Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Communication Breakdown; Confusion; Training / Qualification; Troubleshooting
Aircraft Equipment Problem Critical
Flight Crew Regained Aircraft Control; Flight Crew Overcame Equipment Problem; General Maintenance Action
Procedure; Aircraft; Human Factors
I would like to bring to your attention an unsafe condition that I think requires an airworthiness directive and updates to the AMM; FIM; AFM; MEL; FCOM and OM. I bring this up because of what I observed with the brake system on a CRJ-700 aircraft. The sequence of events was as follows: Upon landing at ZZZ the Pilot Flying (PF) the First Officer (FO) determined that the aircraft veered to the right due to inadequate braking on the left side. Brake Temperature Monitoring System (BTMS) and a post flight tactile touch check of the brakes indicated that there was no energy absorption to the left inboard brake and the others had above normal energy absorption; particularly the left outboard brake. A Logbook entry was made and the Corrective Action was to safety wire the hydraulic coupling and perform an ops check of the brakes. During the Ops check the mechanic demonstrated to me that the left inboard brake was actuating. Upon landing in ZZZ; the aircraft veered to the right as before except this time the Asymmetry/Loss of Braking immediate action and QRH items were performed. Braking returned to normal and an appropriate Logbook entry was made. I had landed this aircraft on March 2015 but braking effort was light so I did not notice the asymmetry. I did at that time however; observe zero energy absorption on the left inboard brake and made an appropriate Logbook entry which I feel was misdiagnosed as a BTMS malfunction and deferral.The problem; once identified by Maintenance was that the left inboard anti-skid transducer was binding. This resulted in a false locked wheel signal to the Anti-Skid Control Unit (ASCU) which in turn; and by design; completely disabled the left inboard brake upon wheel spin up. This CRJ-700 was operating under this unsafe condition for at least the weeks of the Logbook history that I reviewed. The Logbook records a history of discrepancies with the left inboard brake; the anti-skid system and the left inboard BTMS. Discrepancies include: anti-skid faults; aircraft veering to the right during braking on landing roll; left inboard BTMS of 00 degrees with accompanied brakes 'cold to the touch' on post flight inspection and left outboard brake significantly hotter than normal. Upon review of the respective Logbook Corrective Actions; I can see that there is a lack of awareness of this unsafe condition for all corrective actions except the last one that addressed the Asymmetry/Loss of Braking Immediate Action/QRH items. That entry directed them right to the problem and required a Functional Check Flight (FCF).To avoid recurrences of prolonged unsafe conditions like this one; it is essential that brake temperature related indications always be viewed from an energy absorption perspective. If a brake is not getting up to operating temperature during use; then it is not operating properly. Just as turbine or exhaust temperature is a conclusive indicator of proper engine function so is brake temperature an indication of proper brake function. To avoid this unsafe condition in the future there are two things that the above mentioned publications must illustrate clearly to all concerned: First; after landing; a BTMS reading of 00 or significantly uneven BTMS readings on the same landing gear require further inspection. If this is observed then the post flight inspection must include a tactile/proximate check of the respective brakes (use caution).Second; if the brake with a BTMS reading of 00 is cold to the touch that's a huge red flag! The MEL should not allow deferral of a BTMS that reads 00 when post flight inspection reveals the respective brake is cold to the touch after landing. NO NO NO! The proper way to address this unsafe condition is to perform an Ops check of the brakes. If a mechanical problem can be conclusively identified and corrected then the discrepancy can be cleared. If not; then the discrepancy should be deemed anti-skid related; be troubleshot and an FCF must be accomplished with max effort braking on landing to verify that braking is symmetric and that all brakes reach an appropriate operating temperature. As a troubleshooting tool; a long distance taxi test with the anti-skid 'Off' and reference to the BTMS might further demonstrate energy absorption and BTMS functionality. If a reasonable brake functionality is demonstrated by this test; then the discrepancy is most likely anti-skid related. Unsafe condition.
A Captain reports about a CRJ-700 aircraft with a history of discrepancies involving Anti-Skid System faults and the aircraft veering to the right during braking on landing roll that were misdiagnosed until the Asymmetry/Loss of Braking Immediate Action/QRH items were addressed in a Logbook write-up. Maintenance then found the left MLG inboard Anti-Skid Transducer had been binding resulting in a false-locked wheel signal to the Anti-Skid Control Unit (ASCU).