navigation on Earhart's flight....
Subject: navigation on Earhart's flight....
From: Russell Sher (rsher@XXX.XXX)
Date: Thu Feb 22 2001 - 01:12:59 EST
The following is taken from
http://www.tighar.org/forum/Forumfaq.html It is a bit of insight into the
navigation by Fred Noonan on Amelia Earhart's flight: --
Our information on this is based upon the actual charts
Noonan and Harry Manning used while going from Oakland to Honolulu in March.
Typically, two stars were used to determine position, with each star
approximately 90 degrees in azimuth from one another. Given only one side
window in the fuselage of the plane, this may explain some anecdotal stories
that Harry Manning was a real pain, because he was in and out of the cockpit
quite a bit, probably getting star sights directly ahead of the plane,
whereas the sights to the side of the plane were made in the back.
Why not more stars? The idea of navigation is to monitor
where you are, and absolute precision is not necessary, only good to 10
miles or so. Two quality star sights can give you that precision.
Occasionally, FN and HM would make a couple of sightings within a half hour
or so, to double-check their readings. All together on that flight, there
were less than a dozen actual fixes. There is no evidence on any charts of
any wind vector determinations.
By using the stars and (during the day) the sun, Noonan
could calculate, by means of pre-figured angles and a printed table, a
position on a map. During the day, multiple sun sightings were necessary;
with only one sun shot, only a Line of Position could be calculated. They
would know they were somewhere on that line, but not exactly where in terms
of north/south. The sun shot Noonan took at dawn on the way to Howland was
such a LOP.
That LOP was then advanced, on paper, until it fell through
the destination, Howland Island. A calculation was made to estimate how long
it would take to get there, and the flight continued until then, at which
time....
When Earhart and Noonan get to their advanced Line of Position, to their
disappointment but not surprise, no island or ship is in sight. Noonan knows
that Howland is either off to the left (337 degrees) or off to the right
(157 degrees), but which way to choose? He knew this problem
could come up and he already has a plan. He knows he is not
hundreds and hundreds of miles off. He also knows that at the time Earhart
says "We must be on you but cannot see you" he has roughly 5 hours of fuel
left.
Happily, there are four islands on or very near his LoP ---
Howland, Baker, McKean, and Gardner. Howland, however is on the left (NW)
end of that string which means that all of his other options are to the SE.
He can afford to search northwestward along the line only a short time
because if he is already NW of Howland there's nothing out there but water.
But as long as he turns and starts heading southeastward along the line when
he still has about four hours of fuel left he is virtually guaranteed to
find land. If he's off to the NW he'll find Howland. If he's off just a
little to the SE he'll soon find Baker and should have enough fuel to
backtrack the 40 miles to Howland. If he's further off to the SE he reach
either McKean or Gardner and least not have to put the airplane in the
drink. It's a failsafe contingency plan provided that 1). He really is on
the LoP he thinks he is on; and 2). He heads SE when he still has 4 hours of
fuel.
We suspect that this is what AE was trying to say in her final message
received by Itasca at 08:43 when they should have had just about 4 hours of
gas remaining. Itasca logged the transmission as "We are running north and
south." but that doesn't make much sense and it's clear from the log that
the transmission caught the operator by surprise when he was doing something
else and he's not entirely sure what she said. The actual message may have
been something like, "Were running northwest, now southeast."
