A B767-300 left air data computer failed in flight causing the captain's airspeed to decrease greatl...

Attributes
ACN	928262
Time
Date	201101
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZZ.ARTCC
State Reference	FO
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B767-300 and 300 ER
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Air Data Computer
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 200 Flight Crew Total 17400 Flight Crew Type 6000
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy Deviation - Procedural FAR

Narrative:

Approximately 7 hours into flight; noticed the throttles advancing significantly. Scanned instruments to see the captain's altimeter was 300 ft low and the airspeed was decaying through 200 KTS. The aircraft pitched up a few degrees and began to climb. Captain disengaged autopilot and autothrottle and pushed the throttles to the stops. The airspeed continued to drop to 120 KTS. The first officer claimed his airspeed was at barber pole. A quick cross scan verified high speed and 300 ft above altitude on his instruments. The aircraft was leveled off; the throttles reduced; and the aircraft was given to the first officer to fly. Left air data computer failure was suspected; the captain's alternate air data computer was selected and initially some of the instruments returned to normal. Dispatch and maintenance were contacted; and the appropriate checklists were performed. Based on a consensus; we elected to proceed on to our planned destination pending no further degradations. The purser was briefed for purposes of awareness. A cabin advisory was determined not necessary.

Original NASA ASRS Text

Title: A B767-300 left Air Data Computer failed in flight causing the Captain's airspeed to decrease greatly while his altimeter slowly dropped. The First Officer recognized the error and after ADC ALTN was selected the flight continued in RVSM with a single altitude source.

Narrative: Approximately 7 hours into flight; noticed the throttles advancing significantly. Scanned instruments to see the Captain's altimeter was 300 FT low and the airspeed was decaying through 200 KTS. The aircraft pitched up a few degrees and began to climb. Captain disengaged autopilot and autothrottle and pushed the throttles to the stops. The airspeed continued to drop to 120 KTS. The First Officer claimed his airspeed was at barber pole. A quick cross scan verified high speed and 300 FT above altitude on his instruments. The aircraft was leveled off; the throttles reduced; and the aircraft was given to the First Officer to fly. Left ADC failure was suspected; the Captain's alternate ADC was selected and initially some of the instruments returned to normal. Dispatch and maintenance were contacted; and the appropriate checklists were performed. Based on a consensus; we elected to proceed on to our planned destination pending no further degradations. The purser was briefed for purposes of awareness. A cabin advisory was determined not necessary.

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.

A B767-300 left air data computer failed in flight causing the captain's airspeed to decrease greatly while his altimeter slowly dropped. The first officer recognized the error and after air data computer altn was selected the flight continued in rvsm with a single altitude source.