# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Message:αβγ
Message:abc
 Add Images & Files Posting Code: Name: Email:
Re: Most Probable Position (MPP)
From: David Pike
Date: 2022 May 14, 17:19 -0700

Ed re your question about MPP calculation as per AFM 51-40 Vol II Apr 1960

This is from an Air Navigator training manual.  Because aircraft go so fast, Air Navigators must be particularly well organised, so said manual is as much about teaching students a practical routine as it is about teaching theory.  When qualified the Navigator will go to a Command and an aircraft where there will be a particular set of rules for calculating MPPs depending upon the fixing aid used and the DR system used.  Also, the technique chosen will be the most practical for the time available to complete the MPP and the best that can be expected to be learned by an Air Navigator, not necessarily the most statically accurate method that a professor of mathematics might come up with after a week to think about it.

In general, the perpendicular from the LOP to the DR position will be divided in the ratio of the expected error in the LOP to the expected error in the DR position.  The expected error in the LOP will be a fixed amount depending on the aid used, and the expected error in the DR position will depend upon what’s driving it and the time since the last MPP.  Clearly there are many different fixing aids and many different equipments driving the DR position all with different expected errors, so what the authors have done here is construct a quasi-general case using p, the difference between fix and DR position, and t, the time the DR plot has been running.  This makes the student aware that there is such a thing as an MPP and that he has to include its calculation in his operating routine.  D=tp/t+p can also be written as 1/ (1/p + 1/t) and maybe one of you mathematicians can relate this to a ratio calculation.  We did something similar in the RAF except, as far as I recall, we used the 'school geometry' method of dividing the line. Usual caveat; I might be compleatly wrong.  DaveP

Browse Files

Drop Files

### Join NavList

 Name: (please, no nicknames or handles) Email:
 Do you want to receive all group messages by email? Yes No
You can also join by posting. Your first on-topic post automatically makes you a member.

### Posting Code

Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
 Email:

### Email Settings

 Posting Code:

### Custom Index

 Subject: Author: Start date: (yyyymm dd) End date: (yyyymm dd)