A ZAB supervisor; investigating a TCAS conflict event; discovered a misconception he and other controller's had regarding the limitations of various types of TCAS equipment.
Synopsis
A ZAB supervisor; investigating a TCAS conflict event; discovered a misconception he and other controller's had regarding the limitations of various types of TCAS equipment.
Narrative
I became aware Aircraft X was flying in our airspace to Siver City; New Mexico. I was curious why this aircraft had not responded to a TCAS RA. I asked the pilot to contact me once he was on the ground. He called and I asked him about the event. He informed me his TCAS equipment only provided TA's. The equipment just advises him where the traffic and changes color as it becomes closer. I was not aware of any equipment in the system that did not provide an RA. I thought that's how the system works and why controllers are not to issue any clearances to aircraft responding to a RA. I have talked to numerous people; including people in AOV; since this discussion and no one was aware of this type of TCAS in the system. Air Carrier Y responded to a RA to descend due to the rate of climb of Aircraft X. Aircraft X on another frequency responded to a control instruction to descend back down to FL400. One aircraft responding to a RA; one aircraft responding to a control instruction sounds very similar to a midair in Europe. We are briefing our workforce on this information. If it is the case that TCAS equipment as described are in the system this information needs to be disseminated. There should be a way to recognize these types of equipped aircraft. If TCAS is the failsafe system for this type event then all aircraft should receive RA's to prevent a midair.
Second reporter narrative
At FL400 we began to experience light chop and advised ATC that we would like to climb to FL430. The controller asked us to 'Standby for coordination'. A few moments later; ATC cleared us to climb and maintain FL430. We immediately began the climb. As we were passing through approximately FL410; ATC requested us to immediately descend back down to FL400. We complied with the instructions and began a descent. ATC then advised us of traffic and instructed us to turn forty degrees to the right which we also complied with. During the maneuvers we did acquire and maintain a visual of the conflicting traffic. We also received a TCAS Traffic Alert. Once clear of the conflict we were cleared back up to FL430 and continued on to our destination. I'm not sure of the contributing factors for this close call. I can't speak for ATC and what they saw on their scopes which lead to a clearance we should not have received. I do know that we were not on the same frequency as the other airplane.I know as a pilot that I will be more vigilant in checking my TCAS and visually looking for possible conflicts before accepting a clearance. It is very easy to be trusting of technology and ATC watching over us; but nothing can replace two sets of eyes and two brains in the cockpit looking out for the safety of the aircraft.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.