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As explained in this Q/A:

What does a dollar sign mean in a METAR?

The presence of a Dollar Sign ($) at the end of a METAR is

included when an ASOS/AWSS detects that maintenance is needed on the system.

Does this therefore imply we should not trust this METAR? If so - why do they even continue to publish it? If not, why are pilots informed that the system requires maintenence?

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Not necessarily.

Automated stations have a number of sensors for detecting,

  • Wind speed and direction
  • Visibility
  • Obscurations to vision
  • Cloud coverage and ceiling
  • Temperature and dew point
  • Barometric pressure and altimeter setting
  • Precipitation
  • Freezing rain (Icing)
  • Lightning (thunderstorms)

It is likely that some of these are not functioning properly, while the others are working correctly. In such cases, the METAR reports contain sensor status indicators which give information about the sensor which has failed. For example, consider the following METAR:

KMEM 230853Z AUTO 18014G18KT 10SM CLR 16/M02 A3008 RMK AO2 SLP117 T01561022 TSNO $

Here, TSNO indicates that the automated station is equipped with a lightning detection system and that sensor is not operating. Following is a list of sensor status indicators:

  • RVRNO- Runway Visual Range is missing.

  • PWINO- Present weather identifier sensor (is fitted and) is not operating

  • PNO- Tipping bucket rain gauge sensor is not operating.

  • FZRANO- Freezing rain sensor is not operating

  • TSNO- Lightning detection system sensor is not operating

  • VISNO_LOC- Secondary visibility sensor is not operating.

  • CHINO_LOC- Secondary ceiling height indicator and that sensor is not operating.

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    $\begingroup$ So the dollar sign would follow the specific item for which the sensor is not working, and it's not simply tacked on the end to indicate "something's broken"? $\endgroup$ – FreeMan Nov 16 '15 at 18:41
  • $\begingroup$ Well, the dollar sign is always the very last item in the metar, if something needs maintenance (not necessarily "broken"). The "thing that is broken" is not always indicated (see the link in the question - nothing is indicated). Those 7 items in the answer come from AC 00-45H, Para 3.1.5.14. If it is one of those things that is broken, then that will be the very last thing in the remarks section, immediately followed by the dollar sign. So yes: the dollar sign will follow the specific item that is broken (if it is listed), AND the dollar sign is always "tacked on to the end". $\endgroup$ – Jimmy Mar 9 '17 at 18:03

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