The key mistakes that led to Titanic sub tragedy as oxygen runs out

With the oxygen supply onboard the missing Titanic submersible feared to have run out, rescuers have now abandoned hope - barring a miracle - that the five people inside can be found alive.

British billionaire Hamish Harding, OceanGate CEO Stockton Rush, French navy veteran PH Nargeolet and Pakistani businessman Shahzada Dawood and his son Suleman, who is just 19, are all believed to have died in the tragedy.

While dealing with the pain of losing their loved ones in such a horrific way will be the primary focus for their families, attention will soon turn to what could have been done to avoid their deaths.

The minivan-sized Titan sub, operated by US company OceanGate Expeditions, began its descent around midday UK time on Sunday. The final 'ping' to its mothership came around 3pm - putting it just above the famous wreck.

The US Coast Guard estimated Titan would run out of oxygen at 12.08pm GMT (7.08am EST and 9.08pm Sydney).