Narrative:

In july 1989, I departed from williamsburg, va with 3 passenger (my wife and another couple), in our small aircraft. The WX at williamsburg was marginal VFR, and en route and destination WX was marginal VFR to IFR, forecast ceilings of 800-1500', with 2-4 mi visibility. I received an IFR clearance and departed williamsburg. On V16, between patuxent VOR and kenton VOR, we experienced heavy rain and light to moderate turbulence, with significant updrafts and downdrafts. I had difficulty maintaining the assigned altitude of 5000' and informed ATC of this difficulty. Approximately 30 NM southwest of the kenton VOR, after what seemed to be significant changes in the wind (and wind correction angle) I noticed a serious discrepancy between the dg and the magnetic compass. I informed my wife (also an instrument rated pilot) of the discrepancy, and she immediately discovered a low vacuum indication (2.5' instead of the normal 5'). The low vacuum indicator light did not come on, it tested fine during the preflight, maybe my mechanic can explain this. I called ATC (dover approach) and requested an immediate descent to a lower altitude below the clouds. Dover approach told me to stand by. Then the dg failed completely and began to fill with water. I declared an emergency and again requested a lower altitude. Dover approach immediately cleared me down to 2000'. The dg problem had caused me to fly around in circles and dover gave me a heading to fly toward kenton. I requested the nearest VFR airport and they suggested a surveillance radar approach into dover AFB. I had difficulty maintaining a heading using the magnetic compass and accepted the surveillance approach into dover AFB. The WX conditions at landing were about 1000 ceiling with 1.5 visibility, rain and fog. In retrospect, there were only a few things that would have improved our ability to deal with this emergency. First, I wish I had some more recent partial panel IFR practice. This might have enabled me to maintain a better heading after the gyro failure. Second, the magnetic compass is very hard to read in instrument conditions and turbulence during an emergency. We will probably install a vertical card compass in our aircraft. Throughout the emergency, the controllers maintained me above the MOCA. I did not verify this until after the flight. After the flight I realized that I was too busy to check the chart for minimum altitudes. I requested a lower altitude without checking what the lowest safe altitude would be. There was one factor that significantly improved my ability to deal with the emergency. My wife, who is also an instrument rated pilot, was riding in the right front seat.

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Original NASA ASRS Text

Title: GA SMA EXPERIENCED PARTIAL INSTRUMENT FAILURE AT CRUISE ALT. EMERGENCY DECLARED AND FLT ASSIST RECEIVED FROM DOV APCH CTLR.

Narrative: IN JULY 1989, I DEPARTED FROM WILLIAMSBURG, VA WITH 3 PAX (MY WIFE AND ANOTHER COUPLE), IN OUR SMA. THE WX AT WILLIAMSBURG WAS MARGINAL VFR, AND ENRTE AND DEST WX WAS MARGINAL VFR TO IFR, FORECAST CEILINGS OF 800-1500', WITH 2-4 MI VISIBILITY. I RECEIVED AN IFR CLRNC AND DEPARTED WILLIAMSBURG. ON V16, BETWEEN PATUXENT VOR AND KENTON VOR, WE EXPERIENCED HEAVY RAIN AND LIGHT TO MODERATE TURBULENCE, WITH SIGNIFICANT UPDRAFTS AND DOWNDRAFTS. I HAD DIFFICULTY MAINTAINING THE ASSIGNED ALT OF 5000' AND INFORMED ATC OF THIS DIFFICULTY. APPROX 30 NM SW OF THE KENTON VOR, AFTER WHAT SEEMED TO BE SIGNIFICANT CHANGES IN THE WIND (AND WIND CORRECTION ANGLE) I NOTICED A SERIOUS DISCREPANCY BETWEEN THE DG AND THE MAG COMPASS. I INFORMED MY WIFE (ALSO AN INSTRUMENT RATED PLT) OF THE DISCREPANCY, AND SHE IMMEDIATELY DISCOVERED A LOW VACUUM INDICATION (2.5' INSTEAD OF THE NORMAL 5'). THE LOW VACUUM INDICATOR LIGHT DID NOT COME ON, IT TESTED FINE DURING THE PREFLT, MAYBE MY MECHANIC CAN EXPLAIN THIS. I CALLED ATC (DOVER APCH) AND REQUESTED AN IMMEDIATE DSCNT TO A LOWER ALT BELOW THE CLOUDS. DOVER APCH TOLD ME TO STAND BY. THEN THE DG FAILED COMPLETELY AND BEGAN TO FILL WITH WATER. I DECLARED AN EMER AND AGAIN REQUESTED A LOWER ALT. DOVER APCH IMMEDIATELY CLRED ME DOWN TO 2000'. THE DG PROBLEM HAD CAUSED ME TO FLY AROUND IN CIRCLES AND DOVER GAVE ME A HDG TO FLY TOWARD KENTON. I REQUESTED THE NEAREST VFR ARPT AND THEY SUGGESTED A SURVEILLANCE RADAR APCH INTO DOVER AFB. I HAD DIFFICULTY MAINTAINING A HDG USING THE MAGNETIC COMPASS AND ACCEPTED THE SURVEILLANCE APCH INTO DOVER AFB. THE WX CONDITIONS AT LNDG WERE ABOUT 1000 CEILING WITH 1.5 VISIBILITY, RAIN AND FOG. IN RETROSPECT, THERE WERE ONLY A FEW THINGS THAT WOULD HAVE IMPROVED OUR ABILITY TO DEAL WITH THIS EMER. FIRST, I WISH I HAD SOME MORE RECENT PARTIAL PANEL IFR PRACTICE. THIS MIGHT HAVE ENABLED ME TO MAINTAIN A BETTER HDG AFTER THE GYRO FAILURE. SECOND, THE MAG COMPASS IS VERY HARD TO READ IN INSTRUMENT CONDITIONS AND TURBULENCE DURING AN EMER. WE WILL PROBABLY INSTALL A VERTICAL CARD COMPASS IN OUR ACFT. THROUGHOUT THE EMER, THE CTLRS MAINTAINED ME ABOVE THE MOCA. I DID NOT VERIFY THIS UNTIL AFTER THE FLT. AFTER THE FLT I REALIZED THAT I WAS TOO BUSY TO CHECK THE CHART FOR MINIMUM ALTS. I REQUESTED A LOWER ALT WITHOUT CHECKING WHAT THE LOWEST SAFE ALT WOULD BE. THERE WAS ONE FACTOR THAT SIGNIFICANTLY IMPROVED MY ABILITY TO DEAL WITH THE EMER. MY WIFE, WHO IS ALSO AN INSTRUMENT RATED PLT, WAS RIDING IN THE RIGHT FRONT SEAT.

Data retrieved from NASA's ASRS site as of August 2007 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.