Hundreds of passengers were stranded at Vancouver International Airport today, scrambling for flights after their British Airways plane to London made an emergency landing late Monday night.

We know that 22 cabin crew and three pilots from the plane went to hospitals in the Vancouver area and were released shortly after.

And that's about where the official information stops.

British Airways is investigating, the airport hasn't commented, and neither has the union representing flight attendants, which says it's still trying to figure out what happened.

Accounts from the passengers give some clues, and even more speculation.

Over the Prairies, passengers were initially told they'd be landing in Calgary, but then learned the plane would land in Vancouver.

Here are five questions about the emergency landing of Flight 286.

1. What happened on that plane?

Passengers told CBC News that things seemed normal on Flight 286 until a couple of hours after takeoff.

Then, as dinner was being served, an announcement came from the captain.

"The captain came on and said there was some minor technical difficulties and we were diverting to Calgary instead of London," recalls passenger Jaakko Virtanan.

"I didn't smell any smoke.… I just smelled the roast beef or whatever that I didn't get, because they stopped serving dinner at that point."

Passenger Stefan Orberg said one attendant asked him if he felt anything in his eyes, before Flight 286 made an emergency landing in Vancouver. (CBC)

Then, another announcement: someone was sick, and they'd land in Vancouver.

Making an emergency landing with such a big plane suggests a major problem, according to a retired pilot and former Transport Canada flight safety officer.

"Something serious was happening," said Jock Williams. "You don't turn around an Airbus A380 … without thinking long and hard about it."

Don Blaser, sitting in business class, said the crew members didn't look sick when they grabbed their luggage and left the plane. (CBC)

2. How many people got sick?

The airline has said 25 crew members went to hospital — as a precaution — but it's not clear how many were actually ill.

An initial statement said "a crew member required medical attention," but by Tuesday afternoon the company said "several crew members reported feeling unwell."

"When we landed, the crew came and got their luggage and left immediately, and we're all sitting there looking around," said passenger Don Blaser, irritated that customers were left on the plane.

Video from the airport shows an ambulance leaving the scene, accompanied by a city bus filled with a number of crew members and paramedics.

At Vancouver General Hospital, flight crew could be seen walking through the emergency room doors with their carry-on bags, escorted by paramedics. All were discharged.

Crew members, transported by bus to Vancouver General Hospital, could be seen walking into the emergency entrance with their luggage. (Ryan Stelting)

3. Was there a problem with smoke?

Health officials initially said crew were being treated for smoke inhalation, but later said it was unclear what made people feel unwell.

One passenger told CBC News that rescue personnel came on the plane wearing "gas masks" or some kind of respirator, but that he didn't smell smoke.

Another passenger, Stefan Orberg, wondered if there was something in the air.

"The [flight] attendants asked me, did you feel anything in your eyes? I thought, well, maybe I had."

A number of technical problems can lead to smoke or air problems on the plane, said Williams, but the air conditioning system would be shared by the whole plane — not just a few crew members.

Alternatively, a malfunction in the cockpit could affect just the cockpit crew, said Williams.

But we don't know which crew felt unwell, or whether air quality had anything to do with it.

The double-deck wide-body A380 is the largest commercial passenger aircraft in the world. (British Airways)

4. Why didn't the plane land in Calgary?

The passengers were initially told they'd land in Calgary, but actually touched down over the Rockies in Vancouver.

Some speculated that the size of the A380 — the largest commercial passenger jet in the world — meant it couldn't land at Calgary International, but the airport said it is "designed for and capable of accommodating A380 aircraft."

It's possible, said Williams, that burning more fuel en route to Vancouver made the landing easier.

"This airplane is too big and too heavy to land right down underneath us … but by the time we get to Vancouver … we'll be down to landing weight and that's a good move to make," said Williams.

The airline hasn't commented on why the plane landed in Vancouver.

Passengers lined up at Vancouver International Airport trying to find flights out to London after the British Airways plane made an emergency landing. (CBC)

5. Did anything happen on the plane?

With details so vague and conflicting, it can be tempting to wonder whether anything actually happened to make one or several people "unwell."

Passengers seated on the lower deck told CBC News they heard the problem was on the upper deck, whereas those seated above said the problem was below.

So-called "mass hysteria" does happen, including on a Vancouver bus in 2004, where a suspected poisoning — from what turned out to be harmless plant material — left passengers and paramedics ill.

Williams, however, thinks that's unlikely with crew trained to handle emergency situations.

"The kind of people that are flight crew, cabin crew, they're not the type who normally … go crazy when they see someone else feeling badly."