Narrative:

We were cleared for the ILS approach to runway xx. Established on the localizer at 3;000 ft; we got multiple egpws warnings commanding; 'pull up; terrain;' 'pull up; pull [up];' and 'too low; terrain.' also; the radar altimeter (RA) indicated that we were on the ground at 0 ft. We were at 3;000 ft and established on the approach; but since it was IMC; I initiated an immediate climb to 4;000 ft. We contacted ATC and told them of our climb. At that altitude; we broke out on top of the clouds. We were still getting the warnings and the RA was still indicating 0 ft. Then the radar altimeter resolved itself and the warnings ceased. The first officer and I agreed that it was likely an error and attempted the approach again. This time the approach was successful with no problems. On the ground; I wrote up the discrepancy and called maintenance. I explained the problem and we agreed that it was likely an anomaly. As a precaution; we reset the GPWS circuit breaker and ran the egpws test and the RA test. Both were successful. Maintenance and I agreed that the problem was likely resolved and the aircraft safe for flight. I signed off the discrepancy with the information maintenance provided. On the return flight; the same warnings happened on approach at 4;000 ft. This time we were VMC and the first officer and I agreed that it was in error and the approach was safe to continue. The warnings sounded intermittently all the way down the approach; but the approach and landing were normal. The threat came from having an egpws warning in IMC conditions with subsequent climb to higher altitude. Another threat was the mistaken diagnosis that this was an anomaly and one time event.

Related reports:

Google
 

Original NASA ASRS Text

Title: A radar altimeter malfunctioned on approach; causing EGPWS terrain warnings; so the crew executed an IMC missed approach. The indications were normal during the following approach; but the malfunction repeated at the next destination while VMC.

Narrative: We were cleared for the ILS approach to Runway XX. Established on the localizer at 3;000 FT; we got multiple EGPWS warnings commanding; 'Pull up; terrain;' 'Pull up; pull [up];' and 'Too low; terrain.' Also; the Radar Altimeter (RA) indicated that we were on the ground at 0 FT. We were at 3;000 FT and established on the approach; but since it was IMC; I initiated an immediate climb to 4;000 FT. We contacted ATC and told them of our climb. At that altitude; we broke out on top of the clouds. We were still getting the warnings and the RA was still indicating 0 FT. Then the radar altimeter resolved itself and the warnings ceased. The First Officer and I agreed that it was likely an error and attempted the approach again. This time the approach was successful with no problems. On the ground; I wrote up the discrepancy and called Maintenance. I explained the problem and we agreed that it was likely an anomaly. As a precaution; we reset the GPWS circuit breaker and ran the EGPWS test and the RA test. Both were successful. Maintenance and I agreed that the problem was likely resolved and the aircraft safe for flight. I signed off the discrepancy with the information Maintenance provided. On the return flight; the same warnings happened on approach at 4;000 FT. This time we were VMC and the First Officer and I agreed that it was in error and the approach was safe to continue. The warnings sounded intermittently all the way down the approach; but the approach and landing were normal. The threat came from having an EGPWS warning in IMC conditions with subsequent climb to higher altitude. Another threat was the mistaken diagnosis that this was an anomaly and one time event.

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.