I am evaluating an aircraft for use under IFR. I want to know if the GPS that is installed is acceptable for use under IFR. I have access to the logbooks and documentation. I want to check:

  • That the GPS unit itself is acceptable
  • If the installation is acceptable
  • If the database is current

Operational considerations and limitations may be discussed, but are secondary to the scope of this question. Citations to the AIM and AC 20-138 should be in a bulletized summary.

  • $\begingroup$ Which GPS is it? $\endgroup$
    – CrossRoads
    Commented May 28, 2018 at 15:15
  • 1
    $\begingroup$ Should not matter. Ideally an answer would tell me where to look to see which TSO a unit was manufactured under and what magic logbook words are that show me the installation meets the requirements of AC 20-138 and STC requirements. Checking the database is pretty easy. Extra upvotes expected if there are things that I have not thought of. $\endgroup$ Commented May 28, 2018 at 19:59

2 Answers 2


The easiest way is to read the Aircraft Flight Manual (AFM) or Aircraft Flight Manual Supplement (AFMS). If the the GPS was installed at the factory, it will be addressed in the AFM. If it was installed later via an Supplemental Type Certificate (STC), there must be an AFMS to cover the operation of the GPS.

If the GPS installation was not at the factory, there should be an a/c logbook entry showing the installation and STC approval.

As specified in AC 20-138D:

19-9. Operations manual or AFMS/RFMS.

An AFMS/RFMS must be provided that contains the limitations and operating procedures applicable to the installed equipment configuration. The AFMS/RFMS must address the operation of the equipment and the related components as they are installed (e.g., remote source selector). An AFM/RFM supplement is required if the installation is based on a prior approval that had an AFM/RFM, or if there are any limitations associated with the operation of the equipment.

The key information is covered by the first sentence -- limitations and operating procedures. If the GPS is not approved for IFR, there must be an operation limitation in the AFM/AFMS that states that (and in all of these cases I've seen, the FAA also required a placard stating "GPS not approved for IFR flight.")

If the information is not included in the AFM or AFMS, I would question the approval of the installation as all installations require the AFM/AFMS.

As for the database, it expires every 28 days. Turn the GPS on. If the database is not present or expired, you will get a message to that effect.

  • 2
    $\begingroup$ Note that there are often multiple databases configured with a GPS unit. There may be one or more of: basemap, terrain data, obstacles, instrument approach procedures, STARs, SIDs, radio frequency names (e.g. to associate with an airport), other navigation waypoints, user-defined waypoints, etc. Each of these will have a revision date and/or expiration date, and the map provider's website will provide the current information. In some cases, you might obtain some information, such as the terrain database, from the manufacturer, and instrument approach procedures from a provider like Jeppesen. $\endgroup$ Commented May 31, 2018 at 3:07
  1. It has to be a unit that meets TSO (Technical Standards Order) 129, or for newer units that can use Wide Area Augmentation for LPV approaches and has other features, TSO 146 (the significance of each TSO and how they apply, you can look that up). That'll be in the unit's specification in the operating manual.

  2. Installed and signed off by an approved avionics shop in the log entry.

  3. There will be a database information page in the unit that will show the expiry date of the installed database. The manufacturer's website should also have a listing of its database library with dates etc.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .