Medium Large Transport; Low Wing; 2 Turbojet Eng
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 104
Workload; Confusion; Human-Machine Interface
Deviation - Altitude Overshoot; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance
Flight Crew Returned To Clearance
Human Factors; Procedure
On arrival into IAH we were assigned to descend via the LINKK1 RNAV arrival and subsequently cleared the ILS Runway 27 approach. We selected 1;500 ft. in the MCP to comply with the restriction at the FAF. Over GILLL intersection ATC asked me to maintain present speed of 240kts. I speed intervened to comply with the clearance as the aircraft would have started to slow to 210kts over RDFSH. The aircraft came out of VNAV Path into VNAV Speed and descended below the path. I went into vertical speed mode and selected a descent rate to approximate the path using the VDI (Vertical Descent Indicator) scale. My expectation was that I was going to be given a 'resume normal speed' clearance fairly quickly as there was not any traffic behind us as was apparent to me. Unfortunately; we were not given the clearance and I was slow to stop the descent using vertical speed mode over SYYKO intersection and elected to disengage the autopilot and hand flew the aircraft to stop the descent in a more expeditious manner. We climbed back to 3;000 ft. and resumed the profile uneventfully.
Captain reported failing to level at assigned altitude due to compliance with ATC's requested speed increase.