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Why do some charts not have the "TRACKs are MAG" notification, while others do? As seen in the examples I gave below, some charts have "BRGs and TRACKs are MAG" notifications, while others only have "BRGs are MAG" notifications. While "BRGs are MAG" is written on the VOR Y and VOR X charts published in the AIP Turkey, "BRGs are MAG" is written on the VOR Z chart. When I compared all the direction information given in the charts, I could not see any difference, but there is such a distinction, what is the reason? Is there something about their definition (Track and Bearing)?

Charts

VOR X : enter image description here

VOR Y : enter image description here

VOR Z : enter image description here

enter image description here enter image description here

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  • $\begingroup$ Also, as can be seen from the same example, some charts write "in FEET" while others say "in FEET MSL". Is there any special reason for this difference too? $\endgroup$
    – pilot162
    Sep 1, 2023 at 22:29

2 Answers 2

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That may be nothing more than a case of a change in the "boilerplate" language between the time that one was designed & published and when the others were designed and published. Or even that a designer copied "this" text in one case and different text in the other. I don't see anything there indicating that the difference in verbiage makes any actual difference in anything.

It's certainly not like they're publishing a track referenced to True North in one but Magnetic North in the other!

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    $\begingroup$ What you said might have made sense to me, but 3 of these 3 charts were amended with the same amendment document (AIRAC AMDT 02/21). In addition, the validity dates of these 3 charts are the same (22 APR 21). Considering that these documents, which were changed at the same time and whose validity date began at the same time, were prepared by the same people at the same time, the only thought that would justify what you said might be that the chart was prepared without paying attention to the details. @Ralph J $\endgroup$
    – pilot162
    Sep 2, 2023 at 19:37
  • $\begingroup$ The amendment may have been something else, and the BRNG or TRK+BRNG notations may have been from longer ago (like when the procedures were created) and nobody bothered to harmonize those notations across the charts. Bureaucratic process, if it doesn't need to be changed, leave it alone, even if it would seem to make sense to change it -- maybe somebody else had a reason for doing it this way. (Even though they often really didn't.) I really wouldn't read too much into this. $\endgroup$
    – Ralph J
    Sep 2, 2023 at 19:42
  • $\begingroup$ @pilot162, to Ralph J’s point, an amendment does not mean that the procedure documentation is completely rewritten. If the amendment didn’t actually change that boilerplate language, it would not be changed. $\endgroup$
    – Timbo
    Sep 3, 2023 at 5:14
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    $\begingroup$ I got the point, but it bothers me that the authorities that make up the chart are so careless. Even though it is boilerplate language, some things should be standard so that the chart reader is not confused when comparing. $\endgroup$
    – pilot162
    Sep 3, 2023 at 5:54
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The changes you see on Turkey AIP charts are likely an anticipation of future reference changes, both in bearings and altimetry. To prevent confusion, the current references are explicitly mentioned.

Instruments of the past: Barometer and compass

As you know the current convention for aviation, except for ADS-B is to use magnetic direction and MSL barometric altitude. There is an exception only for polar areas, where the magnetic declination is not reliable enough, and where true directions are used.

However these two references create problems. They were very useful prior to GNSS generalized deployment, but are now two burdens.

  • Magnetic directions are the legal reference as of today, and must be used to interact with crews and ATCOs. However, modern navigation computers internally store and manipulate true directions, this is a simple mathematical model to make calculations for navigation.

    The legal magnetic value, when needed to interact with the crew, is just derived from the stored true direction, based on a magnetic model for Earth. As I already explained in another answer, the conversion is not done homogeneously by all units, different values can coexist in the system, creating a risk.

  • Likewise the legal reference for altimetry is still the pressure-altitude determined by measuring the static pressure and converting it with the law in the ISA model.

    It's well known this measure is not accurate at all, except in the vicinity of a weather station delivering the local pressure, hence the need to use two methods: QNE flight levels in cruise, and QNH altitudes close to the ground.

    Modern navigation equipment use the geometric altitude above MSL, derived from the ellipsoidal height (HAE), which is what a GNSS receiver determines, and a model of the mean sea level above the ellipsoid (geoid).

Instrument of the future: GNSS, opportunity to switch to geometric altitude and true bearing

There are two projects to replace the old legal references by modern ones more suitable for computers, and more accurate:

Confusion during the transition

There will be a transition period for the documentation to be updated. Today directions are magnetic and altitudes are barometric. There is no need to mention it on charts, as this is a requirement from ICAO (Annex 4 and Doc 8168). But at some point in time the assumptions will change. Without adding explicitly which references are used, it'll be impossible to decide whether a chart has been designed using the old or the new conventions. There will be a transition period where the conventions used have to be explicitly indicated.

Turkey authorities are likely adding the explicit annotation, in order to anticipate the need to know in the coming years: These charts have been designed with "magnetic bearings" and "altitudes MSL" (barometric).

"Tracks and bearings" vs. "bearings" only

There is a difference between a track and a bearing: A bearing is measured relatively to a fix or a facility, while a track is the direction of the path in general.

  • On the holding pattern depiction in your question, 206° is a bearing. This bearing also defines the track of the inbound leg.
  • On the other hand 26° is not a bearing, but a track.

It's more appropriate to talk about bearings (which also include radials) and tracks. Turkey likely updated their template in order to be more accurate, though this makes little difference here.

Altitude unit: Foot

Foot is a secondary unit for altitude. ICAO, deeply rooted in the Old World, has embraced its metric system since its creation, and stated since a long time the meter is the primary unit to be used for altitudes and distances.

Nobody used it when it was decided, a transition period principle was agreed, without specifying a deadline (typical of projects which are not going to complete). We are still in the transition period, and there is little craze for moving on.

So far a few States use this unit. The Russian Federation (as a legacy of USSR) and China do work with it as their standard. Russia, China and Turkey are all partly or totally Asian countries, close to each other.

It's possible the non-standard altitude unit (foot) is mentioned because of this proximity with large fully compliant countries .

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