Date: 201509
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: IMC
Light: Daylight
Aircraft: MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pneumatic Ducting
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Commercial
Human factors: Workload; Troubleshooting; Training / Qualification; Communication Breakdown
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Attendant; Person Passenger
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Diverted; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Landed in Emergency Condition; Flight Crew Took Evasive Action; General Maintenance Action
Contributing factors: Aircraft; Procedure; Weather
Primary problem: Aircraft

Narrative: FL310 we encountered Cirrus with visible ice crystals under the wipers. Anti-ice was selected on; engine and wing. The cabin temperature had been stable to that point. Not long after selecting anti ice we were called that it was getting warm in the back of the cabin. The cabin temp was adjusted lower. Probably 7-10 minutes elapsed and we were called to cool off the back more as it was too warm in the aft cabin. The temperature was adjusted again. Then we got a call in cirrus with anti-icing on. The flight attendants notified us of a hot area on the floor from [row] 22 to 27 and that there was a lady in one of the 'A' seats forward of the back galley that was in tears as the floor was so hot it was burning her feet through her shoes; along with a hot burning smell similar to a clothing iron burning on a shirt; electrical; and paper burning smell. Several conversations passed back and forth. As heat increased on the floor the passengers were moved from those seats to other vacant seats. Both air conditioning systems were selected full cold. There was a commuting pilot in the cabin that confirmed to the flight attendants that the heat was not normal and they advised us of that. There were no abnormal cockpit indications. No Cargo fire indication or anything showing any system anomalies. No odor in the cockpit. The recirculation fan; and galley power were turned off. The odor intensified; a ground service individual checked the floor and determined temp was increasing. No cargo fire indication. Concurrently we started the smoke/fire/fumes checklist; [notified ATC of the situation]; and diverted. We did a left descending 360 and landed. We were in icing conditions in the descent until lower 20's as I remember and Anti ice was procedurally turned off. We turned into a wide high speed exit area and parked the aircraft. ARFF checked the aircraft after we came to a stop and found no active/increasing heat on the exterior or in the cargo compartments. According to the flight attendants the temperature started to decrease just prior to landing. We then taxied to the gate. Station Chief met us at the gate. On gate arrival the area on the floor showed higher temp than the surrounding area; but had cooled substantially from its peak airborne. As passengers exited the aircraft another air carrier MD-80 [pilot] that was a passenger stopped and told us we did have a problem; but didn't interrupt the flight attendants as he could tell we were diverting and knew we were busy. The entire elapsed time from the call of excess floor temp to the descent and touch down was not very long and quite busy.


Second narrative: After inspecting the aircraft; maintenance found an anti-ice duct seal had separated and was the cause of the hot floor.While this suggestion would not avoid a recurrence of this event; I feel that the checklist could be improved upon. The MD-80 QRH Smoke/Fire/Fumes checklist is a lengthy but relatively straight-forward checklist. That being said; if landing is imminent; it advises you to reference Operational Considerations; time permitting. The Operational Considerations list is contained within the Smoke/Fire/Fumes checklist at the end but since it is such a long checklist it is actually 8 pages away. I feel that [action] would become clearer if it mentioned a page number for the Operational Considerations list. Likewise; the last step of the Operational Considerations list mentions referencing the Ground Evacuation Checklist. This is a very familiar checklist for all pilots but I still feel it would be worth noting that it is on the Back Cover to help clarify and expedite the process for aircrew running it.


Synopsis: A MD-80 developed a dangerously overheated cabin floor between rows 22 to 27 with anti-ice ON. The flight diverted where Maintenance discovered an anti-ice duct seal separation.