What happened
On November 26, 2015, an Airbus A330-343, registration HB-JHC, operated by Swiss International Air Lines, departed Zurich (LSZH) for Newark (KEWR). Approximately five minutes into the climb, shortly after the flaps were retracted, the crew received a master caution warning indicating a leak in the green hydraulic system. This was followed by warnings of low reservoir levels and low pressure in both engine-driven pumps.
The flight crew immediately interrupted the climb, maintained a speed of 210 knots, and requested a holding pattern over the GIPOL waypoint at flight level 120. During the event, a noticeable smell of hydraulic fluid entered the cabin and cockpit. Due to the odor, the copilot donned an oxygen mask, and several passengers and crew members later reported symptoms of nausea and headaches. To mitigate further contamination, the crew switched the cabin air source from the engines to the auxiliary power unit (APU).
Because the situation was not immediately time-critical, the crew spent approximately one hour in holding, managing the aircraft's weight. They decided to land at a weight above the maximum landing mass (MLAM) to avoid a prolonged holding period that would have increased exposure to potential fumes. The aircraft landed safely at Zurich with a sink rate of approximately 300 ft/min.
The investigation
SUST examined the hydraulic system components and the physical condition of the aircraft following the incident. The investigation focused on the two engine-driven pumps (EDP1 and EDP2) responsible for the green hydraulic system. Post-incident inspections of the pumps revealed metal particles in the case drain filters. Further analysis showed internal damage to both pumps, with EDP1 exhibiting significant seizure of the rotating components and wear on the piston shoes.
Findings
- The leak originated from the engine-driven pumps, specifically caused by internal damage to EDP1 due to pre-existing wear on the piston shoes.
- As the hydraulic fluid level depleted, both engine-driven pumps eventually ran dry during the high-load phase of takeoff (flaps and gear retraction), leading to pump failure and low-pressure warnings.
- The hydraulic fluid fumes in the cabin were likely caused by the contamination of engine bleed air. During the initial takeoff run, a small amount of fluid was likely ingested through the engine inlet and subsequently distributed through the ventilation system.
- The crew's decision to switch the air source to the APU and their choice of landing parameters effectively minimized the duration of exposure to the hydraulic vapors.