A Los Angeles-bound American Airlines flight carrying 188 people was forced to return to London’s Heathrow Airport after several flight attendants and crew members fell ill mid-flight, the airline told ABC. 
 
 One flight attendant "literally just fainted... just fell forward, put her hand out and hit the floor," passenger Kris Evans told ABC News. "It was crazy." 
 
 The Boeing 777, which took off at 12:05 p.m., landed safely in London about five hours later, where it was met by ambulances, American Airlines said. 
 
 Paramedics examined, then discharged, six patients who complained of feeling unwell, according to the London Ambulance Service. 
 
 It was unclear what caused the patients to feel sick, but crews investigating the plane found no evidence of hazardous substances, according to the London Fire Brigade. 
 
 ABC News' Matt Hosford, Becky Perlow, Daniel Steinberger, and Rashid Haddou contributed to this report. ||||| An American Airlines flight to Los Angeles was forced to return to London Heathrow after seven flight staff and many passengers collapsed due to mysterious illness. 
 
 Passengers were shocked to see flight attendants collapse in the aisles, sparking fears about contamination in the air conditioning. 
 
 When Flight AA109 was airborne near Keflavik in Iceland, an announcement in the passenger cabin asked for any doctors onboard to come forward. 
 
 One passenger, Lee Gunn, told the Mirror: "About 2.5 hours into the flight just as we were passing Iceland we had a tannoy announcement asking for any doctors, nurses or medical professionals on board to report to the boarding doors to assist with unwell passengers. 
 
 "The lights then came on in the cabin and there was lots of commotion. 
 
 "It was also reported that seven of the crew - 13 on board in total I believe - had fallen ill, along with 'many passengers'." 
 
 The welcome into Heathrow earlier! #AA109... What a day! pic.twitter.com/qg0ge99Zvi — Lee Gunn (@gunn_lee) January 27, 2016 
 
 Another passenger, Alan Gray, told MailOnline: "One of the flight attendants was walking down the aisle when she collapsed. Then up to six other cabin crew members said they felt light-headed and as though they were going to faint. 
 
 "It was at that point the captain said he was turning the plane around. He said he wasn't willing to take the risk to keep going and hadn't got the crew to do it. 
 
 "It was just a bit mad. We didn't really know what was going on." 
 
 Why you need to watch the in-flight safety briefing 
 
 The American Airlines flight landed at Heathrow airport, five hours after it had left. 
 
 Passengers were not allowed to disembark while the plane was surrounded by police cars, ambulances and fire crews. 
 
 London Ambulance crews checked over six patients who were feeling unwell and discharged them on the scene. 
 
 A spokesperson for American Airlines confirmed the plane turned round due to a medical emergency and said it was not security-related. ||||| Get daily updates directly to your inbox + Subscribe Thank you for subscribing! Could not subscribe, try again later Invalid Email 
 
 Mystery surrounds an unknown illness which has spread though a passenger jet and forced it to turn round. 
 
 Up to seven of 13 crew members and "many passengers" were struck down with the strange disease - but at this stage no one knows what it is. 
 
 A British passenger has described panic on board the American Airlines flight from London Heathrow to LAX a when crew asked if there was a doctor on board. 
 
 A spokesman for the airline said there was "medical emergency" and people on the flight were "ill" but had no other information. 
 
 Read more: Doctor describes burning smell on mystery illness plane 
 
 Flight AA109 was close to Keflavik, a town in southwest Iceland, when crew declared a medical emergency and decided to head back to London. 
 
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 Passengers were asked if there was a doctor on board before the decision to abort the flight was taken at approximately 2.50pm. 
 
 Read more: British passenger describes panic on American Airlines flight as '7 of 13 crew and many passengers taken ill' 
 
 Paramedics and fire crews surrounded the plane as it landed at Heathrow moments ago. 
 
 Lee Gunn, who was on board the flight, told the Mirror Online: "About 2.5 hours into the flight just as we were passing Iceland we had a Tannoy announcement asking for any doctors, nurses or medical professionals on board to report to the boarding doors to assist with unwell passengers. 
 
 (Image: Lee Gunn) 
 
 "The lights then came on in the cabin and there was lots of commotion. 
 
 "I'm a bit of a plane geek myself so thought 'here we go, Reykjavik here we come' but it was announced about 20 minutes after we were going to divert back to LHR. 
 
 "It was also reported that 7 of the crew - 13 on board in total I believe - had fallen ill, along with 'many' passengers." 
 
 (Image: Lee Gunn) 
 
 The flight was met by Paramedics as it touched down at Heathrow just moments ago - five hours after it first took off. 
 
 It is thought the passengers luggage may have been retained for checks by the carrier. 
 
 Read more: American Airlines flight attendants taken to HOSPITAL after hitting bad turbulence on way to Manchester Airport 
 
 A statement from American Airlines said: "American Airlines Flight AA 109, a Boeing 777-300, operating to Los Angeles International Airport (LAX) from London Heathrow, is returning to Heathrow due to a medical emergency. 
 
 "The aircraft departed London Heathrow at 1205 local time and is expected to land at Heathrow at 1700 local time. 
 
 "We apologise to our customers for the inconvenience to their travel plans."
– An American Airlines flight bound for Los Angeles had to return to London on Wednesday after passengers and crew fell ill on board. One flight attendant "literally just fainted ... just fell forward, put her hand out and hit the floor," one of 188 passengers on board tells ABC News. "It was crazy." Another passenger tells the Daily Mirror there was "lots of commotion" as crew members asked if there were any doctors on board to treat the ill, which included at least two passengers and four crew members, some of whom said they felt light-headed. (The numbers are all over the map: The Independent, for instance, says seven members of the crew and "many passengers" initially fell ill.) The flight was near Iceland when the pilot made the decision to return to Heathrow Airport, making an emergency landing about five hours after takeoff. "There were police cars, ambulances, and firefighters who escorted us down the runway and then we were held for 45 minutes before docking," a passenger says, per the Telegraph. Crews searched the plane but found no hazardous substances. All unwell passengers and crew members were examined and released. Officials say the plane was being inspected by maintenance engineers.