B737 Next Generation Undifferentiated
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 214
Communication Breakdown; Workload; Confusion
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Human Factors; Procedure
On the DIRTY 3 Arrival; passing HAARY; Approach asked how the turbulence was.  When we said it was ok; ATC asked if we were deviating without advising ATC of a deviation. After we said no; we looked at our course map and advised we were on course. The phase of flight did not afford time to expand on the discrepancy because we were switched to another Approach frequency. Our flight instruments showed no anomalies. Upon arrival into Atlanta; while monitoring the PRM Tower frequency;  monitoring frequency Tower asked us our airspeed. Shortly before switching from Approach to Tower; Approach told us to reduce to 180 until the FAF.  So; we were in the process of slowing our airspeed when PRM monitor frequency asked our airspeed.  After I responded on PRM frequency that we were reducing airspeed; ATC Tower frequency asked us if we were on the main frequency. I replied 'Yes; and also monitoring 132.55.'This is the fourth or fifth time I have had a radio check; confirm airspeed; and confirm altitude on the PRM monitoring frequency. My understanding; and I might be wrong; of the PRM frequency is that it is for traffic alert and notice of deviations of an urgent and safety nature. We already diverted before this; so this just added to our complex day. My suggestion is to communicate on PRM frequency for immediate safety concerns. I don't understand why Main Tower frequency doesn't communicate such concerns.
Since it was not relayed to us the level of the discrepancy seen by ATC; we are unsure of the severity of their perceived deviation. If the size of the deviation was revealed as substantial or consistent; the FMC would have been written up. Because it was a one time event in an aircraft we had flown for multiple hours; we attributed it to a glitch.
A B737NG crew on approach to ATL reported communication issues and confusion with ATC inquires.