Digital Flight Data Recorders (FDRs) and Cockpit Voice Recorders (CVRs) have become essential tools for accident investigation. With the Boeing 737-800, flight MU5735 having been in-service with China Eastern Airlines for less than 7 years there’s a good chance both recorders will help unravel the events leading to its fatal loss.
Accident flight recorders are dependent upon the aircraft digital and audio sources that are acquired when they are operating. Although the recorders are highly reliable in normal operation the sensors that feed them may not be so reliable. For this reason, the authorities have chosen to highlight the importance of a maintenance program that includes the entire recording system. It can be disruptive to an accident investigation if the information available from the recorders is insufficient, inaccurate, or of poor quality.
It’s rare for the recorders not to be found post-accident but it does happen in some remote locations. They can be recovered from enormous ocean depths and hostile terrain. In the sad story of Malaysia Airlines Flight MH370 in March 2014, neither the Boeing 777-200ER aircraft or flight recorders have been found.
In comparison with the successes of accident flight recording and replay the list of unrecovered and unusable recorders is short. However, it does point to the need to constantly revisit the minimum approval standards, installation, and maintenance requirements for recorders.
Having dual independent combined recorders can increase the chances of success. This is making the recorder a more general-purpose equipment capable of taking video sources and data from the air traffic system as well as an aircraft.
Independent backup electrical power can help keep the recorders going beyond significant damage to an aircraft. This does help pick-up the last possible information from an accident timeline.
There’s a case for a longer duration audio recording and increasing the number of data parameter retained. This demand for more information is insatiable since there’s always a scenario that can be imagined where more data would help an investigation.
Video recording has long been talked about. It’s happening in a few situations but has not generally been adopted as a mandatory requirement for large aircraft operations. I think it is needed.
 EASA Safety Information Bulletin, SIB No.: 2009-28R1, Issued: 08 January 2015.