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    Re: Celestial up in the air
    From: Gary LaPook
    Date: 2008 Jul 28, 19:20 -0700

    You can get a copy of the Air Almanac, it is easier to use in flight
    than the
    Nautical Almanac, you get it on disk from the Naval Observatory, cost
    thirty one bucks, here is the link:
    
    http://aa.usno.navy.mil/publications/docs/ord_info.php
    
    Just print out the pages you need for your flight, about 7 pages of
    interpolation and correction tables (which don't change and only need
    to
    be printed out one time) and two daily pages for each day of your
    trip.
    
    gl
    
    On Jul 28, 5:30 pm, "Hewitt Schlereth"  wrote:
    > 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, glap...@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  Airlines no longer use flight navigators, they have been replaced by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=f4449a9057da...
    >
    > >  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
    >
    > ...
    >
    > read more �
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