Last Sunday, some aircraft operators reported issues with GPS and GLU units not acquiring GPS constellations. The reports specifically involve the Collins Aerospace GPS-4000S and GLU-2100. The root cause appears to be a software error that occurred after an almanac update completed by the U.S. on June 9. The next scheduled update is set for next Sunday, June 16, and that update should not include the information that triggered the error. If you have not powered up your units, it is recommended that you leave them off until after June 16, 2019 00:15Z.
Please see the letter from Collins Aerospace for more details.
For more information, contact a Duncan Aviation Regional Avionics Sales Manager.