A lancair pilot deviated from the GPS final approach course heading and descended below the approach...

Attributes
ACN	871366
Time
Date	201001
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	Lancair Undifferentiated
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Route In Use	Other GPS app
Flight Plan	IFR
Component
Aircraft Component	Compass (HSI/ETC)
Person 1
Function	Single Pilot
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Instructor Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 50 Flight Crew Total 7000 Flight Crew Type 200
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Track / Heading All Types Inflight Event / Encounter CFTT / CFIT

Narrative:

While on a GPS approach to runway xxr in IMC conditions and after crossing the final approach fix I experienced a problem with the heading gyro in the HSI. While sorting out the problem I initially drifted off course and descended below the approach segment altitude. I received a course and altitude alert from the tower. Once I recognized the problem I disregarded the HSI heading gyro info and continued the approach to a safe landing. I was caught off guard by the failure of the heading gyro and temporarily lost my situational awareness. The HSI heading gyro never showed a 'flag'; it just drifted 30+ degrees due to a failure in the slaving unit. In hindsight I should have caught the failure sooner by scanning and processing all of the additional information in my panel. I have a back-up directional gyro on the co-pilot side; a wet compass; and a heading indicator in my GPS. Another factor was that I was legally IFR current; but hadn't flown in IMC for over 2 months. I fly quite a bit in IMC conditions at my other base; but rarely here. This incident has reminded me that you can never expect your IFR/IMC flying skills to be as sharp as they were if you don't use them on a regular basis. I also plan on getting re-current training on partial panel procedures.

Original NASA ASRS Text

Title: A Lancair pilot deviated from the GPS final approach course heading and descended below the approach segment altitude after the aircraft's HSI drifted off without a warning. ATC alerted the pilot about his deviation.

Narrative: While on a GPS approach to Runway XXR in IMC conditions and after crossing the final approach fix I experienced a problem with the heading gyro in the HSI. While sorting out the problem I initially drifted off course and descended below the approach segment altitude. I received a course and altitude alert from the Tower. Once I recognized the problem I disregarded the HSI heading gyro info and continued the approach to a safe landing. I was caught off guard by the failure of the heading gyro and temporarily lost my situational awareness. The HSI heading gyro never showed a 'flag'; it just drifted 30+ degrees due to a failure in the slaving unit. In hindsight I should have caught the failure sooner by scanning and processing all of the additional information in my panel. I have a back-up directional gyro on the co-pilot side; a wet compass; and a heading indicator in my GPS. Another factor was that I was legally IFR current; but hadn't flown in IMC for over 2 months. I fly quite a bit in IMC conditions at my other base; but rarely here. This incident has reminded me that you can never expect your IFR/IMC flying skills to be as sharp as they were if you don't use them on a regular basis. I also plan on getting re-current training on partial panel procedures.

Data retrieved from NASA's ASRS site as of April 2012 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.

A lancair pilot deviated from the GPS final approach course heading and descended below the approach segment altitude after the aircraft's HSI drifted off without a warning. ATC alerted the pilot about his deviation.