Air carrier pilots reported an airspeed indicator; that was previously reported as malfunctioning; began to display error flags and caused a rejected takeoff.
Synopsis
Air carrier pilots reported an airspeed indicator; that was previously reported as malfunctioning; began to display error flags and caused a rejected takeoff.
Narrative
I rejected the take-off at the end of the low-speed regime; due to IAS Disagree flags. During preflight in ZZZ; the #2 Mach Airspeed Warning test did not test satisfactorily. After consultation with Maintenance Control; this was deferred. Afterwards; we also noticed both the IAS Disagree flag and the VSI inop flag on both flight directors; which seemed unusual. The IAS Disagree flags disappeared within a couple minutes after Maintenance Control's direction of the cycling of the #2 Mach Speed circuit breaker. The VSI flags disappeared a couple minutes later. Remainder of preflight; start; taxi was uneventful; neither flag was seen again; until the take-off roll. As pilot monitoring; First Officer added the flight director flags into his scan even more; during the take-off roll. Immediately upon annunciation at 85 knots; he announced the IAS disagree flag. I saw the same on my flight director. (At the time; First Officer silently noted a 5-6kt discrepancy between Capt and F/O indicators.). I announced the reject; and we accomplished every single reject step calmly and expeditiously. The 100 knots call was not made; as throttles were retarded beforehand. Initial RTO (Rejected Takeoff) brake application was without delay; at 105kts. I exited at [Taxiway] 1; and parked on Taxiway 2. As no other aircraft had called for take-off clearance; Ground allowed us to remain on Taxiway 2 for about 30 minutes. We completed Rejected Takeoff checklist per QRC/FM (Flight Manual). First Officer had included a request for fire trucks in his initial reject call to Tower; and they arrived within minutes. First Officer monitored their safety checks; while I alerted flight attendants and re-confirmed that Evac was not planned. I ACARS'd Dispatch; made several PA explanations to passengers; and notified Ops of likely gate return. After a 5-10 minute initial inspection; fire crew saw outboard brake temperatures decreasing. As inboard brake temperatures remained above 400F; they recommended a 10 minute delay before taxiing. We were not in caution or warning section of Brake Cooling charts. After 10 minutes; with confirmation of no smoke; both fire crew and pilots were comfortable with taxi to gate; with fire crew following. Taxi was uneventful; with parking brake released at gate as soon as chocks were in. ZZZ Ops did a very helpful job of calling in the offsite contract Maintenance when they saw us abort. After 10 minutes of Maintenance Control discussion; fire crew briefs; several PA announcements by me; and coordination with CSR; passengers were egressed; and plane released to Contract Maintenance. During preflight and postflight inspections no discrepancies noted with any pitot/static ports or equipment. Had the First Officer not noticed the IAS Disagree flag until 3 seconds later; we would have been in the high speed regime. We had the radar on during take-off in the rain; as we were expecting to deviate around storms; in IMC; after take-off. He did a terrific job.
Second reporter narrative
During ground operations on an early takeoff from ZZZ to ZZZ1; the Mach Airspeed clacker #2 on the overhead panel did not test properly. MX (Maintenance) was called and they were unable to fix it. We also noticed an IAS DISAGREE during preflight; and the CA airspeed was 5 kts higher than the FO side. After the Mach clacker was deferred by Maintenance Control and contract Maintenance; we continued with normal ground operations and the IAS DISAGREE EXTINGUISHED and airspeed was normal. We talked about it during the brief and mentioned that there might be a bigger problem with the jet than just the Mach clacker. We had no abnormal indications; and a good Maintenance Release prior to push. Taxi was uneventful. On takeoff; I was very intent on watching the airspeed tapes. Passing through 70-80 Kias; I thought I started to see a 5 kt difference between the airspeed tapes; but wasn't positive due to the small split and the tapes moving quickly. At around 85 KIAS the IAS DISAGREE illuminated on both PFDs (Primary Flight Displays). I called it out immediately and the reject was initiated below 100 knots - probably 95 kias for pulling the throttles to idle (no 100 knot call was made). The speed topped out at 105-110 kias before we decelerated. The reject was uneventful and we cleared the runway. Passengers remained seated; and we opted to call for fire trucks. We were right on the edge of the normal/caution zone for brake heating. We coordinated with Ops; Ground; and Fire for brake checks; taxi back; etc. we had the fire dept escort us to the gate. Taxi back and shutdown was uneventful.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.