MD-11
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Aircraft Equipment Problem Less Severe
Flight Crew Returned To Departure Airport; Flight Crew Overcame Equipment Problem; Flight Crew Landed As Precaution; General Flight Cancelled / Delayed; General Maintenance Action
Human Factors; Aircraft
Preflight and taxi out normal; FO takeoff. At 80 kts callout I thought I heard the FO confirm 80 kts but in debrief what I heard was not his confirmation but rather a hesitation as he was trying to evaluate why he was seeing a much higher airspeed than I. As we continued down runway I could tell something not quite right and started to make some comparisons of the airspeed indicators. By the time I could determine the airspeed was in error it was too late to reject and the FO rotated aircraft and climbed out normally but Captain's airspeed was 30-40 kts lower than the FO's and upon looking at the auxiliary airspeed  it did not appear to match either airspeed indicator so the climb out was pretty much conducted by attitude and power setting (which was done perfectly by the FO). At about the gear up call we had numerous alerts and failures. Trying to evaluate all the information was time consuming and extensive. I elected to have FO continue flying and coordinated with ATC to fly aircraft out over water because we were at least sure we had an airspeed problem and not sure what our actual speed was; it also would put us in position for an immediate approach back to [departure airport] if needed. Level 2 alerts SEL ELEV FEEL MAN and SEL FLAP LIM OVRD; Auto pilot would not engage; Flight directors removed from view; PROF did not appear to function and Flap retract speeds went away also IAS comparator light came on. After being confident the aircraft was flying in a safe regime (airspeed and altitude) began working the checklist initially for SEL ELEV FEEL MAN as it was on top of list. A jumpseater who was in the RFO seat initially suggested we were not in the flight mode but when the flaps came back on at 3000 feet that was discounted later he suggested it might be a central air data computer problem; I elected to continue with the checklist (not John Wayne the situation by pushing switches) as we were in good control and fuel was not an issue. The checklist (SEL ELEV FEEL MAN and SEL FLAP LIM OVRD) directed us to UNRELIABLE AIRSPEED which did eventually take me to the central air data computer and that did clear the problem. The jumpseater was also very helpful in visually backing us up and checking all the circuit breakers and trying to contact the company for us. While maneuvering out over the ocean we were constantly trying to determine our correct airspeed by cross checking the 3 Airspeed indicators/ground speed indications (INS/GPS) and ground speed from ATC; I elected to leave the slats extended throughout as I thought it allowed us a large room for error. When Capt on central air data computer 2 was selected all indications and auto flight systems were restored; but not completely trusted. Speed was again cross checked with GPS and ATC ground speed readout. When all checklists were done and we were confident that what our instruments were displaying was correct we [advised ATC] and maneuvered for the ILS. I elected to fly the approach manually and assumed control from the FO and disconnected the autopilot early to make sure I had a good feel for the aircraft. I added a couple of extra knots to the approach speed for safety sake and we had a normal flaps 35 landing. When we returned to the gate and talked to Maintenance they quickly went to check the pitot tubes and brought back to the cockpit a few pieces of fabric which was pulled from the Captains pitot tube. The fabric was easily traced back to the interior of the worn pitot tube covers onboard the aircraft. I believe these pitot tube covers need to be replaced with some that can hold up to the constant use (being installed and removed) every day. If they are used fleet wide it is easy to see this happening again. Also looking at the 80 kts callout almost in the same vain as a GO/NO GO callout; there really is very little time to evaluate indications before you are at V1 and VR. When pilot monitoring has the bad or in this case slower indications the person flying needs to challenge when he reaches 80 kts and has not heard the reference from the pilot not flying. This call needs to be clear and assertive.
MD-11 Captain reported returning to the departure airport after noting multiple system faults later traced to worn pitot tube cover debris.