Incident Overview
On December 15, 2008, at 2239 central standard time, a Bombardier CL-600-2C10 (CRJ-700), registration N511MJ, operated by Mesa Airlines as Air Shuttle Flight 7164, sustained minor damage during a landing gear emergency at Chicago O'Hare International Airport (ORD). The airplane had departed ORD about 2130 en route to South Bend Regional Airport (SBN) in Indiana. During the landing approach to SBN, a "Gear Disagree" warning message appeared. After performing emergency checklists without success, the flight returned to ORD for an emergency landing on runway 28 (13,000 feet by 150 feet, asphalt).
The aircraft touched down with the nose and right main landing gear fully extended, but the left main landing gear remained retracted. The airplane skidded to a stop with the left wing supported by the wing flaps and outboard leading edge slats. The two pilots, two flight attendants, and 28 passengers evacuated via the main cabin door. Night visual meteorological conditions prevailed, and an instrument flight rules flight plan had been filed.
Personnel Information
The pilot held an airline transport pilot certificate with single-engine, multi-engine, and instrument ratings, as well as flight instructor certificates. He reported 3,100 total flight hours, including 570 hours in the Bombardier CL-600-2C10. The co-pilot held a commercial pilot certificate with similar ratings and reported 1,450 total hours, with 210 hours in the accident aircraft type.
Aircraft Information
The aircraft, a Bombardier CL-600-2C10 serial number 10104, was powered by two General Electric CF34 engines (left: CF34-8C1, right: CF34-8C5B). Seating 64 passengers, it had a maximum gross weight of 75,250 pounds. The last continuous airworthiness inspection occurred on December 13, 2008, and the airplane had accumulated 14,596 total flight hours.
Meteorological Conditions
At 2253, the surface weather observation at ORD reported wind 360 degrees at 10 knots, visibility 10 miles, few clouds at 2,100 feet, broken ceiling at 20,000 feet, temperature -12°C, dew point -17°C, and altimeter 30.59 inHg.
Flight Recorder Analysis
The cockpit voice recorder and flight data recorder were downloaded by the National Transportation Safety Board. The CVR captured key communications, including the captain's emergency declaration, crew coordination, and evacuation commands. The FDR indicated that after takeoff, all three landing gear weight-on-wheels parameters transitioned from ground to air. Approximately 22 minutes into the flight, during descent, the right and nose gear down-and-locked parameters activated, but the left gear parameter did not, accompanied by a master warning and Gear Disagree indication. Subsequent gear cycles produced the same result. Upon landing, the right and nose gear weight-on-wheels changed to ground, while the left gear parameter remained unchanged. After the aircraft came to rest, the FDR recorded a left roll angle of -9 degrees.
Wreckage and Examination
Post-incident inspection revealed gouge marks on the left main landing gear door and a fractured belly fairing. The fractured belly fairing had been temporarily repaired with speed tape. When the airplane was placed on jacks and the gear cycled, the left main landing gear door was found to intrude over the belly fairing. During gear extension, the door's forward edge penetrated the fractured fairing held by speed tape, causing momentary hesitation before breaking through and locking down. No new gouge marks were observed after this test. The clearance between the left landing gear door and belly fairing was measured; the manufacturer's Aircraft Maintenance Manual (AMM) task 32-12-01-220-801-A01 did not specify rigging criteria for the zone corresponding to the fractured fairing.
Functional bench testing of the left main landing gear retraction actuator and Proximity Sensor Electronic Unit determined both components operated within specifications.
Maintenance History
Review of maintenance records showed the left main landing gear door had been replaced in September 2007 after the original was lost in flight. The replacement occurred at the manufacturer's heavy maintenance facility. The maintenance review revealed that the door was rigged using the aircraft hydraulic pumps instead of an external hydraulic power unit as required by AMM Task 32-12-01-220-801 (Config A01).
Subsequent Actions
On December 23, 2008, the aircraft manufacturer issued Service Letter CRJ700/900-SL-32-039 providing guidelines for inspecting the body fairing seal common to the main landing gear inboard doors at the next convenient maintenance opportunity. On January 28, 2009, the Federal Aviation Administration issued Special Airworthiness Information Bulletin No. NM-09-06, recommending compliance with the service letter.