Yet another Bombardier CRJ landed with one side of its main landing gear retracted yesterday. The SkyWest CRJ200, operating in partnership with AirTran as Flight 3074 from Omaha, Neb., made an emergency landing at Milwaukee General Mitchell International Airport at about 5:10 p.m. local time with only its right main and nose gear extended. All 36 passengers and three crewmembers deplaned safely through the main cabin door.

The incident might have proved fairly unremarkable if not for the fact that just three days earlier, on September 25, an emergency landing at New York’s JFK International Airport by an Atlantic Southeast Airlines Bombardier CRJ900 had already raised concerns from authorities about the frequency of landing gear failures on the Canadian manufacturer’s ubiquitous regional jet line. Carrying 60 passengers and three crew, Delta Connection Flight 4951, originating from Atlanta and scheduled to land in White Plains, N.Y., diverted to JFK when the airplane’s right main landing gear failed to extend. The pilots landed at JFK at about 8 p.m. on only the left main and front landing gear while the right wing tip generated a trail of sparks as it dragged along the runway.

The JFK incident came four months after a SkyWest Airlines CRJ200 couldn’t extend its nose landing gear on approach to Ontario (Calif.) International Airport. SkyWest Flight 6467 managed to land with its nose gear in the retracted position. None of the 24 passengers or three crewmembers sustained injuries during the May 23 incident.

Less than a year earlier, on June 11, 2009, another Atlantic Southeast jet–a 50-seat CRJ200–couldn’t fully extend its left main landing gear, but again, managed to land safely at Atlanta Hartsfield International Airport. The airplane came to rest partially on the left side of Runway 27R and the adjoining grass. Nineteen passengers and a crew of three evacuated with no injuries through the right service door and the remaining 20 through the left forward entry door.

On December 15, 2008, a CRJ700 operated by Mesa Airlines returned to Chicago O’Hare International Airport after the crew received an unsafe gear indication for the left main gear as it approached for landing in South Bend, Ind. Unable to resolve the problem, the crew declared an emergency and returned to land on Runway 28 at O’Hare. The aircraft touched down with the left main gear still retracted and traveled down the runway on the remaining landing gear and the left wing’s leading edge. None of the 28 passengers and four crewmembers sustained injuries. Only a day earlier, on December 14, an Air Wisconsin CRJ200 on a repositioning flight from Norfolk, Va., landed at Philadelphia International Airport with its left main gear retracted. The two pilots and one flight attendant on board escaped unhurt.

Outside the U.S., another case of nose gear failure involved a South Africa Express CRJ200 on flight from Cape Town to Windhoek, Namibia, this past April 17. Again, none of the 33 passengers and four crewmembers suffered injuries resulting from the gear-up landing.

In the O’Hare case, investigators found that improper positioning of the inboard main landing gear door during rigging caused premature wear of parts that eventually restricted the movement of the door during its extension. In the Philadelphia case, the preliminary NTSB report indicates that mechanics attached the upper attachment bolt for the left main landing gear uplock assembly to the airplane structure only, rather than both the structure and the uplock mechanism as called for in the design. The report didn’t conclude that the oversight led to the failure of the gear to extend, however.

The NTSB launched a so-called engineering investigation following the JFK incident. An FAA spokesperson told AIN that the agency would evaluate the results “to see if there are any safety actions the FAA needs to take, whether the JFK incident was unique or whether there appears to be some common cause.”

(First para corrected to reflect that Flight 3074 was partnered, not a code-share, with Air Tran.)