Narrative:

While on visual approach; the captain's radio altimeter became erratic from 440 ft AGL to touchdown and the amber message 'rad altitude invalid' displayed on both adp's. I commanded the first officer to reset to the adp's. In the flare; the yaw damper failed and the tail swung a bit; but I was able to maintain centerline. At almost the exact same time; the flight director (FD) failed and an amber 'FD fail' message was displayed on both eadi's in the upper left corner. We landed safely and taxied to the gate. I contacted dispatch and was transferred to maintenance control where we worked together to add mels 33-6; 34-19; and 22-4(b). The onsite mechanic began working to complete the maintenance action required to MEL the captain's radio altimeter. If applied; this would mean that the egpws would be disabled. The first officer and I discussed operating the flight to ZZZ1 at night; IMC; with mountainous terrain and decided that there were 'too many links in our error chain.' I consulted the chief pilot; via cell phone and he agreed that our concerns were legitimate and that he 'would back [us] with whatever decision [we] make.' I contacted dispatch and declined the aircraft due to the mels being added to the aircraft. There is no way to prevent this situation. I feel that we made a good decision to decline the aircraft and credit my training and experience thus far.

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Original NASA ASRS Text

Title: DHC 8-200 Captain experiences Radar Altimeter failure at low altitude during a visual approach. This causes the yaw damper to trip off and the Flight Directors to fail; each with their own failure indications. The approach continues to a safe landing; but the aircraft is refused for the next leg.

Narrative: While on visual approach; the Captain's radio altimeter became erratic from 440 FT AGL to touchdown and the amber message 'RAD ALT INVALID' displayed on both ADP's. I commanded the First Officer to reset to the ADP's. In the flare; the yaw damper failed and the tail swung a bit; but I was able to maintain centerline. At almost the exact same time; the Flight Director (FD) failed and an amber 'FD FAIL' message was displayed on both EADI's in the upper left corner. We landed safely and taxied to the gate. I contacted Dispatch and was transferred to Maintenance Control where we worked together to add MELs 33-6; 34-19; and 22-4(b). The onsite Mechanic began working to complete the maintenance action required to MEL the Captain's radio altimeter. If applied; this would mean that the EGPWS would be disabled. The First Officer and I discussed operating the flight to ZZZ1 at night; IMC; with mountainous terrain and decided that there were 'too many links in our error chain.' I consulted the Chief Pilot; via cell phone and he agreed that our concerns were legitimate and that he 'would back [us] with whatever decision [we] make.' I contacted Dispatch and declined the aircraft due to the MELs being added to the aircraft. There is no way to prevent this situation. I feel that we made a good decision to decline the aircraft and credit my training and experience thus far.

Data retrieved from NASA's ASRS site as of July 2013 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.