B747-400
Flight Crew Air Transport Pilot (ATP)
Time Pressure; Human-Machine Interface; Training / Qualification
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Rejected Takeoff; General Maintenance Action
Aircraft; Human Factors
We were cleared for takeoff and at about 50 knots I noticed my airspeed indicator make a fast and significant speed change to about 75 knots then back down to just over 50 knots at which point I called out 'Airspeed.' I thought we might be experiencing severe windshear so I looked over at the Captain's airspeed indicator to confirm and noticed not the same indications. I then looked back at my PFD and realized I had lost my entire Air Data Computer system and announced 'I have lost everything' and then 'Reject' at which point the Captain performed the Rejected Takeoff Procedure. We rejected below 80 knots and did not activate the RTO autobrakes; contacted Tower and exited the runway. I realize our manuals state the Captain has the sole responsibility for the decision to reject a takeoff but during this event I was concerned with the slow or lack of response from the Captain after I first announced that we had an 'airspeed' problem and then a failure of the Air Data Computer system shortly following. Although I was operating as a First Office on this flight I am also a Check Airman and felt prompting the Captain to perform a Rejected Takeoff before reaching 80 knots per our SOP's was the correct and safest course of action.
A B747-400 First Officer commanded a rejected takeoff after 50 knots when he realized that the right air data computer had failed.