Date: 201303
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Weather elements / visibility: Rain; Snow
Light: Night
Aircraft: MD-11
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Initial Approach
ATC / advisory: TRACON ZZZ
Aircraft component: Air Data Computer
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation - Altitude Overshoot; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Executed Go Around / Missed Approach; General Declared Emergency
Contributing factors: Aircraft; Human Factors; Weather
Primary problem: Aircraft

Narrative: The weather was IMC and rain and clouds were throughout the approach environment. The weather resulted in multiple vectors and long approaches. The First Officer was the Pilot Flying for the arrival. Once we were finally vectored to a long final we set up for the approach. Shortly after the final vector to join the LOC the SEL ELEV FEEL MAN and SEL FLAP LIM OVRD level two alerts displayed and the autopilot disconnected itself. I also noticed a drop in my airspeed into amber numbers. I told the First Officer to add power. His airspeed was reading the assigned speed of 190 [KTS] while I was indicating 154. I immediately checked the AOA gauge in the HUD and it showed us 'in the box.' I was confident that we were at safe flying airspeed and compared all speeds between standby and 1 and 2. The standby agreed with the First Officer's airspeed indicator. I told ATC that we needed to climb to 5;000 FT and work out a flight control problem (I was thinking about ELEV FEEL and FLAP LIM OVRD). I told them that we would need priority once the problem was fixed and we were ready to come back in. ATC did a great job and kept us in the area with minimum vectoring while we worked the issue. I then got into the QRH. The combined level two alerts drove us into the Airspeed: Lost; Suspect or Erratic Checklist. I started the checklist and then all the alerts went away. I then told ATC that our problem fixed itself and we were ready to try an approach. Shortly after our first vector the entire scenario repeated itself. I elected to take the vector and run the checklist that I had already read through. As I was executing the checklist; the First Officer was hand flying the jet in a very challenging environment of busy radios and bad weather. Accomplishing the checklist left him briefly with no Flight Director and no autopilot. At that time he was in a descending turn to 4;000 FT. We both caught the fact that he was going to miss that level off by a little bit and I told him to watch altitude. We dipped below 4;000 FT by 250 to 300 FT as he raised pitch and added power. I then thought that it would be a good idea to get another set of eyes in the cockpit and called up a MD-11 qualified jumpseater that was in the back. I wanted the jumpseater to be watching the pitch and power charts as we finished up the approach. We made it though the checklist and determined that the #1 CADC was bad. We got back on #2 information and were able to get the #2 autopilot and FD back on line. By now we were being vectored in for another approach. I reiterated to ATC that we were an emergency as I wanted approach priority. The weather was degrading and I was concerned about fuel and the loss of the other CADC. The First Officer did a nice job of flying the LOC only approach. Nearing minimums I took the aircraft and used the HUD to fly the final portion of the approach and landing. The altitude deviation could have been prevented by better monitoring. I also should have brought up the jumpseater earlier in the event to help out thereby using all my assets for a safer environment.


Second narrative: The missed altitude level off was due to the many distractions during the descent to 4;000 FT; but ultimately I should have been paying direct attention to the impeding level off and leveled exactly at 4;000. 'Fly the airplane' again proves to be the most important thing.


Synopsis: MD-11 flight crew experiences level two alerts during approach for SEL ELEV FEEL MAN and SEL FLAP LIM OVRD. At the same time the Captain detects low airspeed and alerts the flying First Officer before determining that the Captain's airspeed is in error. A go-around is initiated and the QRH consulted; which leads to the Unreliable Airspeed checklist and CADC switching. A near normal approach and landing ensues.