Large Transport; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance
Procedure; Human Factors
During very busy radio traffic we were given what we heard was a descent from flight level 300 down to 250. The pilot not flying read back to the controller descend to flight level 2-5-0. The controller read back 2-5-0. However his read back must have been cutoff because apparently he said 2-5-0 knots. We began our descent out of flight level 300 passing through FL290 the controller queried our descent. We told him that we were given a descent to flight level 250. At that time he asked us to stop descent at FL280 and fly to 250 knots. We complied.
Cruise at FL300; 50 miles prior to starting the SNKPT1 arrival. Indy Center cleared us to descend to FL250. I read back 'Descend to Flight Level 250'; and Indy Center responded 'Roger'. The FO then dialed in 250 and began descent. Passing FL289; Indy Center called and asked if we were given descent instructions. I replied 'Affirmative; you cleared us down to FL250.' Indy then told us that we were given instructions to SLOW to 250KIAS. Indy Center then cleared us to level at FL280 and slow to 250KIAS. Indy Center told us 'no problem'; then sent us to next controller and said 'Have a nice day.'At this point Indy Center was beginning to vector everyone off the arrival and I believe their initial transmission got stepped on by another aircraft in all the confusion.We were operating into Indianapolis from the East; using the SNKPT1 arrival. For the last several months Indianapolis Center and Approach have been struggling to make their arrivals happen smoothly 'as published'. From approximately 100 miles prior to starting the ODP arrivals into Indy until the final vector to the localizer; the arrivals are a chaotic mess of constantly assigned vectors; speed changes; and altitude changes - many times going against the published parameters requiring more queries to ATC. Add a few similar call signs and stepped on radio calls and the whole situation is a flight violation waiting to happen.
An air carrier flight crew reported receiving a descent clearance to FL250 while on the SNKPT1 Arrival to IND; but the Controller meant to issue a speed of 250.