CGS Ground School Airmanship Altimetry © Crown copyright 2012. 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.

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

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

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

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

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

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

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

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 1013.2 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

Standard altimeter setting With 1013.2 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

Standard altimeter setting When using 1013.2 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

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

Transition level This is the lowest flight level above the transition altitude. The altimeter should be set to 1013.2 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

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

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

THE END Any Questions?