import re
txt = 'Port of Discharge/ Airport of destination\tXYZABC\t\t\t\t\t\t\t\t44B'
pat = r' port.{0,6}discharge.{0,3}/.{0,3}airport.{0,7}destination(?=.*44B)'
reg_ind = [(m.start(0),m.end(0)) for m in re.finditer(pat, txt,re.IGNORECASE | re.VERBOSE)]
print(reg_ind)
aW1wb3J0IHJlCgp0eHQgPSAgJ1BvcnQgb2YgRGlzY2hhcmdlLyBBaXJwb3J0IG9mIGRlc3RpbmF0aW9uXHRYWVpBQkNcdFx0XHRcdFx0XHRcdFx0NDRCJwpwYXQgPSByJyBwb3J0LnswLDZ9ZGlzY2hhcmdlLnswLDN9Ly57MCwzfWFpcnBvcnQuezAsN31kZXN0aW5hdGlvbig/PS4qNDRCKScKcmVnX2luZCA9IFsobS5zdGFydCgwKSxtLmVuZCgwKSkgZm9yIG0gaW4gcmUuZmluZGl0ZXIocGF0LCB0eHQscmUuSUdOT1JFQ0FTRSB8IHJlLlZFUkJPU0UpXQpwcmludChyZWdfaW5kKQ==