Air travel is a question of trust.
We trust the science which says that air pressure over the leading edge of a wing can support a giant passenger plane across thousands of miles of sky.
We trust that the design which shapes the plane matches the needs of this mysterious science.
We trust that the aircraft's manufacturer follows this meticulous design to the very letter.
And we trust that the official regulatory agencies have fulfilled their side of the bargain by monitoring and policing every step of that process - from drawing board to airport runway.
But what happens if that trust is shaken?
Every five seconds
|Three generations of Gigi Prewitt's family had worked for the Boeing company
For more than a year Al Jazeera has been investigating allegations - made in US Federal Court proceedings - that between 1996 and 2004 ill-fitting, illegal and dangerous parts were assembled on to many of the most commonly-used passenger planes in the world today.
The allegations concern the Boeing Company - the most respected name in international aviation and the world's second-largest commercial aircraft manufacturer.
The claims were made by then employees of Boeing in Wichita, Kansas who were working on a radically new passenger plane - the 737 Next Generation (NG).
Boeing had produced 737s since the mid-1960s, and the 737 series is the world's most popular short and medium-haul passenger aircraft. It is estimated that, throughout the world, a 737 takes off or lands every five seconds.
But by the mid-1990s Boeing had begun to lose market share to its European rival, Airbus. To regain its pre-eminent position, Boeing decided to build an entirely new version of the 737 - the Next Generation.
Earlier models were built by hand: as a result the dimensions or accuracy of each individual part would often be marginally different, resulting in the need for assembly workers to pack out gaps with "shims" or fillers. These added to the overall weight of an aircraft, making it more expensive to fly.
Parts for the new 737NG plane were to be designed, manufactured and built by a revolutionary new computerised process called ATA. Not only would this ensure that each individual part was identical, but that each would be precise to within 3000ths of an inch.
According to leading aircraft engineer, Dr Michael Dreikorn: "This ATA was designed so that the tolerances on putting the aeroplane together would be so tight that the aircraft would have higher strength and reliability. And in response to that, this aeroplane was certified to have higher gross weight and be able to operate at higher altitudes."
Boeing through and through
Every new aircraft design has to be assessed and approved by a regulatory authority: for American manufacturers like Boeing, the regulator is the Federal Aviation Administration (FAA).
Boeing submitted all its engineering drawings and data to the FAA and, in 1996, the FAA gave Boeing the thumbs up. It issued what the industry calls a Type Design Certificate - essentially a licence to manufacture the aircraft provided to all the specifications laid out in the engineering data which had been submitted and approved.
Boeing planned to assemble the 737NG fuselages in Wichita. But it subcontracted the manufacture of some key parts to a company called AHF Ducommun, based in Gardena, California.
Gigi Prewitt was Boeing through and through. Her family had worked for Boeing in Wichita for three generations and she was excited when she was asked to look after buying key parts for the 737NG. But within a short space of time, she noticed something was wrong.
"The minute that I took the desk of buying 737NG parts I had shop personnel coming to me talking to me about the problems and the issues they were having with the parts not being manufactured accurately. [They reported] Shy-edge margins and were, out of contour, parts not fitting correctly ..." Prewitt says.
|Lawyer Bill Skepnek has become intimately acquainted with almost every nook and cranny of the 737NG
The parts in question were some of the most crucial elements of an aircraft fuselage - parts known as "chords" and "bear-straps".
An aircraft fuselage is like a giant tube. That tube is made up of interlocking semi-circular pieces of metal - these are the "chords" and put together they form the 'frame' around which every other part of the airframe is built ... and on which the external 'skin' is assembled.
Exit doorways and cargo hatches are potential weak points in this fuselage: to strengthen them, huge re-enforcing sheets are assembled around the holes - these are the "bear-straps".
So vital are these parts to the safety of an aircraft, that Boeing's own 737NG Structural Repair Manual - obtained by Al Jazeera in the course of its investigation - lists them as "Primary Structural Elements" and warns: "The failure of PSE's could result in the catastrophic failure of the airplane."
According to lawyer Bill Skepnek - who for the last six years has become intimately acquainted with almost every nook and cranny of the 737NG design - when Boeing talks of the potential for these parts to cause "catastrophic failure", it means exactly what it says.
"These are the parts of airplanes that, if they fail, we can have a decompression at altitude or we can have a rupture in the vessel, in the fuselage vessel of the aircraft. And as long as we can make that [fuselage] hold together we can keep the passengers safe."
But in Wichita, Gigi Prewitt was not the only Boeing employee coming across reports of ill-fitting and badly made parts. In another building on Boeing's vast factory site, Taylor Smith was getting very similar-sounding complaints.
"One of the shop managers sent me an email saying they were having problems with the fail-safe cords which are the long ribs that go all the way along the aircraft [...] They were telling me that from the beginning of the 1996 timeframe when they started manufacturing these parts, that they were coming in with shy edge margins, they were out of contour," Smith says.
Boeing's internal documents, which Al Jazeera obtained, give a snap-shot of the scale of the problem.
Part out of contour: quantity 1 … Part width – oversize: Quantity 4 … Material thin: Quantity 6… Part undercut: Quantity 26 … Hole mis-located: Quantity 17….
They also show the source of the problem: AHF Ducommun.
'Putting our foot down'
But, according to Gigi Prewitt and Taylor Smith, Boeing rejected only a handful of these defective parts. The rest were assembled on to 737NG aircraft.
"We were putting our foot down and not going to participate in allowing non-conforming parts to come in and be put on planes. But one of the managers was very upset in procurement and wrote an email and said 'this is stupid - there are already 300 of them out there on planes; why would we scrap them now?' So they used them, they put them on planes," Prewitt says.
Finally, in early 2000, Boeing sent Prewitt, Smith and 12 other specialist employees to conduct an audit of the Ducommun manufacturing plant. What they found - and documented with photographs as well as reports - shocked them profoundly.
Instead of being manufactured by the approved computerised process, Ducommun employees were cutting the parts by hand - literally using a felt-tipped pen to mark out the shape and then cutting the metal with a hand-cutter.
Not only did this result in parts which could never meet the mandated 3000ths of an inch accuracy - but the Boeing team realised it violated the official type design: any aircraft with these parts on them would be legally "unairworthy" - and therefore not allowed to fly.
But there was worse to come: every part in the production process has to be signed off at each stage of its manufacture on a document called a "shop traveller". This records that each individual stage of manufacture has been carried out in accordance with the type design.
The Boeing team discovered that Ducommun had apparently falsified these records: it had two sets of "books" - the official one recording that each part had been made by the computerised process and a second set recording the actual, handforming process which had really been used.
What that meant, in the eyes of the Boeing team, was that every single chord and bear strap manufactured by Ducommun had to be viewed as unlawful.
|Taylor Smith says: 'We met with the government and told them our story'
Initially Boeing itself seems to have agreed: Al Jazeera obtained an internal draft memorandum prepared by senior Boeing officials in August 2000 and intended to be sent to the company's top management. It warned:
"The severity of these conditions is documented via photographs and poses a quality risk to the production of quality airplane parts ...
"Misrepresentation of the manufacturing process jeopardises the integrity of airplane parts ...
" ... this situation cannot be ignored ...
" ... the integrity of AHF-Ducommun as a partnered supplier places the Boeing Company at risk.
"Immediately cease all new business activity with AHF-Ducommun and consider disengagement ..."
What happened to this memorandum is a mystery: today, Boeing refuses to discuss it - or what actions it took on the recommendations.
But Gigi Prewitt and Taylor Smith say that ill-fitting and out of contour parts continued to arrive from AHF Ducommun - and that assembly workers in Wichita took dangerous short-cuts to get them to fit.
Some parts were so badly out of shape that they had to be beaten on to the airframe with hammers - a process which builds in potentially lethal pre-stress.
The FAA had given Boeing "delegated authority" to police itself on matters like this - provided it reported problems voluntarily.
Both Smith and Prewitt wanted to come clean to the FAA, but claim that Boeing management threatened to sue them if they did so.
Reluctantly, they turned whistle-blower - taking their concerns to the US Justice Department, which, under American law, is responsible for protecting whistle-blowers.
According to Taylor Smith: "We actually met with the government and told them our story - they had the same reaction most people have when they first hear the story - we will protect you, we will not let you be retaliated against, we will keep you safe."
The Department of Justice ordered two investigations - one by the FAA and, because Boeing had sold some 737NGs to the military, one by the Defence Criminal Investigative Service.
But the whistle-blowers have been dismayed by these investigations. Al Jazeera obtained a copy of the FAA investigation - which the administration redacted. The only publicly-viewable "investigative actions" appear to be that the FAA looked up Ducommun's address and visited its website.
The DCIS report was another matter altogether. Again, Al Jazeera obtained a copy of its investigative files - and these appeared to confirm some of the allegations about the manufacture and the safety of the Ducommun parts.
Yet the Department of Justice finally ordered that both investigations be closed without action.
The Boeing whistle-blowers lost their jobs during this period. For the past six years they and their lawyer, Bill Skepnek, have spent their own money trying to bring a legal action against Boeing and Ducommon on behalf of the American public.
They are supported by highly-respected aircraft industry specialists and engineers like Dr Michael Dreikorn, a former FAA official.
"It is getting to the point where there is going to be a catastrophic failure of a 737NG. We do not know when that hour is going to hit but we know it is going to happen," Dreikorn says.
"I am very seriously concerned about a catastrophic cabin failure at altitude. And I think it would be a 737NG that will lose its ability to stay together and unfortunately will be a smoking hole in the ground."
But the story of what has happened during this legal battle reads like the plot of a John Grisham novel. And it has left the whistle-blowers convinced that today they are fighting not simply one of the world's most powerful companies - but the power of the US government itself.
As Taylor Smith tells the Al Jazeera filmmakers: "It's a tough road if you take a stand against large companies and the government and it's had a personal effect on me ... and my family. It's a heavy burden to bear. But my greatest fear is that the aircraft will start having big issues and there will start being crashes and there will be hundreds of people that are being killed and I'll wonder whether I did enough."
This specially-extended episode of People & Power airs from Wednesday, December 15, at the following times GMT: Wednesday: 1900; Thursday: 1400; Friday: 0300; Saturday: 1900; Sunday: 0030; Monday: 1400.