It has been over a year since the crash of Sriwijaya Air flight SJY-182, and the investigation isn’t over. But more details have now emerged.
62 people perished in this crash, that took place on the 9th of January last year. In general, investigators aim to have a final report on an accident or serious incident within a year. At least this is the ICAO standard, but aviation authorities (in all countries) often need more time. And it appears that this will be the case for SJY-182.
However, the Indonesian authorities have now issued an Interim Statement about the Sriwijaya crash investigation (link at the end). And it contains some new information, regarding the state of the cockpit voice recorder (CVR). As a reminder, divers found the CVR over two and a half months after the crash. This was because its pinger/beacon had separated itself from the unit’s memory casing. Divers found the entire unit in pieces.
CVR – A Partial Insight
Fortunately, the investigators managed to download the memory unit of the CVR a few days after its discovery. Unfortunately, we now learn that the investigation team only got a partial picture of the Sriwijaya crash, from the CVR. This is because the recorder did not capture readable inputs from all four available audio channels. These channels are as follows:
- Channel1 recorded the passenger announcement system,
- Channel2 recorded the SIC station audio,
- Channel3 recorded the PIC station audio,
- Channel4 recorded the cockpit area microphone.
In its Interim Statement, the investigation team into the Sriwijaya crash reveals that only channels 1 and 2 worked properly. In Channel 3, the voice of the PIC (Pilot in Command, i.e. the Captain) is unreadable. However, Channel 2 (the First Officer’s) recorded the Captain when the latter spoke loudly enough. Channel 4 only recorded a prominent tone, which interfered with other signals.
This partial picture has to be a hurdle for the investigation into the Sriwijaya crash. Previous statements showed a notable lack of inputs from the flight crew, during the event. But as we saw previously, this was an experienced crew. The Captain had nearly 18,000 flying hours, nearly half of which were on the 737. Similarly, the First Officer had 5,107 hours, nearly all of which was on type, as well.
Sriwijaya Crash Investigation – Background
The investigation into the Sriwijaya Air crash has shown that the aircraft experienced an asymmetric thrust condition. An unusual combination of malfunctions, relating to the autothrottle and the operation of the flaps, led to this condition. There were some distractions to the crew from weather and radio communications.
But the Sriwijaya crash investigation is also looking at how maintenance and flight crews routinely logged/reported malfunctions, at this airline. To that end, the team has been testing aircraft components that maintenance crews previously removed from the aircraft. These include the autothrottle computer, an autothrottle servo and a flight control computer.
Furthermore, we learned that the Sriwijaya crash investigation team has conducted test flights with other 737 Classic aircraft. The aim was to understand the interrelation between the autothrottle system and the flap, spoiler and aileron positions. The rigging of sensors for the aircraft’s flaps and spoilers appear to have played a role in the crash.
Investigators have also conducted several simulator sessions, to understand key factors in the crash. These took place in training centres in both Indonesia and in the United States. We will have more information on these and all other aspects of the investigation when the final report is ready. Unfortunately, this could still be several months away.