Date: 201502
Local time of day: 1801-2400
Location: IAH.Airport, TX
Flight conditions: VMC
Light: Night
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 IAH
Second aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Reporter organization: Government
Reporter function: Ground
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown
Second reporter function: Pilot Not Flying; First Officer
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: Taxi
Result: Flight Crew Took Evasive Action
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: Aircraft X called asking to taxi to his gate on the south ramp.  Aircraft Y was told to push tail east do not block taxiway WB.  I instructed Aircraft X to taxi via taxiway NA and NR and hold short taxiway WB.  I went back to Aircraft X and told him behind Aircraft Y pushing [from] gate to continue his taxi to spot 3 and then contact ramp.  I noticed Aircraft X at spot 3 when Aircraft Y called and asked if the Aircraft X was supposed to have given way because they had to slam on their brakes and flight attendants were instructed to take their seats.  Aircraft Y asked me what his callsign was because he was going to call his company.  I told Aircraft Y his callsign at that time I informed the supervisor of the event taken place.  Gate A29 and A30 are not visible from the tower nor do the aircraft show up on the ASDE-X when pushing from the gate do they show up sometimes when the push is complete.If a camera was hung close to the gates and a monitor was at the GC1 position so they could see the aircraft push and possibly have the city paint another spot on the ramp just for those 2 gates to push back onto.


Second narrative: While taxiing down NR we were issued to hold short WB.  We were then cleared to taxi behind Aircraft Y who was pushing from the A terminal.  Our understanding was that Aircraft Y was to remain clear of taxiway WB and we were to remain clear of them.  We slowed as we approached their aircraft; Aircraft Y rampers were not pushing the aircraft so we contacted ramp and were cleared into the ramp via RC.Threats would include unfamiliarity with Aircraft Y's push procedure from the A gates into the taxi way as well as ATC clearing a push but with our understanding of them to remain clear of our taxiway.  Also with Aircraft Y not appearing to push we made the assumption they were not under tow at the immediate moment allowing us to move behind them.While this is the first time I have met Aircraft Y in push from those gates; I feel a hotspot or note regarding Aircraft Y's push procedures onto one of the most active taxiways at IAH; would be a good start to increase crew's awareness of the unusual and sometimes confusing procedure.


Synopsis: IAH Controller reports of taxi instructions given to two aircraft. One aircraft doesn't follow instructions and causes the other aircraft to slam on the brakes. Pilot of violating aircraft reports that they thought they were clear to taxi behind the other aircraft because it wasn't moving.