For those who have not yet read the report. My bold.
The contents of the non-volatile memory (NVM) from the equipment known to record data have been successfully recovered and are being analysed. The majority of the recorded data have no form of time stamp. So, whilst the order of some of the snapshots can be determined, their relative timing is unknown. Other systems use time references but ones that are not directly linked to UTC.
The Warning Unit has provided information on the order in which warnings were triggered during the flight but not when they occurred. The unit recorded the normal warnings associated with starting the helicopter, followed by a warning free status. It subsequently recorded intermittent LOW FUEL 1 warnings for the left fuel supply tank, then a permanent LOW FUEL 2 warning for the right fuel supply tank. This was followed by a further temporary LOW FUEL 1 warning, before it became permanent for the remainder of the
flight. These LOW FUEL warnings are triggered by thermal sensors in the supply tanks.
For this helicopter build configuration, they indicate when there is approximately 32 kg and 28 kg of fuel remaining in the left and right supply tanks, respectively. On receipt of these warnings, the manufacturer’s flight manual for the helicopter instructs the pilot to ‘LAND WITHIN 10 MINUTES’.
An alarm gong was also recorded followed by intermittent warnings relating to low rotor rpm. The penultimate warning recorded related to the battery discharging, which occurs when there is insufficient engine-driven generator power. The last warning related to an autopilot system failure. Investigation into the possible causes for the individual warnings is continuing.
Preliminary analysis of the FADEC data indicates that the right engine flamed out, followed, a short time later, by the left engine also flaming out. Since the maintenance reports only give timings relative to the moment the FADECs were turned on (which is not recorded), the exact times at which these flameouts occurred is unknown.
The recorded radio transmissions do not contain any reference by the crew to difficulties with the aircraft.
The AAIB investigation continues to examine all the operational aspects of this accident and to conduct a detailed engineering investigation.
In particular, the investigation will seek to determine why a situation arose that led to both the helicopter’s engines flaming out when 76 kg of fuel remained in the fuel tank group, why no emergency radio transmission was received from the pilot and why, following the double engine failure, an autorotative descent and flare recovery was not achieved.