Narrative:

We were on approach to landing at sdf. Descending out of 8000 ft to 7000 ft in clean confign 237 KIAS in heavy snow with light turbulence, night IMC on radar vectors from sdf approach. We got a 'terrain, terrain' GPWS alert. As I was initiating the escape maneuver, I noticed the radar altimeter indicating 362 ft. The escape maneuver terminated with a leveloff at 10000 ft stabilizing at 11000 ft. After leveloff, we reported the altitude deviation required by the GPWS maneuver to sdf approach. Approach said MVA was 2300 ft. We confirmed the altimeter setting with ATC, crosschecked all instruments and could find no reason for the warning. We started another descent. At 4000 ft we acquired visual ground contact. We then received a 'too low gear' warning. At 4000 ft MSL (approximately 3000 ft AGL), we also received 4 separate 2500 ft radar altitude aural alerts. On one of the alerts, the first officer's radar altimeter indicated 1300 ft with no reading on captain's side. The remainder of approach and landing were uneventful. Erroneous GPWS warning was cause for climb above assigned altitude. Supplemental information from acn 568856: suspect heavy snow changing to heavy rain below us somehow triggered false surface, or ice on antenna. Possible malfunction of unit also.

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Original NASA ASRS Text

Title: MD11 CREW HAD A GPWS 'TERRAIN, TERRAIN' WARNING WHILE BEING VECTORED IN SDF CLASS E AIRSPACE.

Narrative: WE WERE ON APCH TO LNDG AT SDF. DSNDING OUT OF 8000 FT TO 7000 FT IN CLEAN CONFIGN 237 KIAS IN HVY SNOW WITH LIGHT TURB, NIGHT IMC ON RADAR VECTORS FROM SDF APCH. WE GOT A 'TERRAIN, TERRAIN' GPWS ALERT. AS I WAS INITIATING THE ESCAPE MANEUVER, I NOTICED THE RADAR ALTIMETER INDICATING 362 FT. THE ESCAPE MANEUVER TERMINATED WITH A LEVELOFF AT 10000 FT STABILIZING AT 11000 FT. AFTER LEVELOFF, WE RPTED THE ALTDEV REQUIRED BY THE GPWS MANEUVER TO SDF APCH. APCH SAID MVA WAS 2300 FT. WE CONFIRMED THE ALTIMETER SETTING WITH ATC, XCHKED ALL INSTS AND COULD FIND NO REASON FOR THE WARNING. WE STARTED ANOTHER DSCNT. AT 4000 FT WE ACQUIRED VISUAL GND CONTACT. WE THEN RECEIVED A 'TOO LOW GEAR' WARNING. AT 4000 FT MSL (APPROX 3000 FT AGL), WE ALSO RECEIVED 4 SEPARATE 2500 FT RADAR ALT AURAL ALERTS. ON ONE OF THE ALERTS, THE FO'S RADAR ALTIMETER INDICATED 1300 FT WITH NO READING ON CAPT'S SIDE. THE REMAINDER OF APCH AND LNDG WERE UNEVENTFUL. ERRONEOUS GPWS WARNING WAS CAUSE FOR CLB ABOVE ASSIGNED ALT. SUPPLEMENTAL INFO FROM ACN 568856: SUSPECT HVY SNOW CHANGING TO HVY RAIN BELOW US SOMEHOW TRIGGERED FALSE SURFACE, OR ICE ON ANTENNA. POSSIBLE MALFUNCTION OF UNIT ALSO.

Data retrieved from NASA's ASRS site as of July 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.