NavList:

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From: Gary LaPook <NoReply_LaPook@fer3.com>
To: luabel{at}ymail.com
Sent: Friday, July 17, 2015 11:11 AM
Subject: [NavList] Re: What precision is required in cel nav?

David Pike wrote:

I would say that for a modern high speed, high altitude aircraft a celestial fix accuracy of ten miles was not unknown and wouldn’t have raised eyebrows.  Three miles was pretty good and less than three miles would have been thought exceptional.  

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This is the required accuracy for flight navigtors contained in Federal Aviation Regulation Part 63 (14 CFR 63) navigator flight test. This is item 37 of the flight test. 

(37) Take celestial fixes at hourly intervals when conditions permit. The accuracy of these fixes shall be checked by means of a Loran, radio, or visual fix whenever practicable. After allowing for the probable error of a Loran, radio, or visual fix, a celestial fix under favorable conditions should plot within 10 miles of the actual position.

Here is a link to the entire regulation.

https://sites.google.com/site/fredienoonan/resources/fedaral-aviation-regulation-part-63-certification-of-flight-navigators

As part of the test the application must also take sextant observations on the ground and the standard for those shots is:

(3) Precompute a time-altitude curve for a period of about 20 minutes and take 10 single observations of a celestial body which is rising or setting rapidly. The intervals between observations should be at least one minute. Mark each observation on the graph to show accuracy. All observations, after corrections, shall plot within 8 minutes of arc from the time-altitude curve, and the average error shall not exceed 5 minutes of arc.

(4) Take and plot one 3-star fix and 3 LOP's of the sun. Plotted fix or an average of LOP's must fall within 5 miles of the actual position of the observer.

And for those interested in what Fred Noonan was doing as Earhart's plane approached Howland island, the regulations require that a flight navigator know how to do the same single line of position approarch (sunline approach) to an island:

(34) Select one of the celestial LOP's used during the flight and explain how to make a single line of position approach to a point selected by the agent or examiner, giving headings, times, and ETA's.

 

gl