Japan Air Lines Flight 123 was a scheduled domestic passenger flight from Tokyo to Osaka, Japan. On August 12, 1985, the Boeing 747 flying the route suffered a severe structural failure and decompression 12 minutes into the flight. After flying under minimal control for a further 32 minutes, the 747 crashed in the area of Mount Takamagahara, 100 kilometres (62 mi; 54 nmi) from Tokyo.

The aircraft, featuring a high-density seating configuration, was carrying 524 people. The crash killed all 15 crew members and 505 of the 509 passengers on board, leaving only four survivors. An estimated 20 to 50 passengers had survived the initial crash, but died due to their serious injuries a few hours later while awaiting rescue. The crash of Flight 123 is the deadliest single-aircraft accident in aviation history.

Japan's Aircraft Accident Investigation Commission (AAIC), assisted by the U.S. National Transportation Safety Board, concluded that the structural failure was caused by a faulty repair by Boeing technicians following a tailstrike incident seven years earlier. When the faulty repair eventually failed, it resulted in a rapid decompression that ripped off a large portion of the tail and caused the loss of all on-board hydraulic systems, disabling the aircraft's flight controls.

The accident aircraft, a Boeing 747SR-46 with registration JA8119 (serial number 20783, line number 230), was built and delivered to Japan Air Lines in 1974 (prior to them changing their name to "Japan Airlines"). It had accumulated slightly more than 25,000 flight hours and 18,800 cycles at the time of the accident (one cycle consisting of takeoff, cabin pressurization, depressurization, and landing).

On June 2, 1978, while operating Japan Air Lines Flight 115 along the same route, JA8119 bounced heavily on landing while carrying out an instrument approach to runway 32L at Itami Airport. The pilot then excessively flared the aircraft, causing a severe tail strike on the second touchdown. No fatalities occurred among the 394 people on board, but 25 people sustained injuries, 23 minor and 2 serious. The tailstrike cracked open the aft pressure bulkhead. The damage was repaired by Boeing technicians, and the aircraft was returned to service. The aircraft had flown for 8,830 hours at the time of the tailstrike incident.

At the time of the 1985 fatal accident, the aircraft was on the fifth of its six planned flights of the day. The flight had 15 crew members, including 3 cockpit crew and 12 cabin crew.

The cockpit crew consisted of:

• Captain Masami Takahama (高浜 雅己, Takahama Masami), aged 49, served as a training instructor for First Officer Yutaka Sasaki on the flight, supervising him while handling the radio communications, and also acting as the first officer. Takahama was a veteran pilot, having logged around 12,423 total flight hours, roughly 4,842 hours of which were accumulated flying 747s.
• First Officer Yutaka Sasaki (佐々木 祐, Sasaki Yutaka), age 39, was undergoing training for promotion to the rank of captain, and flew Flight 123 as one of his final training/evaluation flights, acting as captain on the flight. He had about 3,963 total flight hours to his credit, and had logged roughly 2,665 hours in the 747.
• Flight Engineer Hiroshi Fukuda (福田 博, Fukuda Hiroshi), age 46, was a veteran flight engineer with approximately 9,831 total flight hours, of which roughly 3,846 hours were accrued flying 747s.

Nationality	Passengers	Crew	Survivors	Total
Japan	487	15	4	502
China	1	0	0	1
West Germany	2	0	0	2
British Hong Kong	4	0	0	4
India	3	0	0	3
Italy	2	0	0	2
South Korea	3	0	0	3
United Kingdom	1	0	0	1
United States	6	0	0	6
Total (9 Nationalities)	509	15	4	524

The flight was around the Obon holiday period in Japan when many Japanese people make yearly trips to their hometowns or resorts. Twenty-two non-Japanese were on board the flight, including four residents of Hong Kong, two each from Italy and the United States, and one each from West Germany and the United Kingdom. Some ostensible foreigners had dual nationality, and some of them were residents of Japan.

The four survivors, all female, were seated on the left side and toward the middle of seat rows 54–60, in the rear of the aircraft. They were Yumi Ochiai, an off-duty flight attendant; Hiroko and Mikiko Yoshizaki, a mother and her 8-year-old daughter; and Keiko Kawakami, a 12-year-old girl who lost her parents and sister in the crash. Among the victims were Japanese singer and actor Kyu Sakamoto, and banker Akihisa Yukawa, the father of violinist and composer Diana Yukawa.

The flight connected two of the largest cities of Japan, and a number of other celebrities initially booked the flight but ultimately avoided the tragedy by either switching to another flight or using the Tokaido Shinkansen instead. These include Sanma Akashiya, Masataka Itsumi and his family, Johnny Kitagawa, and the cast of Shōten at the time. Some members of the Shonentai were also scheduled to travel with Kitagawa, but they ultimately stayed behind in Tokyo.

Flight 123 audio transcript
Flight 123 CVR and ATC transcript in English with map of flight on YouTube

The aircraft landed as JL366 at Haneda Airport in Ōta, Tokyo, Japan, from Fukuoka Airport at 5:12 p.m. After almost an hour on the ground, Flight 123 pushed back from gate 18 at 6:04 p.m. and took off from Runway 15L at 6:12 p.m., 12 minutes behind schedule. Twelve minutes after takeoff, at 6:24 p.m., at near cruising altitude over Sagami Bay 3.5 miles (3.0 nmi; 5.6 km) east of Higashiizu, Shizuoka, the aircraft underwent rapid decompression,  bringing down the ceiling around the rear lavatories, damaging the unpressurised fuselage aft of the plane, unseating the vertical stabilizer, and severing all four hydraulic lines. A photograph taken from the ground shows the vertical stabilizer missing.

The pilots set their transponder to broadcast a distress signal. Captain Takahama contacted Tokyo Area Control Center to declare an emergency, and request a return to Haneda Airport, descending and following emergency landing vectors to Oshima. Tokyo Control approved a right-hand turn to a heading of 090° east back toward Oshima, and the aircraft entered an initial right-hand bank of 40°, several degrees greater than observed previously. Captain Takahama ordered First Officer Sasaki to reduce the bank angle,  and expressed confusion when the aircraft did not respond to the control wheel being turned left. The flight engineer reported that hydraulic pressure was dropping. The captain repeated the order to reduce the bank angle, as the autopilot had disengaged. He ordered the first officer to bank it back, then ordered him to pull up. None of these attempted maneuvers produced a response. The pilots realised the aircraft had become virtually uncontrollable, and Captain Takahama ordered the copilot to descend.

Heading over the Izu Peninsula at 6:26 p.m., the aircraft turned away from the Pacific Ocean and back toward the shore,  but only turned right far enough to fly a north-westerly course. Seeing that the aircraft was still flying west away from Haneda, Tokyo Control contacted the aircraft again. After confirming that the pilots were declaring an emergency, the controller asked the nature of the emergency. At this point, hypoxia appeared to have begun setting in, as the pilots did not respond. Also, the captain and co-pilot asked the flight engineer repeatedly if hydraulic pressure had been lost, seemingly unable to comprehend it.  Tokyo Control contacted the aircraft again and repeated the direction to descend and turn to a 90° heading to Oshima. Only then did the captain report that the aircraft had become uncontrollable. (Tokyo: "Japan Air 124 [sic] fly heading 090 radar vector to Oshima." JAL123: "But now uncontrol." Tokyo: "Uncontrol, roger understood.") 

The aircraft traversed Suruga Bay and passed over Yaizu, Shizuoka,  at 6:31:02 p.m. Tokyo Control asked if they could descend, and Captain Takahama replied that they were now descending, stating that their altitude was 24,000 feet (7,300 m). Captain Takahama declined Tokyo Control's suggestion to divert to Nagoya Airport 72 nautical miles (83 mi; 133 km) away, instead preferring to land at Haneda,  which had the facilities to handle the 747. The flight data recorder shows that the flight did not descend, but was rising and falling uncontrollably.  With the total loss of hydraulic control and non-functional control surfaces, the aircraft entered phugoid oscillations lasting about 90 seconds, in which airspeed decreased as it climbed and increased as it fell. The rise in airspeed increased the lift over the wings, resulting in the aircraft climbing and slowing down, then descending and gaining speed again. Almost immediately after the separation of the stabiliser and rudder removed the only means of damping yaw, the aircraft began to exhibit Dutch roll, simultaneously yawing right and banking left, before yawing back left and banking right. At some points the banking motion became very profound, with large arcs of around 50° in cycles of 12 seconds.

Despite the complete loss of control, the pilots continued to turn the control wheel, pull on the control column, and move the rudder pedals up until the moment of the crash. The pilots also began efforts to establish control using differential engine thrust, as the aircraft slowly wandered back toward Haneda. Their efforts had limited success. The unpressurised aircraft rose and fell in an altitude range of 20,000–25,000 feet (6,100–7,600 m) for 18 minutes, from the moment of decompression until around 6:40 p.m., with the pilots seemingly unable to figure out how to descend without flight controls. This was possibly due to the effects of hypoxia at such altitudes, as the pilots seemed to have difficulty comprehending their situation as the aircraft pitched and rolled uncontrollably. The pilots possibly were focused, instead, on the cause of the explosion they had heard, and the subsequent difficulty in controlling the jet. The flight engineer did say they should put on their oxygen masks when word reached the cockpit that the rear-most passenger masks had stopped working. None of the pilots put on their oxygen masks, however, though the captain simply replied "yes" to both suggestions by the flight engineer to do so. The accident report indicates that the captain's disregard of the suggestion is one of several features "regarded as hypoxia-related in [the] CVR record[ing]." Their voices can be heard relatively clearly on the cockpit area microphone for the entire duration, until the crash, indicating that they did not put on their oxygen masks at any point in the flight.

At 6:35 p.m. the flight engineer responded to multiple (hitherto unanswered) calls from Japan Air Tokyo via the SELCAL (selective-calling) system. Having just been informed about the inoperative oxygen masks, the flight engineer voiced the (erroneous) assumption that the R-5 door was broken and informed the company that they were making an emergency descent. Japan Air Tokyo asked if they intended to return to Haneda, to which the flight engineer responded that they were making an emergency descent, and to continue to monitor them.

Eventually, the pilots regained limited control of the aircraft by adjusting engine thrust. In doing so, they dampened the phugoid cycle and somewhat stabilised their altitude. However, given jet engines' inertia and the resulting response time (to changes in throttle), "[s]uppressing of Dutch roll mode by use of the differential thrust between the right and left engines is estimated practically impossible for a pilot." Shortly after 6:40 p.m., they lowered the landing gear using the emergency extension system in an attempt to dampen the phugoid cycles and Dutch rolls further. This was somewhat successful, as the phugoid cycles were dampened almost completely, and the Dutch roll was damped significantly, but lowering the gear also decreased the directional control the pilots were getting by applying power to one side of the aircraft, and the aircrew's ability to control the aircraft deteriorated.

Shortly after lowering the gear, the flight engineer asked if the speed brakes should be used, but the pilots did not acknowledge the request. The aircraft then began a right-hand descending 420° turn from a heading of 040° at 6:40 p.m. to a heading of 100° at 6:45 p.m., flying in a loop over Otsuki, due to a thrust imbalance created from having the power setting on Engine 1 (the left-most engine) higher than the other three engines. The aircraft also began descending from 22,400 feet (6,800 m) to 17,000 feet (5,200 m), as the pilots had reduced engine thrust to near idle from 6:43 to 6:48 p.m. Upon descending to 13,500 feet (4,100 m) at 6:45:46 p.m., the pilots again reported an uncontrollable aircraft. At this time, the aircraft began to turn slowly to the left, while continuing to descend. The thicker air allowed the pilots more oxygen, and their hypoxia appeared to have subsided somewhat, as they were communicating more frequently. The pilots also appeared to be understanding how grave their situation had become, with Captain Takahama exclaiming, "This may be hopeless" at 6:46:33 p.m. At 6:47 p.m., the pilots recognised that they were beginning to turn toward the mountains. Despite efforts by the crew to get the aircraft to continue to turn right, it instead turned left, flying directly toward the mountainous terrain on a westerly heading.

Around 6:50 p.m., a photographer on the ground captured a photograph of the aircraft, which showed that the vertical stabiliser was missing.

As the aircraft continued west, it descended below 7,000 feet (2,100 m) and was getting dangerously close to the mountains. Because of the thicker air at lower altitude, the cabin altitude alert momentarily turned off at this time, before resuming for the rest of the flight. The captain briefly ordered maximum engine power to attempt to get the aircraft to climb to avoid the mountains, and engine power was added abruptly at 6:48 p.m., before being reduced back to near idle; then at 6:49 p.m., it was ordered raised again. This greatly excited the phugoid motion, and the aircraft pitched up, before pitching back down after power was reduced. When power was added again, the aircraft rapidly pitched up to 40°, and the airspeed dropped down to 108 knots (200 km/h; 124 mph) at 6:49:30 p.m., briefly stalling at 9,000 feet (2,700 m). The captain immediately ordered maximum power at 6:49:40 p.m. as the stick shaker sounded. The aircraft's airspeed increased as it was brought into an unsteady climb. Possibly in order to prevent another stall, at 6:51 p.m., the captain lowered the flaps to 5 units—due to the lack of hydraulics, using an alternate electrical system—in an additional attempt to exert control over the stricken jet. It took 3 minutes and 10 seconds for the trailing edge flaps to reach 5 units. The leading edge flaps except for the left and right outer groups were also extended and the extension was completed at 6:52:39 p.m. From 6:49:03 to 6:52:11 p.m., Japan Air Tokyo attempted to call the aircraft again via the SELCAL radio system. During the entire period, the SELCAL alarm continued to ring, to which the pilots did not react.

The aircraft reached 13,000 feet (4,000 m) at 6:53 p.m., when the captain reported an uncontrollable aircraft for the third time. Shortly afterward, the controller asked the crew to switch the radio frequency to 119.7 for Tokyo Approach. Although the pilots did not acknowledge the request over the radio, they switched frequencies as instructed. Tokyo Approach then contacted the flight via the SELCAL system, briefly activating the corresponding alarm again until the flight engineer responded. At this point, the flight crew requested to be given their position, which, at 6:54 p.m., was reported to the flight as 45 nmi (83 km) northwest of Haneda, and 25 nmi (46 km) west of Kumagaya. At 6:55 p.m., the captain requested flap extension, and the co-pilot called out a flap extension to 10 units, but the flaps had already extended past 5 units at 6:54:30 p.m. and had reached 20 units 1 minute and 2 seconds later. Meanwhile, the aircraft had started banking abnormally toward the right; this might have been most likely due to an imbalance in the lift generated by the left and right flaps. Power was increased at the same time. While the flaps continued to extend, a differential thrust setting caused engine power on the left side to be slightly higher than on the right side, adding to the roll to the right.

One minute later, the flaps were extended to about 25 units, the bank angle exceeded 60°, and the nose began to drop. Captain Takahama immediately ordered the flaps to be retracted and power was added abruptly, but still with higher power settings on the left engines than on the right. The asymmetric thrust settings continued to increase as the bank angle continued and exceeded 80°. The captain was heard on the CVR desperately requesting for the flaps to be retracted and for more power to be applied in a last-ditch effort to raise the nose. The aircraft continued an unrecoverable right-hand descent toward the mountains as the bank angle recovered to about 70° and engines were pushed to full power, during which the ground proximity warning system sounded.

In the final moments, as the airspeed exceeded 340 knots (630 km/h; 390 mph), the pitch attitude leveled out and the aircraft ceased descending, with the aircraft and passengers/crew being subjected to 3 g of upward vertical acceleration.

The aircraft was still in a 40° right-hand bank when the right-most (#4) engine struck the trees on top of a ridge located 1.4 kilometres (0.87 mi) north-northwest of Mount Mikuni at an elevation of 1,530 metres (5,020 ft), which can be heard on the CVR recording. The backward shock of the impact, measuring 0.14 g, in addition to causing the loss of the thrust of the 4th engine, caused the aircraft to roll sharply to the right and the nose to drop again. The aircraft continued on this trajectory for 3 seconds until the right wing clipped another ridge containing a "U-shaped ditch" 520 metres (1,710 ft) west-northwest of the previous ridge at an elevation of 1,610 metres (5,280 ft). It is speculated that this impact separated the remainder of the weakened tail from the airframe, along with the outer third of the right wing, and the remaining three engines, which were "dispersed 500–700 metres (1,600–2,300 ft) ahead". After this impact, the aircraft flipped on its back, struck another ridge 570 metres (1,870 ft) northwest from the second ridge, near Mount Takamagahara, and exploded.

The impact registered on a seismometer located in the Shin-Etsu Earthquake Observatory at Tokyo University from 6:56:27 p.m. as a small shock, to 6:56:32 p.m. as a larger shock, believed to have been caused by the final crash. The shockwaves took an estimated 2.0–2.3 seconds to reach the seismometer, making the estimated time of the final crash 6:56:30 p.m. Thus, 32 minutes had elapsed from the bulkhead failure to the crash.

The aircraft crashed at an elevation of 1,565 metres (5,135 ft) in Sector 76, State Forest, 3577 Aza Hontani, Ouaza Narahara, Ueno Village, Tano District, Gunma Prefecture. The east-west ridge is about 2.5 kilometres (8,200 ft) north-northwest of Mount Mikuni. Ed Magnuson of Time magazine said that the area where the aircraft crashed was referred to as the "Tibet" of Gunma Prefecture.