NTSB Factual Report

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 determining rudder control provided full directional control authority. As the airplane slowed, he reported there was more pronounced drag and tendency to pull to the right during the final seconds of the deceleration. The airplane came to rest on runway centerline, about 3,400 feet from the initial touchdown.

After the airplane came to rest the Purser activated the evacuation alarm and the flight attendants provided the passengers with verbal commands to evacuate the cabin. The passengers exited the airplane using the evacuation slides at both the left and right over-wing exits, door 1L, door 2L and door 2R. The Purser opened the 1L door and observed many passengers evacuated out the 1L exit and gathered along the left side of the airplane.

After the Purser opened the 1L door she went to the 1R door. The first class passenger was attempting to open the 1R door, and she witnessed his hand move the handle but it did not appear to go all the way up. When the door opened it appeared to open differently than the other door (1L) and it looked "cockeyed" from where the Purser stood. The first class passenger who opened the 1R door stated it opened about 75 percent of the way and he did not hear any noise coming from the emergency evacuation slide nor did the slide deploy. The Purser directed the passenger to evacuate via the 1L door and blocked the 1R to prevent other passengers from exiting that way. Shortly afterward the passenger evacuation was complete, and the flight attendants exited the doors at their evacuation stations. The pilots initiated the evacuation checklist and exited out the cockpit door. The pilots stated when they exited the cockpit there was no one remaining in the cabin. The Captain and FO conducted a walkthrough of the cabin to ensure all passengers and crew had departed. Both pilots evacuated the cabin using door 1L evacuation slide.

INJURIES TO PERSONS

Three of the 48 passengers received minor injuries during the evacuation. The injured passengers were seen by EMT's at the site and refused further treatment.

DAMAGE TO AIRCRAFT

The airplane sustained minor damage to the right engine nacelle, fan cowl, and thrust reverser; and right and left main gear doors from impact and abrasion on the runway pavement. The right engine drain mast and support structure, and the right engine integrated drive generator sustained minor abrasion damage. The right main gear door actuator was removed and examined (see Tests and Research). The damaged components were repaired or replaced in accordance with manufacturer instructions, and with FAA authorization, the airplane was returned to service.

OTHER DAMAGE

The gear doors and right nacelle created gouges in the runway surface.

PERSONNEL INFORMATION

The captain, age 41, had worked for United Airlines since July 16, 1990. He held an Airline Transport Pilot certificate, multi-engine land, with type ratings in A320, B737 and B767. The A319 is a variant of the A320 and does not require a separate FAA type rating on the pilot's certificate. He held an FAA first class medical certificate with no limitations or waivers. Company records indicate that he had 14,000 hours total time with 915 hours on the A319. He had no previous accidents, incidents, or violations. The incident flight was the first flight of the day for the Captain.

The first officer, age 46, had worked for United Airlines since July 29, 1996. He held an Airline Transport Pilot certificate, multi-engine land, with type ratings in the A320, B737, and B767. He held an FAA first class medical certificate with no limitations or waivers. He reported a total of 15,000 flight hours, with 240 hours in the A320. The incident flight was the first flight of the day for the FO.

The three flight attendants were all current and qualified on the Airbus A319.

AIRCRAFT INFORMATION

N816UA, manufacturer serial number 871, United Airlines ship number 4016, was an Airbus Industrie A319-100 equipped with IAE Aerospace V2522 engines. The airplane had accumulated approximately 39,679 hours total time on the airframe. Recorded data and airline records indicated no relevant maintenance issues with the airplane. At the time of the accident the estimated landing weight was 108,120 pounds with a center of gravity at 29.6% mean aerodynamic chord. During recovery, it was noted that fuel indicated approximately 600 pounds in the left tank, 120 pound in the center tank and 880 pounds in the right tank, for a total of 1,600 pounds of fuel remaining.

The landing gear control system consists of a forward retracting nose gear and two inboard retracting main gears. The gear and their associated doors are electrically sensed and hydraulically operated. The landing gear control and sequencing is electrically achieved with the use of proximity sensors and two independent Landing Gear Control and Interface Units (LGCIU) computers. The LGCIUs provide sequencing commands to the various components to extend or retract the landing gear and doors.

When the active LGCIU detects that the gear selector lever is in the down position, it commands the door selector valve to open, unlocking and opening all three landing gear doors. If a door has not reached its fully open position within four seconds of the first door reaching its fully open position, a fault will be recorded within the LGCIU. This fault is not displayed to the crew. If both LGCIUs detect that at least one gear does not fully extend and lock in place within 30 seconds of the movement of the landing gear selector, the crew will receive a red warning "LG GEAR NOT DOWNLOCKED" on the ECAM, associated with a flashing Master Warning light and a continuous repetitive chime.

Whenever the landing gear extension sequence is not completed, an ECAM warning is triggered instructing the flight crew to recycle the gear (i.e. moving the landing gear selector lever up then down again). If the landing gear still does not extend, a "gravity extension" (free-fall) should be accomplished. The landing gear gravity extension should be performed in accordance with the QRH, however during the incident, the crew expressed some confusion over the correct steps following the completion of the gravity extension checklist, without successfully locking down the main gear.

Rotating the free-fall extension-handle activates the free fall system. The free-fall extension-handle is located at the rear of the cockpit center pedestal. A system of rods, cables and bellcranks connect the free-fall extension-handle to: the landing gear door up-locks, the landing gear up-locks, two hydraulic vent valves and one hydraulic cut-out valve. When the free-fall extension-handle is turned, uplocks are released and the landing gear doors are opened by the weight of landing gear and aerodynamic force. Gravity extends the landing gears, which are then held and locked in the extended position by their respective MLG downlock mechanism. When the landing gear is extended by the free-fall system, the landing gear doors stay open.

There is no special indication for the position of the landing gear in the free-fall extension mode. The landing gear doors will show OPEN (amber indication) when the free-fall extension system is used. The other indications in the cockpit are the same as those for the normal extension and retraction system.

The main landing gear door actuator includes a cylinder and piston rod. The cylinder is closed at one end by an end fitting sub-assembly and at the other end by a damping housing and piston rod. Both the end fitting sub-assembly and damping housing are of similar design, inside the cylinder; however the end fitting sub-assembly has two damping holes in line and staggered axially, while the damping housing has two holes diametrically opposite and staggered axially. Therefore both the end fitting sub-assembly and housing damping provide progressive damping. The inner ends of the end fitting sub-assembly and damping housing are lipped toward the cylinder wall, and have two cut outs to permit fluid flow.

When commanded to extend, the actuator receives hydraulic pressure (3,000 psi) at its extend port. This pressure reacts against the piston head resulting in the piston rod extending. As the piston rod approaches

NTSB Probable Cause

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.