DC10 flight crew experienced an airspeed indicator anomaly at FL340 and initially suspects the capta...

Narrative:

While cruising at FL340 we initially received an IAS comparator alert; followed by numerous other alerts; autopilot disconnected; etc. I began to run our airspeed; lost; suspect; or erratic checklist. The captain began flying the aircraft by hand. The initial airspeed indications were captain: 270 KTS; first officer: 305 KTS; sby: 310 KTS. It appeared the air data computer was bad on the captain's side; so we chose to transfer my air data to the captain's side. This is a very wordy checklist and as I was trying to finish up the checklist; we began to feel a buffet. Initially; we were trying to guess if high or low speed buffet. Shortly thereafter; stick shaker activated. We immediately decreased pitch; added power and began a descent to FL240. Looking at our checklist; I think there are some important points that need to be highlighted. 1. About half way on the second page it says; 'disregard all alerts and aural warnings; except stick shaker until after the aircraft has stabilized and safe operation achieved.' I think this should be a caution/warning on the first page to remind the crews the importance of stick shaker. (Remember; back side of the clock with a messed up circadian rhythm!) 2. Auto throttles should be disconnected and it should remind crews to initially establish a good pitch/power relationship. I was finishing the checklist and saw the N1% ~ 60% at FL340; shortly after; buffet and stick shaker. The good thing is we immediately pitched down and added power; beginning a descent and declaring an emergency. In training we were always taught to find the airspeed closest to sby airspeed. When 2 of our airspeeds (captain or first officer) are within 5 KTS of another; you would think this is good data. Not the case in our scenario. Eventually we identified a good air data computer using ATC's ground speed readouts and confirmed our #1 air data information was good. Approach; landing and taxi in were uneventful.

Original NASA ASRS Text

Title: DC10 flight crew experienced an airspeed indicator anomaly at FL340 and initially suspects the Captain's air data computer. The error is detected when when buffet and stick shaker occur nearly simultaneously. Descent is initiated and thrust is added with diversion to the nearest suitable airport.

Narrative: While cruising at FL340 we initially received an IAS Comparator alert; followed by numerous other alerts; autopilot disconnected; etc. I began to run our airspeed; lost; suspect; or erratic checklist. The Captain began flying the aircraft by hand. The initial airspeed indications were Captain: 270 KTS; First Officer: 305 KTS; SBY: 310 KTS. It appeared the air data computer was bad on the Captain's side; so we chose to transfer my air data to the Captain's side. This is a very wordy checklist and as I was trying to finish up the checklist; we began to feel a buffet. Initially; we were trying to guess if high or low speed buffet. Shortly thereafter; stick shaker activated. We immediately decreased pitch; added power and began a descent to FL240. Looking at our checklist; I think there are some important points that need to be highlighted. 1. About half way on the second page it says; 'Disregard all alerts and aural warnings; except stick shaker until after the aircraft has stabilized and safe operation achieved.' I think this should be a caution/warning on the first page to remind the crews the importance of stick shaker. (Remember; back side of the clock with a messed up circadian rhythm!) 2. Auto throttles should be disconnected and it should remind crews to initially establish a good pitch/power relationship. I was finishing the checklist and saw the N1% ~ 60% at FL340; shortly after; buffet and stick shaker. The good thing is we immediately pitched down and added power; beginning a descent and declaring an emergency. In training we were always taught to find the airspeed closest to SBY airspeed. When 2 of our airspeeds (Captain or First Officer) are within 5 KTS of another; you would think this is good data. Not the case in our scenario. Eventually we identified a good air data computer using ATC's ground speed readouts and confirmed our #1 air data information was good. Approach; landing and taxi in were uneventful.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	870756
Time
Date	201001
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	DC-10 30
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Air Data Computer
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Flight Instructor Flight Crew Flight Engineer Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 120 Flight Crew Total 6000 Flight Crew Type 1000
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Speed All Types

DC10 flight crew experienced an airspeed indicator anomaly at FL340 and initially suspects the captain's air data computer. The error is detected when when buffet and stick shaker occur nearly simultaneously. Descent is initiated and thrust is added with diversion to the nearest suitable airport.