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On December 15, 2008, at 2239 central standard time (all times cst), a Bombardier CL-600-2C10 (CRJ-700), N511MJ, operated by Mesa Airlines, Inc, dba Air Shuttle Flight 7164, sustained minor damage during a landing gear emergency at Chicago O'Hare International Airport (ORD). The Title 14 Code of Federal Regulations Part 121 passenger flight had departed ORD about 2130 en route to South Bend Regional Airport (SBN), South Bend, Indiana. During the landing approach to SBN, the landing gear "Gear Disagree" warning message appeared. The flight crew performed the appropriate emergency checklists without success. The flight returned to ORD where an emergency landing was conducted on runway 28 (13,000 feet by 150 feet, asphalt). The airplane landed on a fully extended nose and right main landing gear, but the left main landing gear was not extended. The airplane skidded to a stop with the left wing supported by the wing flaps and the outboard leading edge slats. The 2 pilots, 2 flight attendants, and 28 passengers were not injured, and they departed the airplane through the main cabin door. Night visual meteorological conditions prevailed at the time of the incident. An instrument flight rules (IFR) flight plan was filed.
The pilot reported that he was able to keep the left wing up for only a few seconds before it contacted the runway. He maintained runway centerline during the landing and brought the airplane to a complete stop on the runway. The pilot reported that the flight attendants evacuated the passengers, and the emergency responders were on the scene immediately to secure the airplane and evacuate the passengers.
The pilot was an airline transport pilot with single-engine, multi-engine, and instrument airplane ratings. He was a certified flight instructor in single-engine and multi-engine airplanes, and an airplane instrument instructor. He held a first-class medical certificate that was issued on June 23, 2008. He reported a total of 3,100 flight hours with 570 hours in the Bombardier CL-600-2C10.
The co-pilot was a commercial pilot with single-engine, multi-engine, and instrument airplane ratings. He was a certified flight instructor in single-engine and multi-engine airplanes, and an airplane instrument instructor. He reported a total of 1,450 flight hours with 210 hours in the Bombardier CL-600-2C10.
The airplane was a Bombardier CL-600-2C10, serial number 10104, equipped with two General Electric CF34 engines. The left engine was a CF34-8C1 and the right was a CF34-8C5B. The airplane seated 64 and had a maximum gross weight of 75,250 pounds. The last continuous airworthiness inspection was conducted on December 13, 2008. The airplane had a total time of 14,596 hours.
At 2253, the surface weather observation at ORD was: Wind 360 at 10 knots, visibility 10 miles, few clouds at 2,100 feet, sky broken at 20,000 feet, temperature -12 degrees Celsius (C), dew point -17 degrees C, altimeter 30.59 inches of Mercury.
The cockpit voice recorder (CVR) was sent to the National Transportation Safety Board’s (NTSB) Vehicle Recorder Division Audio Laboratory for download. The CVR recorded 30 minutes of cockpit voice communications. A summary of key events recorded on the CVR follows:
At 22:08:58 - Start of recording.
At 22:09:18 - Captain declared an emergency.
At 22:09:42 - Captain took the flight controls.
At 22:13:37 - Captain briefed flight attendants. Aircrew discussed evacuation door and safest location for passengers during landing.
At 22:16:25 - Lead flight attendant briefed passengers on emergency. Crew continued with emergency checklist and secured loose equipment in the cockpit.
At 22:18:27 - First officer reviewed entire checklist for familiarity.
At 22:20:16 - Captain directed first officer to double-check the completed checklist items.
At 22:20:59 - Discussion of landing technique
At 22:22:24, Discussion of completed manual extension procedure
At 22:23:57 - First officer reviewed emergency items to be accomplished after landing.
At 22:25:54 - Captain briefed flight attendants on unlocking the cockpit door, depressurization, the brace command, and evacuation signal.
At 22:28:24 - Crew reviewed emergency checklist items for approach and landing.
At 22:28:25 - Lead flight attendant briefed passengers in detail.
At 22:28:54 – Aircraft cleared for the instrument approach.
At 22:33:34 - First officer notified company operations of emergency.
At 22:35:55 - Cleared to land and told equipment was standing by.
At 22:38:26 - Captain disconnected the autopilot.
At 22:38:35 - Flight attendant gave brace command.
At 22:39:07 - Sound similar to aircraft touchdown.
At 22:39:57 - Captain gave command to evacuate.
At 22:40:02 - End of recording.
The flight data recorder (FDR) was sent to the NTSB Vehicle Recorder Division for download. The data indicated that after takeoff, the weight-on-wheels (WOW) parameters for the left, right, and nose landing gear all transitioned from “ground” to “air”. Approximately 22 minutes later, while the aircraft was in a descent, the gear down and locked parameters for the right and nose gear transitioned to down and locked, but the left parameter did not. The Gear Disagree and master warning parameters also activated at this time. The data indicated that the gear cycled and 3 minutes later, the right and nose gear parameters again showed “down and locked” while the left gear parameter did not. There was an associated master warning and Gear Disagree indication. The down and locked states and the Gear Disagree indication stayed active for the next 38 minutes until landing. Upon touchdown, the WOW right and nose parameters transitioned from “air” to “ground”, but the left gear parameter did not change state. After the aircraft came to rest, the roll angle on the FDR measured –9 degrees to the left.
WRECKAGE AND IMPACT INFORMATION
An on-site inspection of the airplane was conducted at a hangar facility at ORD. The inspection revealed that the left main landing gear door had gouge marks on the door, and the corresponding area of the belly fairing was fractured. The left landing gear door to belly fairing interface examination revealed that the screws used to secure the weather seal retainer on the belly fairing matched the gouge marks found on the left main landing gear door.
The fractured belly fairing was speed taped into its original contoured position. With the airplane on jacks, the landing gear were raised into the stowed position. The left main landing gear door was found to be intruding over the belly fairing. When the landing gear was selected down, the left landing gear door forward edge penetrated the belly fairing fracture (held in place by the speed tape) and the left landing gear momentarily hesitated before breaking through the speed tape and extending to its down and locked position. The left landing gear door was examined and no new gouge marks were noted. The screws holding the belly fairing seal passed over the same gouge marks when the gear door penetrated the fractured belly fairing.
The examination of the left belly fairing weather seal at the fracture area revealed black marks parallel to the seal that were consistent with heavy rubbing with the gear door. The weather seal contained an embedded metal strip in the seal for rigidity.
The clearance between the left landing gear door and the belly fairing was measured while the landing gear was in the stowed position. It was noted that the manufacturer’s Aircraft Maintenance Manual (AMM) task 32-12-01-220-801-A01 did not specify any rigging criteria for zone “E”, which was the zone that corresponded to the fractured belly fairing.
TESTS AND RESEARCH
The left main landing gear retraction actuator and the Proximity Sensor Electronic Unit (PSEU) were removed from the airplane and sent to their respective manufacturers for testing. The functional tests revealed that both components operated within specifications when functionally bench tested.
A review of the airplane’s maintenance records indicated that the left main landing gear door had been replaced in September 2007 because the original door was lost in flight. The maintenance records indicated that the door was replaced at the manufacturer’s heavy maintenance facility. The manufacturer reviewed all maintenance records of the incident door and interviewed maintenance personnel involved in the replacement of the door. The maintenance review revealed that the door was rigged and checked with the use of the aircraft hydraulic pumps instead of the external hydraulic power unit as required by AMM Task 32-12-01-220-801 (Config A01).
On December 23, 2008, the aircraft manufacturer issued Service Letter CRJ700/900-SL-32-039, “Body Fairing Seal Inspection Common to MLG Inboard Door” to provide operators with guidelines for inspecting the body fairing seal common to the main landing gear inboard doors at the next convenient maintenance opportunity (i.e., 72 hour or 100 flight hours). On January 28, 2009, the Federal Aviation Administration (FAA) issued a Special Airworthiness Information Bulletin (SAIB) No. NM-09-06. The SAIB stated that the FAA “strongly recommends that the affected operators comply with Bombardier Service Letter CRJ700/900-SL-32-039 at the earliest opportunity.”