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July 25[edit]

Glassy carbon[edit]

How is glassy carbon made? 2601:646:8E01:7E0B:D013:7C29:7816:F57B (talk) 03:15, 25 July 2016 (UTC)

The Wikipedia article you linked contains links to information on scientific journals and patents which should describe exactly that. --Jayron32 10:23, 25 July 2016 (UTC)
This supplier describes a full range of glassy carbon products, from which you may glean ideas about the processes used to make them. AllBestFaith (talk) 22:16, 25 July 2016 (UTC)

Question about gardasil research[edit]

According to here,http://www.cdc.gov/hpv/parents/questions-answers.html,under the the question about why Gardasil is recommended for preteens,it states that the vaccine provides a higher immune response in preteens. Where can I find research which proves this?


And how less effective is the vaccine for those aged 22-26? 30 percent less? 50 percent? — Preceding unsigned comment added by Uncle dan is home (talkcontribs) 04:16, 25 July 2016 (UTC)

(EC) The vaccine most effective by far if the person does not already have the strains of HPV it's effective against. As the strains of HPV are primarily sexual transmitted, once the person has had sex, there is a risk they've already caughtbeen infected by one or more of the strains of HPV the vaccine targets. Effectiveness will depend significantly on whether this has happened which will vary from individual to individual (although by 22 years old, the percentage of people who have not been sexually active in the US seems to be quite low). You could look at this on a population basis and it's possible there are studies which have done so but it's definitely not a simple estimation. There may be a minor advantage due to increase immune response, but this isn't the primary advantage to vaccinating at an early age and the site you linked to seem to reflect that. Nil Einne (talk) 09:14, 25 July 2016 (UTC)
The immune response to the vaccine is about 50% weaker in young adults than in teens, as measured by circulating anti-HPV antibodies[1]. However, it is unknown whether this makes women immunized in young adulthood more vulnerable to HPV infection than women immunized as teens or pre-teens. Someguy1221 (talk) 09:05, 25 July 2016 (UTC)
And in addition, because of Nil Einne's response, this finding hold's true even if the women have no prior exposure to HPV, at least as can be measured. Someguy1221 (talk) 09:20, 25 July 2016 (UTC)

Kingsfoil[edit]

What real-life plant (if any) was the stand-in for the Middle-Earth medicinal herb Athelas (kingsfoil) in the movie Lord of the Rings? https://www.youtube.com/watch?v=AwYO_4VFAYU 2601:646:8E01:7E0B:D013:7C29:7816:F57B (talk) 08:30, 25 July 2016 (UTC)

This may help. --Jayron32 10:21, 25 July 2016 (UTC)
I searched the internet far and wide, and came across the same article as Jayron, but it doesn't answer the actual question. That page is asking what actual plant matches the description of Kingsfoil from the books, none of which resemble the plant that was shown on screen in Peter Jackson's film version. The internet doesn't seem to know the answer to the question. Someguy1221 (talk) 10:39, 25 July 2016 (UTC)
I can't help today, but OP can likely get some potential answers by posting that clip (or ideally a few still frames) to the plant ID experts at Reddit's /r/whatsthisplant [2]. 14:01, 25 July 2016 (UTC)
I had a look at the clip - but to be honest it is so dark in that scene,and you get such a brief glimpse of the plant, by torchlight, that it could be almost any low-growing, New Zealand plant (though obviously not a grass). Wymspen (talk) 15:13, 25 July 2016 (UTC)
I could not identify it after looking at the clip. It is not inconsistent with native NZ bush, so Jackson may very well have used what was on hand in a typical bush setting. Akld guy (talk) 23:14, 25 July 2016 (UTC)
  • I am not sure why anyone would take Jackson's bastardizations as having anything to do with Tolkien's novel. But basil is an herb known for its aroma (put a teaspoon, even dried, in a small boiling pot to see) and the name comes ultimately from the Greek basileus for king. μηδείς (talk) 01:15, 26 July 2016 (UTC)
  • Here, by the way, is all the canonical description there is: "... long leaves .... a sweet and pungent fragrance." —Tamfang (talk) 06:24, 26 July 2016 (UTC)
Not basil, then. The fragrance might be right, but basil does not have long leaves. Wymspen (talk) 12:00, 26 July 2016 (UTC)
And eagles are not large enough to carry hobbits, Beren, or Luthien--my suggestion is that the inspiration is obvious, and there are indeed varieties with long, rather than round leaves. μηδείς (talk) 21:56, 26 July 2016 (UTC)
However, every schoolboy knows that dock leaves cure nettle rash. Alansplodge (talk) 20:04, 27 July 2016 (UTC)
Anglican schoolboys, perhaps. No Merickan's ever heard of either 'cept in litrature. μηδείς (talk) 22:21, 27 July 2016 (UTC)

Nichrome wire heating element calculation[edit]

Nichrome wire heating element.jpg

So I'm a building myself a heat press for a fashion project of mine. And right now I'm struggling to find a power supply for a structure I've made. The problem is that I don't know how many Volts I need to put through my Nichrome wire heating element to bright it up to the desired temperature of 300-400C and also how much Watts should the power supply be able withstand.

The heating element is made of ~14meters of 2mm thick Nichrome wire. I understand that it is probably too thick, but I've already fixed it in place so I'd rather make the press work with it instead of having to replace all the wire entirely. I've measured the resistance of the wire and it is 5.7ohms in total.

How do I calculate the current and voltage needed to heat it up to 300-400C? Is it even possible to reach such temperature wit the wire such thick? Stepan Drunks (talk) 11:11, 25 July 2016 (UTC)

Our article on Nichrome has a table suggesting that 2 mm diameter wire needs 15-20 Amps to reach 300-400 C in open air. Looking at the picture, you seem to have the wire wound back and forth, which would somewhat reduce air cooling, and probably means you need to use somewhat less current. 15-20 Amps corresponds to 85-115 V, if your resistance measurement is accurate (it seems plausible for the dimensions given). It may go without saying, but you are talking about dangerous voltages, dangerous currents, and dangerous temperatures. If you aren't familiar with the safe handling of these materials, I would strongly encourage you to find someone with more experience to supervise your work. In particular, it looks like you mounted the wire in a metal frame. This could be very dangerous if the current unexpectedly moves through the frame rather than through the heating element. Dragons flight (talk) 11:44, 25 July 2016 (UTC)
Agreed. You would want ceramic insulators separating the heating wire from the frame. This is both for electrical and thermal insulation. You want to avoid the frame becoming so hot you burn yourself if you brush up against it, and you also want to avoid the heating wire cooling down at the edges, for most applications. Look at electrical resistance space heater designs. The good ones use insulators. StuRat (talk) 14:57, 25 July 2016 (UTC)
  • As always, use a spreadsheet model to calculate this, so that you can change the parameters interactively without having to manually recalculate the lot.
You can calculate the power for a nichrome element from standard tables, or from standard tables of its resistance, then . There are online calculators like this http://www.jacobs-online.biz/nichrome/NichromeCalc.html It's not an easy calculation from scratch, as the resistivity of the wire is temperature dependent. This power calculation, and then some estimation based on specific heat capacity, will give you a range limit (but not an estimate!) for the press temperature.
You can also get a triac controller (cheap modules from eBay) and an IR thermometer (again, eBay). Then just do some experimentation, but starting small.
As a wild guess, your wire is too thick. A simple estimate says that on 240V mains voltage that's a 10kW heater. This is too big to supply from a domestic 3kW supply and too big to design and build as a first experiment with the technology. If you run it from a low voltage supply, it's still a very low impedance - that means it's either a difficult high current to manage, or else a very low power. At 12V it's only 25W, at 24V only 100W. These are easy voltages to work with (cheap control modules are available), but I doubt that's enough power to be useful. I'd choose a wire size to make a mains-powered element just powerful enough (allowing scope for control) to achieve the temperature needs. I also don't like the look of all that unsupported wire - nichrome expands a lot when hot, so the elements sag. This takes them away from the press surface and the repeated movement also shortens element life.
You can use constant current supplies for small elements, but not large, hot elements. They're easy to work with, but not once the wire gets hot enough to start changing its own resistance.
I think I'd look at starting again. Calculate the power needed _first_, then design an element to deliver this. The power/temperature relationship depends on the heating time: a fast heat might be dominated by the specific heat capacity of the material being pressed (i.e. heating up a cold item) whilst a long heat becomes dominated by heat losses to the outside, which is all about the insulation.
I'd try phoning a heating element maker, or a wire seller, and asking them for advice from the outset. You might also find a heating blanket or a pre-made flat panel is much easier to work with than bare wire. Andy Dingley (talk) 11:56, 25 July 2016 (UTC)

Construction points:

  • Assuming your heating element is mains powered, the frame must be connected to ground.
  • The target temperature range 300-400C will melt solder so the electrical connections must be by screws or crimped.
  • Ceramic or mica standoff insulators are needed to support the heating wire. The support strips in the photograph look inadequate and possibly conductive(!)
  • For testing it's very desirable to use a Variac [3] (see Autotransformer) to adjust the mains supply, gradually increasing the voltage while monitoring both voltage and current to confirm your calculation.
  • Wires at more than 10V potential should not be exposed to fingers or moisture.
  • For safety, heaters of this kind are usually equipped with a Thermostat, a power "ON" lamp and a fuse and/or Circuit breaker.

The article Electric heating is required reading. AllBestFaith (talk) 22:07, 25 July 2016 (UTC)

I'm sorry but I'm going to repeat what some people above had already said. It appears that you are a fashion student, not an electrical engineering student. I have made many electrical projects and even a few high voltage projects, seeing the box you've made and hearing you are considering plugging it into the mains makes me very nervous. 400c is VERY hot, it's far hotter than a clothes iron and it's even hotter than I ever put my soldering iron on. What do you need that kind of temperature for? Vespine (talk) 22:51, 26 July 2016 (UTC)
Agreed. 400 °C is the sort of temperature where lots of stuff spontaneously catches fire. Projects using high voltage OR high current already require lots and lots of care to do safely, and high-power – i.e. high-voltage AND high-current simultaneously – is the sort of thing you really, really don't want to mess with unless you know exactly what you're doing. With all due respect, if you need help with these calculations, chances are you're not at that point just yet. Please don't get yourself killed! --Link (tcm) 01:03, 27 July 2016 (UTC)

Efficiency of carbohydrates to fat conversion[edit]

Good evening, folks. As you know, the human body can convert excess carbohydrates into fat. What is the average efficiency of this process? Thanks.--90.69.12.160 (talk) 21:22, 25 July 2016 (UTC)

What kind of efficiency are you looking for ?
1) As far as what proportion of the carbohydrates are destroyed in the process, rather than converted to fat, not counting those which are "burnt" to create energy, I would guess that portion is quite low.
2) As far as energy used to do the conversion, that may well be significant (whether that energy comes from carbs, fat, protein, glucose, etc.). Would you measure that energy in proportion with the energy stored in the fat created ? StuRat (talk) 01:56, 26 July 2016 (UTC)
The energy to convert carbs to fat comes from NADPH, which is a byproduct of the conversion of glucose into the precursors to nucleotides and aromatic amino acids. One NADPH per carbon, to be specific, and two NADPH is generated per glucose consumed, so basically it takes three glucose molecules to incorporate one glucose molecule into a fatty acid. It's actually really hard to put an energetic cost and thus efficiency on this, for several reasons. 1) The reactions occur spontaneously; 2) Simply getting to the acyl-CoA precursor to make fatty acids passes through glycolysis, which generates energy; 3) The glucose that was consumed to generate the NADPH needed to be consumed anyway to generate those aforementioned precursors. You could try to ask instead how the energy of the fatty acid compares to the energy of the input glucose. In that case, each gram of fat yields 9kcal, while each gram of sugar yields 4kcal of energy. You might think you actually gained energy by converting to fat, specifically the fatty acid yields about 16% more energy than the glucose used to make it. This is because of all those other glucose molecules that were burned to synthesize it. So in the end, you can look at this a couple of ways. You could think of this as being essentially perfectly efficient since the body is simply making use of waste energy generated by nucleotide/amino-acid synthesis. Or you could ask about opportunity cost, I suppose. What if those NADPH were instead NADH, and shuttled to the mitochondria? That would be about 6 ATP per glucose consumed by nucleotide/amino-acid synthesis, or 18 ATP per glucose that would have been used to make fatty acids. Heck, that's about half the energy you would get from simply consuming one glucose through cellular respiration. So you could say you are taking a 1/6 increase in energy at the cost of a 1/2 increase in energy, so a loss of 22% from the energy you could have had. So ah, I guess in summary, it really depends on how you feel like running the numbers. (Conclusions from this answer were drawn from information at: NADPH, Fatty acid synthesis, Fatty acid metabolism, glucose, glycolysis, NADH, pentose phosphate pathway). Now what I haven't read far enough to figure out yet is how things change if things get unbalanced. Such as, what happens when you are eating so little you require net loss of fatty acids while still making nucleotides and amino acids. Do those NADPH go somewhere else instead? And what about when food intake is so high that NADPH requirements to form fatty acids exceed their production as a byproduct? Is there another method to make them? Does the fatty acid synthesis rate have a ceiling? Does the body just make nucleotides/amino-acids it doesn't need? I guess in both situations your accounting of the efficiency may be altered. Someguy1221 (talk) 02:39, 26 July 2016 (UTC)
So the old adage is true: to keep slim, cut down the carbs and sugar.--86.187.174.194 (talk) 23:17, 26 July 2016 (UTC)
If the goal is weight loss, I'd see an endocrinologist. The one my pharmacist recommended helped me lose 70 lbs, 40 of which my gen prac helped me put on with bad advice. I am cleared as of today for bariatric surgery, which should leave me at ideal weight and totally alleiviate my hyper-glycemia, -lipidemia, and -tension. But this has all been done under MEDICAL advice, and I would not trust anything but a trusted, licensed specialist. If you live in NY or NJ, email me for a reference. Otherwise, shop around in your area. μηδείς (talk) 04:17, 27 July 2016 (UTC)

July 26[edit]

Why do some plates fuse and others don't?[edit]

Why did all these plates become glued and never break up again? Many of these faults are geologically dead, right? (Kansas is not exactly known for viscous vicious Keweenawan Rift earthquakes) Sagittarian Milky Way (talk) 13:10, 26 July 2016 (UTC)

North america basement rocks.png

The tectonic status of a geographical area may be extending, thrusting or strike-slipping, see individual articles. While a geologist should never say never, there is no imminent active spreading ridge, fault line or volcanic center on the North American Plate pictured, with the exception of the earthquakes waiting to happen in California as the Pacific Plate departs north westward, see San Andreas Fault. AllBestFaith (talk) 14:44, 26 July 2016 (UTC)
Also don't be so quick to dismiss mid-plate quakes. See New Madrid Earthquake. --Jayron32 15:33, 26 July 2016 (UTC)
When I was in Rolla, MO, I noticed that the earthquake report showed weekly earthquakes across Missouri, including epicenters outside the state. Most are very tiny and not reported in the news. Every once in a while, a noticeable one happens. I assumed that the nearly constant small ripples keep large earthquakes from happening, not the concept of completely dormant fault lines. 209.149.113.4 (talk) 17:12, 26 July 2016 (UTC)
It should also be noted that earthquakes can be man-made; I don't know what the state of fracking and oil extraction is in the Rolla area, but in Oklahoma, petroleum extraction is closely correlated to an increase in seismic activity. See, for example, here which discusses a precipitous rise in large earthquakes in Central Oklahoma correlated to increased petroleum extraction. --Jayron32 17:15, 26 July 2016 (UTC)

What is an "at-grade road"?[edit]

I've seen the term "at-grade road" in several city articles. A search comes up with a multitude of articles that contain the phrase, but we don't have an article At-grade road, or a redirect to a relevant article that explains the term. Roger (Dodger67) (talk) 14:09, 26 July 2016 (UTC)

An at-grade intersection is an area where two or more roadways join or cross. AllBestFaith (talk) 14:19, 26 July 2016 (UTC)
Have you seen the term just "at-grade road", or was it part of a phrase like "at-grade road crossing"? We have wikt:at-grade (same meaning AllBestFaith found). DMacks (talk) 14:22, 26 July 2016 (UTC)
Cape Town#Road is a fairly brief section with a remarkably high number of ocurrences the term. Roger (Dodger67) (talk) 14:28, 26 July 2016 (UTC)
In some places, this kind of terminology is used to distinguish between types of highways or main roads: an access-controlled highway has no at-grade crossings (no level-crossings) - it has onramps and interchanges. Certain types of other fast-traffic roadways may still be called a "highway" or "expressway" - but if they have at-grade intersections, the free flow of traffic is necessarily interrupted at each place where cross-traffic can occur or where vehicles can enter the roadway.
If you've done all your driving inside the United States (or some parts of, say, Western Europe), it can be a little bit hard to culturally understand why this detail even matters, but that's because we tend to have an absolutely excellent highway system. You might take the assumption that all major highways use controlled access; and you might never have seen a mega-highway with at-grade crossings. Many other parts of the world have large highways too - but sometimes, their urban planners have simply "promoted" the various large surface streets into the main arteries for commuter traffic, without actually engineering and constructing the roadway for high traffic capacity and high velocity. So, in many Wikipedia articles about international roadway transportation, the article authors take the time to call out where the major highways that are actually just surface-streets, to distinguish them from modern freeways.
We do sometimes have such roadways in the United States, too - U.S. Route 1 in North Carolina comes to mind - and you can see our editors discussing where the route turns into an expressway.
Nimur (talk) 14:42, 26 July 2016 (UTC)
In the Cape Town article section, "at grade" is used as a contrast to "highway", which seems in keeping with the idea of it meaning "a road with at-grade intersections". DMacks (talk) 15:27, 26 July 2016 (UTC)
There is an article Intersection (road) - and the intersection is the only point at which the "at grade" description applies. Wymspen (talk) 14:58, 26 July 2016 (UTC)
Perhaps you have never seen an elevated highway, like I-35 in Austin (and many of the other expressways); or the Expressways of Shanghai? Or a subterranean roadway, like the Prague tunnel complex or the Boston Big Dig? In some places, the entire roadway is above- or below- grade. Nimur (talk) 15:05, 26 July 2016 (UTC)
Also, the Cross Bronx Expressway in New York, the Vine Street Expressway in Philadelphia and the Eisenhower Expressway in Chicago are all largely below grade, but they are open cuts rather than tunnels. --Jayron32 12:22, 27 July 2016 (UTC)
Hence the term Grade crossing. ←Baseball Bugs What's up, Doc? carrots→ 18:04, 26 July 2016 (UTC)
Sometimes the main highway rises or dipd to go over/under streets that cross its path (often seen where the streets were there first) and sometimes the crossing streets rise or dip to go over/under the main highway (often seen where the highway was there first). See Underpass and Overpass. Places where a road dips below another have a tendency to become temporary swimming pools during storms, so the overpass is more common than the underpass. --Guy Macon (talk) 14:40, 27 July 2016 (UTC)
The use of this terminology appears to be US-specific. I first encountered it here on Wikipedia; it's not a common usage in the UK, even (so far as I am aware) in urban planning contexts. I think the underlying reason for this is that the precise nuance of 'grade' required is not common in UK English. AlexTiefling (talk) 15:02, 27 July 2016 (UTC)

If you mean simply for a crossing/intersection, I'm pretty sure it's not US specific. See e.g. [4] [5] [6] [7] [8] [9] for various people referring to grade separated crossings in NZ. Also this question seemed to start due to terminology in South Africa.

Referring to the whole road as above or below grade is perhaps less common in NZ. However there is the added confusion here of the usage that started this question which appears to simply refer to whether the road is grade separated; and the usage of Nimur and Jayron32 are referring to namely whether the road is above or below the surrounding terrain. A road which is above or below the surrounding terrain could not have simple at grade crossings. But a road could be grade separated but also on level with the surrounding terrain if crossings are raised or lowered (or simply excluded other than the beginning and end).

BTW we gave an article Grade separation. Also the last external link above mentions how different terms like highway, expressway and motorway are used in NZ which I think partly enters into Nimur's point.

Nil Einne (talk) 19:45, 27 July 2016 (UTC)

Tying off and cutting arteries in surgery[edit]

Books on surgery such as p37 of this 19th century work by Gerster discuss cutting through the skin and underlying tissues until blood vessels appear in the way, then ligating and cutting the vessels. In modern surgical practice "bleeders" sometimes get sealed with an electric cauterization. Are these vessels always veins, are or they sometimes arteries or smaller arterioles? Are these just little negligible unnamed arteries/arterioles or veins? If an artery is thus cut, how does the tissue downstream which it previously supplied get its oxygenated blood supply? (Edited to add: Here I clearly do not include cases of amputation or excision of the supplied tissue. A typical case would be cutting through the abdomenal wall to reach the organs in the abdomen). In the case of the brain or the heart, tissue death seems to result from a blocked artery, as if one volume of tissue is supplied by one single artery. Do arteries network downstream, unlike the nervous system, so that cutting one artery would be analogous to closing one street, where motorists would simply divert to a parallel street and reach the same destination? So how does muscle tissue downstream from an artery, even a small artery or arteriole, survive ligation of its supply? I could not find an answer in Surgery, Artery, Arterial tree or Circulatory system. This is a request for general information and certainly not a request for medical advice. Edison (talk) 17:48, 26 July 2016 (UTC)

So part of this is determining whether the arterial tree is a tree_(mathematics). I'm not really sure, but I thought you might like this schematic [10] I found, which makes the topology easier to understand. According to that diagram, it seems there are some closed loops in the arterial tree, but 1) I don't know what is meant by the white nodes and 2)I don't know how reliable the schematic is. SemanticMantis (talk) 18:03, 26 July 2016 (UTC)
Shit, how do I get to fourth toe? Let's see stay on the aorta train to groin, transfer to the femoral train... Sagittarian Milky Way (talk) 18:32, 26 July 2016 (UTC)
I left out the obvious concomitant case of arteries severed in some accident. If a patient has a spurting arterial wound on the arm, say, does the surgeon just tie off the upstream and downstream parts of the artery, or does he have to do vascular surgery to reattach the two severed ends. to avoid death of tissue downstream? Is there a size of artery below which it is ok to just tie it off? Again, not a request for advice, just a question for general scientific knowledge. Edison (talk) 18:07, 26 July 2016 (UTC)
Anastomoses exist in many tissues; for example the coronary arteries often withstand single blockages, and the brain has the Circle of Willis. See here for a diagram of some important differences; note that an abrupt coronary blockage often can't be compensated for, but a blockage to a tissue with a lower energy requirement might not be as bad. I don't know about skeletal muscles but should not be surprised. It's also worth noting that angiogenesis is reactive, and can completely remodel the blood supply for tissue - for example, consider the desperate treatment a century ago for noses lost to syphilis, where the forearm was sutured to the nose for a couple of weeks, then part of the flesh separated entirely from it to form something like a nose. Wnt (talk) 00:59, 28 July 2016 (UTC)

Cross check[edit]

You know when you are on a plane, you hear that broadcast "cross-checking". I'm having trouble finding out exactly what it is. Anyone? Anna Frodesiak (talk) 21:45, 26 July 2016 (UTC)

According to this,[11] it means one person checking that a task was done by another person. ←Baseball Bugs What's up, Doc? carrots→ 22:18, 26 July 2016 (UTC)
As long as neither person is an ice hockey player, I trust. Collect (talk) 22:29, 26 July 2016 (UTC)
Yes. That would send the offending flight attendant to the penalty box for two minutes. ←Baseball Bugs What's up, Doc? carrots→ 22:34, 26 July 2016 (UTC)
I don't have a source but I believe this specifically refers to cross checking the doors. If one person forgets to lock the door, or if two people think it was the other person's job to do it that time, or whatever, it can cause an aborted takeoff. Also the doors have to be armed before flight and disarmed before disembarkation, I believe that refers to the emergency slides that automatically (and quite explosively) inflate if the door is opened while it is armed. Vespine (talk) 22:40, 26 July 2016 (UTC)

I posted here because I was having trouble understanding here. (Sorry to split up the discussion.) Please feel free to comment further there. Many thanks. Anna Frodesiak (talk) 23:32, 26 July 2016 (UTC)

For an official reference from the FAA, see: Advisory Circular 120-51e, Crew Resource Management Training, and Advisory Circular 120-71a, Standard Operating Procedures for Flight Deck Crewmembers. "Several studies of crew performance, incidents and accidents have identified inadequate flight crew monitoring and cross-checking as a problem for aviation safety. Therefore, to ensure the highest levels of safety each flight crewmember must carefully monitor the aircraft’s flight path and systems and actively cross-check the actions of other crew members."
Individual airlines or other operators may have additional procedures that exceed FAA guidance.
Nimur (talk) 23:54, 26 July 2016 (UTC)
On United Airlines, I always hear "cross check and verify straps" right before takeoff. I assume a message to flight attendants to make sure everything is tied down...or something. Someguy1221 (talk) 01:55, 27 July 2016 (UTC)
Hi Nimur. I think those FFA pdfs are using cross-checking as meaning simply checking what each other is doing. As explained here, the term is about the "...emergency escape slides, which inflate automatically if the cabin doors are opened with the slides armed to deploy, are disarmed; and the cabin crew then cross-check each other to make sure the disarming has been done properly..." Anna Frodesiak (talk) 02:48, 27 July 2016 (UTC)
The definition above is not how I've used the term "cross check". The definition above is "one person checking that a task was done by another person." The definition I've used is "repeating a task done by another person." As an example, suppose you have Alice and Bob. Alice checks the thingamagig. That's a check. Bob is supposed to cross-check it. According to the first definition, if he saw Alice check it, he did the cross-check. According to the definition I've used, he must also check the thingamagig. In other words, a cross-check is not checking a person, it is checking what the other person checked. 209.149.113.4 (talk) 18:26, 27 July 2016 (UTC)
Now that I'm prompted by the question, the exact phrasing I always hear (on airlines in South Africa) is "cabin crew, please disarm doors and cross-check". Finally I know what it means, thanks! Zunaid 18:39, 27 July 2016 (UTC)

July 27[edit]

July 28[edit]