On 5 July this year, the final report on the accident involving Air France flight AF447 from Rio de Janeiro to Paris was released. The disaster, the worst in the history of the French airline, caused the destruction of an Airbus A330-220 aircraft and the death of all 216 passengers and 12 crew onboard as the stricken jet plunged into the south Atlantic.
The crash occurred on 1 June 2009, and the investigation was prolonged because of the lack of eyewitnesses, confused radar tracking and the difficulties of locating the wreckage at the bottom of such a vast and deep ocean. The plane’s black boxes, devices that record cockpit conversation and details of the aircraft’s performance, weren’t located until two years after the crash date.
The exact cause of the accident is still undetermined, but the report states that “The aircraft crashed following an aerodynamic stall caused by inconsistent airspeed sensor readings, the disengagement of the autopilot, and the pilot making nose-up inputs despite stall warnings, causing a fatal loss of airspeed and a sharp descent”.
Although the evidence is inconclusive, the report does point the finger at the Air France jet’s pitot tubes. These rudimentary devices, invented by French engineer Henri Pitot in the early 18th century, determine airspeed by measuring pressure differentials as air moves through them. U.S.-based journal Scientific American asked Ken Powell, an aerospace engineer at the University of Michigan at Ann Arbor in the U.S. to describe the device and the way it works.
“A [pitot tube is a] slender tube that has two holes on it,” explained Powell. “The front hole is placed in the airstream to measure what’s called the stagnation pressure [the static pressure + dynamic pressure caused by the aircraft’s motion through the air]. The side hole measures the static pressure. By measuring the difference between these pressures, you get the dynamic pressure, which can be used to calculate airspeed”.
Powell also nicely summarised what can go wrong: “Basically, if there’s a blockage of that tube, then you will get an incorrect reading for the pressure difference and your airspeed. Ice accretion on wings is a big problem, and it can also build up on a pitot tube. Pitot tubes must be calibrated to work properly, and if ice changes the shape of airflow around the tube, then it will give an incorrect reading”.
Although the claim is contested, in the case of Air France flight AF447, some investigators suggested the pitot tubes were blocked by ice crystals just after the plane entered an area of stormy weather in mid-Atlantic. Starved of accurate airspeed data, the autopilot handed control back to the unprepared pilots and disaster ensued.
The Saint has taken the time to recount this sad story to highlight the potentially huge importance of an invention developed by University of New South Wales (UNSW) engineers in Canberra and reported in Electronics News this week.
The UNSW device is not designed to do away with the pitot tube entirely, but is intended to offer back-up readings should the tube stop functioning due to a blockage. The current back up system is based on the Global Positioning System (GPS) that, according the news item, also tends to be unreliable in the very storm conditions that are likely to block a pitot tube.
The Australian laser system computes velocity by measuring the Doppler shift of light absorbed by oxygen molecules as the plane moves through the air. There are no moving parts in the airstream and the associated electronics are inside the cabin where the temperature can be controlled.
The UNSW engineers’ invention might have saved the Air France passengers because the autopilot, with uninterrupted airspeed indications, likely would not have disengaged, thus avoiding putting the pilots under huge pressure during the turbulence created by the storm.
It’s important to note that the report into the accident says that even though the pitot tubes might have become blocked, the plane’s demise still wasn’t inevitable because the deviation to the flightpath could have been arrested if the pilots had received better training. Sadly, their misguided and continued attempts to fly the aircraft in a nose up configuration ultimately caused a stall that was subsequently impossible to correct.
The Saint hopes that, one day soon, the Aussie engineers’ innovation will become a standard fitment to commercial aircraft. No one should ever have to experience the 3 minutes and 30 seconds of terror that the passengers and crew of AF447 had to endure as their state-of-the-art aircraft plunged over 10,000 meters tail first to hit the freezing south Atlantic at 150 km/h, breaking up on impact.
Notably, the UNSW laser sensor would be the second major contribution this nation could make to aviation safety after the invention of the black box itself by Dr. David Warren in Melbourne in 1953.
Mini Minis just one quirk of London 2012 Olympics
Like many Australians, the Saint has taken sleep deprivation to a new level this week staying up into the early hours to watch the world’s athletes battle for gold at the London 2012 Olympics (but please don’t tell the Editor).
Hailing from England, your correspondent can’t help but be pleased that the GB and Northern Ireland team (a collective that is traditionally known as the United Kingdom, but strangely not during this particular sporting event) has done well in the medal table - even though the success is mainly limited to sports that entail sitting down. But he also proudly sings a lusty – if somewhat out-of-tune - rendition of Advance Australia Fair when an Australian gold medal is awarded (fortunately for Mrs Saint and the Saint children’s ears that has been a rare occurrence this time round).
But between events your correspondent has taken to wondering about some of the quirkier aspects of the world’s largest sporting event. For example, why is lane 1 not being used for the 200- and 400-metre sprints? (Apparently it’s because that lane is a bit too tight for athletes in the faster races.) And why has the British national anthem been rearranged? (The composer claims it’s to “raise goosebumps” when the anthem goes from a minor key to the home key.)
For the answers to more oddities of this particular Olympiad, readers are advised to visit the website of home country broadcaster the BBC where questions such as “Why is there no podium when the rowers get their medals?” and “Why has no one come up with a better solution for attaching the competitor’s numbers to their vests other than using safety pins?” are addressed.
But no need to refer to that source for the explanation of another London 2012 “innovation” - the mini Minis running around the Olympic Stadium’s infield. Electronics News has that one covered in a report published this week.
The Minis are quarter scale replicas of the current road-going BMW models and an adapted sunroof allows access to the inside of the vehicle for equipment storage. The battery-powered, remote-controlled models can carry loads up to 8 kilograms, such as a single hammer, discus or shot, or two javelins.
One small technical detail that did catch the Saint’s attention though, was the fact that the cars have a radio-control range of around 100 metres. That’s going to require some thought as to the positioning of the controller in the javelin events as the current Olympic record holder, Norwegian Andreas Thorkildsen, hurled the spear an incredible 90.57 meters in Beijing. At the time of writing, Thorkildsen has recorded a throw of 84.47 to qualify for this year’s Olympic final. If the mini Minis’ range is attenuated by just a little bit of RF interference in the stadium, controlling them to collect the javelins after launch may become quite a challenge.