N866AS

HISTORY OF FLIGHTOn June 6, 2011, about 2132 central daylight time, N866AS, a Bombardier CL-600-2B19, operated as Skywest Airlines flight 4443, landed with the right main landing gear retracted on runway 19R at the General Mitchell International Airport (MKE), Milwaukee, Wisconsin. The 2 pilots, 1 flight attendant, and 41 passengers reported no injuries. The airplane sustained minor damage. The scheduled domestic passenger flight was conducted under 14 Code of Federal Regulations Part 121. Visual meteorological conditions prevailed and an activated instrument flight rules flight plan was on file. The flight departed Cincinnati/Northern Kentucky International Airport (CVG), near Covington, Kentucky, about 1951, and was destined for MKE. All airplane occupants evacuated the airplane via the main cabin door.

During an interview with the operator's safety staff personnel, the flight crew reported that visual meteorological conditions and calm wind prevailed during the approach. The airplane was on final approach when the gear did not come down, the flight crew informed the tower they needed to go around and flew east over Lake Michigan where they proceeded to complete the quick reference handbook (QRH). They indicated that the gear operated normally on all previous flights.

When the landing gear selector lever was first placed in the down position, the flight crew first noticed that the right main gear did not indicate down and locked. They then received the triple chime warning, gear disagree, and proceeded to go around. Upon running the QRH for "Gear Down Disagree" they would receive different indications from right main to both main landing gear unsafe, and they got the nose gear door open warning and oral messages. They also got a No. 3 hydraulic system high temperature caution message. The flight crew stated that about 28 seconds elapsed between the time that the landing gear selector lever was positioned in the down position to the "Gear Disagree" message posting.

The flight crew stated that the engine indication and crew alerting system (EICAS) primary page landing gear indications with the landing gear selector lever in the up position, initially, was that all lights were out. When the landing gear selector lever was selected down the first time, the flight crew received nose green, left main green and right main unsafe indications.

During the go around, the landing gear selector lever was put in the up position and they received the gear up normal indication. The first officer remembered that the right main would indicate a red unsafe indication very quickly, while the other landing gear would show transit, and then green safe indications. During the third or fourth landing gear selector lever selections, both main landing gears showed unsafe indications, which also happened very quickly.

The flight crew stated that the QRH procedures were followed during the attempted manual landing gear extension. They turned the No. 3 hydraulic system off as directed by the QRH and the system pressure subsequently indicated zero.

The flight crew pulled the landing gear alternate release T-handle as the QRH directed. The T-handle had slipped back a few inches from the fully extended position, which they had achieved during the manual extension.

The EICAS page exhibited red hash marks for the right main landing gear the entire time on the approaches. During one approach, the indications showed both main landing gears were unsafe and a low approach was performed to confirm which of gear were extended. The tower reported that the nose and left main landing gear were down. While returning for the last approach and landing, the left main landing gear subsequently indicated green safe and the right main landing gear still indicated unsafe.

During the alternate landing gear extension, the first officer initiated the QRH. He reported his seat height typically is in a very low seat position and he did not reposition its height. He tilted the seat-back forward. He then moved the seat to the aft position. He pulled the T-handle from his seat and felt like he had complete ability to apply all his strength to move the T-handle. The first time he pulled the T-handle it was an abrupt pull and he felt the T-handle reach the stop. The T-handle then sank back a few inches as if a spring was pulling it back down. The gear did not extend and he pulled the T-handle multiple times holding it at the stop for 5 to 10 seconds each time. The only sound that was heard was oil bypassing under their feet. The first officer, who was right-handed, was using his right hand but at one point used both hands to pull the T-handle. He told the captain that the T-handle would not stay up and the captain decided that he would try manually extending the T-handle himself.

The captain's seat was low and all the way to the aft position. This is the position he always sits when flying. He reached over with both hands, pulled the T-handle and held it there for ten seconds, and then re-pulled the handle a second time even harder. He could feel the T-handle hit a stop at full extension. He then took back the controls from the first officer. Neither crewmember got out of their seats to pull the T-handle.

The flight crew estimated that the elapsed time between the first landing gear selector lever down command and the airplane's touchdown was about 35 to 45 minutes.

The airplane sustained minor damage to its right wing tip, right flap assemblies, and right flap pylon assemblies. The right main landing gear door was up, and the right main gear was in its wheel well. PERSONNEL INFORMATIONThe captain held an airline transport certificate with a multiengine land airplane rating and commercial privileges for single engine land airplanes. He held a first class medical certificate with no limitations. The operator reported that he had accumulated about 8,618 hours of total flight time, which included about 438 hours in the Bombardier CL-600-2B19. The captain had flown about 187 hours in the last 90 days, 69 hours in the last 30 days, and 6 hours in the last 24 hours.

The first officer held a commercial certificate with single-engine land, multiengine land, and instrument airplane ratings. He held a first class medical certificate without limitations. The operator reported that he had accumulated about 5,156 hours of total flight time, including about 2,997 hours in the Bombardier CL-600-2B19. The first officer had flown about 197 hours in the last 90 days, 44 hours in the last 30 days, and 6 hours in the last 24 hours. AIRCRAFT INFORMATIONThe airplane was a Bombardier Canadair model CL-600-2B19, twin engine, transport category Regional Jet (CRJ), with serial number 7517. It was manufactured on June 15, 2001. The CRJ had a maximum takeoff weight of 53,000 pounds. The engines were General Electric model CF-34-3B1 engines that delivered 8,900 pounds of thrust each. The airplane was on a continuous airworthiness maintenance program. The last service check was conducted on June 1, 2011. At the time of the incident, the airplane had 24,969.4 flight hours and 20,132 flight cycles. The airplane was configured with 53 seats, of which 50 were passenger seats located in the main cabin.

The airplane was equipped with a retractable tricycle landing gear system that comprised two main landing gear (MLG) assemblies mounted on the inboard part of each wing, and a nose gear assembly mounted directly below the flight compartment. Both MLG retract inward into recesses in the wing and center fuselage, and the nose landing gear (NLG) retracts forward. The landing gear system, operated by a selector lever, is electrically controlled by a proximity sensor electronic unit (PSEU) and hydraulically operated by the no. 3 hydraulic system. The MLG system comprises a selector valve, run-around and bypass valve, a left and right MLG sidestay actuator and uplock mechanism. The NLG system comprises a selector valve, extension/retraction actuator, uplock assembly, downlock, nose selector valve, and priority valve, bypass valves, restrictors, and check valves.

Two of the three NLG doors are operated hydraulically and are sequenced to operate independently of the NLG position, while the other (single door) is mechanically linked to the nose gear position. During extension, the forward doors open before the NLG is released from the uplock. The nose gear assembly will then extend, simultaneously opening the rear door. Upon reaching full extension (when the NLG is down and locked), the forward doors close and remain in that configuration until a retraction command is selected.

The cockpit is equipped with a landing gear control panel, which contains a landing gear selector lever. When the selector lever is manipulated, an electrical command is sent to the PSEU to extend or retract the landing gear. Both MLG are extended in the outboard direction by their respective MLG sidestay actuators and are hydro/mechanically locked in place for landing. Each gear is retracted by the MLG side stay actuator in the inboard direction and locked in the MLG wheel wells during flight by their respective uplock mechanism.

During normal landing gear extension, when the landing gear selector lever is placed in the gear down position, the selector lever module sends an electrical extension command to the proximity sensor system and provides electrical signals to command the MLG and the NLG selector valves to their gear down position. When the MLG selector valve transitions to its gear down position, the valve is designed to allow no. 3 hydraulic system fluid, from the priority valve, to be ported, via the run-around and bypass valve, simultaneously to the uplock assembly and the extend side of the sidestay actuator for each MLG. The hydraulic pressure causes each uplock assembly to unlatch and release the MLG assembly. When unlatched, an uplock sensor (on the uplock mechanism) provides an input to the PSEU, which in ...