The Indonesian authorities have found that a series of failures led to the fatal crash of an Indonesia Aerospace/Casa C212-100 on Bintan island in February 2011.
These include a failure to properly plan for the test flight, the 61-year-old Indonesian pilot-in-command not having the proper qualifications to conduct a test flight and his medical condition, which may have impaired his ability to fly an aircraft.
According to a final report released by the National Transportation Safety Committee (NTSC), the C212 operated by Sabang Merauke Raya Air Charter (SMAC), with registration PK-ZAI, took off from Hang Nadim airport on Batam on 12 February for a test flight after the aircraft's number one engine was replaced.
Approximately 26 minutes after taking off, the aircraft disappeared from radar and air traffic controllers at Tanjung Pinang and other aircraft in the area were unable to make radio contact.
After a short search and rescue, the wreckage was found at Gunung Kijang forest on Bintan. The five occupants, consisting of two pilots and three engineers, died.
The investigation found that the company was "most likely not well prepared" for the test flight in relation to improper "pilot qualification and test flight procedure" and that was a significant contribution to the incident.
It found that there were discrepancies between the aircraft and engine maintenance manuals and the company's maintenance manuals on whether a test flight should have actually taken place.
The aircraft was certified as a military aircraft, but it was modified for civilian operations. However, the serial number of the aircraft in its military configuration was missing from the certification.
The investigation could not find any details of the flight test plan, even though this should have been filed, according to Indonesian regulations.
The report also says that the pilot-in-command did not have "training or qualification in test flight", and that he did not have authorisation from the company to perform the test flight.
It adds that the pilot's medical records indicated that he showed severe problems with his inner-ear balance system, during a medical check that was close to the incident. This would have meant that he could not respond normally to the three-dimensional motion or movement, says the NTSC.
As a result of the crash, the Indonesian directorate general of civil aviation (DGCA) issued an instruction to all Indonesian operators to ensure that all safety precautions are evaluated before they conduct maintenance practices in an airport area.
The DGCA has to ensure that the flightcrew has a detailed flightplan prior to any test flight, that all critical maintenance tasks are doubly inspected, the cockpit voice recorder is properly maintained and the operator subscribes to the latest manual.
The DGCA also conducted a special audit of SMAC and temporarily suspended its air operator's certificate. As a result of the audit, the company replaced some managerial positions in order to improve its safety management and procedures.
It also recommended that the DGCA ensure that the Aviation Medical Centre conducts additional medical examinations for pilots over 60 years old.
The DGCA should also "reinforce and review the procedure for test flights" and the requirements for company test pilots, adds the NTSC.