DC-10 Undifferentiated or Other Model
Aircraft Equipment Problem Critical
Flight Crew Overcame Equipment Problem
Human Factors; Equipment / Tooling; Procedure
The weather was deteriorating on taxi to the active runway. At the start of taxi there was no restriction to visibility and First Officer was planning to make the takeoff; but visibility dropped to greater than 6;000 touchdown; 800 RVR midfield; and inop rollout half way to the runway. Crew re-briefed that Captain would make the departure; and by the time departure clearance was received; visibility was 800 RVR touchdown; 500 RVR midfield; inop rollout. During the takeoff roll; a normal 80 KT call made; and checked. I verified that airspeeds matched. On rotation; Captain had no flight director bars; and the lower foot was abnormal. By the time he rotated to near 20 degrees pitch up; there was no yellow foot and the airspeed was about 10 KTS into the red foot. There was no stick shaker; and pitch limit indicator indicated that the pitch attitude was not near stall. The aircraft was climbing normally. I cross checked with the First Officer's PFD and his indications were all normal; except there was no flight director. The aircraft was at normal pitch angle; and on correct climb out speed. At some point the IAS miscompare; elevator feel; yaw damper; and other warning lights and alerts illuminated. The First Officer verbalized that he had no flight director; looked at the Captain's airspeed indicator; and indicated that there was an airspeed indicating problem; and correctly diagnosed that the standby airspeed indicator agreed with the First Officer's. The Captain confirmed the diagnosis; and promptly transferred control to the First Officer.The airspeed split between the two primary airspeed indicators was approximately 20 to 30 KTS. By this time the aircraft was in VFR conditions. The Captain requested to continue northeast bound and was assigned an altitude of 16;000 FT. There was a discussion of altitude with a subsequent frequency change that resulted in a block altitude assignment of 16;000 FT-FL200 being requested; assigned; and held. The crew then ran the Airspeed: Lost; Suspect or Erratic Checklist. Although the airspeed discrepancy continued; no differences were noted between altimeters and other flight instruments. The end result was that the Captain switched his flight instrument source to CADC 2. At that point all flight instruments indicated normally. Autopilot; autothrottle; and flight director function returned; and most alerts and warning lights went out. The crew elected to climb to FL250 and discussed whether they were legal to enter RVSM airspace. After referencing the Flight Operations Manual; they decided they did not have two independent primary altimeters as both PFD altitude readouts used the same CADC; and elected to request a final cruise altitude of FL250. They discussed whether they had enough fuel to continue on to destination. They informed Dispatch; received updated fuel burn information; and decided to continue to destination. The crew chose to fly a monitored approach so that the Captain could monitor the flight instruments and compare the primary IAS with the standby IAS throughout the approach. The flight landed without incident. At no time during the flight was there any deviation from an ATC clearance or company procedure. There was never a need for intervention by the Check Pilot. The crew used excellent CRM to ensure that primary focus was to fly the aircraft; then diagnose the problem; and execute the correct QRH procedure to safely complete the flight. If the problem was caused by the loss of one airspeed system; redesign the system so that such an event won't result in the loss of so many aircraft functions.The day after the flight it came to my attention that it is suspected that the pitot cover was left on the Captain's pitot tube prior to departure. At this time I have no direct evidence that this is actually the case. The maintenance log in the aircraft had a current computer generated release accompanied by a separate numbered discrepancy page indicating that the pitot covershad been installed and removed for the layover. It had been signed off by a Mechanic. Both were inside the plastic sleeve of the maintenance log on board the aircraft when I arrived at the airplane. During the First Officer's walk around preflight check; I observed him walk around the front of the aircraft in the area in front of and beneath the pitot tubes. He also looked in the direction of the pitot tubes.If the airspeed problem was caused by an installed pitot tube cover; the following can help prevent a recurrence.1. Always use a pitot tube cover stored in the cockpit with the gear pins and have the captain ensure it is onboard during his cockpit check. 2. Use a more visible pitot tube cover. 3. If not already done; have the pushback crew check for pitot tube covers during their door check prior to pushback. 4. Add checking for pitot tube covers to the captain's exterior safety check. 5. Use non porous pitot tube covers so that during the takeoff roll there is no airspeed indication (in lieu of a false indication) during the takeoff roll.
I arrived to work in the morning and immediately started getting the aircraft ready for departure. I powered up the jet; did a walk around and then proceeded to pull the pitot covers. The aircraft tug was positioned just below the nose; so I climbed on top of the tug; grabbed the 3 streamers and climbed down. I placed the pile of streamers on the GPU location we use to store the covers when not in use. I then signed off the white sheet in the logbook and subsequently loaded that into the maintenance computer. A few hours after the aircraft departed; I got a call; saying the captain's pitot probe cover was still installed. I went back to the GPU where I had stored the covers and discovered one of the streamers had a cover missing. I assume now that when I pulled the streamer to remove the cover; the cloth loop strap that is attached to the pitot probe cover must have broken and I did not notice it. The strap on the pitot probe broke and I did not realize it. When pulling the cover off; it felt the same as I had done many times before with the same resistance. I thought I had it all in my hands. Additionally when you finish it is a large ball of material; probe covers; lanyards; streamers; etc. It was not obvious that the cover was missing when I stowed them. Rework the pitot covers and streamers so it is not weak material. Maybe better visible color then red; such as fluorescent green. Maybe have an inspection program for the pitot probes so the worn ones are discarded before they fail.
DC10 Captain describes airspeed anomalies during takeoff and switching to CADC 2 to return airspeed indication to normal. A report from the Maintenance Technician who signed off the pitot covers as being removed is also included.