DCA10IA021

A mechanical failure of internal components of the right main landing gear door actuator resulting in the flight crew being unable to fully extend the right main landing gear using the normal and alternate procedures. Contributing to this incident was a circular reference in the company Flight Manual in which the Landing Gear Gravity Extension checklist referred back to the Landing Gear Unsafe Indication After Extension checklist rather than the Landing Gear - Partial Gear or Gear Up Landing checklist.

Crew statements and recorded flight data indicate the flight was normal from the departure from Chicago until the first officer selected gear down while on final approach to runway 4R. There were no relevant open maintenance items on the airplane, and all applicable airworthiness directives had been complied with. After the landing gear was selected down during approach to runway 4R, the flight crew observed a warning indicating that one or more of the main landing gear (MLG) was not down and locked and one or more gear doors were not closed. The crew executed a go-around and cycled the landing gear handle in accordance with the electronic checklist. After cycling the landing gear, the warning remained and still indicated that one or more of the MLG was not down and locked and one or more gear doors were not closed. The flight crew coordinated with ATC for delaying vectors and continued to follow the abnormal procedures checklists in an attempt to extend the MLG. The United Airlines A320 Landing Gear Unsafe Indication After Extension checklist referred to the Landing Gear Gravity Extension checklist, which concluded that if the extension was unsuccessful the user was referred back to the Landing Gear Unsafe Indication After Extension. Although the flight crew reported that the checklists were confusing, they were able to accomplish all of the specified actions on the Landing Gear - Partial Gear or Gear Up Landing checklist in an attempt to rectify the MLG problem and prepare for landing. The first officer attempted to get assistance from United's maintenance control, but a difficulty with radio communications prevented effective assistance. After the incident, United amended their checklists for clarity. After completing the checklist items without success, the flight crew coordinated with ATC for a partial gear-up landing on runway 4L at EWR. During approach, the crew discussed when the engines should be shut down. The Landing Gear - Partial Gear or Gear Up Landing checklist specified that if one MLG indicated abnormal both engines should be shut down "at touchdown", and if both MLG indicated abnormal the engines should be shut down "...in the flare, before touchdown." Just prior to touchdown, the Captain acknowledged the correct checklist instruction, but called for the engines to be shut down prior to touchdown. Although not contributory to the landing gear issue, shutting down the engines, and the concurrent loss of electrical generators without the auxiliary power unit running, would result in a loss of various capabilities including nosewheel steering, anti-skid, and some spoiler capability. The airplane's speed at this time would be too low to provide electrical power from the Ram Air Turbine as well. Operation of the fuel cut-off switches and loss of electrical power resulted in the flight data recorder and cockpit voice recorder shutting down prior to touchdown. The loss of power did not affect the cabin emergency lighting. Post incident examination of the airplane revealed that the right MLG door actuator had failed to extend the door to its fully open position. The partially open door obstructed the right MLG from extending to its down and locked position. The outboard tire of the right MLG was found resting on the top of the door assembly. Examination of the door actuator revealed that some of its internal components had failed, one of them producing large quantities of fragmented metallic debris that collected in one location between the piston and the cylinder with smaller particles being embedded in the piston seals. Testing of the actuator revealed that it took more pressure than normal to initiate extension and retraction and it is considered likely that, under the right conditions, the debris might prevent the piston from moving in the cylinder. Although the majority of the debris remained within the cylinder, smaller particles were able to migrate through the actuator's retract line, coming to rest in the retract restrictor and its mounting block. This debris likely restricted the flow of fluid through the actuator which would reduce the speed of extension and retraction, allowing the main gear tire to contact the door and preventing further motion of the gear and door. During the evacuation, the 1R door did not fully open and only 1/8 of the 1R emergency evacuation slide dropped from the pack after the 1R door was opened. Prior to the flight the purser said she felt resistance when she armed the 1R door. Review of the photographs taken of the 1R slide following the incident, revealed that the 1R evacuation slide remained jammed inside its pack, and the girt was taught between the pack and the girt bar, preventing the 1R door from fully opening. Further, no anomalies were found with the 1R power assist actuator. According to the slide manufacturer, improper stowage of the girt bar in the floor brackets and/or improper packing of the evacuation slide can result in excessive bulk at the bottom of the slide pack and may impact the orientation of the slide pack at the initial stages of the deployment sequence. Because no mechanical deficiencies were found with the door, slide or girt bar, the likely reason for the lack of deployment of the 1R slide was improper packing of the 1R slide. The loss of availability of the 1R door and slide did not negatively impact the evacuation.

HISTORY OF FLIGHT On January 10, 2010 at 0915 EST, an Airbus A319, registration N816UA, operated by United Airlines as flight 634, landed with the right main gear partially extended on runway 4 left (4L) at the Newark Liberty International Airport, Newark, NJ (EWR). The airplane was on a regularly scheduled flight from Chicago O'Hare Airport. While on approach to EWR the crew attempted to extend the landing gear and observed an abnormal gear indication. The crew conducted a go-around and attempted to manually extend the gear, but was not able to extend and lock the right main gear, and decided to land before fuel ran low. The flight landed on runway 4L, coming to rest on the left main and nose wheel, and the right engine nacelle. The airplane had minor damage to the underside of the right nacelle and right and left gear doors. Three of the 48 passengers received minor injuries during the evacuation, and none of the 5 crew were injured. The flight to EWR was reported as routine, with clear and cold weather and light traffic prevailing in the terminal area. The First Officer (FO) was the pilot flying and called for the gear to be extended just outside of the final approach fix on the instrument landing system (ILS) approach to runway 4 right (4R). At about 0837, the Captain selected the landing gear down, however the landing gear indication lights remained red, indicating that the gear was not in the down and locked position. The crew received a Master Warning and electronic centralized aircraft monitoring (ECAM) messages indicating that one or more of the main landing gear was not down and locked and one or more gear doors were not closed. The crew performed a go-around and advised air traffic control (ATC). All other airplane systems, including hydraulics were indicating normal prior to the go-around. The FO completed the go-around maneuver and the landing gear handle was cycled in accordance with the ECAM checklist item. The landing gear indicator lights remained red. The Captain took control of the airplane and radio while the FO continued to accomplish the next action item, gravity extension of the gear. Air Traffic Control (ATC) vectored the flight on a wide left hand traffic pattern to the west of the airport. The Captain noted fuel on board as 4,800 pounds. At about 0841, following the gravity extension procedure, the landing gear panel lights annunciating left main gear and the nose gear showed green, but the right main gear light remained red. The crew reported that the checklists were confusing with circular references. The pilots then referred to the PARTIAL GEAR OR GEAR UP LANDING checklist in the Irregular Procedures chapter. Flight Operations procedures at United Airlines were based on the manufacturer's guidance and modified to meet operational needs. Airbus A319/A320 flight crews at United Airlines carried a company produced A319/A320 Flight Manual on the flight deck in lieu of the QRH (Quick Reference Handbook) provided by the manufacturer. The A319/A320 Flight Manual contained an Emergency Procedures chapter and an Irregular Procedures chapter that included both ECAM (Electronic Centralized Aircraft Monitoring) and non-ECAM procedures. The Irregular Procedures chapter included a Landing Gear Unsafe Indication After Extension procedure which referred to the Landing Gear Gravity Extension procedure. A circular reference existed as, at the completion of the Landing Gear Gravity Extension checklist, if the extension was unsuccessful; the user was referred back to the Landing Gear Unsafe Indication After Extension procedure. The circular reference did not exist in the Airbus QRH as the Landing Gear Gravity Extension procedure included a step referring to the Landing with Abnormal L/G procedure, which was also contained in the QRH. The Irregular Procedures chapter of the United A319/A320 Flight Manual did not include the Landing with Abnormal L/G procedure but included a similar procedure entitled Landing Gear - Partial Gear or Gear Up Landing. Between 0844 and 0852, the Captain had control of the airplane and coordinated with ATC for delaying and positioning vectors, while coordinating with the cabin crew to prepare for a possible gear-up landing. During the same time period, the FO was performing the checklist steps and attempting to coordinate with United System Aircraft Maintenance Control and other maintenance support for assistance with the gear problem. The Captain requested a visual inspection of the landing gear from EWR tower personnel. ATC vectored the flight to the ILS runway 11 for a fly over to allow the tower cab personnel an opportunity to view the landing gear. At about 0854, as the airplane was approaching runway 11, the tower controller radioed that the airplane's left main and nose gear looked down, but that the right landing gear "did not look right." The Captain requested radar vectors to set up for landing on the longest runway, runway 4L, and to complete the landing with abnormal gear checklist. ATC vectored the flight northwest of the airport and advised the crew they could plan to land on runway 4L when ready. The Captain declared an emergency and requested fire/rescue equipment. The Captain contacted the flight attendants and informed them of the situation and told them to prepare for an evacuation. They prepared the cabin for landing and made an announcement over the public address system that there would be an emergency evacuation after they landed. The Purser identified a deadheading flight attendant from another airline and repositioned him in order to help open the over wing exits after the airplane landed. Additionally, she asked a first class passenger to assist her with the 1R door if needed. As the aircraft was vectored along a left downwind leg abeam EWR airport, the FO briefed the Captain on the checklist items. They determined there was sufficient fuel to execute another go-around and landing if necessary. At about 0904, the crew advised ATC they were ready to make a landing on runway 4L, and the Captain stated "if we need more time, we'll make a 360 [degree turn]." ATC vectored the airplane to a standard left base and intercept to the final approach. While on final approach, at about 0909, the Captain elected to execute a 360 degree turn in order to ensure all actions were taken and the flight attendants, passengers and airport rescue and firefighting (ARFF) were provided adequate time to prepare for the emergency landing. The visual approach to runway 4L was flown with the autopilot and auto-thrust off. In the flare, just prior to touchdown, the Captain called for the engines to be shutdown. The United Airlines Irregular Procedures Landing Gear - Partial Gear or Gear Up Landing checklist specified that if one main landing gear indicated abnormal both engines should be shut "at touchdown", and if both main landing gear indicated abnormal the engines should be shut down "...in the flare, before touchdown." However, the crew discussed when to shut down the engines numerous times during the preparation for the landing. On final approach, the FO read the checklist item "engine master switch is off at touchdown," but just prior to landing at 0914:15 the Captain said, "you wanna get those engines, ya think, now?" The FO said "at touchdown it says." The Captain acknowledged but said "get ‘em now, we don't need ‘em." The Captain reported he made a normal touchdown on the left main landing gear and held the right wing off the ground as long as possible. The initial touchdown marks appeared just abeam the intersection with taxiway C, and Port Authority personnel measured scrape marks approximately 300 feet beyond the initial point. The right engine nacelle settled to the runway and the pilots reported very little drag initially. The Captain said he applied very light left brake which he quickly released after dete