Date: 201812
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: Citation Excel (C560XL)
Operator: Fractional
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class C ZZZ
ATC / advisory: Tower ZZZ
Second aircraft: B737 Undifferentiated or Other Model
Aircraft component: Traffic Collision Avoidance System (TCAS)
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Time Pressure
Anomaly: Aircraft Equipment Problem Less Severe; Conflict Airborne Conflict
Detector: Automation Air Traffic Control; Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Contributing factors: Company Policy; Aircraft
Primary problem: Aircraft

Narrative: This is being submitted in the interest of enhancing flight safety by treating a failed TCAS as an AOG item; not an MEL 10 day deferrable item as it currently is. The following is an example why. I was the co-Captain SIC Pilot Flying in the right seat on a ferry flight from ZZZ to ZZZ1 in Aircraft X. Enroute to ZZZ1; the TCAS FAIL caution displayed on both PFDs and MFD. It continued to cycle off and on about every 3-4 minutes. ATC gave us a descend via the arrival into ZZZ1. We began the descent and shortly afterwards got a TCAS RA command to 'adjust vertical speed.' We got the command bars to level off; but never the 'clear of conflict' announcement because the TCAS at that moment failed. Not having a visual on this traffic; we reluctantly continued the descent. Approaching the bottom of the STAR; (TCAS still failed); ATC yelled out 'Aircraft X; stop your descent; climb immediately...there is traffic at your 12 o'clock below you.' We never had a visual on this traffic until after taking ATC instructed evasive action. We then saw the VFR [traffic] crossing our flight path below us. We did not violate any assigned altitudes. Just thankful that ATC became our back up collision avoidance because at that time our TCAS was still failed. After landing; we contacted Maintenance and learned that the TCAS system could be deferred for 10 days under an MEL. We questioned the Assistant Chief Pilot (ACP) on why this important safety equipment is being deferred. The procedure is to pull and collar the circuit breaker to disable the entire system. The ACP said he would try to get us another plane to take the passenger trip back to ZZZ. That never happened; so we reluctantly did the passenger trip in Aircraft X. On arrival to ZZZ; Approach Control instructed us to maintain visual separation from a Boeing 737 ahead; cleared us for the visual to RWY XXL and to contact Tower. On final we lost visual with the Boeing. There was no cross reference on the TCAS because it was now MELed with the CB pulled. Now as the Pilot Monitoring; I told the Tower we lost visual with the Boeing and asked how our separation looked? He came back immediately with 'Aircraft X; if you lost visual with the [737]; Go Around!!! Contact [Approach].' We did a go-around; ended up on a right downwind and then told to maintain visual separation from another 737 on final and again cleared for a visual approach to RWY XXL. I realize that instructions to maintain visual contact with an aircraft ahead means just that; maintain outside visual contact. However; it is nice to be able to confirm the visual target with a target on the TCAS screen. I find it ironic that we cannot fly at night with a failed wingtip NAV light but; we can continue to fly for 10 days with a failed Traffic Collision Avoidance System. Deferring maintenance on a TCAS system for 10 days certainly does not support our company philosophy of safety first. 'After' a midair collision is not the time to address our current policy of deferring maintenance on a failed TCAS. As a side note; the ACP made a comment which I have heard before; 'we used to fly [another Citation] around and they never even had TCAS.' My reply to that logic is; 'I remember the day when cars did not have seat belts or airbags.' We have come a long way with safety improvements and technology. Let's use it; not defer it. In the interest of fight safety; a failed TCAS; traffic collision avoidance system should not be an MEL deferrable maintenance item.




Synopsis: CE560 XLS Captain reported the TCAS failed and the MEL permitted the aircraft to fly for 10 days without its operation. The Captain sights two examples where operation of the TCAS system was needed.