Skywest CRJ2 at Milwaukee on Sep 28th 2010, landed without left main gear

Last Update: March 9, 2016 / 16:00:20 GMT/Zulu time

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Photo of Skywest Airlines N498CA, Canadair Corporate Jetliner — Skywest Airlines N498CA, Canadair Corporate Jetliner (Photo credit: col29071962 / Flickr / License: CC by-nd)

Incident Facts

Date of incident
Sep 28, 2010

Classification
Accident

Airline
Skywest Airlines

Flight number
OO-3074

Departure
Omaha, United States

Destination
Milwaukee, United States

Aircraft Registration
N498CA

Aircraft Type
Canadair Corporate Jetliner

ICAO Type Designator
CRJ2

A Skywest Canadair CRJ-200, registration N498CA performing flight OO-3074 from Omaha,NE to Milwaukee,WI (USA) with 36 passengers and 3 crew, was on approach to Milwaukee's runway 07R when the crew reported an unsafe gear indication and aborted the approach maintaining 4000 feet. The aircraft joined a long left downwind for troubleshooting, the crew declared emergency reporting they could not resolve the unsafe indication showing their left hand main gear up and indicated they could do only one low pass. The aircraft performed a low approach to runway 07R for a visual inspection, the tower reported the left hand main gear is up. The crew joined a right hand downwind for runway 07R and touched down on runway 07R about 25 minutes after aborting the first approach. The airplane skidded to a halt on the runway on its nose gear, right hand main gear and left wing. The aircraft was evacuated, no injuries occurred.

The airport was closed for about one hour.

The FAA reported, that the left hand main gear remained up. Following landing the passenger left the aircraft through the aircraft main door. The airplane sustained unknown damage.

The NTSB reported on Sep 30th, that the aircraft sustained minor damage to the left wing tip, flap assemblies and flap pylon assemblies. The left main gear door was up and locked and the left main gear in the wheel well.

The landing gear assemblies for the CRJ1/CRJ2 and the CRJ7/CRJ9 aircraft are different designs and are manufactured by different vendors.

On Mar 9th 2016 the NTSB released their final report concluding the probable cause of the accident was:

The failure of the left main landing gear (MLG) to extend normally and manually for reasons that could not be conclusively determined.

The NTSB summarized:

While the flight crew was configuring the airplane for landing and shortly after placing the landing gear selector in the "down" position, they noted a "gear disagree" warning message displayed on the engine indication and crew alerting system that showed that the nose gear and the right main landing gear (MLG) were down and locked but that the left MLG was in transit. The flight crew followed the quick reference handbook directions to troubleshoot the landing gear issue without success. The flight crewmembers then tried to extend the landing gear by pulling the alternate landing gear release handle; however, the left MLG failed to extend, and they subsequently landed the airplane with the left MLG retracted. During postincident activities, the airplane was lifted, and an examination revealed that the left MLG remained in its full-up position within the wheel well. The alternate landing gear release handle was found in its fully extended position.

The incident airplane's left MLG uplock pin exhibited signs of slight wear and flat spotting, consistent with in-service usage, and the uplock mechanism latch had wear marks that were within the in-service maintenance wear limits.

After the incident, functional ground testing of the airplane's landing gear system found that, although wear was observed on these system components, the left MLG extended as designed when the landing gear was selected down normally and manually. Additionally, the incident airliner's left MLG uplock pin was found properly rigged within its mating uplock mechanism. Therefore, it is unlikely that the worn components alone would have prevented the left MLG from extending during the incident flight.

Functional performance testing of the left MLG sidestay actuator showed that it operated within all test specifications. Although an examination of the actuator's restrictor assembly found that it contained two small pieces of aluminum and several particles of debris this contamination did not prevent the actuator from operating during ground tests after the incident. Therefore, it is unlikely that the contamination within the left MLG sidestay actuator would have prevented the left MLG from extending during the incident flight.

The force to operate the lever on the bypass valve was measured and found to be 60 lbs, which exceeded the acceptance test procedure -specified force requirement of 40 lbs. However, during the incident flight, the nose and both MLG uplock assemblies did unlock when the alternate landing gear release handle was pulled indicating that the bypass valve functioned during the flight.

As previously discussed, neither hydraulic contamination within the left MLG actuator nor any single MLG system component was identified as preventing the left MLG from extending during the incident flight. However, because the left MLG failed to extend when the crew used either the normal or alternate extension systems, it is likely that a combination of several factors contributed to the system malfunction. Some potential factors are: uplock pin rigging and/or wear, uplock mechanism latch wear, hydraulic system pressure and contamination, and bypass valve operation. Even though these items may be within maintenance limits when considered individually, there may be combinations of these factors that result in failure of the gear to extend. When combined with environmental and flight related conditions such as temperature, humidity, and landing gear component deflection due to in-flight loading, the interaction results of all of these factors are difficult to predict and to demonstrate during testing.