2011-09 · NASA ASRS report 969489
An MD11 CADC failed and the panel switch would not latch to the alternate CADC so the Captain had no airspeed; autothrottle or flight director in severe weather conditions. The AIRSPEED LOST Checklist was in the Emergency Procedures; not the Emergency Non Alerts as indicated.
After entering foreign airspace; we were briefed and ready for descent. ATC instructed us to descend from FL360 to FL280. Followed by instructions to continue the descent to FL150. Passing FL 280 (and just a minute from entering the weather) we received a LVL 2 alert 'SEL ELEV FEEL MAN' and a LVL 2 'FLAP LIM OVRD.' At the same time the autopilot kicked off and the autothrottles kicked off; and were unrecoverable. Additionally; we lost our Flight Directors and the Captain's airspeed indicator was extremely inaccurate. While in the process of attempting to follow ATC's instructions I had the First Officer in the jumpseat running the checklists while the First Officer in the right seat was constantly calling out standby airspeed values; selecting headings and altitudes to avoid weather and comply with ATC. Passing FL180; the jumpseat First Officer was unable to locate the 'AIRSPEED LOST; SUSPECT or ERRATIC' Checklist; which was where our checklist for 'SEL ELEV FEEL MAN' and 'FLAP LIM OVRD' leads us to. At this time we all agreed his time would be better spent assisting to get the aircraft on the ground. I requested a 30 mile final vector for the ILS. After slat extension and flap 15 extension I called for Flaps 28. The flaps only extended to a split of 20/22 with a 'FLAP DISAG' alert. Gear down; Flaps 35; still split 20/22. Captain's airspeed indicator was unusable. Landing was [normal]. During the debrief we all tried to locate the 'AIRSPEED LOST; SUSPECT or ERRATIC' checklist and could not find it. After arriving at the hotel around dawn we all got together with the company CD to try to find it. After 15 minutes we located it; not under the 'Emergency Non-Alerts' where our checklist leads us; but under 'Emergency Procedures.' I would like to commend both First Officers for their professional and controlled performance under extremely stressful conditions.
The Reporter stated this was possibly the worst weather he has ever seen in this area and that all three pilots were extremely busy. When the Central Air Data Computer (CADC) initially failed the aircraft was night VMC and about 2 two minutes from entering the weather. The Reporter attempted to switch CADC's using the control panel but the transfer button would not latch to the alternate CADC although his instruments transferred for just a second then failed again. He pushed the transfer at least a half a dozen times with the same effect and now believes that the transfer switch failed leaving a still functioning second CADC unreachable. After the aircraft entered IMC in the thunderstorm all three pilots were concentrating on flying. The added complexity of the split flap increased the work load so that the landing was flown at a high airspeed to a wet runway. The confusion that resulted when the crew was unable to find the AIRSPEED LOST; SUSPECT OR ERRATIC Checklist added to the workload and so finally the Reporter told the First Officer to abandon searching for it and prepare the aircraft for landing. The Reporter is not certain if his Company or Boeing is responsible for the checklist error directing the crew to 'Emergency Non-Alerts' instead of 'Emergency Procedures' but corrective action should be taken to ensure the correct reference is made on future checklist revisions.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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