Despite advisories of unusual sounds on taxi from both a passenger and a deadheading; qualified in type; Captain the flight crew of an A320 elected to continue the flight and later encountered multiple hydraulic system anomalies eventually determined to have been the result of a faulty PTU 'O' ring.
Synopsis
Despite advisories of unusual sounds on taxi from both a passenger and a deadheading; qualified in type; Captain the flight crew of an A320 elected to continue the flight and later encountered multiple hydraulic system anomalies eventually determined to have been the result of a faulty PTU 'O' ring.
Narrative
We taxied out 2 hours 20 minutes late because of maintenance. On taxi out a Flight Attendant called up and said a passenger reported hearing a strange noise that he insisted was not normal. We then had him ask a deadheading Airbus Captain what he thought of the noise who said (I believe) that it sounded like the PTU might be coming on and off. However; indications in the cockpit were normal so we continued. After taking off and climbing to cruise altitude; the Flight Attendant called again and said the deadheading Captain would like to come up to the cockpit. Once in cockpit he said he could still hear the noise in the cabin. We checked hydraulic page and saw that PTU was running and green and yellow quantities were both below normal indication and the indicator was 'bouncing'. After watching for a while the yellow quantity seemed to be getting lower. The Captain contacted Dispatch and Maintenance through ACARS and mad the decision to divert. During the descent the master caution with ECAM for yellow system low quantity and later low pressure was indicated. At that time the Captain declared an emergency. At 4;000 FT we asked approach for delaying vectors for approximately 15 minutes to burn off fuel to avoid an overweight landing. Landing was uneventful.In retrospect; we should have investigated further on the ground or returned to gate.
Second reporter narrative
Upon preflight; hydraulic system green and blue quantity were over serviced. Upon cargo door closure; yellow hydraulic system quantity was found to be over serviced. Maintenance corrected the conditions.[Maintenance determined] the PTU valve 'O' ring failed.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.