The US Air Force crammed 640 people onto a C-17 jet that flew out of Kabul on Sunday, four times its usual capacity, as part of the ongoing effort to extract thousands of stranded Americans and Afghans from the city which has fallen to the Taliban.

The C-17, numbered RCH 871, took off from Hamid Karzai International Airport on Sunday for the Al Udeid Air Base in Qatar. It is one of at least two that have flown out of Afghanistan since the Taliban claimed Kabul on Sunday. 

Another C-17 - numbered RCH 885 - took off on Monday as hundreds of desperate Afghan nationals flooded the airfield in the hopes of being taken with it. Three people clung to the engines and fell to their deaths as the aircraft ascended. Two others died after being shot by US forces, CBS News reported, and two are said to have been crushed beneath the wheels of a departing plane. 

New audio from RCH 871 reveals the US Air Force pilot communicating with a controller who asked how many people were on board. 

'Ok, how many people do you think are on your jet? 800 people on your jet?! Holy... Holy cow... Ok..' the controller said. Despite initial reports saying the jet was carrying 800, the true passenger number was later confirmed to be 640. 

The jet can carry 171,000 pounds of cargo but its interior is designed to carry fewer than 150 soldiers. It's unclear who exactly was on board and how many Americans remain on the ground in Afghanistan.  

In 2013, a CR-17 rescued 670 from a typhoon in the Philippines, but Sunday's flight is a new record.