From Reuters:

LONDON — British Airways apologized on Friday after a crew member mistakenly played an emergency message warning Hong Kong-bound passengers that the plane they were on was about to plunge into the sea.

About 275 passengers on a Tuesday flight out of London's Heathrow Airport heard the message: "This is an emergency. We may shortly need to make an emergency landing on water," NBC News reported.

"People were terrified, we all thought we were going to die," passenger Michelle Lord, 32, told Britain's The Sun newspaper, which first reported the incident. "They said the pilot hit the wrong button because they were so close together."

"I can't think of anything worse than being told your plane's about to crash," the Sun quoted another passenger as saying.

The plane was flying over the North Sea at the time.

Cabin crew on the Boeing 747 quickly reassured passengers that the message was a mistake and there was no emergency, NBC News reported.

"We would like to apologize to passengers on board the flight for causing them undue distress," British Airways said in a statement.

"Our cabin crew immediately made an announcement following the message advising customers that it was played in error and that the flight would continue as normal," the airline said.

The airline is investigating the incident to determine whether it was human error or a computer glitch, British Airways told Reuters.

Similar incident last year

Britain's Telegraph newspaper on Friday reported that a similar incident occurred on an Aer Lingus flight from Dublin to Paris in 2009.

Crew played an announcement in English warning of turbulence, followed by one in French saying the crew was preparing for an emergency landing about twenty minutes into the flight, the newspaper reported.

An Aer Lingus spokesman apologized for that incident, saying a malfunction of the public address system was to blame, according to the paper.

"This sort of thing happens very rarely," the spokesman told the paper.

There is no such button on the flight deck! In the Senior Cabin crew members office under the stairs there is a PRA (Pre-recorded announcement) panel.

In this instance, there is a rumour that a selection was incorrectly made when an IFE seat reset was being attempted by a cabin crew member (which seems improbable to me). Whether or not this is correct will doubtless come out (at least internally) in the fullness of time.

I believe a similar event a few years ago resulted because of a passenger activating a guarded switch!

Whatever the cause, it for sure wasn't 'because of a pilot pushing the wrong button'.

Okay, first it's a crewmember ... fine.

And now it's "the pilot". We now, apparently, have a single-pilot 747 . And who the $%#! is "they"?

Agreed, although I've never flown a 747. All I've seen on the Boeings I've flown is an evacuation button, which just lit up a light in the cabin attendants' panel.

I can assure you that it does more than just put a light on in the cabin attendants panel

Whatever. The aural warning in question wasn't the evac horn. The source of the problem wasn't on the flight deck. My goodness, please take it easy with the frown "smilies" (frownies?). This isn't an oral. Geez!

You are the weakest link! Goodbye !


....

No frownie, at least.

(Reuters) - British Airways apologized to passengers after an emergency message warning they were about to crash into the sea was played by mistake.
About 275 passengers were on the London Heathrow to Hong Kong flight on Tuesday evening when the automated message went out. The plane was flying over the North Sea at the time.
Cabin crew quickly realized the error and moved to reassure the terrified passengers.
"We all thought we were going to die," Michelle Lord, 32, of Preston, northern England, told The Sun newspaper.
Another passenger was reported saying: "I can't think of anything worse than being told your plane's about to crash."
A spokesman for British Airways said an investigation was under way to discover whether it was human error or a computer glitch.
"We apologize to passengers on board the flight for causing them undue distress," he added in a statement.
"Our cabin crew immediately made an announcement following the message advising customers that it was an error and that the flight would continue as normal."


We're about to crash, passengers told in error | Reuters