Communication Radio Limitations
Aircraft communication radios are subject to line of sight limitations. This means that terrain blocks these radio signals. In mountainous areas, terrain might directly block radio communications. Anywhere on the planet, the curvature of the earth limits the maximum distance of communications radios, as it does with FM car radio receivers. Additionally, this maximum distance increases with altitude. The higher an airplane flies, the further it can communicate. These limitations result in a number of places where radio communications might be weak or blocked completely, especially at lower altitudes.
Radio transmissions may also have background noise, interference, or be effected by problems with the communications equipment being used.
Standard Terminology and Phraseology
Every person communicates differently, depending on their way of thinking and culture. It is easy for a person to misinterpret something they've heard based on the way it was said.
Standards ways of speaking are used in aviation in an attempt to reduce these miscommunications. It has been found that saying things in a certain way helps both parties better understand each other. Pronouncing words in a certain way helps the message to be more easily understood by the receiver, who will hear the speaker's voice with a lower quality.
The common practice in aviation is to use standard phraseology. Plain language may then be used to expand and clarify, if necessary.
Letters and Numbers
The following table lists the standard way in which numbers and letters are broadcast. Saying each letter as a word is used to avoid confusing one letter for another.
Character | Telephony | Pronunciation | Character | Telephony | Pronunciation | |
A | Alpha | AL-FAH | T | Tango | TANG-GO | |
B | Bravo | BRAH-VOH | U | Uniform | YOU-NEE-FORM | |
C | Charlie | CHAR-LEE | V | Victor | VIK-TAH | |
D | Delta | DELL-TAH | W | Whiskey | WISS-KEY | |
E | Echo | ECK-OH | X | X-Ray | ECKS-RAY | |
F | Foxtrot | FOKS-TROT | Y | Yankee | YANG-KEY | |
G | Golf | GOLF | Z | Zulu | ZOO-LOO | |
H | Hotel | HOH-TEL | ||||
I | India | IN-DEE-AH | 0 | Zero | ZEE-RO | |
J | Juliet | JEW-LEE-ETT | 1 | One | WUN | |
K | Kilo | KEY-LOH | 2 | Two | TOO | |
L | Lima | LEE-MAH | 3 | Three | TREE | |
M | Mike | MIKE | 4 | Four | FOW-ER | |
N | November | NO-VEM-BER | 5 | Five | FIFE | |
O | Oscar | OSS-CAH | 6 | Six | SIX | |
P | Papa | PAH-PAH | 7 | Seven | SEV-EN | |
Q | Quebec | KEH-BECK | 8 | Eight | AIT | |
R | Romeo | ROW-ME-OH | 9 | Niner | NIN-ER | |
S | Sierra | SEE-AIR-RAH |
Time, Speed, Direction, and Frequencies
Time, speed, direction, and frequencies are stated by saying each number individually.
Examples:
Time | 1230 Zulu | One Two Three Zero |
1945 Local | One Niner Four Five | |
Speed | 140 Knots | One Four Zero |
Direction | 100 degrees | One Zero Zero |
Frequency | 122.85 MHz | One Two Two Point Eight Five |
Altitude
Altitudes are spoken as individual numbers, as well. "Hundred" or "thousand" is used in lieu of saying several zeroes at the end of every altitude. Flight levels are spoken as "Flight Level", plus the individual numbers which make up the flight level.
Examples:
500 | Five Hundred |
2,000 | Two Thousand |
4,500 | Four Thousand Five Hundred |
10,500 | One Zero Thousand, Five Hundred |
17,000 | One Seven Thousand |
FL190 (19,000) | Flight Level One Niner Zero |
FL370 (37,000) | Flight Level Three Seven Zero |