Singha wrote:floation devices will only work if the recorders are fitted into a VL tube atop the cockpit and a altimeter fires them off if the plane is about to crash, or a water sensor lets loose a compressed air cartridge later. adds to the expense and complexity I would think...
Currently, EUROCAE specifies that a recorder must be able to withstand an acceleration of 3400 g (33 km/s²) for 6.5 milliseconds. This is roughly equivalent to an impact velocity of 270 knots and a deceleration or crushing distance of 450 cm. Additionally, there are requirements for penetration resistance, static crush, high and low temperature fires, deep sea pressure, sea water immersion, and fluid immersion.
FDRs are usually located in the rear of the aircraft, typically in the tail. In this position, the entire front of the aircraft is expected to act as a "crush zone" to reduce the shock that reaches the recorder. Also, modern FDRs are typically double wrapped, in strong corrosion-resistant stainless steel or titanium, with high-temperature insulation inside. They are generally fire engine red. They are designed to emit a locator beacon for up to 30 days, and can operate immersed to a depth of up to 6,000 meters (20,000 ft).
Since the recorders can sometimes be crushed into unreadable pieces, or even located in deep water, some modern units are self-ejecting (taking advantage of kinetic energy at impact to separate themselves from the aircraft) and also equipped with radio and sonar beacons (see emergency locator transmitter) to aid in their location.
Alternatively, other aircraft such as the Space Shuttle Orbiter do not possess an FDR but instead use down-links to transfer such data. This kind of system could potentially see wider use in aviation in modified form.
On 19 July 2005, the Safe Aviation and Flight Enhancement Act of 2005 was introduced and referred to the Committee on Transportation and Infrastructure of the U.S. House of Representatives. This bill would require installation of a second cockpit voice recorder, digital flight data recorder system and emergency locator transmitter that utilizes combination deployable recorder technology in each commercial passenger aircraft, currently required to carry each of those recorders. The deployable recorder system would be ejected from the rear of the aircraft at the moment of an accident. The bill was referred to the Subcommittee on Aviation and has not progressed since. One problem for the military is that these commercial devices offer no protection of the data that has been recorded. Therefore, they have the potential for exposing military secrets if the device is captured by non-friendly forces and exploited.