loop the test steps in soapui with the help of groovy

I would suggest to loop at the test case level.

1. you define properties on TestSuite (or TestCase) level:

- airports with value: London,Prague,Paris

- counter with value: 0

2. create a 'Flight' TestStep and in your test step get the airport value and increment the counter:

def s = testRunner.testCase.testSuite.getPropertyValue( "airports")
def list = s.split(',')

def i = Integer.parseInt(testRunner.testCase.testSuite.getPropertyValue( "counter"))

// Do your action here
log.info list[i]

// increment the counter
i++
testRunner.testCase.testSuite.setPropertyValue( "counter", i.toString())

3. Put a Groovy script test step called 'Continue ' afterwards, with a script:

def s = testRunner.testCase.testSuite.getPropertyValue( "airports")
def list = s.split(',')
def i = Integer.parseInt(testRunner.testCase.testSuite.getPropertyValue( "counter"))

if (i < list.size()) {
        // Looping as long as we have values
	testRunner.gotoStepByName ('Flight')
} else {
        // Otherwise we set counter to initial value
	testRunner.testCase.testSuite.setPropertyValue( "counter", new Integer(0).toString())
}

3. This code prints following output:

Thu Aug 04 14:26:53 CEST 2016:INFO:London

Thu Aug 04 14:26:53 CEST 2016:INFO:Paris

Thu Aug 04 14:26:53 CEST 2016:INFO:Prague

I hope this helps, however the looping is not on a TestSuite level. TestSuite level looping is also possible, you need to utilize the TestSuite TearDown script for looping.