-- in that order.
July 2, 1937 at 0000 GCT, the Lockheed Electra Model
10E began its take-off
role at Lae, New Guinea. It was the beginning of
a tragic flight
and the biggest aviation mystery in
history. The over-water
flight of 2,556 miles along the Equator to Howland
Island would place extreme
demands on all navigation resources and skills of that
navigator for the round-the-world
adventure was arguably the best in the world, Fred
the successful conclusion of the flight could be
assured only by RDF
-- Radio Direction Finding (see Live Reckoning)
performed by the Pilot-in-Command, Amelia
Navigating, Communicating (in that order)
Piloting requires multitasking
aloft. Each task has its own primacy; each is a sine
qua non for the successful completion of
every flight. Contrary
to the simplistic mandate
cited above, priorities must change with the various
phases of flight.
Thus, during take-off and
early stages of climb-out,
the pilot will be focused most intensely on Aviating
Nightmare). Same during the final stages
of approach and landing
(see Sloping in the Dark).
Still, are there occasions when Communicating
must take center stage? Indeed yes, when radio
essential for Navigating.
bene, the principles of RDF have not changed over
the decades, only
the radio technologies. There are two modes...
In between, often for hours-on-end, Navigating
takes first priority, as satirized in one definition,
"Latitude is where we are lost, and Longitude
is how long
we have been lost there."
So it would seem that Communicating
belong as the lowest
"Never drop the plane to fly the microphone," goes
an old saying.
To establish a course
directly toward Howland Island, Amelia
Earhart would need to operate an
RDF antenna, which is the loop being
displayed on the right and visible
as it was mounted atop the Electra in the
photograph above. With an appropriately
tuned radio receiver, she would be able to
rotate the loop to "get a minimum"
signal and thereby determine the direction
from which a radio signal is
being transmitted. Using that bearing
angle, the Electra would be turned to take
up a heading
directly toward the source. In this
mode, airborne RDF equipment
operates "receive-only" -- simplex
in radio parlance. However...
In 1937, no permanent
was installed on Howland. Such a
facility would be transmitting an
identification signal continuously on a
dedicated frequency identified
by Morse Code.
Instead, the US Coast
Guard cutter Itasca had been
positioned at anchor offshore Howland
to support RDF for the Earhart
flight. A qualified radio operator
on board Itasca was supposed to
broadcast an improvised
signal in compliance with a time-of-day schedule
on an assigned
with station identification to be
recognizable by Amelia Earhart
-- all by protocols coordinated in advance
of the inbound flight.
For guidance from the ground ('DF
steer'), two-way communications had to
be established with USCG Atasca,
which is shown on the right.
Communications were to take place by
voice or by Morse Code on assigned
frequencies. Amelia Earhart would
then be requested over the radio to transmit
a steady signal long enough
for the Itasca radio operator to
ascertain the direction of the
source in the sky using a loop antenna on
the ship. Having obtained
Electra relative to the ship's heading, the
operator must compute the appropriate
compass direction for the Electra to fly and
transmit that information
to Amelia Earhart as a heading
by voice or Morse code. All of that
takes time, of course, and all
the while, the Electra would be flying at
over a hundred miles per hour
on an uncorrected heading.
In concept, Duplex RDF
operates as a reciprocating, two-way, simplex
system -- half-duplex
in radio parlance. By the way,
wireless telephony, which we take
for granted today, supports what is called
duplex communications, with
transmitting and receiving going on in
both directions simultaneously. Full
duplex is a feature still not
found in radio equipment installed on even
the most complex airliners of
the Twenty-First Century.
As readily seen in the descriptions
above, for RDF to
be successful in either mode, equipment and people on
the ground and in
the sky must all be in good working order and coordinated.
Last Words of
The figure below is based on
transcriptions from the radio
room aboard the USCG Itasca standing by
Howland Island on July 2,
1937. These are the last six radio messages
received from Amelia
Earhart over a period of two and a half hours on that
The pre-arranged 'radio schedule'
during which Earhart was supposed to transmit
simplex at quarter-to
and quarter-passed each hour In between, Itasca
supposed to transmit simplex on the hour and
taken special notice of the potential for confusion
two time-zones: Earhart and Noonan operated on
Greenwich Civil Time (GCT)
while the Itasca clocks were all set on local
time at Howland ("IST"
for 'Itasca Standard Time'), such that IST
= GCT minus
11:30. A source
of confusion for sure, but if everybody stuck to the
script, those time-slot
assignments ought to have worked just fine in
Sophisticated solvers will immediatly
observe the following
For the many technical issues and facts
beyond those appropriated
for Simplexity Aloft,
there can be no doubt
that the most comprehensive reference in all of Amelianna
is the fascinating e-book entitled Amelia
Earhart’s Radio: Why She Disappeared by Paul
Three different radio frequencies
being called out by Amelia
Earhart: 3105, 6210, and 7500 Kcps (thousands of
cycles per second, "Hz"
in today's terminology).
Three different forms of modulation:
"noise," "voice," "whistling"
-- but not "code" (neither Amelia Earhart
nor Fred Noonan understood
trumped simplicity for
Amelia Earhart and Fred Noonan that day, hence the
appropriation of "simplexity"
in the title of this puzzle. As the Electra
approached the end of its final
flight, a lot could go wrong. And apparently
many critical issues
can you identify by parsing the last words
of Amelia Earhart?
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