How accurate is a sky navigation

Do pilots need to know how to use a sextant?

Ooh, a question about sky navigation ... about airplanes ... I never thought I'd see one of these in the 21st century!

To answer the basic question: pilot training does not cover the use of sextants, but there is still a "Flight Navigator" certificate (you can find it in Part 63 of the FARs) and a corresponding Flight Navigator Manual (FAA-H- ). 8083-18), last updated in 2011. The written test question bank is also available if you would like an idea of ​​what the FAA expects you to do in order to receive this certificate.


Can a sextant be used while flying?

Yes, if you have a clear view of the sky.
In the past, airplanes were constructed with "sextant ports", as shown in Stelios' answer, and special airplane sextants (indirect sighting, with a bubble as the horizon and usually some sort of averaging mechanism and timer).


How accurate / reliable is a sextant, both stationary and at over 500 mph?

A sextant is a pretty accurate tool, given the right conditions, if you know how to use it. Stationary on the floor you can do a surprisingly good job with a sextant, see for example the border monuments USA / Canada. I have run out of practice, but on calm water I was able to fix my position on a specific line within about a 1 minute of arc (1 nautical mile). To put this into perspective: This is a slightly better navigational performance than a VOR at a distance (2 to 4 nautical miles), but a significantly worse performance than GPS (within a few feet).

In terms of reliability, the reliability of a ship's sextant is pretty good: similar to an E6B mechanical flight computer, it will work just fine unless you abuse it (drop it, kick it, etc.).
The reliability of an aircraft sextant (or any other bubble sextant with an averaging timer) isn't quite as good because of the more moving parts involved, but with proper maintenance they can be assumed to work when needed (and most errors could be compensated for) by a decent navigator).

The problems with sextants that make them impractical for modern air travel are:

  1. speed
    Sextants don't tell you where you are are , they tell you where you have been , when you made the observation. The averaging mechanisms mentioned earlier allow the aircraft sextant to take into account, in part, the fact that the aircraft was moving (both vertically and horizontally), but at modern speeds you travel an arc minute fairly quickly. Radio navigation systems and GPS provide position updates much faster than with a sextant.

  2. Complexity of the instrument
    Aircraft sextants are precision instruments. They need to be maintained and calibrated, or they won't be accurate when you need them, and as I mentioned earlier, an airplane bladder sextant contains a lot more moving parts than a simple ship sextant.

  3. Complexity of the process
    The use of a sextant also requires an operator (navigator) who knows what he is doing to capture the view and calculate the position compared to radio navigation (VORs, VOR / DME or GPS). Most pilots have no training in using a sextant (my experience is from sailing) so it would be useless for them to have one.

  4. Weather
    While the sextant is a reliable instrument, the stars are Not reliable: they are always there, but sometimes they are not visible. You cannot see most of the stars and constellations you would see during the day (usually only one star is visible), and clouds can obscure them if you want to make a sighting, delay or prevent your location from being determined.


Are sextants found in cockpits today?

Certainly not in a light GA cockpit that I can imagine, and probably not in a cockpit with a crew member either: even if you have both a pilot and a flight navigator certificate, a pilot is whose head is buried in the sextant is for that actual flies rather useless The plane .

I would assume that most commercial cockpits no longer have sextants either, as modern jets do not contain a sextant port so there is no way to do a sighting.

There may be some restored vintage aircraft that have a working sextant on board, but I doubt these will be used for practical navigation (they probably won't be used at all, except possibly to demonstrate how it was done).

curious_cat

Fantastic answer. Re "Are sextants found in any cockpits today?" I seem to remember that one of the US military long-range scouts. Airplane (Blackbird?) Still has the system, although it is now obsolete due to retrofitting of GPS etc. The thing about US military aircraft is that many started their lives in the early Cold War era, which likely meant sextant navigation was essential on long transoceanic flights. The same models are still flown today in essentially unchanged forms.

voretaq7

I'm not sure about the blackbird, but I wouldn't be surprised if the B-52 fleet has sextant ports, and if the ports are there the military would likely keep the sextants available too (belts and braces and all ... .)

Hagen von Eitzen

One problem with sextants in flight is that they measure the angle between a star and the horizon. On ships the horizon is in (almost) horizontal direction, at an altitude of 35,000 feet a slight adjustment may already have to be made to account for this (at least for maximum precision).

voretaq7

@HagenvonEitzen For this reason, bubble sextants (which provide a virtual horizon) are used in airplanes. They are also used wherever you don't have a good natural horizon (in the haze, for surveying, etc.).

VJ

Just as a side note: there are ways to bypass bad weather and not see stars that the navigator knows about. For example, Celestron's "SkyAlign" technology only asks the user to locate three "bright" celestial objects, which an on-board computer then compares to a database (and time + approximate location) and pinpoints the user's location. Technologies like these could work well for airplanes if the airspeed and altitude instruments could input more data to calculate position.