The apparent failure of all or part of one ILS signal during PRM approaches at ATL; coupled with a failure of the PRM monitor to provide appropriate clearances for the aircraft involved; forced the Local Controller to attempt to separate three sequential aircraft; two of whom were subsequently involved in a TCAS RA event.
Synopsis
The apparent failure of all or part of one ILS signal during PRM approaches at ATL; coupled with a failure of the PRM monitor to provide appropriate clearances for the aircraft involved; forced the Local Controller to attempt to separate three sequential aircraft; two of whom were subsequently involved in a TCAS RA event.
Narrative
We had just established ourselves on the localizer course inbound on the ILS PRM approach to Runway 10 into ATL after a late final vector and were just intercepting the glide slope; when the final monitor for our runway came on the radio. He canceled our approach clearance and told us to maintain 3;000 FT MSL (which at that point was still below us). About the same time; we received a TCAS TA temporarily and correctly assumed that an aircraft had drifted through the other course and we would be shortly cleared for the approach again. After approximately 30 seconds the Approach Controller asked if we could accept the approach clearance from our present position (one dot above glide slope and on the localizer) and we replied that we could. We were cleared for the approach a second time and wasted no time returning to the glide slope.At approximately 2;800 FT; we again heard the final monitor begin to issue us breakout instructions and; almost concurrently; we received another TCAS TA which then quickly changed to an RA. The Controller's instructions (right turn heading 180; climb and maintain 3;500 MSL) contradicted the TCAS RA (which began with a climb and as we descended below the traffic; turned into a descend command); so I took a second to verify our position/options and chose a descending turn to the right until the TCAS RA was complete and then immediately began a climb to 3;500 FT on a heading of 180 degrees. The other aircraft must have been slowly drifting towards us; because we estimated the other aircraft to be within 1;000 FT laterally and at our altitude at the time of the RA. We were given vectors for another approach; briefed the Flight Attendant shortly after the incident; and landed safely with no further problems.Some threats present in this situation were high workload (pilots and controllers); weather conditions; uncertain/hesitant ATC instructions; and conflicting instructions. The undesirable state (close proximity to another aircraft) was created; in part; due to these threats.
Second reporter narrative
The beginning of the scenario was what I believe to be a glide slope only failure on Runway 10. I say this reservedly because I received conflicting reports. One aircraft also said they were also unable to track the localizer.The first aircraft said he lost the glide slope well outside the TCP [(ATC) Transfer Control Point]. I waited a few seconds [in anticipation of action by the PRM Monitor; but] after the Monitor did nothing; I instructed the aircraft to track the localizer and maintain 3;000 FT. I felt safety would have been compromised if I had not done something; so I turned the aircraft to a heading of 180 degrees; then made an immediate call to PRM MON A. Before I was able to speak; PRM MON A acknowledged control of the aircraft. This should not have been necessary because I never had control in the first place; given the aircraft was outside the TCP when the go around was initiated. PRM MON A turned the first aircraft further right to 240 and climbed them to 4;000 FT.A second aircraft had the same problem; however also stated they were unable to track the localizer. They began to drift north (winds out of the south); PRM MON A noticed this and turned aircraft #2 to a 150 heading and climbed them to 4;000 FT as well. This created the first conflict in this scenario. Once PRM MON A noticed the conflict she climbed the first aircraft to 5;000 FT.Around this time PRM MON A completely stopped working. When a third aircraft checked in I waited a few moments to see if the Monitor was going to issue instructions. She did not; so I instructed them to maintain 3;000 FT and track the localizer. My Supervisor started coordinating with [Approach] directly so I could vector the aircraft and hand them off appropriately.I asked if I should coordinate any further with PRM MON A and was told no.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.