Aviation Radio

My weekend diversionary post today is a little journey into radio as used in General Aviation.  First of all, you may be surprised to learn that, for non-commercial aviation, and apart from certain Radio Mandatory Zones, there is no general legal requirement to carry a radio in an aircraft!

Here's how the panel of the aircraft I normally fly - a Piper 28-161 Warrior II - looks:

The radio stuff is all on the far right.

'A' is the audio control panel, which simply switches various sounds from different sources on and off in my headset.  You can choose to listen, for example, to people inside your cabin (or switch them off!), or hear the Morse code identifiers of radio navigation beacons, to make sure you are using the expected one.

Audio selection and GPS consoles (units 'A' and 'B' in the first image).

'B' is not really radio, but a GPS-based flight navigation system.  These are becoming ever-more sophisticated, but also rather outdated and expensive.  Normal tablets are now commonly used instead, as they are much cheaper, updated daily, and more informative.

Family day out on Saturday.

'C' is the main radio stack, which operates on between 10-25W AM, with 8.33kHz spacing (it was 25kHz spacing until very recently).  This example is rather old, but still commonly found in aircraft. The top two orange windows are where the frequencies are displayed.  The left window contains the active frequency, the right window the 'standby', or 'next radio station to be called' frequency.  A simple button swaps the two frequencies around.

Range of the radio is supposed to be about 1.3x square root of the aircraft height but, like ham VHF, can be greater or less than this, according to atmospheric conditions.

A very calm, warm, but hazy day for flying.

The second set of orange windows on the radio stack at 'C' are for receiving navigation beacons.  These feed the two circular direction instruments immediately to the left of the radio stack.  The top one is for ILS instrument approaches to an airfield, the bottom one is for VOR (en-route) navigation.

VOR transmitting antenna in Belgium.  Image: Wikicommons.

Unit 'D' is a transponder, which sends out a four-digit, pilot selected code on secondary radar, so that controllers can identify your aircraft on their screen.  Transponders can variously be off, on with no altitude reporting ('Mode Alpha'), on with altitude reporting ('Mode Charlie'), or on with altitude and aircraft-specific information (type, callsign, etc) - 'Mode Sierra'.  Some Mode 'S' transponders are linked to automatic collision avoidance.

A typical modern transponder unit.

And that's pretty much it!  To use the comms radio, the PTT switch is on the yoke, sometimes with a standby 'fist mike' stowed in the front.  Aviation headsets are about half the price of amateur radio headsets!  Oh, and in case you were wondering, in the UK, it's illegal to transmit with amateur radio sets from any aircraft, so no chance of a /AM QSO, I'm afraid (though others seem to break this law, anyway).