Cracked windscreens and windshields
“Suddenly, the windshield just cracked…The next thing I knew was that my co-pilot had been sucked halfway out of the window.” These are not the words you want to hear either as a passenger or as a pilot on any flight or airline. However, that was the situation that the captain and his co-pilot experienced on a Sichuan Airlines flight, which was the latest in a series of window malfunctions on commercial aircraft around the world.
On 14 May 2018, Sichuan Airlines Flight 3U8633 took off from Chongqing Jiangbei International Airport (CKG) in the southwestern municipality of Chongqing, China, bound for Lhasa, the capital of Tibet, around 1,500 miles west, when a cockpit windshield broke off mid-flight, forcing the aircraft to divert and make an emergency landing in the southwestern city of Chengdu, Sichuan province.
According to Chengdu Business News, the aircraft, an Airbus A319, had been flying for about half an hour and had just reached the cruising altitude of 32,000 feet when the windshield on the righthand side of the cockpit shattered and broke off, leaving the cockpit exposed and pulling the co-pilot partly through the window. “There was no warning sign. Suddenly, the windshield just cracked and made a loud bang,” the captain of the aircraft, Liu Chuanjian told Chinese media following the incident. “The next thing I knew was that my co-pilot had been sucked halfway out of the window.”
According to the captain, the aircraft experienced a sudden loss of pressure and a drop in temperature.
Everything in the cockpit was floating in the air. Most of the equipment malfunctioned and I couldn’t hear the radio. The plane was shaking so hard I could not read the gauges, he was quoted as saying.
The co-pilot was wearing a seatbelt and was pulled back and the captain was forced to perform emergency landing manually with a damaged flight control unit (FCU) as some of its parts had been sucked out through the window. The A319 lost the windshield at FL332 (flight level corresponding to 33,200 feet) and had to descend to FL240 (24,000 feet) due to mountainous terrain.
The aircraft, carrying 119 passengers and nine crew members, landed safely at Chengdu Shuangliu International Airport (CTU) about 45 minutes after the incident, Chengdu Business News writes. Whilst none of the passengers onboard were injured, Sichuan Airlines said in a post on Weibo that 29 of the 119 passengers were sent to the hospital for examination and were later discharged. The co-pilot and one other cabin crew member suffered minor injuries, an official report by the Civil Aviation Administration of China (CAAC) stated.
Why did the windshield break?
Chinese media reports that an investigative team set up by the CAAC arrived in Chengdu on 16 May 2018. According to Reuters, the CAAC has also said that the French organisation of safety investigations, BEA, as well as Airbus sent staff to China to examine the incident. Investigators focused on the design and manufacturing of the windshield, the CAAC’s safety chief Tang Weibin was quoted as saying. Preliminary investigation found that the failed windshield was an original part of the aircraft and had no previous record of faults since the A319 (registration B-6419) entered into service with Sichuan Airlines in July 2011. The jet had accumulated 19,912 flight hours. At the time the Chengdu-based Chinese regional carrier operated an all-Airbus fleet, consisting of 132 aircraft, with the average age of 5.6 years.
The science behind the (mysterious) windshield
Incidents involving cracked cockpit windshields due to bird or lightning strikes are quite common. Window cracks also occur more often in the cockpit than in the cabin, experts say. However, let us go back to the basics. Aircraft windows are designed not only to be fail safe, but also safe life, points out Luís Almeida, an aerospace engineer and airline pilot. The safe-life concept means that the component can stay installed on the plane until it fails. However, according to him, the design is so robust that theoretically a windshield can stay installed the plane’s entire life cycle. As to the fail-safe design: in general, a windshield is composed of three layers of chemical reinforced glass, connected by two layers of polyurethane type panes.
“The two inner glass layers are the significant ones in terms of a structural point of view. Whilst the outer layer, which is much thinner, will provide the aerodynamic contour,” explains Almeida, “it is precisely this one that usually cracks.” It is also the layer with the most temperature differential and the one that has the most displacement when subjected to pressure differential. “Therefore, as cycles accumulate, any little defect might grow into a layer cracking. However, this cracking doesn’t reduce the structural integrity of the window,” he explained. The main issue, according to Almeida, is that this particular problem relates directly with the cockpit crew. In a situation like this they are to follow the QRH (so-called abnormal procedures). “As it is usually difficult to determine whether the window is deformed or not, pilots will err on the side of caution and will land at the nearest suitable airport, flight diversions are the usual and the most appropriate way to deal with the issue,” says Almeida.
There is a crack in the sky
It seems like something worrisome can be felt in the air. At least for travellers all over the world reading headlines such as the Sichuan Airlines emergency and perhaps a little less worrisome for pilots, until they are faced with similar situation. Vilmantas Rudelis, an Airbus A32O captain, told how he handled the situation when a windshield of his aircraft cracked in mid-flight.“Flying the A320 at cruising level I saw my windshield start to slowly arc and delaminate and crack. As a pilot, first of all I called my FO to perform QRH,” Rudelis recalls. After initial window inspection by the crew, the situation appeared to be minor, as no major cracks seemed to have developed. The aircraft continued on the journey, when, “suddenly… bang… the outer layer cracked into a thousand small pieces,” the captain remembers.
In such a situation, Rudelis emphasises, the most important is to identify which layer – the inner or the outer – is affected, as depending on which is broken, different pilot actions should be applied. One simple way to identify which layer is affected is to touch the crack with a finger, “if you feel the crack, it is the inner layer, if not – it is the outer,” the captain says. If it is the inner layer the pilot should descend and apply procedures according to QRH. After checking the shattered window, Rudelis found that the inner layer was not affected. According to him, a window crack does not necessarily mean an emergency situation. Nowadays cockpit windshields have a complex construction and are designed to withstand extreme conditions. The tempered glass protects the window from impact from small debris or birds. Although the event he described was not an emergency situation, Rudelis admits, “it was a little unpleasant to continue flying with the window cracked into a thousand pieces.”
So, what’s the issue?
Given the recent series of reports of shattered windshields and damaged passenger windows, the question arises whether all of these events can be regarded as isolated accidents or is it a systemic issue. Are the window failures related to the type of aircraft, the manufacturer, or the maintenance procedures? Almeida says that “analysing the data, one can see that the relation between occurrences and flights is very low, almost residual. I would even say that other non-visible structural problems occur with more frequency.” From a maintenance point of view, he explains, most occurrences that lead to windshield removal are related to non-structural problems, such as bubbles, black spots due to arcing or delamination of window pane layers. Maintenance replaces these windows as otherwise they would disturb the pilots’ vision from the cockpit. Almeida maintains that “these problems are residual, caused by normal mechanical defects, that do not jeopardise the flight safety.”
However, a pilot, who asked not to be identified, believes that window malfunctions may be a growing issue, at least in general aviation (GA). He argues that malfunctions result from poor maintenance and / or lack of it. “I don’t think there is any accountability and / or oversight anymore within the aviation industry, maintenance wise. I can personally attest to this statement from being in the GA sector and owning a plane for years,” the pilot says. According to him, the aviation industry is suffering from not only the loss of pilots, but also maintenance personnel. This means that airlines “are now caught up in a personnel shortage and are currently playing catch up in all areas,” adding that, “this situation creates a huge pool of ‘green horns’ or beginners.”