Air Wisconsin CRJ2 at Philadelphia on Dec 14th 2008, left main gear did not deploy

Last Update: April 8, 2020 / 23:58:07 GMT/Zulu time

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Incident Facts

Date of incident
Dec 14, 2008

Classification
Incident

Airline
Air Wisconsin

Flight number
ZW-3918

Departure
Norfolk, United States

Destination
Philadelphia, United States

Aircraft Registration
N407AW

Aircraft Type
Canadair Corporate Jetliner

ICAO Type Designator
CRJ2

ZW-3918 being foamed after full stop (Photo: AP/Joseph Kaczmarek) An Air Wisconsin Canadair CRJ-200 on behalf of US Airways, registration N407AW performing flight ZW-3918/US-3918 from Norfolk,VA to Philadelphia,PA (USA) with no passengers and 3 crew, declared emergency after the crew could not deploy the left main gear. The crew attempted troubleshooting, alternate and emergency procedures to lower the left main gear to no avail, confirmed by at least two low approaches to have the gear inspected by the tower. In the end the airplane touched down on runway 27L on its right main gear, nose gear and left wing in an "impressive show of sparks" at 5:22pm and skidded to a halt. No injuries occured. The airplane was foamed immediately after it stopped.

The airplane had departed Norfolk with a delay of 3:30 hours, all passengers had already rebooked onto other flights.

The airport of Philadelphia was closed from 5:05pm to 6:27pm, as all fire services and 75 fire fighters were engaged in the emergency and no cover was available for any other inbound or outgoing flight.

The NTSB reported in their preliminary statement (Dec 20th), that "the upper attachment bolt for the left main landing gear uplock assembly, which is designed to be attached to both the uplock mechanism and the structure, was attached to the airplane structure only." The airplane received minor damages including scuff marks to the left wing tip and outbourd edge of the left aileron. The left flaps received more extensive damage contacting the ground with their trailing edge and being abrased through the upper and lower skins to the ribs.

On Apr 8th 2020 the NTSB released their final report after adopting the conclusion on Apr 6th 2020, which reads:

the failure of the maintenance personnel to properly complete the installation, and the inspection personnel to conduct the proper functional test, of the left main landing gear uplock assembly.

The NTSB summarized:

During the repositioning flight the flight crew received indications of a landing gear problem prior to landing and stated that after unsuccessfully attempting to lower the left main landing gear, they elected to land with the nose and right main landing gear indicating in the "down and locked " position. In addition, upon arrival in the airport environment, air traffic control tower personnel visually confirmed that the left landing gear was not extended. The crew then made an emergency landing at PHL on runway 27L, with the airplane touching down on the nose and right main landing gear, and subsequently coming to rest on the left MLG and the left wing tip. The crew evacuated the airplane. There was damage to the left wingtip, aileron, and flaps, however no other damage was noted.

Examination of the flight data recorder (FDR) data showed that both MLG received signals simultaneously, with the right MLG signal indicating "Up and Locked", and the left MLG signal indicating "Not Up and locked. See the Flight Data Recorder Specialist's Report.

Post-incident examination of the airplane revealed no anomalies with the right MLG uplock assembly installation; however the investigation revealed that the upper attachment bolt used to mount the left MLG uplock assembly to the structure was installed and cotter pinned, but did not engage the uplock assembly. The lower bolt was installed and did engage the uplock assembly. Such installation permitted the uplock assembly to pivot inboard about the lower attachment bolt.

As a test, the uplock assembly was positioned close to the design orientation, the lock could be released and the main landing gear lowered. When the assembly was pivoted downward as found in the incident investigation, the uplock release cable no longer released the lock since the lock release lever contacted the upper bolt and would not allow the lever to travel fully and release the landing gear.

The investigation revealed that at the maintenance facility two separate mechanics had been assigned to replace each of the uplock assemblies on the airplane.

The installation of both assemblies could not be completed during the midnight shift (2130 to 0730), and the mechanic who replaced the left uplock departed when the shift was over. The mechanic who replaced the right uplock stayed through the morning to finish the installation and departed prior to completing the functional check and manual gear swing on the airplane. Both mechanics signed off the work package as being complete having made a verbal turnover to the day shift supervisor, inconsistent with Air Wisconsin, Inc., policies and procedures (Air Wisconsin GMM Chapter 21, Section 9 - Work Interruption Procedures).

The investigation also revealed that the mechanic that had installed the left gear uplock assembly had never before done such installation, nor had he received pertinent training. The mechanic who replaced the right uplock assembly stated that he had replaced uplocks on other airplanes but not the accident type airplane.

Additionally, removal and installation of the uplock assemblies is a required inspection item (RII) and must be inspected by an RII inspector. The inspection noted discrepancies in the installation of the left gear assembly installation, which were corrected by the mechanic (at the request of the inspector) who stayed past his shift and installed the right uplock assembly; however the discrepancies were not properly documented.

The investigation revealed that the RII inspector performed a functional check and manually extended the landing gear, however the RII inspector stated that he could not actually see the gear being extended from his position during the test as he was only watching the flight instrument panel for the indication of a full extension.

Further discussions with the RII inspector revealed that he did not follow the manual extend procedures outlined in the manuals, but instead followed an abbreviated procedure. In addition, the RII inspector did not use a flash light or inspection mirror as part of the inspection to see in the darkened MLG wheel-well. Furthermore, the RII inspector assigned to check the mechanics work had no previous experience inspecting an uplock assembly and he did not recall if he had ever moved and replaced one during his work as a mechanic.

The investigative team reviewed the Air Wisconsin, Inc. removal and installation maintenance manual for the MLG Uplock Assembly (MM 32-32-05 page 401-407, dated April 20, 2004). The contents of the maintenance manual were the same as the Bombardier CRJ MLG Uplock Assembly manual. Both manuals outline instructions to install both bolts through the uplock assembly and to the aircraft structure. It was noted that the instructions did not mention of the spacer located between the uplock assembly attachment lugs and that the orientation of Figure 401 was confusing when referenced to install the left uplock assembly. The instructions also failed to reference a nearby hydraulic line cover that had to be removed in order to remove the uplock assembly attachment bolts.