Date: 201501
Local time of day: 1201-1800
Location: ATL.Airport, GA
Flight conditions: VMC
Light: Daylight
Aircraft: Medium Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Tower ATL
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Training / Qualification; Situational Awareness; Confusion; Communication Breakdown; Workload
Second reporter function: First Officer; Pilot Not Flying
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Taxiway
Detector: Person Air Traffic Control
When detected: Taxi
Result: Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance
Contributing factors: Human Factors; Procedure
Primary problem: Procedure

Narrative: Landed on runway 28. Cleared to cross runway 27R and join taxiway M by tower controller. Wording was 'Cleared to cross runway 27R and join Mike and keep moving.' We were headed to ramp XX and knew we had to go in XY to get there so we went on com #2 to ramp tower and changed to ground on com #1 when the tower told us to. The ground frequency was busy with outbound traffic and I continued to move as instructed by tower upon reaching XY I cleared Lima taxiway to insure there was no conflicting traffic and turned into ramp XY. Upon entry the ground controller called and ask what we were doing and we replied that we were cleared by the tower to continue moving. He thought we were talking about the ramp tower and we told him it was the tower controller and at this time he told us he did not control the taxiway and that we should have stopped. There was a life flight behind us that may have contributed to the confusion.Nonspecific taxi instructions from the tower and delayed ground controller instructions after clearing the runway.Just stop and wait for instructions even though you are told to keep moving.


Second narrative: We landed on Runway 28. Tower told us to taxi SG; SJ HOLD SHORT 27L @ R7. Tower then told us to monitor tower 119.3. Tower then told us to cross 27L & hold short of 27R @ S. Tower then told us to monitor Tower on 123.85. Tower then told us to cross 27R turn right on Mike 'Keep it rolling' & contact ground 121.75. We turned onto Mike and our ramp was XX. I switched over to ground on 121.75 and the frequency was busy. We were approaching XY. I contacted Ramp Control for clearance to Enter XY. Ramp told us to enter XY; North on DIXIE and enter XX to the gate. We were at intersection MIKE & L10 & turned onto L10 crossing LIMA TO XY. Ground Control finally got to us because he was busy on the radio. Ground Control asked us what we were doing. I told the ground controller that we were cleared into the gate. He told us that the ramp doesn't control the taxiways. We told him that tower told us to turn on to Mike and to keep it rolling. Ground then said that tower doesn't have the authority to give clearance. We should've stopped on Mike at the intersection of L10 to wait for ground to get back to us before we turned on L10 crossing LIMA into XY.


Synopsis: Pilots are told by Tower Controller; 'cross runway; taxi via Mike; keep it rolling; and switch to Ground.' Pilots do as instructed thinking they were cleared to the gate. Ground Control is very busy and calls aircraft asking what they are doing. Pilots respond correctly and then Ground advises them that Tower does not control the taxiways. Pilots thought Tower cleared them to the gate.