GPS Integrity Lost

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   I received the alert in the subject line on a flight the other day.  The GPS seemed to be working fine as I progressed through the way points on my flight plan.  When I looked up the alert in the pilots manual the explanation doesn't really offer any additional insight.  My question is, what does this alert really mean and is there potentially a systemic issue or is this more related to the IFDs ability to receive satellite data at a certain point in time?  


Edited by Walter5 - 08 Sep 2022 at 9:02am

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Walter5 Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 07 Sep 2022 Location: Leesburg Status: Offline Points: 3	Post Options Post Reply Quote Walter5 Report Post Thanks(0) Quote Reply Topic: GPS Integrity Lost Posted: 08 Sep 2022 at 8:51am
	I received the alert in the subject line on a flight the other day. The GPS seemed to be working fine as I progressed through the way points on my flight plan. When I looked up the alert in the pilots manual the explanation doesn't really offer any additional insight. My question is, what does this alert really mean and is there potentially a systemic issue or is this more related to the IFDs ability to receive satellite data at a certain point in time? Edited by Walter5 - 08 Sep 2022 at 9:02am

AviSteve Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 12 Feb 2018 Location: Melbourne, FL Status: Offline Points: 2146	Post Options Post Reply Quote AviSteve Report Post Thanks(0) Quote Reply Posted: 08 Sep 2022 at 3:11pm
	It just means that the GPS didn't have the integrity that's required for the nav mode you were in. You can go to the GPS Status page to check HPL vs HAL. If HPL exceeds HAL, you'll get the alert. Unless you're constantly getting it, I would blame it on poor reception at that point in time.
	Steve Lindsley Avidyne Engineering

Walter5 Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 07 Sep 2022 Location: Leesburg Status: Offline Points: 3	Post Options Post Reply Quote Walter5 Report Post Thanks(0) Quote Reply Posted: 08 Sep 2022 at 3:43pm
	Thanks Steve. I appreciate the quick reply.

eallevato Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: 04 Apr 2018 Location: Northridge, CA Status: Offline Points: 69	Post Options Post Reply Quote eallevato Report Post Thanks(0) Quote Reply Posted: 10 Sep 2022 at 10:37am
	I noticed that the active frequency on the 440 is 132.025. If you multiply it by 12, you will end up with a number that is very close to the GPS frequency of 1575.42. This is called the 12th harmonic. It is very likely that the GPS was clobbered by transmitting on 132.025. The installation manual tells you how to perform a GPS Interference check. It should have been done during the installation of the 440. Basically, you transmit on about a dozen frequencies around the 12 and 13 harmonics and watch the GPS status to see if it loses reception. Gene Edited by eallevato - 10 Sep 2022 at 11:21am
	Gene