SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/pilot-raim-satellites

At minimum, how many GPS satellites must be in view for RAIM, without baro-aiding?

Five satellites (or four plus a barometric altimeter).

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  1. Three satellites
  2. Four satellites
  3. Five satellites ✔

Why: RAIM checks whether a satellite is sending bad data. It needs at least one more satellite than navigation alone, so five in view, or four plus baro-aiding.

Huh, didn't know that: Receivers that can also exclude a bad satellite need six in view, or five with baro-aiding.

The dad joke
Why did the GPS need five satellites? It didn't trust anyone who couldn't get a second opinion.
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References

Answer: Five satellites. RAIM checks whether a satellite is sending bad data. It needs at least one more satellite than navigation alone, so five in view, or four plus baro-aiding.

  1. AIM Chapter 1 Section 1, Air Navigation Aids www.faa.gov/air_traffic/publications/atpubs/aim_html/chap1_section_1.html
    RAIM requires a minimum of 5 satellites, or 4 satellites and barometric altimeter input (baro-aiding), to detect an integrity anomaly.
    Checked 2026-10-09.

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