Bronze & Beyond: A Glider Pilot's Guide - Softcover

McCullagh, John S.

Softcover

ISBN 10: 095487420X ISBN 13: 9780954874209

Publisher: John McCullagh, 2004

Synopsis

Essential information for glider pilots about to fly cross - country in the United Kingdom

About this title

Excerpt. © Reprinted by permission. All rights reserved.:

Excerpt from Chapter One

Altimeter settings
An altimeter does not necessarily show the height above the ground. It merely indicates a distance from a selected datum. By adjusting the sub-scale knob, you can choose one of three datums: QFE, QNH and Standard Setting.

QFE
Zeroing the altimeter before take-off is known as setting it to QFE. You might remember the abbreviation as ‘field elevation’. (The ‘Q’ comes from the days of Morse code.) This is convenient for local soaring, because the altimeter will show the absolute height above your home airfield with reasonable accuracy, though it will be affected by the errors described earlier. The QFE setting need not be for your home airfield. You can also call up another airfield to get the setting for its QFE.

QNH
If your airfield is at an elevation of 500 feet above sea-level, turn the knob to add another 500 feet to the altimeter reading. This setting is known as the local QNH. Remember the abbreviation by thinking of it as nautical height.

Although QFE is the appropriate setting for local flying, it is not relevant when you are out of gliding range of your home airfield. Away from your home airfield, it is more important to monitor your height in relation to controlled airspace, and it is easier to do this using QNH.

Although you should launch on QFE, it is recommended that you set the altimeter to show your altitude above sea-level before setting off to fly cross-country. However, with the altimeter set to QNH, you have to become even more aware of the height of the terrain below.

Note that the term ‘altitude’ in aviation means specifically the vertical distance from sea-level. If you fly using QNH, your altimeter shows your altitude. If you fly on QFE, it shows your height above a chosen datum, in this case an airfield.

Standard Setting
Your third choice of altimeter datum is Standard Setting. This setting is important because some airspace is defined with reference to it.

Standard Setting is obtained by turning the sub-scale of the altimeter so that it reads 1013mb. The altimeter set in this way will only show a correct altitude when the sea-level pressure just happens to be 1013mb. At all other times, the altimeter is just measuring a pressure on a common basis. When the Standard Setting is used, the altimeter reading is known as the ‘pressure altitude’.

The advantage of the Standard Setting is that all aircraft are using the same datum, even if they fly though places with different pressures.

Flight levels
The Standard Setting is used to define flight levels. Flight levels are named by removing the last two zeros from the pressure altitude, so FL45 is at 4500 feet pressure altitude. The flights levels only ever step up in units of 500 feet, eg FL35, FL40, FL45 etc.

Flight levels are used to define the upper and lower limits of airspace such as airways and parts of some control areas and control zones. For example, the base of an airway may be defined at FL45. On a day when the sea-level pressure is 1013mb, this boundary will be at 4500 feet above mean sea-level (AMSL). However, on other days FL45 will be found at other altitudes depending on the atmospheric pressure at that place. On a high pressure day you have to go higher before the air pressure falls to the pressure that defines each flight level.

This provides a slight, but fortuitous, safety margin for thermalling glider pilots. We tend to fly higher in thermals on days with higher pressure. On the days when sea-level pressure is over 1013mb, the flight levels at the base of an airway will be at higher altitudes. For example if the actual sea level pressure is 1023mb (10mb above the standard), the bases of all the flight levels will be 10x30= 300 feet higher.

About this edition

• Publisher: John McCullagh
• Publication date: 2004
• ISBN 10: 095487420X
• ISBN 13: 9780954874209
• Binding: Paperback
• Number of pages: 110