Passengers then had to endure a nine hour delay before a replacement Boeing was brought in for their journey to the States.
A formal report has blamed a mechanical error"that caused incorrect rigging of the landing gear lever system after the landing gear control module had been replaced."
The BA 295 flight had been making its way from London Heathrow to the Chicago O'Hare International Airport.
The plane turned around just south of Iceland after around two hours, due to a technical problem.
Whilst approaching Heathrow, the pilots reported an unsafe gear indication for both main gear and only the nose and body wheels descended.
Twenty minutes later, the Boeing landed safely on only the nose and body wheels after the pilot circled to dump fuel.
There were more than 300 people on board the flight - including 293 passengers and 14 crews members.
Passengers described the experience as 'very scary' and praised the pilot who managed to smoothly land the Boeing 747.
Muriel Gray tweeted: "The hugest kisses and hugs to the British Airways pilot who just landed the plane my husband was on when the landing gear failed.
"Husband says BA pilot typically understated despite telling passengers how close a call that just was."
Passenger Kevin Lang told MailOnline: "It was a dramatic and stressful episode. It all started about two or three hours into the flight when we were just south of Iceland.
"The pilot came on and said there was a technical fault and we had to go back to London. He then said they would have to jettison fuel and all the passengers would see this but was reassuring us not be alarmed.
The Air Accidents Investigation report said: "Passengers reported the crew advised they were returning to London due to a technical problem.
"About 20 minutes prior to landing the crew announced that the landing gear did not fully extend with only three of five sets of gear having lowered.
"After the aircraft was towed to the apron, passengers were told to disembark very slowly, aft cabin first, otherwise the aircraft would tip over and settle on its tail," said the official report.
It continued: "The jammed landing gear lever was attributed to a rig pin not being inserted in the landing gear system during maintenance, which led to additional and unnecessary shims being used to rig the landing gear lever."
The report also said "the distraction of the engineer' and an 'inadequate handover between the night shift and the day shift' contributed to the incident.
The emergency happened on January 30 but details have only just been revealed. The Boeing plane had made its first flight since maintenance work on January 24.
