"Brace, brace, brace."
If you're on an aircraft and you hear these words over the PA system from the flight deck something has clearly gone wrong. And because you're on a plane travelling at huge speeds you may just be wondering what good adopting a brace position - crouched over with your head against the seat in front - will actually do.
Well, quite a lot, it turns out, according to the experts. Here we reveal just why the brace position really can save your life - and why pillows and blankets will do nothing to soften the impact.
Firstly, according to one UK aviation safety expert, 87.7 per cent of aircraft accidents are survivable and result in zero fatalities, the Daily Mail reports.
So the brace position isn't futile (and neither is it a ruse simply to ensure intact dental records for identification).
And just why, according to the safety expert, is because it softens the critical "secondary impact" that passengers experience and means they're then able to escape before the aircraft catches fire.
The "secondary impact", he said, is when the body and head move forward into the object in front as the plane crashes.
He said, speaking anonymously: 'When a plane crashes you have two impacts. The first one passengers feel is a tightening of the seat belt. But as the aircraft stops you continue to move forward.
"But it's the secondary impact that's critical. What will happen is that your upper torso will move forward. And in moving forward you will hit something. That's certainly the case in economy class seats.
"But if you're in a survivable accident the way you brace yourself for impact could be the difference between self-evacuating the aircraft and not.
"If you can't self-evacuate because you're injured, then if you have a post-crash fire, you've got problems."
The importance of the brace position was underlined in an influential 1993 paper written by Richard F Chandler, from the FAA's Protection and Survival Laboratory, called Brace For Impact Positions.
"The best position to adopt is one where you crouch down and reduce the movement of the head in a forward direction.
"Anything you can do to stop your upper torso and your head moving forward is the best position to be in."
He added: "If you're in an aircraft accident you have a very good chance of survival. Very few accidents involve total impact with the ground, and those that do are probably non-survivable.
He explained how a crash involving a "relatively mild level of only 3gs of deceleration"could result in a passenger's head potentially hitting another part of the aircraft at a rate of 24 feet a second - or 215gs of deceleration if it crushed one half inch of material. But possibly peaking at 500g.
This could easily be fatal, he said.
He explained, however, that if the interior of the aircraft is designed to crush six inches on impact and you're in the brace position, this vicious deceleration can be calmed to around 18g, possibly even to 3g, the same rate as the aircraft crash as a whole.
Chandler, in his paper, recommended that pillows and blankets should never be used to aid bracing as "they're not designed to absorb energy or distribute impact loads over the body".
He warned that using them could "increase the likelihood of injury by giving a false impression... that the body is being properly supported".
Other no-no's, according to Chandler, are putting feet on the seat in front and bracing with the legs - this could break the seat - and wedging the legs under the seat in front. This could break the legs and the seat.
THE IDEAL BRACE POSITION
In 2016 Transport Canada Civil Aviation issued its recommended brace position:
1. The lower torso should be firmly against the back of the seat.
2. The lap strap portion of the safety belt should be worn as tight and as low across the hips as possible. The more tightly the lap strap is adjusted, the better restraint it will provide.
3. If the safety belt includes a shoulder harness, the harness should be adjusted so that it is tight but does not pull the lap portion of the safety belt upward.
4. The webbing of a lap strap and shoulder harness should lie flat against the body and should not be twisted.
5. Knees should be pressed together, and feet should be flat on the floor and slightly in front of the edge of the occupant's seat. Legs and feet should not be placed under the occupied seat or the seat forward of it in order to prevent feet/leg injury should either seat collapse during impact.
6. TCCA recommends that shoes be left on, with the exception of very high/spiked heeled shoes that, although unlikely, could puncture an evacuation slide. Leaving shoes on provides protection against sharp or molten metal, fuel, broken trees, debris, etc., acts as an insulator against snow, ice and hot surfaces, and can expedite escape away from the aircraft.
7. If removal of very high heeled shoes is necessary, shoes must be stowed in an approved stowage area (such as an overhead bin), and should not be placed in the seat pocket where they could injure the person while assuming the brace position.
8. Pillows or blankets should not be used between the passenger and the object he/she would brace against. Pillows and blankets are not usually designed to absorb energy or distribute impact loads over the body, and they could increase the likelihood of injury by giving a false impression that the body is being properly supported. Also, pillows and blankets create additional clutter in aisles which can be an impediment in an evacuation. Pillows or blankets may, however, be used as indicated in the information pertaining to the brace position for children in order to raise a small child so that the safety belt will fit securely.