NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Celestial up in the air
From: Hewitt Schlereth
Date: 2008 Jul 28, 20:30 -0400
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.netwrote: > > Airlines no longer use flight navigators, they have been replaced by 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 � > > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---