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    Re: Celestial up in the air
    From: Hewitt Schlereth
    Date: 2008 Jul 28, 20:30 -0400

    Hey, thanks for the thoroughgoing response. One reason for my interest
    was that I began to do celestial when I was living in Allentown PA in
    1965 and got to talking with a neighbor. He turned out to be a
    navigator for JAL. He gave me an expired Air Nautical Almanac - these
    were the days when it was published in three installments; red
    binding, white binding, blue binding, one every four months.
    
    Anyway, I dug out my high school spherical trig book, bought a surplus
    aircraft sextant and started taking sights  from the roof, coached and
    critiqued by my neighbor when he was home between trips.
    
    I took celestial to sea when I moved to the east coast in 1969 and
    it's been with me ever since.
    
    Thanks again, Hewitt
    
    On 7/28/08, glapook@pacbell.net  wrote:
    >
    >  Airlines no longer use flight navigators, they have been replaced by
    >  specialized navigation equipment. In the past
    >  Kollsman periscopic sextants were used which extended through the top
    >  of the
    >  fuselage in B-52s, C-130s, other military planes and also in Boeing
    >  707s, and DC-8s. Airline Flight Navigators used celestial for oceanic
    >  flight up until the early '70s and the military used celestial
    >  routinely
    >  through the  '90s ( they figured the Soviets would turn off their
    >  radio
    >  navigational aids in the event of war.) It is still in the current Air
    >  Force navigation manual,  AFPAM 11-216. Flight navigators were
    >  replaced when the Boeing 747 came along with inertal navigation
    >  systems in the late '60s. And now GPS provides the specialized
    >  navigation equipment that allows tranoceanic operations without a
    >  navigator.
    >
    >  Federal Aviation Regulation (FAR) 121.389 still requires a flight
    >  navigator unless the pilot can fix his position every hour and pilots
    >  can now do that with INS or GPS. I have attached the regulation and a
    >  link to its source.
    >
    >  gl
    >  Title 14: Aeronautics and Space
    >  PART 121�OPERATING REQUIREMENTS: DOMESTIC, FLAG, AND SUPPLEMENTAL
    >  OPERATIONS
    >  Subpart M�Airman and Crewmember Requirements
    >
    >  Browse Previous | Browse Next
    >  � 121.389   Flight navigator and specialized navigation equipment.
    >
    >  (a) No certificate holder may operate an airplane outside the 48
    >  contiguous States and the District of Columbia, when its position
    >  cannot be reliably fixed for a period of more than 1 hour, without�
    >
    >  (1) A flight crewmember who holds a current flight navigator
    >  certificate; or
    >
    >  (2) Specialized means of navigation approved in accordance with
    >  �121.355 which enables a reliable determination to be made of the
    >  position of the airplane by each pilot seated at his duty station.
    >
    >  (b) Notwithstanding paragraph (a) of this section, the Administrator
    >  may also require a flight navigator or special navigation equipment,
    >  or both, when specialized means of navigation are necessary for 1 hour
    >  or less. In making this determination, the Administrator considers�
    >
    >  (1) The speed of the airplane;
    >
    >  (2) Normal weather conditions en route;
    >
    >  (3) Extent of air traffic control;
    >
    >  (4) Traffic congestion;
    >
    >  (5) Area of navigational radio coverage at destination;
    >
    >  (6) Fuel requirements;
    >
    >  (7) Fuel available for return to point of departure or alternates;
    >
    >  (8) Predication of flight upon operation beyond the point of no
    >  return; and
    >
    >  (9) Any other factors he determines are relevant in the interest of
    >  safety.
    >
    >  (c) Operations where a flight navigator or special navigation
    >  equipment, or both, are required are specified in the operations
    >  specifications of the air carrier or commercial operator.
    >
    >  [Doc. No. 10204, 37 FR 6464, Mar. 30, 1972, as amended by Amdt. 121�
    >  178, 47 FR 13316, Mar. 29, 1982]
    >
    >
    >  Link to regulation:
    >
    >  
    http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=f4449a9057da17679158ea72c7ecccde&rgn=div8&view=text&node=14:2.0.1.4.19.13.10.5&idno=14
    >
    >
    >
    >
    >  On Jul 28, 7:53 am, "Hewitt Schlereth"  wrote:
    >  > Hi Gary -
    >  >
    >  > I'd probably missed the answer to this question because I picked up
    >  > the thread in the middle:  Is celestial part of your routine duty of
    >  > navigating an airliner or is it something you do for its own sake?
    >  >
    >  > Thanx,  Hewitt
    >  >
    >  > PS  It's been an absorbing thread to follow.  Keep it coming. HewS
    >  >
    >
    > > On 7/28/08, glap...@pacbell.net  wrote:
    >  >
    >  >
    >  >
    >  > >   For example, using the page from the Air
    >  > >  Almanac found on page 206, a day when the H.P is 60', and an altitude
    >  > >  of 36� we find the parallax in altitude correction to be 48' and this
    >  >
    >  > > would be the correction to use with a bubble sextant. (Page 206 of
    >  > >  AFPAM 11-216.)
    >  >
    >  > >  Additionally, formulas for these correction are found on pages 393 and
    >  > >  394 of the same manual.
    >  >
    >  > >  gl
    >  >
    >  > >  On Jul 28, 5:24 am, glap...@pacbell.net wrote:
    >  > >  > One more thing to discuss before giving an example of in flight celnav
    >  > >  > is corrections to sights taken in flight. We discussed this back on
    >  > >  > December 14, 2007 in the thread "additional corrections... (just
    >  > >  > search "additional corrections") which include an excerpt from AFPAM
    >  > >  > 11-216. You should download the entire manual 
    here:http://www.e-publishing.af.mil/shared/media/epubs/AFPAM11-216.pdf
    >  >
    >  > >  > Review chapters 10 through 13.
    >  >
    >  > >  > I want to add to the manual on this.
    >  >
    >  > >  > Coriolis can be handled in a number of ways. You can move the A.P. to
    >  > >  > the right (northern hemisphere) 90� to the course (track) prior to
    >  > >  > plotting the LOPs by the amount of coriolis correction shown in the
    >  > >  > table in the Air Almanac and in H.O. 249 (previously posted). Or you
    >  > >  > can move the final fix the same way. Or, the most complicated way, is
    >  > >  > to make a correction to each Hc by multiplying the coriolis correction
    >  > >  > by the sine of the relative Zn, the Polhemus makes this relatively
    >  > >  > painless.
    >  >
    >  > >  > Rhumb line correction is avoided by steering by directional gyro
    >  > >  > during the two minute shooting period and this is what is normally
    >  > >  > done anyway.
    >  >
    >  > >  > Wander correction is small at low airspeeds and it can be avoided by
    >  > >  > making sure the heading is the same at the end of the shot as it was
    >  > >  > at the beginning of the shot. It doesn't matter how the heading
    >  > >  > changes during the shot (within reason) as the errors will average
    >  > >  > out.
    >  >
    >  > >  > Ground speed correction can also be avoided by making sure the
    >  > >  > airspeed is the same at the end as at the beginning, any changes in
    >  > >  > between will also average out.
    >  >
    >  > >  > Auto pilots do a good job of maintaining airspeed and heading for the
    >  > >  > two minute shooting period so eliminating the need for the above
    >  > >  > corrections.
    >  >
    >  > >  > The AFPAM states you must figure the refraction correction based on
    >  > >  > the actual Hs as opposed to using the refraction correction based upon
    >  > >  > the Hc but this is a needless refinement and keeps you from completing
    >  > >  > the pre computation prior to the shot. Look at the refraction table in
    >  > >  > H.O. 249 (previously posted) and you will see for altitudes exceeding
    >  > >  > 10� that the brackets are at least two degrees wide. So only in the
    >  > >  > rare cases where the altitude is almost exactly at the break point
    >  > >  > could you come up with a different refraction correction using Hc
    >  > >  > rather than Hs and even then it could only be a difference of one
    >  > >  > minute of altitude. For example the break point between a 5'
    >  > >  > correction and a 4' refraction correction is 12� so if Hs were 11� 50'
    >  > >  > and Hc were 12� 15' then using Hc would get you a 4' correction and
    >  > >  > using Hs would get you a 5' correction. This is actually only 1/2 of a
    >  > >  > minute error because the corrections are rounded to the nearest full
    >  > >  > minute.
    >  >
    >  > >  > The parallax in altitude correction for the moon is printed on each
    >  > >  > page of the Air Almanac based upon the horizontal parallax (H.P.) for
    >  > >  > the moon on that particular day. This parallax varies with the
    >  > >  > distance to the moon and moves in lock step with the S.D. since they
    >  > >  > are both related to the distance to the moon. The H.P varies from 54'
    >  > >  > to 61' during the year. For example, using the page from the Air
    >  > >  > Almanac found on page 206, a day when the H.P is 60', and an altitude
    >  > >  > of 36� we find the parallax in altitude correction to be 48' and this
    >  > >  > would be the correction to use with a bubble sextant. If using a
    >  > >  > marine sextant and shooting the lower limb we would add the S.D. of
    >  > >  > 16' to produce a total correction (but not including refraction yet)
    >  > >  > of 64'. Subtract the refraction correction of 1' gives the total
    >  > >  > correction of 63'. Using the correction table in the Nautical almanac
    >  > >  > for the identical parameters you get 63.5'. The Nautical Almanac moon
    >  > >  > correction table includes a procedure for using it with a bubble
    >  > >  > sextant and what this does is just backs out the S.D. correction which
    >  > >  > is included in the correction table and not needed for a bubble
    >  > >  > observation. Using this procedure produces a correction for a bubble
    >  > >  > observation of 47.2' which compares with the 48' from the Air Almanac.
    >  >
    >  > >  > Remember to reverse the signs of these corrections and apply them to
    >  > >  > Hc to produce Hp (pre computed altitude) which you then compare
    >  > >  > directly with Hs to compute intercept.
    >  >
    >  > >  > gl
    >  >
    >  > >  > On Jul 25, 7:48 pm, Gary LaPook  wrote:
    >  >
    >  > >  > > We can also use the Polhemus computer to calculate the MOO adjustment.
    >  > >  > > We do this by setting the ground speed  in the setting window and read
    >  > >  > > out the MOO in the "ZN-TR" window adjacent  to the relative Zn. (See
    >  > >  > > Pol1.jpg) (Zn-TR is another way of saying "relative Zn" since you
    >  > >  > > calculate relative Zn by subtracting Track from Zn.) Looking at the top
    >  > >  > > of the TR-ZN window where the relative Zn of 000� is adjacent to "5" in
    >  > >  > > the MOO window showing that the aircraft moves 5NM per minute which
    >  > >  > > causes the altitude to also change 5' every minute when the body is
    >  > >  > > directly ahead of or directly behind the aircraft. This MOO is
    >  > >  > > equivalent to the MOO table at page 6 of the original PDF which
    >  > >  > > tabulates the MOO adjustment per minute. Multiplying this 5' times the
    >  > >  > > same eight minute period gives the same 40' adjustment we got from the
    >  > >  > > MOO table on page 4 of the PDF. You will also find that the adjustment
    >  > >  > > is 2.5' adjacent to the relative Zn of 60� which multiplied by eight
    >  > >  > > minutes gives the 20' adjustment we found in the table on page 4.
    >  >
    >  > >  > > The Polhemus makes it easy to figure the relative Zn. You place the "SET
    >  > >  > > TRACK" pointer on the track of the aircraft ,130�  as shown in the
    >  > >  > > attached image. (see Pol2.jpg) Look at the next image (Pol3.jpg) for the
    >  > >  > > second case, a track of 70� and you find the relative Zn, 60� on the
    >  > >  > > inner scale.
    >  >
    >  > >  > > The Polhemus also makes it easy to figure the sign to use for the
    >  > >  > > adjustment, if the relative Zn is on the white scale, meaning the body
    >  > >  > > is ahead, then the sign is minus and if found on the black scale (the
    >  > >  > > body is behind) then the sign is plus when these adjustments are made to
    >  > >  > > Hc, the normal method. This same pattern is revealed in the two MOO
    >  > >  > > tables, the top of the tables show the body ahead and the bottom has the
    >  > >  > > body behind.
    >  >
    >  > >  > > gl
    >  >
    >  > >  > > glap...@pacbell.net wrote:
    >  > >  > > > Now let's talk about the "motion of the observer" (MOO) adjustment.
    >  > >  > > > Every fix in the air is a running fix because the aircraft moves a
    >  > >  > > > considerable distance between the first and last sight. Assuming the
    >  > >  > > > normal eight minute spacing between the first and last shot, a slow
    >  > >  > > > airplane, say 100 knots, will have traveled 14 NM while a 450 knot
    >  > >  > > > plane will have traveled 60 NM. In marine practice the navigator will
    >  > >  > > > advance the earlier LOPs to cross them with the last shot. The MOO
    >  > >  > > > adjustment accomplishes the same thing.
    >  >
    >  > >  > > > As an example of how this works consider a sun shot taken at 1000Z
    >  > >  > > > resulting in an observed altitude, Ho, of 35� 55'. After doing the
    >  > >  > > > normal sight reduction you end up with an Hc of 35� 45' at the chosen
    >  > >  > > > A.P and a Zn of 130�. This results in an intercept of 10 NM toward the
    >  > >  > > > body, 130�. To plot this LOP you draw the azimuth line from the A.P
    >  > >  > > > and measure off the 10 NM intercept toward the sun and plot the LOP
    >  > >  > > > perpendicular to the Zn.
    >  >
    >  > >  > > > Then, two hours later at 1200Z you take another altitude of the sun
    >  > >  > > > and to obtain a 1200Z running fix you must advance the 1000Z sun line
    >  > >  > > > to cross the 1200Z line. There are three ways to advance the LOP.
    >  > >  > > > First, you can pick any spot on the LOP and lay off a line in the
    >  > >  > > > direction of travel of the vessel, measure off the distance traveled
    >  > >  > > > along that line, make a mark there and then draw a line through that
    >  > >  > > > mark that is parallel  to the existing LOP and label the advanced LOP
    >  > >  > > > "1000-1200Z SUN." A second way is to advance each end of the LOP and
    >  > >  > > > then just draw a line through these two points, this avoids having to
    >  > >  > > > measure the azimuth when laying down the advanced line. The third way
    >  > >  > > > is to advance the original A.P and then from the ADVANCED A.P. plot
    >  > >  > > > the LOP using the ORIGINAL intercept and Zn. Any of these methods will
    >  > >  > > > produce the same advanced LOP.
    >  >
    >  > >  > > > Now let's consider a simple case. Suppose the vessel's course is the
    >  > >  > > > same as the Zn, in this case, 130� and the vessel's speed is 20 knots
    >  > >  > > > meaning it has traveled 40 NM in the two hour period. In this simple
    >  > >  > > > case we can just extend the Zn line an additional 40 NM and then plot
    >  > >  > > > the
    >  >
    >
    > > ...
    >  >
    >  > read more �
    >  >
    >
    
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