Wikipedia:Reference desk/Archives/Science/2018 February 22

= February 22 =

Missed approaches
How come almost all of the holding patterns charted at the end of missed approach procedures are set up in such a way as to require a parallel entry (or in a few cases a teardrop entry), but hardly ever a direct entry? Is there a reason for this? 2601:646:8E01:7E0B:0:0:0:64DA (talk) 07:56, 22 February 2018 (UTC)
 * IANAP, but naĩvely it would seem to me that the paths flown to achieve a parallel entry would minimise the likelihood of conflict or collision with other aircraft in the vicinity. However, doubtless a more knowledgeable contributor can shoot me down in flames! {The poster formerly known as 87.81.230.195} 90.220.212.253 (talk) 14:58, 22 February 2018 (UTC)
 * I know nothing about this, but this site seems to have useful graphics that are more detailed than the ones in holding pattern. If I understand #3 rightly, the pilot who misses an approach has to turn around and fly back to the holding area.  The holding area appears to be set up with pilots already in a holding pattern flying toward the navigational fix in a straight line while they're flying toward the airport, hence one flying away from the airport is going the "wrong way" to do the direct approach and has to do something else. Does that make sense? Wnt (talk) 17:18, 22 February 2018 (UTC)


 * I'm not sure the claim is accurate - maybe I'll do a quick survey of the plates for approaches I commonly use, and see if "most" or "almost all" missed approach procedures do satisfy this claim; but here are a few observations:
 * as a proficient instrument pilot, you should be equally comfortable with all entries to the hold - so it doesn't really matter;
 * ATC doesn't care how you enter the hold as long as you stay in protected airspace. I just checked the current AIM, and it says: "other entry procedures may enable the aircraft to enter the holding pattern and remain within protected airspace, the parallel, teardrop and direct entries are the procedures for entry and holding recommended by the FAA, and were derived as part of the development of the size and shape of the obstacle protection areas for holding."  (5-3-12 3.(d)).  However, I'm certain that previous versions of the AIM actually had text to the effect that the PIC could select any entry they liked, so long as that procedure remained in the protected airspace.  I can't find that quote in the October 2017 edition.
 * Missed approach points, published entry procedures, holding points, and so on, are designed to guarantee protected airspace does not overlap (and obstacle clearance requirements are met). They aren't primarily designed to be easy to fly!
 * On a practical note - if you're operating in a RADAR environment, you'll frequently receive RADAR vectors long before you reach the hold or have to fly a hold entry or course-reversal of any kind (unless you specifically ask to fly the published missed). Obviously, don't expect vectors unless you are instructed to expect, (§91.185(c)(1)(iii)).
 * Be sure to consult the AIM (5-3-8), and the Instrument Procedures Handbook (Chapter 4, in particular), and always check with a CFII if you're really unsure.
 * Nimur (talk) 21:38, 22 February 2018 (UTC)
 * As far as the accuracy of the claim: it's true for the missed approaches for the Sea-Tac VOR Runway 34R approach (parallel), Paine Field VOR Runway 16R (parallel), Yakima VOR/GPS-A (parallel), Pullman/Moscow VOR Runway 5 (parallel), Arlington LOC Runway 34 (parallel), Juneau LDA X Runway 8 (parallel), Paine Field ILS Runway 16R (parallel), Hoquiam VOR/GPS Runway 6 (parallel), Montgomery Regional RNAV/GPS Runway 28 (missed approach course is exactly opposite to the holding course inbound -- so either parallel or teardrop entry at the pilot's discretion), Boeing Field ILS Runway 13R (same as at Montgomery), Portsmouth (Pease) RNAV/GPS Runway 16 (ditto), Bremerton GPS Runway 1 (teardrop), Tacoma Narrows ILS Runway 17 (parallel), Tacoma Narrows NDB Runway 35 (parallel), Olympia VOR-DME/GPS Runway 35 (teardrop), Salem LOC BC Runway 13 (same as at Montgomery, Boeing Field and Portsmouth), and the infamous Yakima LOC/DME BC-B approach (parallel); the only exceptions I know of are Shelton GPS Runway 23 (direct), Oak Harbor RNAV/GPS Runway 7 (direct, although at a rather sharp angle) and Friday Harbor RNAV/GPS Runway 34 (direct). And that's all the approach plates I have with me (unless you count the really old ones for Berlin Tegel and Tempelhof from the days of the Berlin Airlift), but you see the pattern, don't you? 2601:646:8E01:7E0B:0:0:0:64DA (talk) 08:06, 23 February 2018 (UTC)
 * I have seen "some" published procedures that imply direct entry; other procedures do not. Have a look at all the plates for KSJC - for example, the approaches for the 12 runways have a missed approach hold at GILRO, but each hold is different.  I'll reserve comment on statistics until I have reviewed enough procedures to be statistically significant!  I've browsed maybe a dozen plates, and that's hardly enough to merit a bold claim - but with a booklet full of paper plates, one can quickly review hundreds of approach procedures!
 * If you don't have paper copies, you can search one-at-a-time via d-TPP (or Foreflight). But consider purchasing the paper copies!  Electrical failures are real, not-hypothetical occurrences.  Just nine dollars will buy you the better half of California.
 * I've got a paper copy of all the plates for Northern and Southern California, so I can collect some actual statistics when I've got time... it's Friday, and studying missed approach procedures is a great way to start the weekend!
 * Nimur (talk) 16:26, 23 February 2018 (UTC)

evolution and human Reproduction special case; specially subordination of lunar cycle
Reproduction of many many animals occurs as they have  season for fertilize and baby birth   ,as we know  human fertilize time occurs in all over the year. the question of evolution specialists is that when in human evolution  process it had begin? how man forget year duration periodic fertilize ,the women monthly period may be remained from that time. kindly guide me please. --Akbarmohammadzade (talk) 09:05, 22 February 2018 (UTC)
 * This book, page 144, does seem to answer your question, and contains citations to more detailed studies. To wit "Early humans also probably had seasonal birth peaks, as these persist in modern day humans"  Which is to say, humans do have a vestigal mating season, as evidenced by the fact that births are not evenly distributed throughout the year, but vary with the seasons; This article for example suggests that there is a nadir of birthrates in the spring owing to lower sperm counts during the warmer summer months.  -- Jayron 32 11:48, 22 February 2018 (UTC)


 * Our closest article is at concealed ovulation. The two things are not completely synonymous, but obviously related; a female could not be said to be "in heat", if there was no way of detecting that it happened. Matt Deres (talk) 13:40, 22 February 2018 (UTC)


 * To describe the issue as one of "forgetting" to have a mating season is to miss the issue. It begs the question of why there are mating seasons in the first place.  That is, why aren't animals always fertile?  The human system is one of nominally constant frtility, limited by the fact that we are mammals, and hence tend to develop and shed a uterine lining conducive to implantation (menstrual period), and we release an egg (ovulation) in synchronization with the receptive part of that cycle.  That the cycle is 'hidden' as mentioned above encourages male mate loyalty; at least the attentiveness of a 'steady date' who will be a potential father to one's children, rather than just a random hook-up, which could have disastrous consequences for an unwed mother both as a social stigma and due to lack of biparental support through much of human history.


 * Animals have mating seasons mostly based on the availability of food and the advantage of producing offspring all at once, for which see masting. Humans who breastfed their children also do not tend to ovulate during this period, to avoid the burden of having children back to back, rather than, say, every two years, when the newborn's elder sibling will at least be of the age to eat and walk without having to be carried and manually fed non-adult food. Putting the question in terms such as "forgetting" a breeding cycle sounds like old-wives tales or folk religion, not evolutionary biology. μηδείς (talk) 20:14, 22 February 2018 (UTC)

thank you  -and about lunar cycle ; and how human period obey moon rotation cycle, why accurately lunar based duration ?--Akbarmohammadzade (talk) 05:25, 25 February 2018 (UTC)--Akbarmohammadzade (talk) 05:08, 25 February 2018 (UTC)


 * It's not entrained to the "moon rotation cycle" at all.  The moon rotates in the same time that it revolves (relative to the stars).   The strength of the tides (which have some influence on the human body, which is 97% water) depends on the distance.   The intervals between closest approach (perigee) are slightly longer.   The major factor affecting the strength of the tides is the angular separation between the moon and the sun - the time between succcessive alignments is longer still. 86.131.187.242 (talk) 12:41, 25 February 2018 (UTC)


 * You might like to have a look at Culture and menstruation. "Menstruation" and "moon" have an etymological link (not only in English) and people around the world have asked the same question as you, about the similar length of the lunar and (human) menstrual cycle. As for times of the year, women generally only ovulate when they have enough fat to sustain the pregnancy. Modern athletes often cease to menstruate, and in times of famine, so too would our ancestors. Carbon Caryatid (talk) 16:16, 26 February 2018 (UTC)


 * The association seems reasonable. Remember, the rod photoreceptors in the human eye are basically designed to see by moonlight.  They don't seem much good under the stars alone, at least.  In an era before artificial lighting, the moon might have meant an all-night party.  And what do people do to pass the time? Wnt (talk) 13:05, 27 February 2018 (UTC)