1. A Pilot’s Guide to Using HFDL
Prepared
July 2016

2. HFDL Propagation Ionosphere Refraction of signal
works by bouncing signals off the ionosphere. Aircraft might be one hop or more away. This bouncing allows HFDL to provide worldwide coverage with only 15 stations.
Ionosphere
Refraction
of signal
One hop
Multi-hop

3. Does Solar Activity Affect Propagation?
Propagation is affected by solar events.
How do we compensate?
We need less bandwidth than voice.
Full Fidelity Voice kHz
Intelligible voice kHz
Data 2.4 kHz
We monitor for solar events and change the operating frequencies.

4. Worldwide Coverage HF Ground Stations Alaska Bahrain Bolivia
California
Canary Islands
Guam
Hawaii
Iceland
Ireland
New York
New Zealand
Panama
Russia
South Africa
Thailand
Legend
HFDL ground
station
Areas of
Primary coverage
Areas of
Secondary coverage

5. HFDL Flights - Positions reported through HFDL automated performance packets

6. Connectivity between HFDR and HF ground station
When not transmitting or receiving data, the HFDR (HF data radio) will check other HF data frequencies to keep a current list of frequencies to use.
The HFDR will tune to the next frequency/ground station if the connection fails.
The ground station also polls the HFDR to make certain that the aircraft has a good connection.
The aircraft periodically sends performance data that gives the lat/long of the aircraft and UTC. This allows for route tracking/mapping without bothering the crew for position reporting.

7. Airborne Architecture
HF Antenna
HF Coupler (x2)
Multi-functional
Cockpit
Display Unit
ACARS MU/CMU/ATSU
Flight Management
System
HF Data Radio (x2)

8. Flight Crew Operational Use - Preflight
Radio tuning panel is always placed in ON position
One HFDR is tuned to DATA mode during pre-flight prior to push back
The HFDR will passively listen for HF stations.
Both Boeing and Airbus inhibit HFDL transmission on-ground unless the override switch (GTIO) is “ON”.
HF SENS
VHFL
VHFC
VHFR
HFR
HFL AM
OFF
P N L
ACTIVE
13.348
STANDBY
DATA

9. HFDL Use On The Ground – when outside VHF coverage
Ground Transmit Inhibit Override (GTIO) – The “ON” position enables HFDL send/receive
Always follow company policy and procedure for use of this switch.
present in most Boeing and Airbus aircraft.
Our recommendations:
When on-ground at an airport without VHF coverage.
Put the GTIO in the ON position after pushback (when refueling/defueling is complete)
When no ground personnel are within 10 feet of the vertical stabilizer during transmission
When outside VHF coverage, this will allow the OUT message and any pre-flight messages to be sent and received.
Put it back to the OFF position before landing in VHF coverage - anytime during the flight.
Upon approach to an airport with no VHF coverage
Put the GTOI in the ON position before landing
This will allow the ON and IN reports to be sent.
Turn it to the OFF position in the gate (for fueling or when ground personnel are near the aircraft).

10. Flight Crew Operational Use - Inflight
Keep the same HFDR in DATA mode for the entire flight (pre-flight to post-flight)
If no VHF ground coverage is available, it is essential to leave the HFDL equipment on so that OOOI messages (ON/OFF/OUT/IN) can be transmitted.
Do not switch between left and right HFDRs
This will cause the HFDR to begin frequency search which can last several minutes, possibly interrupting message transmission
Do not tune the data frequency on the radio tuning panel.
The HFDR will automatically tune to the proper HF data frequencies.
Be patient.
HF is slower than VHF, where VHF might deliver a large message in seconds, HF might require a few minutes.

11. Flight Crew Operational Use - Inflight
HF voice use will pre-empt DATA use since they share an antenna.
Do not key or tap the mic prior to voice use to “tune the antenna”
This is not needed and can interrupt data.
Do not key the mic when “HF in PROG” is displayed.
This will interrupt data transmission.
Be patient after a voice exchange.
Once the mic is released, the HFDR will stay locked in voice for 60 seconds which prevents data transmission
Use of the mic for more than 3 minutes requires the HFDR to log back onto a ground station, so data will take a few minutes.

12. Questions or Problem Reports
Carolyn Bray – HFDL Technical Project Manager
US & Int’l Access (Sprint) HDQHDXA