One wonders if it is that syndrome where one person faints/falls ill and others then believe that they have the same symptoms?

Like this???

The fact that the baggage is being checked seems to indicate they think it was something noxious. That could be simply something leaking from cargo, but it could also be an attempt at something nefarious.
Screening is very tight for explosives, but how many gases/chemicals could be smuggled on which would incapacitate/kill crew and pax? It's another vector which should be (is probably being) looked into.

Seems very odd they did not land in Iceland or one of the multitude of airports between Iceland and LHR.

If multiple passengers and/or crew were, in fact, unconscious, I would agree.

Probably not "odd" at all, especially if those involved in the decision making process considered matters carefully and decided the best solution wasn't to throw the aircraft on to the nearest runway.

(I suspect none of us here have a scooby doo what went on, but I'd put money on the newspaper reports being somewhat inaccurate)

The weather could have been completely shyte at keflavic.

Keflavik wx was not an issue.

Reports of a "burning" smell....

American Airlines crew reported BURNING smell on aborted Flight AA109 | Daily Mail Online

They were squawking 7700 on the way back and I would guess an emergency was declared since it was a U.S. carrier. We've had this discussion on other threads, recent guidance for us is to declare the emergency if in doubt since it gives you more latitude as far as compliance issues, e.g. diverting to an airport not in your ops specs, landing overweight etc.

Diversion choice
 

Could it be (and I am certainly no expert) That American may have better access to engineers and ground handling back at 'base' (in this case Heathrow) and better options to transfer passengers onto alternate flights from LHR for those who wanted to? If the situation on board is considered stable enough and the cabin is still secure then why divert to an unknown airport when you can just go back to where you started (fuel permitting)?

Granted we don't know what went on and all of our comments are purely speculative on here but if the affected passengers were not worsening, if I was in that situation I would want to return to LHR.

Maybe?
 

There have been a number of crass posts mocking the term 'equilibrium' . Maybe nobody has considered labyrinthitis, which I understand is a viral infection of the middle ear. I assure you, from personal experience, is extremely unpleasant. Getting the aircraft on the ground was a very wise decision.

Looks like no one was transported according to this London Ambulance tweet:

https://twitter.com/Ldn_Ambulance/st...55244563898370

Depends on what the doctor on board told the captain. If people have baro-trauma affecting their ears and causing vertigo (which I think is what was meant in the original reports) then rapid descent and the associated rapid pressure changes may not be advisable (or advised). A slow cruise descent with slow pressure change and minimum maneuvering may be the ideal. If you are going to take over an hour or so to get down and there doesn't appear to be an acute emergency, then choice of 'suitable airport' is wide open and return to an airport which is a maintenance base starts to figure higher in the decision making. They were not far out of Scottish airspace so 7700 and direct LHR in slow descent seems eminently sensible. If things did change there were several suitable airports en-route LHR for an emergency descent and land.

You can bet that the captain was not without advice :ok:

AA has diverted before to KEF as have the other legacy carriers in the US as KEF is one of the most common airport being as a suitable airport for ETOPS.

The PIC requested to divert back to LHR, even though Icelandic ATC had suggested KEF. The weather was not an issue. It would be very interesting to see why they went back to LHR

If burning was reported, then similar symptoms have been seen before with oil leaks from the HP compressor into the AC system.

Best guess - it's not unusual in similar situations for medics (possibly remote) to say that the medical condition(s) are not serious enough to necessitate an immediate landing but if an individuals condition deteriorates further a diversion may be required.

In the case of the AA flight I'd say that might well be a pretty compelling argument for not continuing westwards, and after discussion with "company" a decision was made to return to somewhere where the flight could be most easily "rebooted"....whilst retaining the option to drop into the likes of Kef, Glasgow or Manchester if required etc.

In any event it's perhaps also worth considering that given that we now know that no-one was admitted to hospital after landing so just maybe events weren't quite as dramatic as the papers would make us believe.

The aircraft concerned spent nearly 24 hours at LHR, then took what was presumably a test flight down to Cornwall and back;

N723AN - Aircraft info and flight history - Flightradar24

It was scheduled to operate AA9276 LHR-LAX today departing at 13:00 but this was delayed and it didn't depart until 15:43;

http://www.flightradar24.com/reg/n723an