PHP acces complex xml elements

I have the following XML file I would like to retrieve some value. TH problem that I tried to use x-path but it didn't work.

Here is the xml file:

<soap-env:Envelope><soap-env:Header></soap-env:Header><soap-env:Body><OTA_AirAvailRS Version="2.2.0"><stl:ApplicationResults status="Complete"></stl:ApplicationResults><OriginDestinationOptions OriginTimeZone="Z2"><OriginDestinationOption RPH="1"><FlightSegment ArrivalDateTime="01-05T01:05" DOT_Ind="N" DepartureDateTime="01-04T22:00" FlightNumber="642" RPH="1" SmokingAllowed="false" StopQuantity="0" eTicket="true"><BookingClassAvail Availability="9" RPH="1" ResBookDesigCode="J"/><BookingClassAvail Availability="0" RPH="2" ResBookDesigCode="Z"/><BookingClassAvail Availability="5" RPH="3" ResBookDesigCode="C"/><BookingClassAvail Availability="4" RPH="4" ResBookDesigCode="D"/><BookingClassAvail Availability="0" RPH="5" ResBookDesigCode="I"/><BookingClassAvail Availability="9" RPH="6" ResBookDesigCode="Y"/><BookingClassAvail Availability="9" RPH="7" ResBookDesigCode="B"/><BookingClassAvail Availability="0" RPH="8" ResBookDesigCode="P"/><BookingClassAvail Availability="9" RPH="9" ResBookDesigCode="H"/><BookingClassAvail Availability="0" RPH="10" ResBookDesigCode="W"/><BookingClassAvail Availability="9" RPH="11" ResBookDesigCode="K"/><BookingClassAvail Availability="0" RPH="12" ResBookDesigCode="R"/><BookingClassAvail Availability="9" RPH="13" ResBookDesigCode="M"/><BookingClassAvail Availability="9" RPH="14" ResBookDesigCode="L"/><BookingClassAvail Availability="9" RPH="15" ResBookDesigCode="V"/><BookingClassAvail Availability="9" RPH="16" ResBookDesigCode="S"/><BookingClassAvail Availability="9" RPH="17" ResBookDesigCode="N"/><BookingClassAvail Availability="9" RPH="18" ResBookDesigCode="Q"/><BookingClassAvail Availability="9" RPH="19" ResBookDesigCode="O"/><DaysOfOperation><OperationSchedule><OperationTimes><OperationTime Fri="true" Mon="false" Sat="true" Sun="true" Thur="false" Tue="false" Weds="true"/></OperationTimes></OperationSchedule></DaysOfOperation><DestinationLocation LocationCode="KWI"/><Equipment AirEquipType="E95"/><FlightDetails Canceled="false" Charter="false"/><MarketingAirline Code="RJ" FlightNumber="642" ParticipationLevel="DCA"/><Meal MealCode="D"/><OriginLocation LocationCode="AMM"/></FlightSegment><FlightSegment ArrivalDateTime="01-05T06:10" ConnectionInd="Y" DOT_Ind="N" DepartureDateTime="01-05T03:25" FlightNumber="859" RPH="2" SmokingAllowed="false" StopQuantity="0" eTicket="true"></FlightSegment><FlightSegment ArrivalDateTime="01-05T12:30" ConnectionInd="Y" DOT_Ind="N" DepartureDateTime="01-05T10:20" FlightNumber="501" RPH="3" SmokingAllowed="false" StopQuantity="0" eTicket="true"></FlightSegment></OriginDestinationOption><OriginDestinationOption RPH="2"></OriginDestinationOption><OriginDestinationOption RPH="3"></OriginDestinationOption><OriginDestinationOption RPH="4"></OriginDestinationOption></OriginDestinationOptions></OTA_AirAvailRS></soap-env:Body></soap-env:Envelope>

I would like to retrieve the values from 'Flight Segment' element

Thanks in advance!