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As the title suggests, Is a magnetic compass required equipment for VFR (day) flight? I have always been under the impression it was.

My question arises from reading CFR section 91.205, article b:

b) Visual-flight-rules (day). For VFR Flight during the day, the following instruments
   and equipment are required:

  (1) Airspeed indicator
  ...
  (3) Magnetic direction indicator
  ...

This sort of implies I can use anything, including my GPS that indicates magnetic direction. Is my interpretation correct? Has this changed recently?

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The phrase "magnetic direction indictor" is interpreted as "magnetic direction-indicator", not "magnetic-direction indicator".

You need a device based on magnetism that indicates your direction. That could be a floating-card type compass, or a fluxgate compass, for example.

Some interpretation of this phrase is given in AC 23.1311-1C section 8.8:

Under VFR operation, part 91, § 91.205, requires a magnetic direction indicator (that is normally intended to be a compass) for heading information.

[...]

Section 23.1303(c), Amendment 23-62, amended the requirement from “A direction indicator (non-stabilized magnetic compass)” to “A magnetic direction indicator.” As new technology becomes more affordable for part 23 airplanes, many electronic flight instrument systems will use magnetically stabilized direction indicators (or electric compass systems) to measure and indicate the airplane heading to provide better performance.

[...]

Part 23 does not prescribe specific accuracy requirements for magnetic gyroscopically stabilized heading systems. Specific accuracy requirements for avionics may be found in the related TSO and, as acceptable means of compliance to § 23.1301, in ACs, notices, or policy statements/letters.

Further, installation of the magnetic direction indicator is regulated by §23.1327:

Each magnetic direction indicator must be installed so that its accuracy is not excessively affected by the airplane’s vibration or magnetic fields.

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  • $\begingroup$ So does that means usage of a GPS depends upon how the GPS device (standalone or phone or ??) implements deriving heading direction? Because you could do it based on change in location over time, or you could have a magnetic sensor, MEMS geomagnetic sensors like in some a cell phones, or perhaps even a combination. $\endgroup$ – JerryKur Aug 4 '14 at 4:00
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    $\begingroup$ @Jerry: I believe Articuno's point is that GPS isn't magnetic. You might have a device (e.g. smartphone) with both GPS and a magnetic sensor. You cannot infer local magnetic declination from changes in GPS location, so that isn't useful as a source of magnetic heading. $\endgroup$ – RedGrittyBrick Aug 4 '14 at 10:06
  • $\begingroup$ @RedGrittyBrick - magnetic declination can be looked up based on current position. Also, my point is that there nothing that keeps a GPS manufacturer from adding a MEMS or other geomagnetic sensor. (Anyone remember the Garmin GPSphone?) Would doing so make the GPS legal as defined Part 91.205 , "Magnetic direction indicator" referenced by the OP? $\endgroup$ – JerryKur Aug 4 '14 at 19:17
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    $\begingroup$ @JerryKur It depends. Is the smartphone system accurate to within 10° and does it have a correction placard to account for the local magnetic anomalies in the aircraft? You're sort of getting into a separate issue, though, and it seems it would be better handled in its own question. $\endgroup$ – user2168 Aug 4 '14 at 19:32
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    $\begingroup$ @JerryKur Also, according to 23.1301, the equipment is required to "be installed according to limitations specified for that equipment". I don't think you could consider a smartphone "installed". $\endgroup$ – user2168 Aug 4 '14 at 19:34

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