B737 FIRST OFFICER REPORTS TCAS RA; ALTITUDE DEVIATION AND DEGRADED PERFORMANCE ON APPROACH AND LANDING. DISCOVER LOSS OF PERFORMANCE DUE TO AIRFRAME ICING ON THE HORIZONTAL AND VERTICAL STABILIZERS.

Narrative

WE WERE APPROXIMATELY 10 DME ON THE ILS 35L INTO DEN IN DARK IMC IN MODERATE MIXED ICING CONDITIONS. WE RECEIVED A RESOLUTION ADVISORY FROM OUR TCAS WHICH CALLED FOR A CLIMB. THE CAPTAIN DISCONNECTED THE AUTOPILOT AND AUTOTHROTTLE AND STARTED TO CLIMB. I ADVISED ATC THAT WE WERE CLIMBING FOR A RESOLUTION ADVISORY. ATC STATED THAT THEY WERE CONDUCTING SIMULTANEOUS APPROACHES IN A TONE OF VOICE THAT SEEMED TO MEAN THAT WE SHOULD NOT BE RESPONDING TO THE RESOLUTION ADVISORY. HE THEN GAVE US A HEADING AND ALTITUDE ASSIGNMENT TO TRACK THE LOCALIZER AND CLIMB TO 10000 FT. A FEW SECONDS LATER HE GAVE US A RIGHT TURN TO 095 DEGREES. AS WE LEVELED AT 10;000 FT THE STICK SHAKER ACTIVATED FOR SEVERAL SECONDS. I SAID POWER AND PITCH. THE CAPTAIN ADDED POWER AND PITCHED DOWN SLIGHTLY AND THE AIRCRAFT LOST APPROX 300-350 FT WHILE RECOVERING AND BEGAN CLIMBING BACK TO 10000 FT. ATC STATED THAT HE REALLY NEEDED US AT 10000 FT. I STARTED THAT WE HAD COLLECTED SIGNIFICANT ICE AND WERE RETURNING TO 10000 FT. I TURNED ON THE WING ANTI-ICE AT THAT TIME. DURING THE APPROACH; THE ENGINE ANTI-ICE WAS ON BUT THE WING ANTI-ICE WAS NOT. ATC THEN CONTINUED TO VECTOR US TO THE ILS 35R FOR THE FINAL APPROACH INTO DENVER. WHEN THE CAPTAIN FLARED FOR LANDING; IT WAS AS IF THE CONTROL MOVEMENT HAD LITTLE IF ANY EFFECT AND THE LANDING WAS FAIRLY FIRM. WE TAXIED TO THE GATE AND PARKED. DURING THE POSTFLIGHT INSPECTION; I NOTED THAT THE LEADING EDGES OF THE ENTIRE HORIZONTAL AND VERTICAL STABILIZERS WERE COVERED WITH HORNS OF ICE SEVERAL INCHES THICK. I HAD NEVER SEEN SO MUCH ICE ON A B737. I ALSO NOTICED THAT ATTACHED TO THE TOTAL PRESSURE PROBES IN BOTH ENGINES WERE LARGE FIRST-SIZED BALLS OF ICE. DURING THE APPROACH AND GO-AROUND; THE CLOUDS WERE TOO THICK TO SEE THE LEADING EDGES OF THE WINGS. I DON'T KNOW HOW MUCH ICE MAY HAVE COVERED THE WING LEADING EDGES PRIOR TO THE WING ANTI-ICE BEING ACTIVATED.