Date: 201602
Local time of day: 0601-1200
Location: ZDV.ARTCC, CO
Flight conditions: VMC
Light: Daylight
Aircraft: Embraer Jet Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class A ZDV
ATC / advisory: Center ZDV
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Distraction; Situational Awareness
Anomaly: ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met; Deviation - Speed All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Flight Deck / Cabin / Aircraft Event Passenger Misconduct
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: I was speaking to the flight attendants regarding disruptive passengers; which ultimately resulted in us having to call law enforcement to meet the aircraft at the gate after arrival.  There was no specific physical threat; so we did not declare an emergency; but I had to split my attention between monitoring ATC and speaking to the flight attendants.  The First Officer (FO) was Pilot Flying and we had just begun the descent on the MOLTN arrival.  Per SOP I continued to monitor ATC; and I heard the new clearance issued to fly direct WOOKY; then TISHNR arrival to DEN.  This clearance was very late; as we were only approximately 4NM from WOOKY and the next fix would now be different; as would the crossing altitudes.  I told the Flight Attendant (FA) that we would have Ground Security and Law Enforcement Officers (LEOs) meet us at the gate and that I had to go.  I called 'back on one' and saw the FO attempting to get the new arrival entered into the FMS.  We were at about FL300 at 200KIAS in a very shallow descent.  It took me a moment to assess the situation; as my moving map showed WOOKY ahead but we were not moving towards it; and when the FO activated direct WOOKY in the FMS; we were not proceeding in that direction and a discontinuity appeared below with the remainder of the STAR disappearing.  I couldn't immediately determine whether it was an entry error or FMS malfunction; so I asked ATC for a heading to WOOKY while we reprogrammed the FMS.  He told us to turn 5 degrees left.  Then he told us to go direct to RAMMS; which gave us enough time to properly program the remainder of the STAR.  Once on our route; I asked the FO whether he set 200 KIAS; or if the FMS commanded that.  He said that he couldn't remember.  I returned to FMS speeds since as far as I could tell we were supposed to be at 250 KIAS as per the STAR.  At that moment; ATC asked if we were going to make it down.  We were still in a shallow descent; so I steepened it; deployed the speedbrakes; and said yes.  He gave us a new frequency.  I checked in and realized that we could not make the next crossing altitude.  I informed ATC and he told us to descend and maintain 13;000 feet.  We complied and I asked if he needed the speed restrictions but he said to just worry about the altitude first.  When we reached 13;000 feet; he cleared us to 11;000 feet; then gave us a last minute runway change to 17R.  We entered the approach in the FMS; then he told us to turn to intercept the 17R localizer.  When he gave us that clearance; the localizer course was already behind us.  Realizing his error; ATC asked us if we had the airport in sight.  We replied that we did; made the right turn to intercept the final approach course and flew the remainder of the approach in green needles to a safe landing.I had to address this cabin emergency and leave the FO at a time when DEN ATC decided to give multiple last minute instructions.  Even if I were able to devote my full attention to Pilot Monitoring duties; this would have been a challenging clearance to accept with so little time.  The FO was effectively single pilot momentarily; and he was overwhelmed with these last minute changes.  Assigning a different STAR at that point changed the entire descent planning of the aircraft. So we needed a few moments to even determine whether it was possible at that point to make all the STAR restrictions.  From the time I got off the interphone with the FAs we received several route; altitude; speed and frequency changes; many at the same time.  At the end of the descent to get a last minute approach change and a vector in the wrong direction just added to an already too high workload situation.The situation in the cabin needed to be addressed; as I had to assess whether we had a cabin emergency or not.  Per SOP I monitored ATC; but I believe that DEN ATC's last minute instructions are a hazard even in normal operations.  It can be a challenge to program a new arrival in the [this aircraft]; and we are required afterward to verify that we can make all published restrictions.  This kind of short notice change greatly increases the probability of route errors and altitude or speed deviations in my opinion.




Synopsis: An Embraer RJ Captain reported difficulty complying with last minute ATC changes to route; altitude; and speeds while at the same time dealing with a passenger issue in the cabin.