Investigation Summary
During the descent into Yogyakarta, the crew identified thunderstorm cells on their weather radar and attempted to navigate through what appeared to be a gap in the precipitation. However, the intensity of the storm likely caused radar attenuation, where heavy rain and hail absorbed the radar pulses, creating a 'shadow' that looked like a clear path but was actually the core of the storm. As the aircraft entered this cell at 19,000 feet with engines at flight idle, the massive ingestion of water and hail caused both CFM56 engines to flame out. The crew attempted multiple relights, but these failed because the aircraft was still within the high-density precipitation. Crucially, the aircraft's nickel-cadmium battery was in a degraded state due to improper maintenance, showing only 22 volts instead of the required 24. The repeated restart attempts exhausted the remaining charge, leaving the crew with no electrical power to start the APU or maintain flight instruments. Emerging from the clouds at 8,000 feet, the pilots spotted the Bengawan Solo River and performed a gear-up ditching. The aircraft remained largely intact, but the tail struck the rocky riverbed, causing the rear galley floor to fail.
Final Conclusions
The NTSC concluded the primary cause was the ingestion of hail and rain exceeding the engine's certified capabilities at flight idle. Contributing factors included the crew's failure to follow the engine relight procedure (waiting only one minute between attempts instead of three) and the failure to start the APU first. The total electrical failure was attributed to inadequate battery maintenance, which left the crew without the power necessary for emergency systems and engine restarts.
Video Analysis
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Airframe & Maintenance
Crew Experience
Captain
Abdul Rozaq, age 44
First Officer
Harry Gunawan, age 46
Systems & Failure Modes
CFM56-3B1 Engines
High-bypass turbofan engines that flamed out due to water and hail ingestion levels exceeding their certification limits at low RPM.
Weather Radar
The onboard radar likely suffered from attenuation, leading the pilots to believe a severe storm core was a safe passage.
NiCd Battery
The aircraft's emergency battery, which failed to provide sufficient power for an APU start due to inadequate maintenance.
Interesting Facts
- 01The aircraft was a Boeing 737-300 delivered in 1989.
- 02The ditching was performed with flaps and landing gear retracted to minimize drag and impact forces.
- 03The only fatality was a flight attendant seated in the rear of the aircraft where the floor was ripped away.
- 04The battery was found to have only 22 volts of charge prior to the flameout due to poor maintenance.
- 05The captain, Abdul Rozaq, later survived the 2018 Sulawesi earthquake and tsunami.
Safety Actions & Advisories
Engine Power Management
The NTSB recommended that pilots be advised to maintain higher engine power levels (above flight idle) when flying through moderate to severe precipitation to prevent flameouts.
Radar Training
Investigators highlighted the need for formal pilot training in interpreting weather radar images, specifically regarding radar attenuation and tilt management.
Known Controversies & Unanswered Questions
Engine Certification Standards
Reference ↗The accident raised significant concerns regarding the adequacy of FAA and engine manufacturer certification standards for water and hail ingestion. The CFM56 engines flamed out despite being within their certified limits, leading to a re-evaluation of how engines perform at flight idle in extreme precipitation.