The tragic loss of all those on board China Eastern Airlines Flight MU 5735 continues in my thoughts and prayers. It’s good to hear announcements that progress is being made at the crash site.
It’s excellent news to see, from photographs published, that the aircraft accident recorder Crash Survivable Memory Units (CSMUs) are intact. Both the Digital Flight Data Recorder (DFDR) and Cockpit Voice Recorder (CVR) have been recovered.
The CVR records at least 2 hours of flight audio on a solid-state memory. Special procedures exit to recover the recordings from the recorder’s internal memory chips. This becomes difficult if the memory chips have suffered impact damage, like a crack for example. Investigators and the equipment manufacture are incredibly skilful extracting what data can be extracted.
The DFDR records at least 25 hours of flight data on a solid-state memory. There should be around 1000 parameters available for the analysis.
The technical specifications for these accident flight recorders were originally developed in the 1990s. At that time there was a transition from magnetic tape-based recordings to the use of solid-state memory. If the records are fully recoverable there should be a story of what happened in the critical moments before the aircraft started its fatal dive.
It’s possible to synchronise the recordings from the CVR and DFDR to reconstruct the actions of the crew. There are no video recordings. However, the audio and flight data can give a comprehensive picture of what happened during the accident.
Pilot commands and flight control system positions are recorded.
In parallel to the investigation of the material coming from the crash site, no doubt the authorities will be checking that no defect or deferred maintenance was reported in the technical log before departure of the aircraft.
By bringing all the evidence together a complete picture can be constructed. There are over 4,500 Boeing 737-800s now in service worldwide. This investigation will have a global impact.