CHI08IA182

The inadvertent partial inflation of the evacuation slide within the tailcone during takeoff and subsequent binding of the elevator control cables. The partial inflation resulted from the tailcone evacuation slide cover failing to be secured to the floor fittings on the walkway for undetermined reasons.

The incident occurred during a charter flight for a political candidate, his staff, news reporters, and United States Secret Service (USSS) personnel. According to postincident flight crew statements, during the initial climb, the MD-81 airplane’s pitch increased without a corresponding flight control input and exceeded normal limits before the captain was able to regain control. Although the flight crew was able to regain airplane control, a significant restriction in pitch control still remained. Consequently, the flight crew elected to land instead of continuing to the intended destination. Normal pitch control pressures returned during descent, and no further flight control restrictions or anomalies were encountered during the remainder of the flight. Postincident inspection of the airplane indicated that the tailcone evacuation slide had inflated inside the tail area of the airplane as the airplane lifted off. The pitch control restriction was caused by the inflated slide and a subsequently damaged walkway railing that impinged on a set of elevator cables in the tailcone. The investigation further revealed that the slide cover had not been secured to the floor fittings on the walkway before the flight. It could not be determined why the slide’s cover was not secured. In normal circumstances, the cover is secured by the mechanic who installs it and should remain secured until it is removed from the airplane. The airplane’s tailcone is attached to the aft end of the fuselage and can be jettisoned, either from inside or outside the airplane, to provide an opening for an emergency exit. In an evacuation, when the aft bulkhead door is opened, an integrated door mechanism jettisons the tailcone, thus initiating the evacuation slide deployment. The tailcone falls away from the aft fuselage, and an attached lanyard pulls open the evacuation slide cover. This, in turn, rotates the slide pack aft, and a second lanyard triggers the inflation cylinder to inflate the slide. Results of calculations performed using flight data recorder data indicated that, during the incident flight’s takeoff rotation and initial climb, there were inertial loads of sufficient magnitude and duration to allow an unsecured slide cover to rotate open and initiate slide inflation. Postincident testing showed that the slide pack could not have rotated enough to activate its inflation cylinder if the slide container had been properly secured. Further, a properly secured slide cover would have contained the slide if the inflation cylinder had improperly discharged. Postincident testing of the inflation cylinder did not reveal any anomalies that would have resulted in an unintentional discharge of the cylinder for other reasons. The tailcone evacuation slide’s last service check before the incident flight was performed by the airline on June 5, 2008, and no anomalies were noted. That check was a general visual examination of numerous items throughout the cabin, which included inspection of the forward tie-down straps that secure the slide cover to the floor fittings. There would be no reason for the mechanic to touch the straps during this inspection. In addition, on June 20, 2008, the tailcone slide’s inflation bottle pressure was inspected; this inspection did not specifically call for looking at the straps. A review of flights since that service check indicated that the airplane had experienced load magnitudes that were similar to the incident flight; however, the duration of the inertial loads experienced was not long enough to result in slide inflation. Since the last service check, the incident airplane had flown three flight legs with the presidential candidate aboard. Because a presidential candidate was aboard the airplane, the USSS performed security sweeps of the aircraft before flight. Following the incident, an internal USSS investigation revealed that no USSS personnel or USSS support personnel interfered with or altered the aircraft’s hardware or systems related to the tailcone evacuation slide. Shortly after the July 2008 incident, the airline released a maintenance alert bulletin describing the incident and initial findings from the investigation. The airline also released a revision to the service check work card which added specific language calling for airline maintenance personnel to examine the tie-down straps to verify their proper installation and security during reoccurring service checks. Only two previous incidents of inadvertent tailcone evacuation slide inflation in MD-80 series airplanes have been reported (one to the Federal Aviation Administration’s Service Difficulty Reporting system and one to Boeing, which holds the MD-80 type certificate); the causes of each of these inflations could not be definitively determined. No actions were taken.

HISTORY OF FLIGHT On July 7, 2008, at approximately 0845 central daylight time, a McDonnell Douglas MD-81, N804ME, operated as Midwest Airlines Flight 8663, experienced a tailcone evacuation slide inflation shortly after takeoff from Chicago Midway International Airport (KMDW), Chicago, Illinois. Visual meteorological conditions prevailed at the time of the event. The charter flight was operating under the provisions of 14 Code of Federal Regulations (CFR) Part 121 on an instrument flight plan. There were no injuries to the 2 flight crew members, 4 flight attendants, 2 airline representatives, and 43 passengers. The flight was en route to Charlotte-Douglas International Airport (KCLT), Charlotte, North Carolina, when the evacuation slide inflated. The airplane diverted to Lambert-St. Louis International Airport (KSTL), St. Louis, Missouri, and made an uneventful landing at 0930. Flight crew statements indicated that they did not hear the slide inflate in flight, nor did an airline mechanic who was seated in the rear of the airplane. The captain reported that after liftoff the airplane's pitch continued to increase without a corresponding flight control input. The airplane's pitch reached 20-25 degrees nose up before he regained control using control column and stabilizer pitch trim inputs. The flight crew noted that the pitch control pressure required to level the airplane was "higher than normal." After the incident, the flight crew consulted with the airline's maintenance staff, in addition to completing the abnormal checklist procedures. The corrective actions taken by the flight crew were ineffective in reducing or eliminating the restriction in the pitch control system. Consequently, they elected to divert to KSTL instead of continuing to KCLT. The captain noted that normal flight control pressures returned during cruise descent, as the airplane passed through 15,000 feet mean sea level (msl). According to the fight crew, no additional flight control restrictions or anomalies were encountered during the remainder of the flight. PERSONNEL INFORMATION According to Federal Aviation Administration (FAA) records, the captain, age 50, held an airline transport pilot certificate with airplane single and multiengine land ratings. The airplane single-engine land rating was limited to commercial privileges only. He also held a flight instructor certificate with single and multi-engine airplane, and instrument airplane ratings. He was type-rated in the Cessna Citation, Learjet, and McDonnell Douglas DC-9 airplanes. His last aviation medical examination was completed on June 18, 2008, when he was issued a first-class medical certificate with the limitation that he have corrective lenses available for near vision. At the time of the medical examination, the pilot reported having 15,014 hours of flight experience. A search of FAA records showed no accident, incident, enforcement or disciplinary actions. The airline hired the captain on January 3, 1990, to fly variants of the Douglas DC-9, McDonnell Douglas MD-80, and Boeing 717 airplanes. He had flown 850 hours during the previous 12 months, 413 hours during the prior 6 months, 200 hours during the past 90 days, and 60 hours during previous month. He had flown about 0.4 hours during the 24 hour period before the incident flight. His last regulatory checkride was completed on June 9, 2008, in the same make/model as the incident airplane. According to FAA records, the first officer, age 42, held an airline transport pilot certificate with airplane single and multiengine land ratings. The airplane single-engine land rating was limited to commercial privileges only. He also held a flight instructor certificate with single and multi-engine airplane, and instrument airplane ratings. He was type-rated in the McDonnell Douglas DC-9, Gulfstream G-IV, Learjet model 60, Saab-Fairchild model 340, and Boeing models 737, 757, and 767 airplanes. His last aviation medical examination was completed on September 28, 2007, when he was issued a first-class medical certificate with no restrictions or limitations. At the time of the medical examination, the pilot reported having 6,400 hours of flight experience. A search of FAA records showed no accident, incident, enforcement or disciplinary actions. The airline hired the first officer on August 21, 2000, to fly variants of the Douglas DC-9, McDonnell Douglas MD-80, and Boeing 717 airplanes. He had flown 603 hours during the previous 12 months, 282 hours during the prior 6 months, 148 hours during the past 90 days, and 47 hours during previous month. He had flown about 0.4 hours during the 24 hour period before the incident flight. His last regulatory checkride was completed on August 13, 2007, in the same make/model as the incident airplane. AIRCRAFT INFORMATION The MD-81 is a low-wing, twin engine, 14 CFR Part 25 certified transport-category airplane. The MD-81, which the FAA certified in 1981, was derived from earlier DC-9 models. As a result, much of the MD-81's structure and many of its systems, components, and installations are similar to earlier DC-9 models. According to Boeing, the first DC-9 airplane entered service in December 1965; the final DC-9 airplane entered service in October 1982. The MD-80 series, including the MD-81,-82,-83,-87 and -88 were in production through 1999. The DC-9 family of airplanes also includes the McDonnell Douglas MD-90 and Boeing 717 series airplanes. The incident airplane, N804ME, an MD-81, serial number (s/n) 48030, was manufactured in 1981 and was registered to Midwest Airlines on September 23, 1998. The airplane was added to the airline's operating certificate on April 23, 1999. According to airline records, the airplane had accumulated about 46,844 total hours of operation at the time of the incident. The airplane was configured for charter operations and seated a maximum of 82 passengers, in addition to the 2 flight crew and 5 cabin crew members. The incident airplane was equipped with two Pratt & Whitney JT8D-217C turbofan engines, each producing 20,000 lbs of thrust. Airline records indicated that the left engine, s/n 725625, had operated about 28,089 hours since new and 18,447 hours since its last overhaul. The right engine, s/n 718459, had operated about 34,384 hours since new and 8,528 hours since its last overhaul. The airplane's tailcone is attached to the aft end of the fuselage and can be jettisoned to provide an opening for an emergency exit. This exit is accessible from the passenger compartment through the aft bulkhead pressure door and aft accessory compartment. The tailcone can be released either from inside or outside the aircraft. A mechanism is integrated into the aft bulkhead door, that when armed will jettison the tailcone and initiate the evacuation slide deployment. The tailcone falls away from the aft fuselage, and an attached lanyard pulls open the evacuation slide cover. This in turn rotates the slide pack aft and a second lanyard triggers the inflation cylinder which inflates the slide. The tailcone evacuation slide (p/n 100503-117 Rev. J, s/n PAI058) was installed on December 10, 2007. Since its installation, no logbook discrepancies were noted for the evacuation slide. The airline's maintenance program called for a general visual inspection (service check) of the tailcone evacuation slide area every 99 flight hours. The last service check occurred on June 5, 2008, at which time no anomalies were noted with the slide installation. A less frequent operations (phase) check of the inflation cylinder pressure was last completed on June 20, 2008, without any significant findings. METEOROLOGICAL INFORMATION The closest weather station to the incident site was at the departure airport. The Chicago Midway International Airport (KMDW) was equipped with an automated surface observing system (ASOS). At