how to append to an array in groovy

I'm having a little issue with arrays in groovy. I am performing a data driven test where I am using a CSV and I am iterating through groovy script steps. What I am trying to do is for each iteration of my soap request, i should receive two flight ids. I want to place each set of the two flights ids in an array, so the array should just keep adding flight ids in the array:

Example:

After Iteration 1: [[123, 321]]
After Iteration 2: [[123.321. 454, 345]]

The problem I am having is that it is not adding into the array but instead replacing the values already in the array. So it looks like below:

After Iteration 1: [[123, 321]]
After Iteration 2: [[454, 345]] 

How can I append the flightids in the array?

Below is the code:

import groovy.xml.XmlUtil
def groovyUtils = new com.eviware.soapui.support.GroovyUtils(context)
def response = context.expand( '${SOAP Request#Response}'  )
def parsedxml = new XmlSlurper().parseText(response)


def flights = parsedxml.'**'.findAll { it.name() == 'FlightId'}[[0],[1]]


def flightsarray = [];

flightsarray.push(flights)

context.setProperty('flights', flights)
context.setProperty('flightsarray', flightsarray)

log.error flightsarray.toString()

FYI I tried replacing flightsarray.push(flights) with flightsarray << flights but it does the same thing.