Intermezzo
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I hope the ping wasn't from one of the search planes.
Do all planes have black boxes ?
the search planes beacon would not be sending a ping
Once the beacon becomes immersed into water, a built-in "water switch" activates it (water closing an electric circuit), and the beacon starts emitting its "pings"; the battery power should be sufficient for at least 30 days after the activation.
A 37.5 kHz (160.5 dB re 1 μPa) pinger can be detectable 1–2 kilometres (0.62–1.24 mi) from the surface in normal conditions and 4–5 kilometres (2.5–3.1 mi) in good conditions. A 37.5 kHz (180 dB re 1 μPa) transponder pinger can be detected 4–5 kilometres (2.5–3.1 mi) in normal conditions and 6–7 kilometres (3.7–4.3 mi) in good conditions. Transponder 10 kHz (180 dB re 1 μPa) range is 7–9 kilometres (4.3–5.6 mi) in normal conditions and 17–22 kilometres (11–14 mi) in good conditions.
http://avstop.com/history/flightrecorder.htm
Both recorders are installed in the most crash survivable part of the aircraft, usually the tail section. Each recorder is equipped with an Underwater Locator Beacon (ULB) to assist in locating in the event of an overwater accident. The device called a "pinger", is activated when the recorder is immersed in water. It transmits an acoustical signal on 37.5 KHz that can be detected with a special receiver. The beacon can transmit from depths down to 14,000 feet.