Will the above mentioned equipment still work and transmit data/location information if an explosion occurs inside the aircraft?
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2 Answers
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As ratchetfreak noted, the recorders don't transmit data, attached to them is a location beacon that operates for up to 30 days.
This location beacon isn't always successful in enabling searchers to find the recorders. In the case of AF447, it took two years before a search located the aircraft debris field on the sea floor and recovered it's recorders.
As for withstanding the stresses of an explosion, it obviously depends on the strength of the explosion and it's location in the aircraft. In the case of Pan Am 103, destroyed in flight by explosives, the recorders were recovered and data extracted.
A DFDR must obviously have a high degree of ‘crashworthiness.’ The first units were required to withstand a momentary shock force of 1,000gs, the latest test standards now call for a test to 3,400gs for a duration of 6.5 milliseconds. The units also have to withstand a static crushing force at all of its six axis points of an applied load force of 5,000lbs for 5 minutes on each axis. Third, it must withstand a 500lbs piercing force test conducted by dropping it onto a ¼ inch steel pin from 10 feet. Lastly it must withstand a 1,100°C fire test for 60 minutes, and a 260°C oven test for 10 hours.
It is also required that these units are mounted within the tail area of an aircraft, away from the potential crushing force of any engines mounted nearby. The DFDR must be watertight to a depth of 20,000 feet in sea water, and survive at this depth for 30 days - and it must be fitted with an underwater locator beacon which will act like a sonar transmitter, by ‘pinging’ a signal through the medium of water that it might be laying in.
From http://www.avbuyer.com/articles/detail.asp?id=1858
- 1G is the force you feel on your feet standing up.
- 12G is the most a fighter-jet pilot normally experiences in combat.
- 16G sustained for 1 minute will kill you.
- 25G for an less than a second will hospitalize a fit racing car driver
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350G results in total body fragmentation
In a 727 crash landing
Impact forces at the front of the plane peaked at 12 G (12 times the force of gravity), in the centre the force was less, 8 G, at the rear it was 6 G, half that at the front and no greater than being hit in a fairground bumper car.
In a 720 crash, the maximum force was 14 G vertically for 0.8 seconds
This F4 phantom striking a concrete block at 480 MPH produced average peak forces of less than 60 G (see fig 7). The most solid elements (the engines) experienced forces of up to 700 G (fig 11).
3400G is therefore a lot.
answered Mar 18, 2014 at 14:04
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4$\begingroup$ 12g is what fighter pilots can manage with help of anti-g suit and good training. Without those anybody will be knocked unconscious much earlier. $\endgroup$ Mar 18, 2014 at 16:41
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$\begingroup$ The "total body fragmentation" link is broken. $\endgroup$– VikkiApr 17, 2019 at 21:43
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$\begingroup$ To get a feeling of the dimensions, a depleted uranium tank shell impacting on tank armor is decelerated with around 10.000 G. So with 3400 G we're in that area of forces that high energy projectiles recieve on striking a target. And decelerating from 1000 m/s to 0 m/s at 10.000 G will take approx. 10ms. So you could almost launch these things out of a cannon and they would still survive. $\endgroup$ Apr 18, 2019 at 14:52
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FDR and CVR don't transmit anything they just record data onto a magnetic tape or in a solid state drive, when the plane crashes/explodes they become just part of the debris and wait until they get found. The boxes are rated to survive nearly any feasible aircraft crash.
The special case is if they get submerged, then the attached locator beacon will activate and send out pings for at least 30 days.
The transponder will likely not survive and it needs power to work either way.
answered Mar 18, 2014 at 10:45
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1$\begingroup$ Adding to ratched freak's answer: the underwater locator beacons have a survival rate of 90% spanning 27 air accidents over the sea. Previous to the BEA AF447 investigation the rate was believed to be 80%. $\endgroup$ Mar 18, 2014 at 15:05