Date: 201505
Local time of day: 1201-1800
Location: PHL.Airport, PA
Flight conditions: VMC
Light: Daylight
Aircraft: A330
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B PHL
ATC / advisory: Tower PHL
Second aircraft: Widebody; Low Wing; 3 Turbojet Eng
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Anomaly: Deviation - Speed All Types; Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter Wake Vortex Encounter
Detector: Automation Aircraft Other Automation
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Environment - Non Weather Related
Primary problem: Environment - Non Weather Related

Narrative: During approach at approximately 1200 feet MSL; with the aircraft in the landing configuration; we received a brief 'windshear windshear windshear' aural message and 'windshear' displayed on PFD. The airspeed momentarily indicated approximately VLS (minimum selectable speed) -10 kts while the auto thrust was increasing engine power to correct the airspeed deviation.Prior to receiving the 'windshear' message; the pilot flying was flying on the glideslope; however; after encountering some wake turbulence from a preceding [heavy aircraft]; he decided to intentionally fly above the glideslope in order to avoid the wake turbulence.There were no meteorological indications or ATC or pilot reports that suggested windshear was possible or likely. None of the factors listed in the 'Severe weather/Windshear' decision aid were reported or present. The tower reported winds of 320 degrees at 11 knots. Our display at the time showed a wind of 340 degrees at 14 knots. Given all of the foregoing; I suspect that airspeed fluctuation was due to a wake turbulence encounter and not an actual windshear event.The pilot flying (PF) did not execute a go-around since the event was of such a short duration that by the time we processed what was going on; the event was over.I am unsure why the reactive windshear sounded; however; since there were no windshear conditions present; I suspect the warning was triggered by an indicated airspeed fluctuation caused by wake turbulence from the preceding aircraft. I would have instead expected a 'Speed Speed Speed' warning given the momentary speed excursion.Given that I am not entirely sure what triggered the warning; if faced with the same situation again; I will suggest that the PF apply the windshear recovery procedures and execute a go-around; even though I did not feel the flight path was threatened at any point.An additional consideration is that a destination alternate was not required and therefore the landing fuel was projected to be approximately 13;300 lbs. The PF and I had discussed the fact that we did not feel it was good practice to dispatch an A-330 with a planned arrival fuel of less than 18;000 pounds since it left insufficient margin should we encounter any unforeseen delays or need to execute a go-around. It should be standard operating procedure to dispatch with sufficient fuel for one go-around; plus a minimum of 14;000 of additional fuel in situations where no destination alternate is required.




Synopsis: A330-300 First Officer reported airspeed fluctuation on approach probably due to wake vortex encounter caused by a heavy aircraft ahead.