When a 737 Strays Off Course: The 2021 Sriwijaya Disaster
What Went Wrong, Plain and Simple
The fatal crash of a Sriwijaya 737‑500 on January 10, 2021, killed all 62 passengers and crew and was a grim reminder of Indonesia’s shaky aviation safety track record.
- Faulty autopilot throttle – the “autothrottle” that should keep engine power in line was misbehaving. Its logs were marked “problem” 65 times since 2013, yet nothing was fixed.
- Neglected asymmetry – after take‑off the left engine dropped to 34 % while the right stayed at ~92 %. The cockpit saw it, but didn’t act.
- A “normal” 737 doesn’t need a working autothrottle – pilots can control the levers manually, but they chose not to check the big red flags.
- Switched autopilot – at ~10,700 ft the autopilot disengaged and the plane began rolling left more than 45° straight into the Java Sea.
- Whispers, not orders – the first officer shouted “upset, upset” and “captain, captain” just before the recording cut. The captain’s channel was dead, making the mystery even tougher.
Why the Pilots Fell Short
When an aircraft goes out of the normal flying box—speed, angle or altitude—it’s called an upset. Pilots must spot these hiccups early, or they’ll be sidelined in the wings. In this case, the crew either felt confident enough to ignore the red alerts or simply didn’t recognize the telltale signs.
The report warned that confirmation bias and complacency were suspected culprits. For instance, while engine data and throttle positions were available, they didn’t trigger a recovery plan.
Training: A Missing Piece of the Puzzle
Indonesia hadn’t enforced any formal upset‑prevention or recovery training before this crash. The 2014 AirAsia tragedy had already taught that a 737 could crash if pilots ignore such oversights.
- Post‑2014: Training introduced after the investigation, but it remained incomplete.
- 2017: Regulatory mandate required upset training, yet oversight failed.
- 2018: The UN body ICAO recommending that the training also cover upset prevention was ignored.
- Today: Korean Air’s regulator is updating the curriculum to include both prevention and recovery.
Take‑Away: The Voice of Caution
As the investigators revealed, the tragedy stemmed not just from a mechanical flaw, but from a mental one: pilots remaining blind to dangerous asymmetry in engine power. In aviation, the “autothrottle” is a helpful tool, but it’s unreliable if you don’t keep an eye on the knobs.
In short, the Sriwijaya disaster is a high‑profile signal that maintenance schedules and pilot vigilance must go hand‑in‑hand—or else we’ll keep diving into the sea.
