Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Aircraft Equipment Problem Less Severe
General Release Refused / Aircraft Not Accepted; General Maintenance Action
Aircraft
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.
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.