa)
High pressure 1026 hPa
Low pressure 980 hPa

7. Regional pressure setting
The Regional Pressure Setting is the lowest forecast QNH within an altimeter setting region.
The airspace over the UK is split into 13 different altimeter setting regions (ASRs).
It is valid for one hour and is forecast two hours ahead.
Portree
Orkney
Belfast
Tyne
Barnsley
Humber
Holyhead
Yarmouth
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING
Chatham
Wessex
Cotswold
Scillies
Portland

8. Regional pressure setting
With the RPS set the aircraft's vertical distance is measured above the lowest forecast mean sea level pressure setting within the region and is called altitude.
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING
Altitude

9. Standard altimeter setting
Confusion could occur if multiple aircraft were
flying on different QNH/RPS settings in the same region.
To overcome this possible confusion a standard altimeter setting of hPa is used when aircraft operate above a given altitude (usually 3000 ft).
This ensures that all aircraft are operating from the same datum.
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING

10. Standard altimeter setting
With mb set vertical distances are referred to as Flight levels (FL);
where 3000 ft = FL 30, 3500 ft = FL 35 and so on.
6000ft
FL60
5500ft
FL55
5000ft
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING
FL50
4500ft
FL45
4000ft
FL40
3500ft
FL35
3000ft

11. Standard altimeter setting
When using mb, IFR pilots are to (and VFR pilots are advised to), use the quadrantal system.
Even
+500ft
Odd
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING
Heading = 205°
Fly at even thousands of feet, e.g. FL40, 60, 80 etc.
Heading = 135°
Fly at odd thousands of feet + 500ft, e.g. FL35, 55, 75 etc.
Heading = 080°
Fly at odd thousands of feet, e.g. FL30, 50, 70 etc.
Heading = 290°
Fly at even thousands of feet + 500ft, e.g. FL45, 65, 85 etc.
Odd
+500ft
Even

12. Transition altitude
This is the altitude, in the vicinity of an airfield,
at or below which the vertical position of an aircraft is controlled by reference to altitude.
For airfields in the UK, this is usually 3000 ft.
Transition
altitude
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING
Altitude

13. Transition level
This is the lowest flight level above the transition altitude. The altimeter should be set to hPa, therefore height is measured as flight levels.
It is not fixed but changes as the QNH changes.
Transition
level
Transition
altitude
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING
Flight level
Altitude

14. Transition layer
This is the space between the transition level and the transition altitude.
The depth of the layer is not significant as it never exceeds 500 ft.
Transition
level
< 500 ft
Transition layer
Transition
altitude
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING

15. Minimum flight level
In order to provide vertical separation between aircraft flying at the transition altitude and those using flight levels, the lowest available flight level is 500 ft above the transition level.
Minimum
flight level
Transition
level
Transition
altitude
SENDING A FIRST SOLO
DISCUSS THE FOLLOWING

16. THE END
Any Questions?