AIRBUS A320 — Las Vegas, NV, USA, 2012-06-17

NTSB summary

Before the Airbus A320-232 departed on the incident flight, one flap control computer channel was inoperative and deferred for maintenance, which was in accordance with the Federal Aviation Administration (FAA)-approved minimum equipment list. During landing gear retraction after takeoff, the Green hydraulic system on the airplane lost pressure, and the flight warning computer detected a flight control flaps system fault followed by a reservoir overheat condition for the Yellow hydraulic system 2 minutes later. Normal inhibition of alerts and warnings from the flight warning computer prevented notification of the faults to the flight crew until the airplane was climbing out of 1,500 above ground level. The crew subsequently experienced a period of high workload as they received multiple aural and visual warnings on the flight deck. The captain, who was the pilot flying, transferred airplane control to the first officer and began to accomplish the abnormal procedures that were displayed on the electronic centralized aircraft monitor. Accomplishing the manufacturer-recommended procedures included turning off the Green and the Yellow hydraulic systems' engine-driven pumps and the power transfer unit (PTU), resulting in low pressure in the Yellow hydraulic system (in addition to the existing low pressure in the Green hydraulic system), the airplane's reversion to alternate law in which flight envelope protections are reduced (most critically, stall protection), and autopilot and autothrust disconnection. The crew attempted to raise the flaps from position 1 (the takeoff position) to 0, but the flaps remained at position 1 because the loss of the Green hydraulic system and subsequent loss of the remaining flap control computer channel resulted in the flaps being inoperable. At this point, of the airplane's three hydraulic systems, only the Blue hydraulic system was providing useable pressure. The flight crew coordinated with air traffic control to enter a holding pattern at 12,000 feet to accomplish checklists, communicate with company maintenance and dispatch, and calculate landing distance performance using the procedures in the quick reference handbook. During this time, the captain recognized that the Yellow hydraulic system reservoir was no longer in an overheat condition and followed the appropriate procedures to restore the Yellow hydraulic system. It was restored about 36 minutes after takeoff and remained operative for the rest of the flight. To calculate landing distance performance with two inoperative hydraulic systems, the captain initially calculated a required landing distance of over 11,000 feet. After recovery of the Yellow hydraulic system, the captain calculated a revised landing distance of about 8,500 feet. The flight control flaps system fault required a higher-than-normal landing speed, and the Green hydraulic system malfunction resulted in loss of normal braking, loss of nosewheel steering on the ground, and loss of the ability to retract the landing gear once extended. Due to the system malfunctions and the inability to raise the landing gear in the event of a go-around, the flight crew decided to remain in the holding pattern to burn fuel and reduce aircraft weight below the maximum landing weight of 142,200 pounds. The airplane landed 3 hours 35 minutes after takeoff and was towed to the gate. Postincident examination of the airplane found a leak in the Green hydraulic system, in the right main landing gear door retraction flexible hydraulic line due to a kink in the line and a collapsed sidewall. An article in the June 2007 issue of Safety First, Airbus' safety magazine published for use by operators' flight and ground crews, described a scenario in which a leak in the Green hydraulic system results in that system's loss of fluid, which can lead to the loss of the Yellow hydraulic system. As the hydraulic pressure decreases and reaches a 500 psi differential between the Green and Yellow system, the PTU, by design, automatically activates and operates at maximum speed in an effort to transfer pressure to the Green system. Due to low fluid levels in the Green system, the maximum speed of the PTU results in overheating and subsequent loss of the Yellow hydraulic system within about 2 minutes. The loss of the Green hydraulic system would normally trigger a caution message that guides the flight crew to shut off the PTU. However, because the caution message was inhibited below 1,500 feet after takeoff, the PTU remained activated until the flight crew accomplished the abnormal procedures checklist. In response to previous incidents in which a loss of pressure in the Green hydraulic system led to the overheating and subsequent loss of the Yellow hydraulic system, Airbus issued service bulletins (SB) over a period of 2 to 5 years before this incident that included wiring changes and new PTU inhibit logic. The modifications were designed to prevent dual Green and Yellow hydraulic system losses in flight (mainly after takeoff) due to a low fluid level in the Green (or Yellow) reservoir followed by overheating and loss of pressure in the other system. At the time of the event, the SBs had not been incorporated on the incident airplane. Jet Blue decided not to incorporate the SBs based on available information indicating a low probability of occurrence for this type of event.

Probable cause

the failure of the right main landing gear door retraction flexible hydraulic line in the Green hydraulic system, which led to prolonged operation of the power transfer unit and subsequent overheating and loss of pressure in the Yellow hydraulic system, resulting in the airplane's operation with only one hydraulic system. Contributing to the incident was the lack of incorporation of aircraft manufacturer service bulletins that describe procedures for aircraft modifications intended to prevent this occurrence.

Flight data recorder

Airbus A320 · N552JB — 14,401 samples, 43 parameters, 15:53:00.0 to 19:53:00.0.

Sequence of events (FDR factual report)

Recorder documents in the docket

Docket: data.ntsb.gov/Docket/?NTSBNumber=DCA12IA096. This brief is an analytical aid assembled from public records; it is not an investigative finding.