The Earth
The Solar System & Time
Using Aeronautical Charts
Basics of Navigation
Distance, Speed & Time
Vertical Navigation
Fuel Planning
Practical Navigation Techniques
Radio Navigation
Practice Exam

Other Aeronautical Information

There are many other symbols used on aeronautical charts and some of these are outlined below. If you’re ever unsure about a symbol on the chart, you will find a description of all the symbols in the chart’s legend.


Different types of aerodromes have slightly different symbols on our charts.

The name of the aerodrome, its ICAO code, and its elevation in feet are written next to the aerodrome symbol.

These glider launching site symbols show the maximum altitude of winch launching above mean sea level (AMSL). In this case, it is 2,500ft AMSL:

Visual Reference Point (VRP)

At larger airfields, Visual Reference Points (VRPs) are often used when communicating with air traffic controllers.

VRPs are marked on the chart with a blue cross inside a circle. The name of the VRP is written alongside in a box.

Area of Intense Aerial Activity (AIAA)

An Area of Intense Aerial Activity (AIAA) is airspace within which the intensity of civil and/or military flying is exceptionally high or where aircraft (often many together) regularly participate in unusual manoeuvres. You are strongly advised to be in contact with a radar unit when passing through these areas.

AIAAs are outlined on the chart by blue diamonds.

Pilots are strongly advised to use the available radar service if they plan on transiting an area of intense aerial activity (AIAA)

High Intensity Radio Transmission Areas (HIRTA)

Inside a High Intensity Radio Transmission Area (HIRTA) you may experience interference with your communication and navigation radios.

HIRTAs are marked on the chart by a red circle with cross hatching through the circle.

The Fylingdales HIRTA, marked as extending up to 40,000ft (Fylingdales/40.0)

Gas Venting Sites

Gas Venting Sites can cause severe turbulence up to the marked altitude when the ground stations are venting natural gas under high pressure.

Severe turbulence means you should plan to fly around them!

A gas venting site that extends up to 3,600ft AMSL

Click Here to Start the Charts Quiz

Quizzes are a proven way of reinforcing your learning and improving your knowledge of the key facts. Click here to review what you’ve learnt with this memory refreshing Charts Quiz.

Lesson Content