4.
8 Propagation of Radio Waves
Types of Propagation
1. Ground Waves
o Travel along the Earth’s surface.
o Use diffraction (bending around obstacles/curvature).
o Used for VLF, LF, and MF frequencies.
o Example: AM radio signals.
2. Sky Waves
o Travel up, get bent back to Earth by the ionosphere.
o Ionosphere = part of the atmosphere ionized by solar radiation.
o Affected by day/night (stronger at night).
o Used mostly for HF (High Frequency).
o Example: Long-distance international broadcasts.
3. Direct Waves (Line-of-Sight)
o Travel in a straight line from transmitter to receiver.
o Limited by Earth’s curvature.
o Used mostly for VHF and UHF (e.g., aircraft comms).
o MTR formula:
MTR = 1.25 × (√height of transmitter + √height of receiver)
(Heights in feet, MTR in nautical miles)
CHAPTER 5: Aeronautical Mobile Service (AMS)
5.1 Carriage of Radio Equipment
• Aircraft must have radio equipment that:
o Meets the laws of the state of registry
o Matches the type of flight (VFR/IFR)
o Can receive weather info at any time
• Must support two-way comms with ground stations on assigned frequencies.
5.2 Important Definitions
• AMS: Mobile radio service between aircraft & ground, or aircraft to aircraft.
• Aeronautical Station: A ground (or ship/sea-based) radio station.
• Aeronautical Fixed Service: Between fixed points, ensures air safety & efficiency.
• Air-Ground: Two-way aircraft ↔ ground
• Air-to-Ground: One-way aircraft → ground
5.3 Discipline in AMS
• Always use standard phraseology
• Don’t send unauthorized messages
• Ask permission before testing radio equipment
o Keep tests under 10 seconds
o Use numbers (e.g., “ONE TWO THREE”) + your call sign
• If no answer after 10 seconds, repeat the call.
• If many aircraft call at once, ground station picks who goes first.
• Aircraft-to-aircraft comms need permission unless it’s a brief exchange.
5.4 Categories & Priorities of Messages (RTF Signals)
Priority Message Type Example Signal
Distress MAYDAY ×3 (e.g., engine failure)
Urgency PAN PAN ×3 (e.g., medical emergency)
Direction finding. Location tracking help
Flight safety Weather alerts, control instructions
Meteorological Regular weather info
Flight regularity Crew, passenger, or flight schedule info
5.4.2 Flight Safety Messages
Include:
• Aircraft movement/control (e.g., takeoff clearances)
• Urgent info from airline or other aircraft
• Weather updates that may affect aircraft
5.4.3 Movement & Control
• Flight plan messages
• Cancellations/updates
• Clearances
• Position reports
5.4.4 Meteorological Messages
• Regular weather reports (excluding urgent ones)
5.4.5 Flight Regularity
• Maintenance info
• Change in crew/passenger needs
• Spare parts urgently needed
• Flight delays/schedule changes
CHAPTER 6: Radiotelephony Procedures
6.1 Standard Phraseology
• Always use ICAO standard phrases for clarity and speed.
• Helps avoid confusion especially in noisy or emergency situations.
6.2 Language
• Use the language of the ground station.
• In Kenya, it’s English.
6.3 Word Spelling
• Use the ICAO phonetic alphabet for clarity.
o Example: “Nairobi” = November Alpha India Romeo Oscar Bravo India
6.4 Transmitting Numbers
Numerals (ICAO Pronunciation)
Number Say as…
0 ZE-RO
1 WUN
2 TOO
3 TREE
4 FOW-er
5 FIFE
6 SIX
7 SEV-en
8 AIT
9 NIN-er
. (Decimal) DAY-SEE-MAL
000 (Thousand) TOU-SAND
How to Transmit Numbers
(a) All numbers (except whole 1000s):
Say each digit separately.
• Example: 75 = SEVen FIFE
• 100 = WUN ZERO ZERO
• 583 = FIFE AIT TREE
(b) Whole Thousands:
Say the number then TOUSAND
• 5000 = FIFE TOUSAND
• 25,000 = TOO FIFE TOUSAND
• 25,500 = TOO FIFE FIFE ZERO ZERO
Decimals
Use “DAY-SEE-MAL”
• 118.1 = WUN WUN AIT DAY-SEE-MAL WUN
• 3814.9 = TREE AIT WUN FOW-er TREE DAY-SEE-MAL NIN-er
VHF Frequencies
Only two digits max after the decimal are used.
Frequency Transmit as…
118.0 WUN WUN AIT DAY-SEE-MAL ZERO
118.125 WUN WUN AIT DAY-SEE-MAL WUN TOO
118.150 WUN WUN AIT DAY-SEE-MAL WUN FIFE
Transmitting Time
• Minutes: Say each digit.
• Hours: Include if it might cause confusion.
Examples:
• 0920 = TOO ZERO or ZERO NIN-er TOO ZERO
• 1643 = FOW-er TREE or WUN SIX FOW-er TREE
Radio Transmitting Techniques
• Read message before sending.
• Speak clearly, not too fast (max 100 words/min).
• Keep volume steady.
• Know how to use mic properly.
• Pause if you turn away from mic.
Use of Abbreviations & Phonetics
• Avoid abbreviations unless common (e.g., ATC, ETA).
• Skip phonetic spelling unless clarity is at risk.
Long Messages
Pause occasionally to:
1. Check the channel is clear.
2. Let receiver ask for repeats.
Message Format (AMS)
Format:
• (i) Call (addressee + originator)
• (ii) Message
Example:
• WILSON TOWER 5Y-BBC
• REQUEST JOINING INSTRUCTION
RTF Callsigns
For Ground Stations:
• Use location + service
e.g., NAIROBI TOWER, WILSON GROUND
For Aircraft:
• Type A: Registration only → 5Y-ASA
• Type B: Operator + Reg. → ZEBRA 5Y-BSA
• Type C: Aircraft Type + Reg. → BUFFALO 5X-BFL
• Type D: Operator + flight no. → KQA275
• Type E: Plain reg. → N3782B
Abbreviated Forms:
• First + last 2 letters: 5-SA
• RTF Designator + last 2: ZEBRA-SA
• Aircraft type + last 2: BUFFALO-FL
• No abbreviations for flight numbers
• USA style: First and last 3: N-82B
RTF Procedures
• Don’t change callsign mid-flight unless told by ATC.
• No calls during takeoff/landing unless it’s for safety.
• Always use full callsign first, then abbreviate later if ATC does so.
• Readbacks required for:
o Route clearances
o Runway instructions
o Altimeter, SSR, level/heading/speed instructions
If readback not needed, just reply with callsign.
Radio Check Format
1. Who you’re calling
2. Your aircraft ID
3. Say “RADIO CHECK”
4. Mention frequency
Reply must include:
• Receiver’s ID
• Feedback on readability (scale 1–5)
Scale Meaning
1 Unreadable
2 Readable now & then
3 Readable but hard
4 Readable
5 Perfectly clear
Radio Communication Failure (RCF)
• Try another frequency or call other aircraft/stations.
• If all fail, say: “TRANSMITTING BLIND” twice, send your message.
• If total failure (aircraft radio dead), set SSR code 7600.
• Transmitting Blind ≠ Broadcasting.
o Blind = to one station, no reply
o Broadcast = to everyone, no reply expected
If RCF Mid-Flight: Follow this
1. Stick to flight plan to destination’s holding point.
2. Try to arrive at planned ETA.
3. Land within 30 mins of descent start time.
o If not possible:
▪ Land visually if safe.
▪ Or leave airspace via known route & fly visually to alternate.
4. Missed approach?
o Land at planned field if possible in 30 mins.
o Otherwise, exit controlled airspace safely.
“Delay not determined” ≠ Expected Approach Time (EAT).
If RCF after this message, don’t land at planned destination, divert.
Nairobi FIR Coverage
• Extends from North Kenya (04°N 034°E) across the country.
• Covers airspace from ground level to unlimited altitude.
• Extra zone from 04°42’S to 08°30’S above FL245.
Frequencies in Nairobi FIR
Use Frequency
ACC – South 120.5 / 125.3 MHz
ACC – North 121.3 / 118.5 MHz
ATIS 126.2 MHz
Unmanned fields 118.0 MHz
VHF Emergency 121.5 MHz
HF Primary 11300 KHz (day), 5517 KHz (night)
HF Secondary 13288, 3467, 17961, 8870, 6574, 8879 KHz
Unmanned Aerodromes (e.g., rural airstrips)
Broadcast on 118.0 MHz and include:
Inbound Call:
• “ALL STATIONS (Name)…”
• Aircraft type and callsign
• Direction
• ETA
• Current position + next call point
In Circuit or on Ground:
• Repeat type + callsign
• Where you are now
• Your intention (e.g., “joining downwind”)
• When/where next call will be
If ATS is usually available, do not use 118.0 MHz. Use the normal airfield frequency.
CHAPTER 8 – Air Reports (AIREP)
Air Report Format
SECTION I (Mandatory)
• Aircraft ID
• Position
• Time
• Level
• Next position + ETA
SECTION II (If asked)
• ETA
• Endurance (how much fuel time left)
SECTION III (For Met Reports)
• Temp, Wind, Turbulence, Icing, Other info
Must include:
• Section I: Always
• Section II: If ATS/operator asks
• Section III: For IFR flights > 2 hrs, unless within 1 hr of destination
Special AIREPs
• Send when:
o Severe icing or turbulence
o Any dangerous weather seen by pilot
Prefix with “AIREP SPECIAL”
AIREP ADD
• Sent when requested before/during flight by Met Office
Prefix with “AIREP ADD”
CHAPTER 9: DISTRESS AND URGENCY TELEPHONY
COMMUNICATIONS
9.1 Definitions
• Distress (MAYDAY ×3):
Serious/imminent danger – needs immediate help.
E.g.: Engine failure over mountains.
• Urgency (PAN PAN ×3):
Concerning safety, not requiring immediate help.
E.g.: Passenger sick or low fuel.signals are used at the start of communication.
9.2 Radiotelephony Distress Communication
What to say during a MAYDAY call:
On the working frequency, say:
1. Station addressed (e.g., “Nairobi Control”)
2. Your callsign (e.g., “5Y-BBC”)
3. Nature of distress (e.g., “engine failure”)
4. Your intention (e.g., “attempting forced landing”)
5. Position (e.g., “10 NM east of Wilson at 4000 ft”)
Use 121.5 MHz if all else fails. Others:
• 243 MHz (military)
• 500 kHz, 2182 kHz (maritime)
• Any usable frequency.
When distress is received:
The first station must:
• Acknowledge it
• Take control or clearly hand over
• Notify ATS, operator, and warn other stations
• Keep the frequency clear
To stop interference:
Say:“ALL STATIONS, STOP TRANSMITTING – MAYDAY.”
When distress ends:
Send:“DISTRESS TRAFFIC ENDED”
9.3 Radiotelephony Urgency Communication
What to say during a PAN PAN call:
1. Station name
2. Aircraft callsign
3. Nature of urgency
4. Intention
5. Position, level, heading
6. Any extra info
Urgency has priority over normal traffic, but NOT over distress.
9.4 Medical Transports
Use:“PAN PAN PAN – MEDICAL”
Include:
• Callsign
• Position
• Number/type of patients
• Route and ETA
• Other info: altitude, language, SSR code
CHAPTER 10: SEARCH AND RESCUE (SAR)
10.1 SAR Emergency Phases
Phase Meaning Keyword
(a) Uncertainty Aircraft might be in trouble INCERFA
(b) Alert Aircraft likely in trouble ALERFA
(c) Distress Aircraft in grave danger DETRESFA
10.2 When to Declare SAR Phases
10.2.1 UNCERTAINTY (INCERFA):
• No contact for 30 mins
• 30 mins overdue at destination
10.2.2 ALERT (ALERFA):
• Still no info after INCERFA
• Aircraft missed landing by 5 mins
• Possible impairment (but not crash)
• Hijacking suspected
10.2.3 DISTRESS (DETRESFA):
• No contact after ALERFA
• Fuel exhausted
• Likely crash or forced landing
• Info proves aircraft in danger
10.3 SAR Units
• RCC (Rescue Coordination Centre): Near Nairobi ACC
• Rescue Sub-Centres:
o Type I → in all ATC Units
o Type II → at provincial police HQs
10.4 SAR Notification Content
Include:
1. Emergency phase (INCERFA / ALERFA / DETRESFA)
2. Who’s calling
3. Type of emergency
4. Flight plan summary
5. Last known contact/time
6. Position report
7. Aircraft markings
8. Dangerous goods
9. Any actions taken
10. Extra remarks
10.5 Ground-Air Visual Codes
Message Symbol
Need help V
Medical help X
No/Negative N
Yes/Affirm Y
Proceed this direction. →
10.6 SAR Facilities in Kenya
Air: KQ, Police Air Wing, Aero Clubs
Ground: Army, NYS, Rangers, Police
Marine: Navy, Port Authority
Radio: Nairobi FIR manages
10.7 406 MHz Emergency Beacons
• Replaced old 121.5/243 MHz ELTs in 2009
• Signals go to COSPAS-SARSAT satellites
Advantages:
• Faster and more accurate location
• Can call owner to check false alarms
• Database helps SAR know aircraft details
CHAPTER 11: DIRECTION FINDING (DF)
11.1 Types of DF Stations
Solo Station:
Can tell:
• QTE: True bearing from aircraft
• QDR: Magnetic bearing from aircraft
• QDM: Magnetic heading to station (zero wind)
• QUJ: True heading to station (zero wind)
Network of Stations:
• Bearings from several stations sent to DF Controller
• Gives position via:
o Latitude/longitude
o Bearing + distance
11.2 DF Accuracy Classes
Class Bearing Error Position Accuracy
A ±2° within 9.3 km
B ±5° within 37 km
C ±10° within 92 km
D >10° Less accurate
11.3 Requesting DF Services
Use QDL followed by needed Q-code.
Example RTF:
• Pilot: “Wilson Homer, 5Y-AAK request QDL QDM”
• DF Station: “5Y-AAK, transmit for QDM”
• Pilot (holds transmit): “5Y-AAK”
• Station: “QDM 110° Alpha”
• Pilot: “QDM 110° A, 5Y-AAK”
CHAPTER 12: METEOROLOGICAL SERVICES
12.1 Authority
• Provided by Kenya Meteorological Dept
• Based on ICAO Annex 3 & Doc 7030
12.2 Area Covered
• Entire Nairobi FIR
• Main centre: Dagoretti Corner, Nairobi
12.3 Observation Stations
Aerodrome Frequency
JKIA, Moi, Eldoret, Wilson Every 30 mins + specials
Kisumu, Malindi, Eastleigh, Lokichoggio, Wajir Hourly + specials
12.4 Services Offered
• Personal briefing at major aerodromes
• Flight docs include:
o Significant weather charts
o Upper winds & temperatures
o Forecasts for destination + alternate
Request forecasts 6 hours before flight.
Include route, period, and destination.
12.5 Aircraft Weather Reporting
• Captains fill AIREP forms
• Submit at debriefing
12.6 Order of Weather Elements Transmission
1. Station & time
2. Wind direction/speed
3. Visibility (or RVR)
4. Present weather (if any)
5. Cloud base/type
6. Temperature/Dewpoint
7. QNH (or QFE if asked)
8. Extra info (plain language)
Use “CAVOK” to mean:
• Visibility > 10km
• No cloud < 5000 ft
• No precip, fog, or storms
Only mention cloud type if CB (Cumulonimbus)
Pilot responds:“Weather copied. QNH 1024. 5Y-BBC”
