JAL Flight 123 – Mount Takamagahara Crash
Date of Incident: August 12, 1985
Location: Mount Takamagahara, Gunma Prefecture, Japan
🧭 What Happened
Japan Airlines Flight 123 was a scheduled domestic flight from Tokyo Haneda to Osaka Itami. Twelve minutes after takeoff, the Boeing 747SR suffered explosive decompression due to a failed rear pressure bulkhead. The aircraft lost its vertical stabilizer and all hydraulic systems, rendering it nearly uncontrollable. After 32 minutes of erratic flight, it crashed into Mount Takamagahara, killing 520 of the 524 onboard. It remains the deadliest single-aircraft accident in aviation history.
✈️ Aircraft Details
Flight Number: JL123 / JAL123
Aircraft Type: Boeing 747SR-46
Registration: JA8119
Departure: Tokyo Haneda Airport (HND)
Destination: Osaka Itami Airport (ITM)
Fatalities: 520
Survivors: 4 (all seated in rear rows)
🔍 Key Factors
The aft pressure bulkhead had been improperly repaired by Boeing technicians following a 1978 tailstrike. Instead of a single splice plate with three rows of rivets, two plates were used, compromising structural integrity. Fatigue cracks developed over 12,319 pressurization cycles, eventually causing the bulkhead to rupture.
📆 Timeline of Events
- 09:12 UTC – Takeoff from Haneda (Runway 15L)
- 09:24 UTC – Explosive decompression over Sagami Bay
- 09:26 UTC – Emergency declared; aircraft begins phugoid oscillations
- 09:33 UTC – Crew reports “uncontrollable” to Tokyo ATC
- 09:47 UTC – Aircraft enters final descent over Gunma
- 09:56 UTC – Impact with Mount Takamagahara
🎙️ Cockpit Voice & Flight Data
“Hydraulic pressure down… amber light on…” — Flight Engineer
“We cannot do anything now!” — Captain Takahama
The CVR captured the crew’s struggle to control the aircraft using engine thrust alone. The FDR showed extreme pitch and roll oscillations. Both recorders were recovered and analyzed by AAIC Japan and NTSB USA.
⚙️ Aircraft Systems & Failures
- Improper bulkhead repair in 1978 led to fatigue cracks
- Explosive decompression severed all hydraulic lines
- Loss of vertical stabilizer and rudder control
- Aircraft entered phugoid and Dutch roll cycles
🛡️ Aftermath and Reforms
- AAIC Final Report published in 1987
- JAL paid ¥780 million in condolence payments
- Mandatory TCAS installation on Japanese aircraft by 1998
- Boeing revised bulkhead repair procedures globally
- Memorials erected at crash site and in Tokyo