King Air C90 E90
Flight Crew Multiengine
Flight Crew Last 90 Days 125; Flight Crew Total 12250; Flight Crew Type 8650
Confusion
Aircraft Equipment Problem Less Severe
Aircraft Equipment Problem Dissipated; Flight Crew Requested ATC Assistance / Clarification
Aircraft
I was on a ferry flight (long range fuel tanks) to Honolulu HI (HNL) and using dual (independent) Garmin WAAS GPS units. Approximately 350 NM out from Honolulu I got a message warning 'GPS Signal Lost' on the Garmin WAAS 530 (primary); then about 15 seconds later the same thing happened on the secondary unit Garmin WAAS 430. I always make it a habit of keeping the heading bug on the direction that keeps me on track; so I used that figuring that it would get me close enough to pick up the VORs on Hawaii once I got within range. I left the units on the satellite status page and saw that both of them showed absolutely nothing - no constellations; no bars or anything - it was as if the satellites didn't even exist. I tried shutting down the Garmin units (one at a time) and turning them back on to see if cycling them would help. Still nothing. Periodically a fault message would pop up - something to the effect 'GPS not communicating with satellites - check antenna connection'. I was using an iPad with electronic charts and it has a GPS receiver; which I use as an emergency backup (just in case of total electrical failure). Previously I had seen the iPad showing the aircraft position on the map; but now the iPad showed no position as well. I left it up on the glare shield to make sure that it had good visibility with the sky; but still nothing. I communicated my situation to ATC on HF and on VHF once I got closer; with the idea that they could give me some guidance as soon as they got me on radar until I could receive the VOR signals. I asked them if they were aware of any GPS outage NOTAMS or jamming activities; but they weren't aware of anything like that. This aircraft also has a Sky Connect tracking/satellite phone system and apparently that lost signal as well. (Found out later when my company was monitoring my flight on our own tracking website and saw me 'disappear').Just about the time I started receiving the VOR signal (about 55 NM from Koko Head - CKH) both GPS units picked up all the satellites at exactly the same time with full bars. (I had left them on the satellite signal page and spotted it right away). No more issues for the rest of the flight. I checked the iPad and it displayed my position on the map too.I have seen GPS signal integrity lost before on ferry trips (mostly the Atlantic); but usually it only lasted for about 10 minutes. This one lasted for about 1.5 hours.The next day I did some research with the US Coast Guard for info on any GPS outages; jamming; or testing in the area at the time. They reported that nothing like that was happening.  I called Garmin tech support about the problem. They mentioned that there have been issues with dual GPS installations. Apparently if an antenna goes bad on one GPS unit; it will then cause interference and completely blank out the signal for all units using GPS satellites. That seems to fit exactly with what I had. That is a potentially lethal design fault - especially with the extremely long distances over the Pacific (or Atlantic) and very tiny 'target' islands where there is no other navigational guidance unless one gets close enough to the destination to pick up the ground based navigation signals (VOR) or NDBs (which are being phased out).
BE90 pilot; on a ferry flight to HNL from the west coast; reports a complete loss of GPS signal about two hours out of HNL. At about the time a VOR signal comes in range the GPS begins to function normally. Interference from a GPS antenna failure is thought to be the cause.