<?php

$re = '/^\h+|\h+$|(\R){2,}|(\s){2,}/m';
$flightinfo = ' 1 . BritishAirways 15FEB LONDON HONGKONG


     2 . CathayPacific  01MAR     HONGKONG   SHANGHAI


  3 . Qantas   12MAR SINGAPORE SYDNEY';
$flightinfo = preg_replace($re, '$1$2', $flightinfo);
echo $flightinfo;