A B747 captain rejected a takeoff at about 100 KTS because he detected a difference between his and ...

Narrative:

Takeoff was aborted at approximately 100 KTS due to discrepancies between my indicated airspeed and the first officer's indicated airspeed. [We] accomplished all applicable sops and relevant irregular procedures. After the first officer had applied takeoff thrust I briefly monitored the engine parameters (especially egt) for normal range and function. Then I briefly checked my airspeed indicator and the first officer's airspeed indicators for normal acceleration. My indicator appeared normal and showed smooth acceleration. When I glanced at the first officer's indicator it appeared to indicate less speed and was somewhat erratic. I thought this may be due to the right crosswind conditions. At 80 KTS I looked over at the first officer's indicator to verify. It was fluctuating and indicating something other than 80 KTS. I felt the safest thing to do was to reject the takeoff and sort out the issue on the ground rather than in the air. I did not make the 80 KTS call but announced and executed the abort maneuver. I believe my intentions and actions are in accord with the training I have received at my airline with regard to when and how to abort a takeoff.

Original NASA ASRS Text

Title: A B747 Captain rejected a takeoff at about 100 KTS because he detected a difference between his and the First Officer's airspeed. An air data computer was changed upon return to the gate.

Narrative: Takeoff was aborted at approximately 100 KTS due to discrepancies between my indicated airspeed and the First Officer's indicated airspeed. [We] accomplished all applicable SOPS and relevant irregular procedures. After the First Officer had applied takeoff thrust I briefly monitored the engine parameters (especially EGT) for normal range and function. Then I briefly checked my airspeed indicator and the First Officer's airspeed indicators for normal acceleration. My indicator appeared normal and showed smooth acceleration. When I glanced at the First Officer's indicator it appeared to indicate less speed and was somewhat erratic. I thought this may be due to the right crosswind conditions. At 80 KTS I looked over at the First Officer's indicator to verify. It was fluctuating and indicating something other than 80 KTS. I felt the safest thing to do was to reject the takeoff and sort out the issue on the ground rather than in the air. I did not make the 80 KTS call but announced and executed the abort maneuver. I believe my intentions and actions are in accord with the training I have received at my airline with regard to when and how to abort a takeoff.

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	899021
Time
Date	201007
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B747-400
Operating Under FAR Part	Part 121
Flight Phase	Takeoff
Component
Aircraft Component	Air Data Computer
Person 1
Function	Captain Pilot Not Flying
Experience	Flight Crew Last 90 Days 80 Flight Crew Total 22000 Flight Crew Type 8000
Person 2
Function	Relief Pilot
Experience	Flight Crew Last 90 Days 189 Flight Crew Total 14150 Flight Crew Type 5723
Events
Anomaly	Aircraft Equipment Problem Critical

A B747 captain rejected a takeoff at about 100 KTS because he detected a difference between his and the first officer's airspeed. An air data computer was changed upon return to the gate.