Narrative:

The issue presented as a dual air data and altitude heading reference system (adhrs) failure. Adhrs 1 was already MEL'd. It had been written up two days prior. The plane had known issues with adhrs 1. As I had been doing since writing up adhrs 1; I had selected the left side pfd to adhrs 2. It was my first officer initial operating experience leg for an empty reposition flight. The weather was low IMC; we were cleared for takeoff and climbing through about 500 to 700 feet (gear were up but we hadn't started our turn at 800 feet for the SID) we experienced what appeared to be an adhrs 2 failure. I say it appeared because we didn't get a yellow ecas message (like I had with the adhrs 1 failure) but both of our screen were blue with xs over the airspeed; altitude; and heading. I took controls and continued to climb. As I was continuing the climb; I told tower we needed to return to the airport immediately and they said approach could get us right back around on the ILS. I started to hit the adhrs swap button just to see if I could get either one to come back online. Both adhrs came back online and I continued to fly in that condition. We were given vectors back around for the ILS. I did not identify as an emergency since we had both adhrs back but I would have if either one failed again. On the ILS just past the final approach fix; we got a heading flag on both sides. I decided to continue the approach to get on the ground. I grounded the plane upon landing. I believe we should seriously consider making 'VFR only' an MEL limitation with a single adhrs failure in the nextgen. It is in the legacy and I believe we should follow suit in the nextgen.

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Original NASA ASRS Text

Title: PC-12 Captain reported the second ADHRS malfunctioned on climb out that resulted decision to return to the departure airport.

Narrative: The issue presented as a dual Air Data and Altitude Heading Reference System (ADHRS) failure. ADHRS 1 was already MEL'd. It had been written up two days prior. The plane had known issues with ADHRS 1. As I had been doing since writing up ADHRS 1; I had selected the left side PFD to ADHRS 2. It was my first officer Initial Operating Experience leg for an empty reposition flight. The weather was low IMC; we were cleared for takeoff and climbing through about 500 to 700 feet (gear were up but we hadn't started our turn at 800 feet for the SID) we experienced what appeared to be an ADHRS 2 failure. I say it appeared because we didn't get a yellow ECAS message (like I had with the ADHRS 1 failure) but both of our screen were blue with Xs over the airspeed; altitude; and heading. I took controls and continued to climb. As I was continuing the climb; I told tower we needed to return to the airport immediately and they said approach could get us right back around on the ILS. I started to hit the ADHRS swap button just to see if I could get either one to come back online. Both ADHRS came back online and I continued to fly in that condition. We were given vectors back around for the ILS. I did not identify as an emergency since we had both ADHRS back but I would have if either one failed again. On the ILS just past the final approach fix; we got a Heading flag on both sides. I decided to continue the approach to get on the ground. I grounded the plane upon landing. I believe we should seriously consider making 'VFR only' an MEL limitation with a single ADHRS failure in the NextGen. It is in the Legacy and I believe we should follow suit in the NextGen.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.