The Rot Within: The crash of British European Airways flight 706
On the 2nd of October 1971, a British European Airways flight from London to Salzburg, Austria abruptly plunged from the sky while en route over Belgium, as the pilot broadcast his chilling final words to air traffic control: “Mayday, mayday, we’re going down vertically!”
The fiery crash of the four-engine Vickers Vanguard in a field outside the Belgian town of Aarsele killed 63 people and left investigators with a monstrous mechanical puzzle. Something had ripped apart the Vanguard’s tail section in flight, leaving debris scattered for miles downwind of the crash site, where the impact of the inverted aircraft had left behind only mangled wreckage and a smoldering crater. Only after painstaking analysis did investigators come to understand that the disintegration of the horizontal stabilizer and the subsequent loss of control were actually the result of a structural failure that occurred farther forward, where the pressurized passenger cabin met the unpressurized tail section. It was there that glaring gaps in the Vanguard’s inspection regime had allowed corrosion to take hold in the rear pressure bulkhead, resulting in a failure scenario that would be mirrored 14 years later in the much more famous crash of Japan Airlines flight 123. That dramatic follow-up has left the crash of BEA flight 706 as little more than a footnote — a lack of interest that this article seeks to address by giving this fascinating but forgotten disaster the attention that it deserves.
Prior to the creation of the unified British Airways in 1974, the state-owned British European Airways operated short to medium range flights within the United Kingdom and to destinations in Europe and the Near East. For most of its post-war history, the airline dominated these routes with the state’s blessing, straddling the line between an airline and a municipal transportation system — in fact, BEA and its international counterpart, the British Overseas Airways Corporation, collectively accounted for 90% of Britain’s scheduled airline capacity in 1969. The airline also served as a vehicle to support Britain’s domestic aircraft manufacturing industry, operating only British aircraft types, including the Hawker-Siddeley Trident, the BAC 1–11, and the Vickers Viscount, among many others.
Perhaps the most troubled aircraft type made possible by BEA’s “buy British” mandate was Vickers-Armstrongs’ hulking, four engine turboprop, christened the Vanguard. Designed specifically for BEA and Trans-Canada Air Lines, the Vanguard was conceived as a successor to the much smaller and highly successful Vickers Viscount, which became the first turboprop airliner when it entered service in 1953. A significant upgrade over its predecessor, the Vanguard could carry up to 139 passengers, almost double the capacity of the Viscount, at higher speeds and altitudes. If that sounds like a lot of passengers for a turboprop, you would be right: no modern civilian turboprop carries that many, because the medium-to-high capacity market has been dominated by jets since the early 1960s. This very fact rendered the Vanguard obsolete from almost the moment it entered service. By the time the first prototype flew in January 1959, the first Boeing 707 jets were already flying passengers, and subsequent teething problems with the Vanguard’s Rolls Royce Tyne engines further delayed its entry into commercial service. BEA did not begin flying its Vanguards until March 1961, fully six years after it ordered them, and 11 years after it proposed the concept to Vickers-Armstrongs. By then, the market for which the Vanguard was conceived had already been supplanted by jets, and only 44 were ever built, all of them for BEA and Trans-Canada Air Lines. No one else ordered even a single airframe.
By 1971, BEA was still operating its Vanguards on domestic and international routes, despite their obsolescence. It is unclear whether the route from London Heathrow to Salzburg, Austria, was normally one of these: some contemporary sources suggest that this route was usually operated by a smaller Viscount 800. Either way, on the 2nd of October 1971, this route was assigned to a Vanguard type 951 registered as G-APEC.
Operating as flight 706, G-APEC left Heathrow at 9:34 a.m. with a crew of 8 and only 55 passengers, leaving the plane less than half full. In command was a three-person flight deck crew consisting of 40-year-old Captain E. T. Probert, 38-year-old First Officer J. M. Davies, and an additional pilot, 27-year-old B. J. S. Barnes; in the cabin, four flight attendants oversaw the passengers. Also riding in the cockpit was a BEA Viscount pilot who was observing the flight in order to gain experience with Salzburg air traffic control procedures.
As flight 706 passed overhead Dover and climbed out over the English Channel, bound for its cruising altitude of 19,000 feet, none of the crew were aware that their aircraft was already on the brink of catastrophe.
The Vickers Vanguard featured a cabin area that was separated from the unpressurized tail section by the rear pressure bulkhead, a basic structural feature of any pressurized airliner. Shaped like a sideways dome facing rearward, the bulkhead was constructed of aluminum sheets 0.7 mm in thickness, consisting of 11 wedge-shaped sections arranged around a central hub. The joints between these sections were covered by doubler plates — additional sheets of metal — that doubled their thickness to improve the bulkhead’s strength and cohesion as a single unit.
Around its circumference, the bulkhead was joined to the fuselage frame and skin at a location called fuselage station 1223.
The fuselage frame of the Vanguard, like any aircraft, consists circumferential (hoop-shaped) frames and lengthwise stringers, forming a tube-shaped lattice to which the thin aluminum fuselage skin is riveted. Each frame is referred to by a “station” number. At station 1223, the bulkhead is held in place by slipping its outer edge in between the fuselage skin and the frame, incorporating it quite solidly into the aircraft’s overall structure. You can picture this joint as a six layer sandwich, consisting of frame 1223 and its doubler plate on the inside; the fuselage skin and its doubler plate on the outside; and the bulkhead and its doubler plate in the middle. (Just like in the bulkhead structure itself, the doubler plates at the joint serve to increase the strength of the individual components.) All six layers of metal are riveted together and then coated liberally in a layer of polysulphide sealant to prevent moisture from penetrating between the layers. A cross section of this joint, which will hereafter be called simply “the joint,” is shown above.
Although this joint is continuous around the entire circumference of the bulkhead, the following story focuses on its lowest point, located below the floor level at the very back of the cabin, just behind the aft toilets. This part of the bulkhead-to-fuselage joint was particularly notable for two mutually exacerbating features: first, its tendency to trap water; and second, its resistance to adequate visual inspection.
As anyone who has seen the exterior of an airplane is probably aware, the bottom of the fuselage curves upward toward the tail, creating a slope running downhill from aft to fore. Furthermore, because the convex side of the bulkhead faces aft, the angle between the lower part of the bulkhead and the fuselage skin below is rather acute, almost asymptotic, and as one approaches the joint from the rear the space between these two components becomes very narrow indeed. Not only does this make the joint hard to inspect visually, but any fluids that may enter the unpressurized tail section are funneled into this dark crack, straight down to the joint. To prevent water from becoming trapped there, the tip of this crack is filled with a “watershed wedge” that instead redirects flowing liquid to a drain hole in the fuselage skin, which leads directly to the atmosphere.
However, the forward side of the bulkhead presented an even bigger problem. While the aft face of the bulkhead could be directly observed, the forward face below the cabin floor was covered in soundproofing insulation that was time consuming and difficult to remove. Furthermore, any liquids that spilled or condensed on the bulkhead would flow down its face until they became trapped by frame 1223, which rises vertically above the joint like a dam. A drain hole is drilled through the lowest point of the frame to allow water to pass through — but on G-APEC, this hole had been inadvertently covered up by the polysulphide sealant protecting the joint.
There are several theories regarding which of these factors contributed most directly to the events that befell G-APEC, and this article will examine them later. For now, however, it’s sufficient simply to recognize that the design of this joint provided multiple avenues for water damage to both occur and go undetected. In fact, on G-APEC, water damage at some point in the past had caused corrosion to set in at the lowest point on the joint, from which it began to spread outward in both directions. Since these structures were made of aluminum alloys, the corrosion was not, strictly speaking, “rust,” which is a byproduct of the corrosion of iron, but it would have looked superficially similar, with a degraded, orange-and-white crusty appearance. Once underway, the chemical process that causes corrosion tends to continue and spread indefinitely, and across some undetermined timeframe it began to eat through the joint layer by layer, affecting frame 1223, the forward face of the bulkhead skin, and the bulkhead doubler. This doubler, which was bonded to the bulkhead skin using an adhesive, eventually began to delaminate, reducing the joint’s material strength even further.
Every time the fuselage was pressurized, a differential load of about 5 to 6 pounds per square inch (about 0.34 to 0.41 standard atmospheres) was applied to the entire pressure vessel, including the bulkhead. As the corrosion worsened, the lower part of the bulkhead joint became unable to withstand this load, and the damaged material began to crack. In many previous articles, I’ve discussed slow-acting metal fatigue, where cracks spread over thousands of cycles, but that model is not directly applicable to corrosion-induced cracking. In fact, by the time the cracks developed, the material was already close to its point of ultimate failure, and the cracks spread not in infinitesimal increments but in leaps and jumps, becoming visibly longer with every flight — or they would have been visibly longer, if anyone was looking.
Needless to say, there is no alarm that tells the crew that a bulkhead is cracking, nor could the corrosion be seen without significant disassembly of the rear passenger cabin. Countless passengers came and went from the restrooms, situated directly on top of the damage, emerging none the wiser. Whether it could have been caught is a question that will be considered later. But it was not, and as BEA flight 706 reached its cruising altitude over Belgium — the highest G-APEC had flown in weeks — the last few grains of sand slipped down through the hourglass of disaster.
After contacting the Brussels area control center at 10:01, flight 706 reported level at 19,000 feet at 10:05, estimating waypoint Mackel at 10:10. But they would never reach it.
Just after 10:09, the crack in the bottom of the rear pressure bulkhead reached its critical length, and with a massive bang, the bulkhead failed. In a split second, the ends of the crack raced upward and outward across the bulkhead skin until they reached the joints between the wedge-shaped sections in the 120 and 240 degree positions. Following these joints, the cracks then turned inward toward the center of the bulkhead, where they stopped 15 centimeters short of meeting in the middle. The entire lower section of the bulkhead between 120 and 240 degrees thus became a giant flap, hinging around the 15-centimeter intact portion, and under the force of pressurized air bursting forth from the passenger cabin, it opened rearward and upward, releasing the air blast into the tail section.
The unpressurized tail housed a few control system elements and the flight data recorder, but other than that it was mostly empty space. As the cabin air exploded into this space, the pressure spiked within a fraction of a second, subjecting the empennage structure to a sudden, unexpected load. This part of the airplane was never designed to withstand the forces associated with internal pressurization, and the air blast immediately found the structure’s weakest point: the upper skin of the horizontal stabilizer.
The stabilizer, or tailplane, provides downforce to balance the center of lift and center of gravity, enabling stable flight. On some airplanes, the stabilizer is movable (or trimmable), but on the Vanguard it was a fixed part of the structure, its interior space continuous with that of the empennage. Like the fuselage itself, each half of the stabilizer consisted of a thin aluminum skin riveted to an internal frame made up of spanwise spars and chordwise stringers. When the pressurized air entered the internal space within this frame, the force of the blast lifted the stabilizer’s upper skin straight off the spars. The rivets attaching the skin pulled through, numerous internal structural elements disconnected from one another, and the stabilizer lost its structural integrity. Within moments, both halves of the stabilizer experienced a rapid unscheduled disassembly, separating from the airframe in several pieces and taking with them the elevators — the plane’s only means of pitch control.
As soon as the horizontal stabilizer and elevators departed the airplane, the loss of downforce on the tail caused the plane to pitch violently and irrecoverably downward. If it helps, imagine a 2-dimensional airplane pinned to a wall by a thumb tack driven precisely through its center of lift. If the 2-D airplane’s center of gravity is forward of the center of lift, it will pivot around the thumb tack into a nose down position. On the other hand, if you place a finger above the tail, preventing the tail from moving upward, then the nose will not drop, and the airplane will balance perfectly. This is how airplanes maintain stable flight, with this delicate balance between the center of lift, the center of gravity, and the downforce from the horizontal stabilizer. So when this downforce was suddenly removed on flight 706, the plane plunged immediately into a vertical nosedive, just like the 2-D airplane pinned to the wall would if you removed your finger from the tail.
From the inside, this sequence of events would have been marked by chaos and confusion, masking the cold physics that ripped the plane from the sky. There would have been a sudden rush of air toward the rear of the cabin, followed almost instantly by an incredibly violent pitch down that would have thrown loose objects and people into the ceiling with considerable force. The pilots would have tried instinctively to recover from the dive, but their control columns would have moved freely to their stops with no effect, because the elevators were no longer attached to the airplane.
As the Vanguard plunged headlong from the bright blue sky, shattered pieces of its horizontal stabilizer trailing behind it, both pilots simultaneously keyed their microphones and broadcast their final moments to air traffic control, leaving behind a chilling record of their futile fight for survival. Their voices half drowned by howling wind and the scream of the propellers, they shouted, “We’re going down, 706, we’re going down! Mayday, mayday, mayday! Mayday, mayday, mayday, we’re going down vertically, Bealine 706, [unintelligible], out of control! Out of control!”
The sound of the wind over the fuselage grew to a mighty roar, through which only fragments of conversation could be heard: “… no rudder…,” “…ah, this is it…”
As the hair-raising cacophony continued, Brussels Area Control Center asked, “Aircraft calling mayday, would you transmit in blind, over?”
There was no reply, only the roar of the wind. And then, after 54 seconds, the transmission ceased.
At that moment, witnesses in a rural area outside the Belgian village of Aarsele caught sight of the airplane in its final moments, plunging from the sky like a stone. Its nose was pitched so far down that it had passed beyond the vertical by 20 to 30 degrees, falling essentially inverted, while slowly rotating to the right, its engines still straining to pull the plane from its death dive.
Seconds later, the Vanguard impacted nose-first in a field, narrowly missing a row of trees and an irrigation ditch. A massive explosion rocked the countryside; fire rolled in waves across the field and debris flew high into the air as the airplane disintegrated utterly. The blast hurled pieces of the airplane as far as 300 meters, where some of them struck a car on a passing road, shattering its windshield and injuring the driver. Although emergency services hurried to the scene, this unlucky passerby would prove to be the only one in need of aid — all 63 passengers and crew aboard BEA flight 706 were killed instantly on impact.
The day after the accident, Belgian and British investigators joined forces to piece together what happened, braving crowds of thousands of “disaster tourists” who had descended on Aarsele from as far away as the Netherlands to catch a glimpse of the carnage. At the scene, they found that most of the aircraft had been damaged beyond recognition, leaving behind a smoking airplane-shaped crater in the field. But not all of the airplane was at the crash site. Numerous pieces of the horizontal stabilizer and elevators were found scattered downwind of the plane’s last known position along a trail stretching for 7.6 kilometers, suggesting a high altitude breakup. However, examination of these fragments turned up no evidence that the failure originated in this part of the airplane. Aviation publications wrote that these components probably separated only as a result of the plane’s sudden dive — which is usually true, but would turn out not to be the case this time.
In fact, closer examination showed that both the left and right horizontal stabilizers had failed due to an internal overpressure event that pulled the stabilizer skin straight off the rivets that should have held it in place. As for why the pressure inside the tail would suddenly spike, there was only one real suspect: the rear pressure bulkhead.
The rear pressure bulkhead was found at the main crash site, having shattered into several pieces, which were carefully reassembled in their original layout. Having done so, the problem with the bulkhead was obvious. Across a 48-centimeter section of the lowest portion of the bulkhead-to-fuselage joint, severe corrosion had badly degraded the structure, penetrating clear through the bulkhead itself in several places. Red-orange and white corrosion byproducts coated the joint like rust on an old farm truck — a nightmarish level of damage to find on an airplane. Bulkhead material had corroded away and fallen off, and the doubler plate overlying the bulkhead skin had delaminated extensively. And from this area ran the two cracks that split the bulkhead apart at the moment of the catastrophic in-flight failure, rupturing it in a fraction of a second. Over the first few centimeters of these cracks, step marks in the metal showed that their growth repeatedly stopped and started, jumping a considerable distance each time over a very low number of cycles. By counting these step marks, investigators concluded that the crack that destroyed the bulkhead only progressed out of the corroded area about 14 flights before the accident.
To prove that the failure of the badly weakened bulkhead caused the separation of the horizontal stabilizer, investigators modified another Vickers Vanguard with a valve that could suddenly release pressure through the bulkhead into the tail section. Using flight data, they calculated that the largest pressure differential during flight 706 would have been 5.75 psi, so they pressurized the test fuselage to this value and then opened the valve in the bulkhead. Within 0.12 seconds, the pressure spiked to 5.5 psi in the tailcone area, followed 0.03 seconds later by a large spike in the right horizontal stabilizer. This spike distorted the upper skin, pulled out several rivets, and disrupted multiple internal structural elements — damage that would have been catastrophic had it occurred in flight.
Notably, however, the left horizontal stabilizer showed no signs of any damage after the test. This appeared to be because that stabilizer incorporated a non-mandatory modification that was made on the production line in 1959 to increase the size of the rivets securing the stabilizer’s internal frame elements. The accident airplane, G-APEC, originally incorporated this modification when it was built in October 1959, but in service it developed an unpleasant vibration, so in 1962 the aircraft was removed from service and overhauled in an attempt to correct the problem. Among the solutions employed was the replacement of both the left and right horizontal stabilizers, swapping them out for a version with damping weights to reduce vibration. These “new” stabilizers didn’t incorporate the 1959 modification, nor was there any requirement to incorporate it. Better resilience against a sudden pressurization of the tail section was not an intended effect of the modification, but investigators noted that had it been incorporated, the collateral damage caused by the bulkhead failure might have been greatly reduced.
The next question facing investigators was why the corrosion took hold in the first place.
Looking through the plane’s maintenance records, it was clear that it had experienced chronic problems with fluid accumulation in various locations. Between December 1970 and September 1971, eight entries had been made in the maintenance logs concerning water, ice, or hydraulic fluid in the tail cone area, each of which mentioned a need to “rectify the seal of the tailcone access panel.” Additionally, investigators found “tide marks” left behind on the frame behind frame 1223, indicating that water had pooled behind the bulkhead on at least 12 occasions. This suggested chronic drainage problems in the area where the aft face of the bulkhead converged with the fuselage skin, as described earlier in this article. Although a blockage in the drain hole to the atmosphere could have caused the problem, this drain hole was forced full of mud during impact with the ground and its pre-accident condition couldn’t be determined.
In any case, only minimal corrosion was apparent on the aft face of the bulkhead, and what corrosion was present appeared to have penetrated through from the forward face. Therefore, the source of the corrosion was probably inside of the pressurized part of the aircraft. In this area, the drain hole at the low point in frame 1223 was blocked by polysulphate sealant, raising the possibility that water had collected between the frame and the forward (concave) face of the bulkhead. Furthermore, if water had collected in this area, it could have worked its way between the forward face of the bulkhead and the bonded doubler laid atop it, because the upper edge of the doubler was not protected with sealant. This would explain why the doubler had delaminated so extensively. However, no tide marks were found in this area that could conclusively prove that water was trapped there, even though this was plausibly the origin point of the corrosion. Nor was it clear where the hypothetical water had come from. Although maintenance logs showed write-ups for toilet leakage in April and December 1970, investigators couldn’t establish a direct connection between leaking toilet water and the corrosion.
Realistically speaking, the toilet was by far the most obvious water source in that part of the aircraft, and despite the lack of direct evidence, it’s hard to imagine that it came from anywhere else. But without proof, investigators stopped short of definitively announcing that toilet water brought down a passenger airliner.
The last and most glaring question was whether the corrosion could have or should have been detected before it progressed to the point of failure.
Obviously, we should all hope that established inspection regimes can catch corrosion as egregious as that which afflicted G-APEC. But when the Vickers Vanguard entered service in 1961, the science of corrosion control was not as advanced as it is now, and gaps in inspection regimes sometimes existed. At first glance, at least, this problem was likely particularly acute on early aircraft types, designed prior to 1960, and those types that saw only limited production runs, resulting in a dearth of in-service experience. The Vanguard checked both of these boxes, having been designed in the 1950s and produced in limited numbers for only two airlines. Modern best practices for corrosion control rely on thorough and accurate predictions of the most vulnerable locations, but at that time there was insufficient institutional experience to reliably make those predictions for the Vanguard. That’s not to say that people in the 1950s were incapable of predicting that certain features of the Vanguard’s rear pressure bulkhead were at risk of corrosion — but it does help explain why this possibility was not given the attention that it deserved.
The inspection regime for BEA’s Vanguards featured a superficial “Service A” inspection every 72 hours; a series of moderate Checks 1A through 1F to be carried out on intervals of 400 flying hours or 80 days; two heavier Checks S1 and S2 on 1,800 flying hour intervals; a Check S3 every 2,100 flying hours; and two Major checks (equivalent to American D-checks, described in previous articles) called M1 and M2, one of which had to be completed every 9,000 hours or four years, whichever came sooner.
All of the Checks 1A-1F called for a visual inspection of the forward face of the bulkhead, where the corrosion was found after the accident. However, these checks did not require the removal of the soundproofing insulation that covered the face of the bulkhead below the floor level. When the inspection regime was devised, it was thought that any “gross spillage” from the toilets into this area would cause detectable damage to the crowns of the fuselage frames, which protruded from the layer of insulation just in front of the bulkhead. But while these frames were in fact visible without tearing out the insulation, neither the corrosion that caused the accident nor the spillage that probably caused the corrosion ever left any permanent markings on the crowns of the fuselage frames, so this assumption proved incorrect. Part of the problem was that BEA’s maintenance procedures called for a thorough cleaning of this area before the inspection, which could have erased evidence of recent spillage that might otherwise have led to the discovery of the gross damage hidden below.
These checks also called for a visual inspection of the aft face of the bulkhead, which was not covered by insulation, but the corrosion likely didn’t penetrate through from the forward side until the damage was already well advanced. It was unclear whether this occurred before or after the last Check 1 on September 9th, about a month before the crash. But even if this damage was visible at that date, it could easily have passed undetected simply because it was hard to see down into the narrow space between the upward-curving lower fuselage skin and the convex aft face of the bulkhead, as described earlier in this article. The joint itself was practically invisible from this side unless specialized equipment were used; however the report does not say whether the possibility of inspecting the area using a borescope or other similar tool was ever considered.
Only the Major inspections M1 and M2 contained any requirement to remove the insulation to perform a complete inspection of the forward face of the rear pressure bulkhead. The last Major check on G-APEC took place between May and June of 1970, during which no corrosion was found. However, at that time the corrosion was most likely hidden between the bulkhead skin and the bonded doubler laid atop it within the joint, where it could not be detected visually. The corrosion later spread out from between these layers, but no further Major checks were scheduled for another 9,000 flying hours, while the airplane crashed after only 3,144 hours. Therefore, the inspection regime was poorly designed because the inspection interval was longer than the time required for corrosion to progress from undetectable to catastrophic — which is exactly what I meant when I said that predictions made in that era were unreliable.
However, by 1970, the science had progressed to the point that these vulnerabilities were recognized, and British European Airways began searching for some way to detect corrosion within the bulkhead-to-fuselage joint earlier in its spread and without the need to conduct an invasive teardown. Later, this type of inspection would be done using ultrasound — the same technology we use to produce images of fetuses inside the womb — or eddy current, which uses electrical currents to detect damage. But ultrasound equipment did not become widely available until several years after the crash of flight 706, and BEA instead opted for radiographic imaging, a category that includes X-ray imaging, CT scans, and similar technologies. In May 1970, BEA conducted a radiographic inspection of the joint explicitly to search for corrosion. But in the lowest area of the joint, where the corrosion was later found, the radiographic images lacked sufficient definition to derive any useful information, because the structure was too complex and the background too busy. Investigators determined that radiography was not an appropriate method for inspecting this area, but BEA had failed to appreciate this at the time due to insufficient understanding of the technology.
In the end, investigators concluded that no technique then in use by BEA could have detected the corrosion within the confines of the company’s inspection cycle. However, they did note that while it’s prudent to conduct more frequent inspections of older airplanes, BEA was actually doing the opposite, extending their inspection intervals as its Vanguard fleet aged. Belgian investigators did not assert any direct connection between these extended intervals and the accident, but the problem nevertheless suggested that BEA had a deficient approach to preventative maintenance.
After undetected corrosion was identified on the accident airplane, BEA conducted pressurization tests on its other Vanguards in an attempt to determine whether any of them were leaking pressurized air at a greater than expected rate. One Vanguard failed the pressurization test, so a visual inspection was carried out, which detected only slight corrosion along the bonded doubler. But when BEA dismantled the bulkhead-to-fuselage joint for a closer examination, they found gross corrosion that had eaten clear through the bulkhead material and penetrated to the other side, where it was observed visually and labeled “slight.” Furthermore, this area of corrosion had generated a crack that had already grown to the astonishing length of 45 centimeters. The accident report does not speculate about how much time this aircraft had left before it would have suffered the same fate as G-APEC, but it was probably not long — perhaps weeks, maybe even days.
As a result of this disturbing discovery, BEA conducted a teardown of the bulkhead-to-fuselage joints on its other Vanguards and found that eight of them had corrosion in the same area as G-APEC. All were repaired and returned to service.
If all of this sounds familiar — an inspection interval that failed to account for unexpected damage, a sudden failure of the rear pressure bulkhead, a blast of air into the unpressurized tail, the loss of key flight controls — then you’re probably thinking of one of the most famous air accidents of all time. In 1985, Japan Airlines flight 123 crashed in central Japan, killing more than 500 people, after a faulty repair led to a premature failure of the rear pressure bulkhead that blew off part of the vertical stabilizer and severed critical hydraulic lines. The root causes of the bulkhead failure in that case were different, but the similarities are sufficiently notable that BEA flight 706 sometimes appears as a “see also” footnote in detailed accounts of the Japan Airlines disaster. But if you read my Japan Airlines article back to back with this one, it should become apparent that the crash of flight 706 is its own self-contained story with rather different lessons.
Much more so than its Japanese lookalike, the 1971 disaster over Belgium was a product of its time, the perhaps inevitable result of extending 1950s design expectations and inspection regimens long enough for their core assumptions to be tested, but not so long as to allow for the introduction of the more advanced non-destructive inspection technologies in use today. Modern imaging technologies would have detected this corrosion during major inspections, and modern aircraft designs take into account decades of additional experience with corrosion prevention. Airlines today are required to implement manufacturer-approved corrosion prevention and control programs designed to predict problem areas and inspect them early and often. But none of this existed yet in 1971, when British European Airways tried and failed to correct known deficiencies in the 1950s inspection protocols still being applied to their Vanguard fleet. The result was a haunting mid-air catastrophe that has perhaps been unfairly forgotten, overshadowed by later and deadlier disasters. Let its story be told, then — if only to show how far aviation has come.
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