Date: 201502
Local time of day: 1201-1800
Location: C90.TRACON, IL
Flight conditions: VMC
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ORD
ATC / advisory: TRACON C90
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Communication Breakdown
Second reporter function: First Officer; Pilot Flying
Anomaly: Inflight Event / Encounter Other / Unknown
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance
Contributing factors: Procedure
Primary problem: Procedure

Narrative: Approach control cleared us for the approach (Rwy 27L); caution wake turbulence following a Boeing 757; maintain 180 knots until TAFFS; contact tower control at TAFFS. We then switched the frequency to tower; and continued the approach. Tower called us prior to TAFFS and told us to go back to approach control. We returned to approach control and he told us to slow to 170 knots until TAFFS and we should have stayed with him till we got closer to TAFFS so we would have heard him when he wanted us to slow an additional 10 knots. If Pilots are told to contact tower and call at a certain fix inbound; then we have to switch frequency at some point. The approach controller assumed I would stay with him longer than I did. However; when he called for us we were no longer with him; because he did not ask for us to stay with him.


Second narrative: As the pilot flying during a visual approach I was 'heads up' and did not notice that the captain immediately switched to tower from the approach frequency. Moments later; tower transmitted a call to us asking if we were on and asking us to switch back to approach control. Chicago approach when contacted had a 10 knot speed change and explained the significance of the phrase 'contact tower at...'No significant aircraft separation was an issue; as the speed change seemed to be for wake turbulence reasons; and no further communications about the incident came from approach or tower; other than approach grumbling something about '...the third one today...'In a debrief of the incident the captain said he has always switched immediately to tower when given that instruction; and we discussed what Chicago approach expects him to do.In our debrief we discussed the fact that Chicago is one of a very few places that uses that procedure for transferring to tower. Also we discussed that depending on the weather conditions the approach controller will give 2 different clearances:'..contact tower at...' meaning stay on approach and switch to tower at the OM.'...contact tower now...' which when complied with TOWER will acknowledge and then say 'report at...' OM.The different clearances depending on weather conditions for this specific airport lead to an expectation bias on the part of the captain. As the pilot flying I should have been monitoring the radio selection.


Synopsis: An Air Carrier flight crew on approach to Runway 27L at ORD is issued a 'contact Tower at the TAFFS intersection' clearance. The Captain switches to Tower immediately after and is told by ORD Tower to go back to Approach Controller. C90 Controller reminds them of the importance of not switching frequencies too soon.