B737-800
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical; Inflight Event / Encounter Unstabilized Approach
Flight Crew Executed Go Around / Missed Approach
Aircraft
Landing at destination airport we did an RNAV approach. With flaps 15 at 2;000 FT the gear warning horn and configuration light and ICAS activated and to stop it we had to put the gear down as we passed 1;700 FT and with VNAV path the slope jumped to 650 FT. I leveled out the plane as this was not right. We broke out of the weather over the runway at 1;500 FT; the FMS still telling us the runway was still 2.5 miles ahead as we went over the runway now in VMC conditions. I was able to circle to the left and come in and land safely. We think we either had a map shift or a radar altimeter problem. We put it in the book and had Maintenance check it out: they found nothing. On the first sign of an abnormal situation such as the gear horn coming on when not supposed to; it should have been a clue of other things that could go bad. If this happened in mountainous terrain; I may have been more spring loaded to go around sooner. As these airplanes get older we have to be very alert to strange things. I hope we get the new planes soon.
B737-800 flight crew on approach received multiple aural and ICAS warning indications and elected to abandon the approach. In VMC they circled and landed without incident.