Narrative:

The primary runway was closed; so the departure runway in use was the shorter runway which required a 15/15 flap takeoff. IFR conditions and light to moderate rain prevailed in the area. Due to the weather we planned a toga (max thrust); flaps 15/15; using wet takeoff data; with a reduced wet V1 of 131 knots. I was the pilot not flying and the first officer was the pilot flying. I taxied the aircraft to the takeoff position and transferred controls to the first officer. The first officer advanced thrust and called 'set takeoff thrust'. He removed his hand from the throttles and I then guarded the throttles as the auto throttles applied toga thrust. I noted my airspeed trend arrow showing acceleration and the first officer controlling the aircraft track on centerline. Due to the toga thrust the aircraft was accelerating rapidly.I then redirected my attention to the EPR gauges to confirm takeoff thrust set. At that time the first officer made a quick backup call 80 90 knots. I then cross checked my primary airspeed indicator; which indicated 40 knots. At that time I called 'reject' and executed a rejected takeoff. I applied reverse thrust and confirmed max auto brakes. The aircraft came to complete stop about 4000 ft down the 8000 ft runway. The first officer reported the rejected takeoff to ATC and indicated we did not need any assistance and turned on the brake fans. My first officer indicated that by the time I had executed the reject and reversed the acceleration trend to deceleration trend; the aircraft had entered the 100 to 110 knot region based on his airspeed indication. I taxied clear of the runway into the ramp. The brake temperatures remained below 300 degrees.since the decision to perform a rejected takeoff is a difficult one that must be made in a split second decision prior to reaching V1; I thought it might be helpful to explain my decision to reject. One might think a quick crosscheck of the standby airspeed indicator would verify which airspeed indications where valid. However; this is where the A300 may be different from other fleets. The A-300 has immediate action items for 'unreliable airspeed' which is also placarded on the control yoke of the aircraft. The first memory item on that checklist is 'all airspeed indications--- disregard'. This checklist starts out by having you establish airspeed based on pitch; thrust; and aircraft configuration. The checklist continues to try to verify which airspeed indication appears to be most reliable (if possible) based on pitch; thrust tables and ground speed sources such as GPS; ATC. As you can see the unreliable airspeed checklist in the A300 does not take a majority rules approach in determining valid airspeed indication; instead it uses pitch thrust tables and other available ground speed sources to determine which airspeed source is accurate. While it appeared the first officer and standby airspeed source was correct; I did not have the necessary information to validate that. This is why I decided to reject the takeoff. Once back on the ramp; troubleshooting by maintenance discovered a bug or bugs clogging the captain's pitot tube.

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Original NASA ASRS Text

Title: An A300 flight crew rejected the takeoff when a large discrepancy between airspeed indicators was noted around 100K.

Narrative: The primary runway was closed; so the departure runway in use was the shorter runway which required a 15/15 flap takeoff. IFR conditions and light to moderate rain prevailed in the area. Due to the weather we planned a TOGA (Max Thrust); flaps 15/15; using wet takeoff data; with a reduced wet V1 of 131 knots. I was the pilot not flying and the First Officer was the pilot flying. I taxied the aircraft to the takeoff position and transferred controls to the First Officer. The First Officer advanced thrust and called 'set takeoff thrust'. He removed his hand from the throttles and I then guarded the throttles as the auto throttles applied TOGA thrust. I noted my airspeed trend arrow showing acceleration and the First Officer controlling the aircraft track on centerline. Due to the TOGA thrust the aircraft was accelerating rapidly.I then redirected my attention to the EPR gauges to confirm takeoff thrust set. At that time the First Officer made a quick backup call 80 90 knots. I then cross checked my primary airspeed indicator; which indicated 40 knots. At that time I called 'reject' and executed a rejected takeoff. I applied reverse thrust and confirmed Max Auto Brakes. The aircraft came to complete stop about 4000 ft down the 8000 ft runway. The First Officer reported the rejected takeoff to ATC and indicated we did not need any assistance and turned on the brake fans. My First Officer indicated that by the time I had executed the reject and reversed the acceleration trend to deceleration trend; the aircraft had entered the 100 to 110 knot region based on his airspeed indication. I taxied clear of the runway into the ramp. The brake temperatures remained below 300 degrees.Since the decision to perform a rejected takeoff is a difficult one that must be made in a split second decision prior to reaching V1; I thought it might be helpful to explain my decision to reject. One might think a quick crosscheck of the standby airspeed indicator would verify which airspeed indications where valid. However; this is where the A300 may be different from other fleets. The A-300 has immediate action items for 'Unreliable Airspeed' which is also placarded on the control yoke of the aircraft. The first memory item on that checklist is 'All Airspeed Indications--- Disregard'. This checklist starts out by having you establish airspeed based on pitch; thrust; and aircraft configuration. The checklist continues to try to verify which airspeed indication appears to be most reliable (if possible) based on pitch; thrust tables and ground speed sources such as GPS; ATC. As you can see the unreliable airspeed checklist in the A300 does not take a majority rules approach in determining valid airspeed indication; instead it uses pitch thrust tables and other available ground speed sources to determine which airspeed source is accurate. While it appeared the First Officer and standby airspeed source was correct; I did not have the necessary information to validate that. This is why I decided to reject the takeoff. Once back on the ramp; troubleshooting by maintenance discovered a bug or bugs clogging the Captain's pitot tube.

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.