A flight level (FL) is a standard nominal altitude of an aircraft, in hundreds of feet. This altitude is calculated from the International standard pressure datum of.....the average sea-level pressure, and therefore is not necessarily the same as the aircraft's true altitude either above mean sea level or above ground level.
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A flight recorder is an electronic recording device placed in an aircraft for the purpose of facilitating the investigation of an aircraft accident or incident. For this reason, flight recorders are required to be capable of surviving the conditions likely to be encountered in a severe aircraft accident. They are typically specified to withstand an impact of 3400 g and temperatures of over 1,000 C (1,832 F) (as required by EUROCAE ED-112). There are two common types of flight recorder, the flight data recorder (FDR) and the cockpit voice recorder (CVR). In some cases, the two recorders may be combined in a single FDR/CVR unit.