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SE Asian Anomaly

by Art on

Both AHRS fail OK, this has to go down as the weirdest flying issue of the trip so far. When we left Phuket, Thailand, a few days ago and flew over to Siam Reap, Cambodia... both our primary and backup AHRS (attitude heading and reference system) had total, simultaneous failure numerous times during the two hour flight. For those who don't know what an AHRS system does, it is the system in the airplane that 'knows where you are'. It is extremely rare to have one of these electronic marvels fail in flight, let alone the redundant backup system, yet here we were in the clouds dodging weather and trying to do an instrument approach into an unfamiliar airport with both systems not having a clue where it (and of course where we!) were. This happened three times during that flight (they reset themselves back to normal after a five minute 'slumber'). Once on the ground I called our Pilatus support people in Atlanta to discuss this issue. They had no idea what was going on and had never heard of such an event but advised me they were ready to fly over with all sorts of parts to try and fix the problem should I need them (thanks Mark, Mike and the Epps guys!). Since it had been raining heavily in Phuket for a few days before we departed as well as pouring down rain while we were flying out, I thought... perhaps the problem was due to the extreme heat, humidity and moisture of this part of the word. After all, our faithful Nikon D300 camera had a couple of days of indigestion trying to work in all that moisture too. I decided to let things dry out a bit in Cambodia and test the system on the way down to Ho Chi Mihn City (aka Saigon), Vietnam in a couple of days.

SE Asian Anomaly A few days later we took off for the one hour flight to Vietnam and both AHRS systems failed twice on the flight with the last failure happening on the ILS to a rainy runway in low visibility. Not a good situation. Having this happen again seemed to confirm my worst fears that I had terrible problems in the guidance system for the airplane and that I would need expensive and time consuming repairs done before I could continue flying the airplane in bad weather (and it fact before I flew it back to the USA). As it was around noontime in Vietnam and my avionics team back in the USA was still sleeping, I decided to call Pilatus Support in Australia. I figured that it might be easier to get them to come help me out rather than rustling up a team from Atlanta. I phoned Val Zimmermann, the field service engineer for Pilatus in Australia and explained to him the problems I was having. Imagine my surprise when he said that this was a known problem with the generation of AHRS system installed in my airplane. He went on to say it was due to the fact that SE Asia was at the center of the strongest magnetic forces on the planet, known as the SE Asia Anomaly. Other Pilatus aircraft have experienced this when flying in this region of the world. It was a fact that very few PC-12's had ever been through here but those that did experienced exactly what I had experienced. He went on to say that when I flew out of the area heading north, my problem should go away and everything should work just fine!

Refueling in Hanoi, Vietnam The next day he and Lip Sebastian ('Seb', the CEO of Pilatus Australia) sent along some service bulletins and links to studies about the phenomena. The company that makes the AHRS system for my airplane, LITEF, has fixed the problem in later generation units and I can get mine replaced when I get back. The real test of this theory would be when I left the Hi Chi Mihn City area and flew north to Hanoi. So this morning (Saturday, June 28th) I flew up to Hanoi and over the entire three hour flight, both AHRS systems worked perfectly. It was a good thing too as the weather was pretty crummy and I had to shoot an ILS in fairly low visibility and rain to make it into Hanoi airport. Without the AHRS working, it would have been a real handful. Assuming all continues to be well with the system from here on out, I can only be amazed that I experienced this issue and further amazed that I could get an answer so quickly to such a wacky problem. But, I shouldn't be, as the support Pilatus has provided over the years to me has been wonderful so this is just another example of how great it is to fly the best airplane in the world!

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