You should consider a passport as expired at the 6-month mark. There is conflicting information out there and carriers will never risk the fines and liability they incur by transporting a person who is not admitted for a self-evident reason. Put simply, if there is any question, they won't board you. Because contracts of carriage put the responsibility on you, if you have a non-refundable ticket, you may also be out its value.
Simple solution is not to chance it and to renew well in advance of the 6 months and thereby not limit yourself.