MD-11
Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Time Pressure; Human-Machine Interface; Distraction; Confusion; Workload
Aircraft Equipment Problem Critical; Inflight Event / Encounter Weather / Turbulence
Aircraft Equipment Problem Dissipated; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Landed in Emergency Condition; General Declared Emergency
Aircraft; Weather
In route at FL370 received reroute due to weather over the entire destination region; direct to intercept the RNAV landing south. Redirected direct a different RNAV waypoint; runway change landing north descend and maintain FL240 expect holding over due to weather over the destination airport; airport closed. In the descent; through FL270; observed IAS alert on both PFDs. Shortly thereafter failure of both autopilots; autothrottles and Captain's Flight Director command bars disappeared. At that point had variations of airspeed; lost; suspected or erratic non-alert emergency. After a couple of minutes autopilots and autothrottles became available and continued in holding. During first turn in holding same alerts reappeared including WSHEAR DET fail alert; SEL ELEV MAN; SEL FLAP LIM OVRD. At that point we asked ATC the status of the destination airport to expedite landing. Once again after a few minutes abnormal alerts disappeared. Center redirected us direct to and RNAV waypoint; new runway landing south. After a minute or two; [we] received all of the alerts once again. At that point we were able to determine that the First Officer's CADC was unreliable with airspeed discrepancies from the Captain's and Standby Airspeed and Attitude by 12 - 15 KTS. At that point we declared an emergency; I took control of flying duties and requested the longest runway due to weather and uncertainty of aircraft condition. We were able to stabilize the aircraft; autopilot re-engaged and we completed the approach monitoring the airspeed through the Standby Airspeed Indicator and Captain's PFD. Due to the time of the alerts and the weather conditions; thunderstorms; the holding pattern; the numerous runway changes and the lengthy checklist; we were unable to make contact with the company for updates on our condition.
The reporter stated that the First Officer was flying when the events began. The IAS Comparator first alerted to an airspeed difference with First Officer's airspeed decreasing while the Captain's appeared stable. Shortly thereafter the equipment alerts began including the Yaw Dampener fail. At some point the First Officer began increasing airspeed as he saw his indicated airspeed decrease and the crew was then uncertain what was going on with the aircraft; so the Captain took over hand flying the aircraft because again there was no autopilot or autothrottle capability. It appeared only the First Officer's indications were erroneous at this point; but the crew was confused about why they could not get the automation to function using the Captain's data. Descending through about 10;000 FT all the instrument indications returned to normal. The reporter was not aware of icing conditions although engine anti-ice was on the entire time.
[Narrative added no additional information].
A MD-11 crew suspected the First Officer's CADC was intermittently malfunctioning during an IMC descent near thunderstorms after IAS appeared on both PFDs; the autothrottle; autopilots (2) and Captain's Flight Director failed. Finally an emergency was declared after the EICAS alerted WSHEAR DET FAIL; SEL ELEV MAN and SEL FLAP LIM OVRD. Systems returned to normal at about 10;000 FT.