Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Human-Machine Interface
Aircraft Equipment Problem Critical
Aircraft Equipment Problem Dissipated; Flight Crew Landed As Precaution; Flight Crew Diverted; General Maintenance Action; General Declared Emergency
Aircraft
On climb passing FL180 we received an ECAM; HYD G RSVR OVHT.  ECAM directed us to turn OFF the PTU; and G ENG 1 PUMP.  After doing so we experienced a significant airframe vibration/flight control flutter.  After completing the ECAM actions; and consulting the FOM; we attempted to find the source of flutter.  We changed the pitch angle; and changed power settings to no avail.  In the interest of safety we declared an emergency and plotted our diversion.  Although the FOM directs you to turn the G ENG 1 pump on for the approach procedure; (G OVHT OUT); based on experience; systems knowledge; and an overall concern for the integrity of the flight controls; we decided to turn the G ENG 1 PUMP; and PTU PUMP on in an effort to stop the flight control flutter; (G OVHT light OUT).  Immediately after turning both pumps on; the flutter abated.  We continued our diversion; had CFR trucks standing by; and made a routine landing.
Climbing through approximately FL180 we received a 'HYD G RSVR OVHT' ECAM; and related Master Caution.  We followed the ECAM Procedure; which involved securing the PTU; and GREEN ENG 1PUMP.  Immediately after doing so; the airframe or flight controls; developed a very pronounced; and continuous vibration that would not go away.  We tried changing pitch; power; and airspeed settings; but the vibration continued; and in my opinion; I felt it even got worse.  We discussed the various possibilities and options available; and decided that diverting  and declaring an emergency would be our best option; as we were very concerned about the vibration; or control flutter; and could not detect the source.  Realizing this; and the fact that the overheat was over; we decided that re-activating the pump may cause the vibration to go away.  We gave it try; and the vibration went away instantaneously.  Enroute we completed the FOM portion of the checklist; and saw that the approach procedure was to turn the pump back on if the the system was no longer overheating.  At that point; we decided that the safest course of action would be to continue the flight with the pump on; rather than waiting for the actual approach phase of the flight to reactivate it.  As a precautionary measure; we had Emergency Vehicles waiting; and informed ATC to expect a normal outcome as we had regained full functionality of all aircraft systems.  We also informed our flight attendants to simply prepare for a normal landing.  As our final preparation; I handed control of the aircraft to the Captain; as I felt it was most prudent for him to accomplish the over weight landing himself.  We then accomplished the Overweight Landing checklist; and as expected; landed uneventfully; and taxied the aircraft to the gate.  The overheat never returned; nor did the vibration from the point we re-activated the green hydraulic pump all the way to landing.  From there Contract Maintenance started looking over the aircraft; as I performed my post flight walk around.  I was not able to see any external anomalies which may have led to this event.  the Captain made the appropriate logbook entries for the hydraulic problem; the aircraft vibration; and the overweight landing.  In closing; it should be noted that we re-activated the pump after securing it; only because we were extremely concerned about the level and intensity of the aircraft vibration; and it was the vibration; and the potential unknown problems with the aircraft; that forced our decision to divert.  I adamantly feel that we erred on the side of safety; both with our decision to re-activate the pump; and to divert.  Allowing the aircraft to vibrate the way it was; while there was a fix for it; was unacceptable; and a very poor option; as was the option of continuing on.
A319 flight crew reports a HYD G RSVR OVHT ECAM during climbout and complies with ECAM actions; turning off the green engine driven pump and the PTU.  Upon doing so a strong vibration is felt in the airframe and through the flight controls.  Attempts to quell the vibration are initially unsuccessful and the decision is made to divert.  The vibration continues and the crew elects to turn the green hydraulic system pumps back on since the overheat had gone away.  This action has a positive effect and a normal landing ensues at the diversion airport.