NTSB Factual Report

HISTORY OF FLIGHT

On August 20, 2006, at 1809 Pacific daylight time, a McDonnell Douglas DC-9-83 (MD-83), N944AS, experienced smoke in the cabin while taxiing to the passenger terminal following a normal landing at Long Beach Airport (Daugherty Field - LGB), Long Beach, California. Alaska Airlines (ASA) operated the airplane as a scheduled commercial passenger flight under the provisions of 14 CFR Part 121. There was minor damage to the airplane as a result of a chaffed wire bundle that had arced and produced smoke in the cabin area. An emergency evacuation was conducted on taxiway K, with the deployment of the L1, R1, over wing, and tail cone exits. There were no injuries incurred by 140 passengers, 2 flight crew, or 3 cabin crew during the ensuing evacuation via the emergency slides. The flight departed Seattle-Tacoma International Airport (SEA), Seattle, Washington, about 1630. Visual meteorological conditions prevailed for the flight, and an instrument flight rules (IFR) flight plan had been filed.

WITNESS STATEMENTS

Cockpit Crew

The captain reported that following a normal landing, he and the first officer heard the sound of circuit beakers opening followed by multiple chimes in the cabin. The emergency interphone call chimes immediately followed the cabin chimes from the "A" flight attendant (FA) notifying them of an electrical smelling smoke that was filling the passenger cabin. He brought the airplane to a stop, set the parking brake, and along with the first officer assessed the situation. The flight crew agreed that an evacuation was necessary and notified LGB tower controllers. The after landing checklist was discontinued, and the engines and APU were shut down. He initiated the evacuation order over the interphone to the "A" FA, who in turn announced it over the PA system.

Cabin Crew

According to the flight attendants, during the taxi to the gate from landing, they heard a call button chime. The FA seated in the "A" position, looked into the cabin, she saw a female passenger turn off her call button and her appearance was not one of panic, so the FA thought it was a mistake. However, two or three more call button chimes immediately followed it. She stood up, looked back in the cabin, and saw a male passenger motioning her to come back into the cabin area. As she got to about mid-cabin, she saw some light smoke. Passengers told the FA that there was smoke emanating from the vent area near their feet. She acknowledged the information and went back to mid-cabin to inform the pilots. She reported that the flight crew did not immediately answer the call but she realized that another FA had already informed them of the situation.

The "A" flight attendant then started knocking on the cockpit door and yelling at the flight crew that there was smoke in the cabin. She then heard the flight crew voices reporting the situation to dispatch and heard the go-ahead for the evacuation. One of the pilots came on the PA system and said 'evacuate,' at which point she opened the L1 door. The slide did not deploy on it's own and she had to pull the red inflation handle to inflate the slide. She then instructed passengers to evacuate through the L1 side. She went to the R1 exit and opened the door; however, the emergency slide did not deploy. She again pulled the red inflation handle, but the slide still did not deploy. At that point, the flight crew had come out of the cockpit, she informed them that the R1 slide would not deploy, and directed passengers towards the L1 slide. The "A" FA tried the red inflation handle again, and this time the R1 slide deployed. She then directed passengers towards the R1 exit as well.

The "C" FA reported that she deployed the tail cone exit with no problems. She stated that there was no smoke or fire. She directed passengers to follow her. Once she reached the platform, she told them how to exit the airplane. At one point there were no passengers coming her way so she went back into the cabin and told the "B" FA to send passengers towards her exit.

AIRCRAFT INFORMATION

The airplane was equipped with a post-delivery Over Wing Heater wiring installation via retrofit (Douglas Service Bulletin MD80-30-78 Rev1 by EM 3010-01006 on November 18, 1998). There were no discrepancies with the installation. The Douglas Standard Wiring Practices (DSWPM) 20-00-06 and 20-10-01 for typical plastic tie strapping techniques were utilized. A review of the ARCTIC write-ups related to the Over Wing Heater System from September 2000, through August 2006, were reviewed with no significant findings.

During the post event airplane inspection, maintenance personnel found the wire bundle damaged in the mid-cargo pit ceiling at station 750 due to chafing and subsequent arcing of the Over Wing Heater Blanket system. They also found that wires in some bundles were damaged to the point of disconnection/separation, while other wire bundles sustained thermal melting to their outer insulation jacket.

Alaska Airlines engineering and Boeing determined that the arcing was likely due to the left and right Over Wing Heater Blanket wiring, wire assembly 7939200 run letter EAB, contacting the edge of the wire bundle bracket that attached to the second inboard lightning hole at station 750 in the mid-cargo pit ceiling on the left side. They also determined that vibration through normal airplane operation allowed the bracket to cut through the wire insulation and then contact was made to the wire conductor, and arcing occurred. The wires are 3-phase power feeders to the left and right Over Wing Heater installations (ref. MD80 WDM 30-11-03 sheet 4). Four twisted pairs and seven single conductor wires were burned and severed while several unrelated near-by bundles in run 7939609-513/route "DDK" sustained damage due to their proximity.

Alaska Airlines inspected their fleet of MD-80's (21 airplanes) and found only one other airplane with a wire bundle discrepancy. "N969AS found the following discrepancy during their inspection 'Insulated wire bundle at STA. 750 from mounting bracket and separated two wire bundles laying on each other at same station - no other defects noted.'"

ADDITIONAL INFORMATION

As a result of this incident, Boeing identified one other operator, American Airlines, that had airplanes of a similar Over Wing Heater Blanket Installation configuration and notified them of the event. Boeing issued /A/ Service Bulletin MD80-30-071 regarding the inspection of the Over Wing Heater Blanket wiring and to adjust the wires according to DMS2109 material per SWP chapter 20. Due to the size of the American Airlines fleet, the SB compliance was identified as the next scheduled maintenance inspection for each airplane. The Safety Board issued Safety Accomplishment RDR-2007-003.

NTSB Probable Cause

The over wing heater blanket wiring installation that had chaffed and arced, which produced an electrical smell in the cabin area.