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06 December 2013

Banner Planes in Action

I’ve long been obsessed with banner planes. They are fascinating and amazing to watch. When I did my PPL in Spain, I was lucky enough to see them in action every weekend.

All excerpts from You Fly Like a Woman:

The weekends were busy at Axarquía now that high summer was here. Broad-shouldered young men with their hair clipped short invaded the airfield. They never spoke, they shouted, laughing and clapping each other on the shoulders as they checked their planes and fueled up. They flew the banner planes: advertising discothèques and cheap restaurants across the beaches of the Costa del Sol.

A young pilot at the fuel pump glanced over at me and then shrugged: crazy foreign lady. The banner pilots had never seen me fly. I retreated when they arrived, watching jealously from the distance. I listened to them on the radio — jokes, maybe insults. The Spanish was too fast and too dialectal for me to follow. They scared me: the energy, the easy-going laughter, as comfortable with the planes as an old bicycle kept in the garage. The airport held no secrets for them, the aircrafts were not a mystery. It’s a culture I would never belong to, even if I spoke the language, even if I were the same age. They must have been born in the cockpit, I thought.

After take-off, the aircraft circles back around in the circuit. Someone on the ground sets up the pick-up point. The banner is laid flat and the towline is strung between two poles across the runway.

The aircraft returns, flying low (about 10m) over the runway. He hooks the towline with a hook mechanism on the back of the plane and then flies straight up into a stall.

OK, not quite but that’s what it always felt like when I was watching. The pilot applies full power and goes into a steep climb. The tow-rope unfurls and then the banner lifts off the ground, in a way that literally seems like it is going to jerk the aircraft back down to the ground. The aircraft levels out and magic, the banner is flying behind it gracefully.

The following Saturday, I asked to use the radio so I could listen in. The first banner plane took off and made a left turn. He didn’t make any standard calls, it was chitchat, the roaring of the engines in the background. I watched the plane in the circuit when I noticed the man in the long-sleeved shirt was unfurling the banner, rolling it out centered along the runway. The plane came around, low and fast, just a few feet above the runway. On the back of the plane was a hook and as he came over the edge, it swooped down and hooked the banner. I felt vaguely sick as I watched. Having seen the weight of the banner, it seemed like it would jerk the plane backwards towards the ground as the hook tugged it. There wasn’t even a shudder, not a flinch, and he was away, an advertisement for Star-Spangled Disco fluttering behind. The next plane was already entering the runway, ready to follow the same sequence. Finally, all three circled with their banners on proud display before they called that they were leaving the station and the radio went silent.

They flew towards the coast. I dialed in the Málaga frequency on the radio. They would be flying through Málaga airspace and I wanted to hear how they sounded, once talking to air traffic control, once they had to be professional. But there was no call. It was as if they’d left us and disappeared. I waited a few more minutes and then changed the frequency back for local flights. Where had they gone?

Rick Witt, a banner pilot on the BeechTalk forums, describes what it’s like in the cockpit.

“Banner towing is 1 minute of adrenaline rush (the pick up) followed by hours of boredom followed by 30 seconds of fun (the drop).

If it weren’t for the fact that you’re in a 0g push at the moment the banner lifts, the plane would surely stall (more adrenaline). In a perfect pickup, the airplane is directly over the banner when it starts to lift, meaning you have climbed 100 ft while covering 100 ft across the ground.

I never had any passengers except for training. For towing billboards, we were at the limit of the plane’s capability. If we had excess power, they made the sign bigger!”

Somehow my explanations have always seemed rather flat compared to the reality, so I was thrilled to have found this video by C172skyhawk2 posted on /r/aviation showing banner pick ups in action.

(Note: if you are reading this on the mailing list, you’ll need to click through to view the videos on the Fear of Landing website)

We got back before the banner pilots arrived. The banner planes flew out to the coast and turned right, making their way to Marbella and then turning around to glide over the beaches, adverts trailing behind them.

I couldn’t face all of them together, that maelstrom of easy virility that flattened everything in its path. But I spotted one of the pilots on his own, sipping cold water at the bar. “Where do you go, when you leave?”

My Spanish was unsteady but he waited patiently for me to find the words. “When you leave the radio frequency, where do you go? You don’t speak to Málaga. I was listening on the radio.” I knew I sounded like a stalker but I wanted to know.

He laughed. “Es un secreto.” I scowled, feeling made fun of, but he kept on. “It’s true, it’s a secret channel. We fly low across the coast, low enough that Málaga does not even know we are there and we talk to each other.”

I was shocked. This was, well, against the rules! “So you just say nothing?”

“We say nothing to Málaga. We stay out of their way, and they are just as happy not to have the distraction,” he said. “We talk to each other, so we know where everyone is.”
Where “everyone” meant “banner fliers” only. I made a mental note to stay away from coast on weekends, at least until I found out their secret channel.

That would have been a fun way to learn more Spanish!

Here’s one more set of banner planes (picking up and dropping) video’d by C172skyhawk2 with obligatory aviation-video-music:

See you next week!

01 November 2013

The Story Behind an Unbelievable Photograph

A reader mailed me this amazing aviation photograph and I knew I wanted to know more. I was surprised at how much I discovered about the photo, which at first glance I thought might be a fake. But the story of who took the photograph and how he managed to get the shot is a good one.

The aircraft is an English Electric Lightning F1. It was designed and created by the English Electric Aviation Company, who’d been contracted to develop a jet bomber at the end of World War II.

Lightning Development

The ER103 design study was sufficiently impressive for English Electric to be awarded the contract for two prototypes and a structural-test airframe. The early prototypes evolved into the Lightning, an aeroplane which was to span the time from when the Spitfire was our primary front-line fighter to the end of the Cold War.

The Lightning was the only British designed and built fighter capable of speeds in excess of Mach 2 to serve with the Royal Air Force.

The aircraft in the photograph was XG332. It was built in 1959, one of 20 pre-production Lightnings. Alan Sinfield took a photograph of XG332 in 1960 at Farnborough:


However, the very last photograph taken of XG332 is deservedly the most famous one. How does someone manage to take a photograph like this? Planning, quick wits and a healthy dose of luck.

Jim Meads is the man who took the picture. He was a professional photographer who lived near the airfield, next door to de Havilland test pilot Bob Sowray.

So, the story goes: Bob Sowray mentioned to Jim Meads that he was going to fly the Lightning that day. When Meads took his kids for a walk, he took his camera along, hoping to get a shot of the plane.

His plan was to take a photograph of the children with the airfield in the background as the Lightning came in to land. They found a good view of the final approach path and waited for the Lightning to return.

As it happened, Bob Sowray didn’t fly the Lightning that day. The pilot was George Aird, another test pilot working for De Havilland.

George Aird was involved in the Red Top Air-to-Air Missile programme and seems to have been a well-respected test pilot.

I found this a video of Aird in 1984 preparing and flying a DH Mosquito RS712. It’s one of the few videos I’ve seen that shows as much of the pilot as the plane!

But let’s get back to the story of the photograph on the 19th of September. That day, George Aird was in the Lightning doing a demonstration flight off of the south coast. He was approaching Hatfield from the north east when he realised there was trouble.

ASN Aircraft accident 13-SEP-1962 English Electric Lightning F1 XG332

Whilst carrying out a demonstration flight, there was a fire in the aircraft’s reheat zone. Un-burnt fuel in the rear fuselage had been ignited by a small crack in the jet pipe and had weakened the tailplane actuator anchorage. This weakened the tailplane control system which failed with the aircraft at 100 feet on final approach.

The aircraft pitched up violently just as Aird was coming up to land. Aird lost control of the aircraft and ejected.

Luckily, because the nose pitched up he had just enough time to eject.

The tractor in the photograph was a Fordson Super Major. If you look closely at the grill, you’ll see it reads D H Goblin, as in the de Havilland Goblin jet engine.

The tractor driver was 15-year-old Mick Sutterby, who spent that summer working on the airfield. He wasn’t posing for the camera. In fact, he was telling the photographer, Jim Mead, to move on, because he shouldn’t be there.

Mead saw the plane coming in and the nose pitch up. Then Aird ejected and Mead says he had just enough time to line up the shot as the Lightning came down nose first.

Here’s an email from Mick Sutterby the tractor driver, sent to John Palmer, which was posted on The Funny Noise.

From: Mick Sutterby
Subject: Re: Lightning aircraft crash at Hatfield
Date: Thu, 19 May 2011 20:16:41 +0100

I followed my father into work at de Havilland, Hatfield in 1954 when I was 15. My father was the foreman in charge of the aerodrome and gardens. My job in the summer was gang-mowing the airfield and at the time of the crash in 1962 the grass had stopped growing and we were trimming round the ‘overshoot’ of the runway with a ‘side-mower’.

I stopped to talk to a chap with a camera who was walking up a ditch to the overshoot. I stopped to tell him that he shouldn’t be here, I heard a roar and turned round and he took the picture! He turned out to be a friend of the pilot and had walked up the ditch to photograph his friend in the Lightning. I saw some bits fly off the plane before it crashed but it was the photographer who told me he had ejected.

There was not a big explosion when it crashed, just a loud ‘whhooooof’. I was about 200 yards from the crash scene. I saw men running out of the greenhouses and checking the scene of the crash. The works fire brigade were on the scene within a minute. Somewhere at home I have a picture of it burning. Although the picture shows it nose diving to the ground, in fact it was slowly turning over and it hit the ground upside down nose first.

I was later told that if the pilot had ejected a split second later he would have ejected himself into the ground. I was very lucky. If I had known he was coming into land, I would have been positioned near the ILS (Instrument Landing System) aerial which was only 20 yards or so from the crash site! I believe the photographer had his photo restricted by the Air Ministry for – I think – about 3 months because the plane was secret.

He then took it to the Daily Mail who said it was a fake. The photo was eventually published by the Daily Mirror. From there it went round the world, and I remember seeing a copy in the RAF museum at Hendon. I recollect the photographer usually photographed hunting scenes for magazines like The Field. I recollect that the pilot broke his legs but really was very lucky. I hope this is interesting. All from memory!

Best wishes,
Mick Sutterby

Meanwhile, George Aird landed on a greenhouse and fell through the roof, breaking both legs as he landed unconscious on the ground. The water from the sprinkler system for the tomatoes woke him. He’s reported to have said that his first thought was that he must be in heaven.

118 Squadron – Personnel 002 George Aird

George landed in a greenhouse sustaining several fractures. The hole where George and the ejection seat went through the glass roof can be seen in the above picture in the near end of the roof of the second greenhouse from the left. They landed in adjoining rows of tomatoes! The damage at the far end of the greenhouse was made by the arrival of the Lightning canopy. The remains of the Lightning can be seen on the left just into the airfield. George was back flying again within six months and on Lightnings a year after the accident.

The photographs taken that day first went to the Ministry of Aviation. Once they were released, Mead sold them to the Daily Mirror.

It was featured as a centre page spread in the newspaper on the 9th October 1962.

Jim Meads is a Mirror reader who was trying to amuse his two children, Paul, 4, and Barry, 3, by taking a picture of them as the Lightning was coming in to land at the De Havilland airfield near their home at Hatefiled, Herts.

The Daily Mirror paid Mead £1,000 for the rights to the photograph: £18,000 by today’s standards. In my opinion, he deserved every penny.


If you found this post interesting, you might like to pick up my new book, a detailed analysis of MH370: The Mystery of Malaysia Airlines Flight 370

01 February 2013

5 Things About the Dreamliner That I Didn’t Know

1) The Dreamliner’s noise reduction tech is the results of decades of NASA research

The Dreamliner has chevrons – serrated edges on the engine nacelles – in order to reduce the noise. Passengers on the plane before it was grounded say that it is quite noticeably quieter but I hadn’t understood the background.

“Evolution from ‘Tabs’ to ‘Chevron Technology’-a Review”

As evident from this paper, maturing the technology followed a long and arduous path with multiple dead-ends and parallel efforts. Seedling observations from laboratory-scale experiments eventually migrated to applications, a process that required prodding from noise regulations, inspired tests and finally a concerted NASA/ industry effort. It is emphasized that jet noise remains a major component of aircraft noise for moderate to low bypass ratio engines. Chevron technology has provided a modest relief. Unfortunately, a complete understanding of jet noise mechanisms is still not in our grasp.

The insight of fundamental experiments coupled with application of CFD allowed the development of the subject technology with tools slightly better than cut-and-try. Hope for further control and reduction of jet noise hinges on advancement of our understanding of the relevant mechanisms. This has been and will continue to be an emphasis of NASA’s noise related projects.

2) Lithium-ion batteries sound like something from a science fiction novel

Lithium-ion batteries are both a lot more complicated and a lot more interesting than I thought they were.

A primer on the science fueling the lithium-ion battery market

Lithium in its purest form – a silvery-white metallic element – is not found in lithium-ion cells. Rather, a chemical compound containing lithium (in some cases, lithium cobalt oxide) is used. The term “lithium-ion” refers to the positively charged atoms responsible for the battery’s charging and discharging. A lithium-ion battery’s metallic case contains a lithium-ion cell consisting of anodes (negative electrodes) that are commonly composed of lightweight elements, such as carbon, and cathodes (positive electrodes), a ceramic material made from the lithium cobalt oxide or other materials. The cathodes and anodes are placed onto individual copper or aluminum foils, separated by a porous piece of film, and submerged in an organic solvent known as an electrolyte. As the battery charges, the electrolyte aids the lithium ions (charged atoms created by the lithium salt in the electrolyte) that move through the film from the cathode to the anode. The direction of the ions is reversed during discharge, creating a flow of an electrical current. The batteries produce a higher voltage and can be recharged for hundreds of cycles, making these devices an increasingly popular power source.

3) If the battery is not the issue, then that’s bad news

The Japanese transport ministry official has stated that they have found no technical problem with the batteries in their investigation. That’s an even bigger problem for Boeing.

BBC News – Dreamliner: No fault found with Boeing 787 battery

Keith Hayward, head of research at the Royal Aeronautical Society, said that if the issue is no longer about replacing a faulty battery, it raised the prospect of Boeing having to do a major re-design.

“I think people had their fingers crossed that it was a battery fault… it looks more systemic and serious to me. I suspect it could be difficult to identify the cause,” he said.

He added that aviation regulators will have to put the 787 through another airworthiness certification process, which itself could become a complicated and lengthy process depending on the final cause of the problem.

4) Boeing’s flight test program included being struck by lightning

The unexpected event neatly helped to show that the conductive material added to the composite fuselage was doing its job.

Boeing 787 Withstands Lightning Strike | Autopia | Wired.com

The 787 flight test team gathered the unexpected data last month after one of the Dreamliner test aircaft was struck by lightning. Unlike traditional aluminum aircraft where the entire aircraft is conductive, on a composite airplane the charge from a lightning strike would find its way to the conductive parts such as wiring or hinges. In order to avoid the risk of the charge damaging these kinds of parts, Boeing had to add conductive material to the composites in order to provide a pathway for lightning strikes.

The added weight to protect the airplane from lightning strikes ended up being more than Boeing anticipated. The material was one of the factors that pushed the Dreamliner past its target weight earlier in the development process.

5) The outsourcing strategy being blamed now actually started with McDonnell Douglas

According to the New Yorker, the cuture change after the merger is why the development of the Dreamliner was outsourced all over the world.

James Surowiecki: The Trouble with Boeing’s 787 : The New Yorker

To understand why, you need to go back to 1997, when Boeing merged with McDonnell Douglas. Technically, Boeing bought McDonnell Douglas. But, as Richard Aboulafia, a noted industry analyst with the Teal Group, told me, “McDonnell Douglas in effect acquired Boeing with Boeing’s money.” McDonnell Douglas executives became key players in the new company, and the McDonnell Douglas culture, averse to risk and obsessed with cost-cutting, weakened Boeing’s historical commitment to making big investments in new products. Aboulafia says, “After the merger, there was a real battle over the future of the company, between the engineers and the finance and sales guys.” The nerds may have been running the show in Silicon Valley, but at Boeing they were increasingly marginalized by the bean counters.

Despite the problems, I’m still firmly on Team Boeing. I think the Dreamliner is an amazing machine and I hope the complications get ironed out in record time.

14 December 2012

Why do aircraft still have ashtrays in the lavatory?

We’ve all seen this in the toilets of commercial aircraft: a large no-smoking sign with a plainly marked ashtray underneath. Obviously airlines who allow in-flight smoking have ashtrays as a part of the standard model. But are there any of those left?

The US banned smoking on domestic flights in 1990 and soon followed up with international flights. The UK does not have a ban on smoking in flight; however British Airways banned it on all their flights in 1990 with Virgin and other UK airlines following suit. By 1995, it was rare for a UK airline to allow smoking on board. By 2003, only a very few airlines around the world allowed smoking on international flights.

And yet, even the most modern aircraft have ashtrays built into the toilet door. These ashtrays are accompanied by big placards which announce that it is prohibited to smoke in the lavatories under any and all circumstances – so why have the ashtrays there in the first place?

The FAA and CAA have airworthiness requirements / directives mandating that these ashtrays are in place, along with the placards prohibiting smoking. The airline is required to have ashtrays in the toilets and they must be inspected regularly to ensure they are still working. It is part of the minimum equipment list (MEL) that an aircraft must have onboard, which means if an ashtray breaks or is removed, it must be replaced promptly (3-7 days in the US, 10 days in the UK). Although smoking is not permitted on the flight, if someone does light a cigarette, they must be able to extinguish it safely.

Legally, a plane could be grounded by not complying, as happened to a Canadian airline in February 2011.

The Jazz Air flight from Fredericton to Toronto was scheduled to depart at 14:50 local time when the crew discovered that the ashtray receptacle had been removed. The airline flew the empty plane to Halifax to have a new ashtray installed and then returned to Toronto where the flight departed nine hours late at 23:45.

The reason for this directive is that despite the prohibition, there is always the risk that a passenger will smoke anyway, and hidden away in the lavatory is the only real place someone might hope to get away with it. Surveys have shown that it continues to be a problem, despite years of prohibition and warnings in bold red fonts. When the fire alarm kicks off and the cabin crew start banging on the door, a panicked passenger should not be tempted into shoving the cigarette into the paper towel dispenser.

This may sound far-fetched, but the scenario does not simply occur in the nightmares of airline industry bureaucrats. In 1983, Varig Flight 820 crashed, killing one hundred and twenty three people, with the probable cause of a cigarette.

The scheduled flight from Rio de Janeiro for Paris-Orly was on approach for runway 26 when the flight crew contacted Orly to state they had a problem with fire on board and needed an emergency descent. The fire was at the rear of the plane and the cabin was filling with smoke. At 13:59 the flight was given clearance to descend to 3,000 feet for runway 07, to allow the aircraft to make a straight-in landing.

Meanwhile, smoke was entering the cockpit and the flight crew, who were wearing oxygen masks, were struggling to read the instruments. At 14:03, the captain attempted an emergency landing 5 kilometres short of the runway.

The aircraft landed on a field, where both main gears collapsed and the engines were torn off. By the time the firemen arrived, the fire had burned through the roof. Ten occupants evacuated through the roof. Firemen rescued four unconscious occupants but only one survived. One hundred and twenty three were killed from the inhalation of the smoke, most of them dead before the plane even landed.

The fire started in the washbasin unit of the aft right toilet. The FAA responded directly to this accident with the requirement to install placards and ashtrays in all aircraft.

So when you see that no smoking sign next to the ashtray, you’ll know the reason why. It’s not meant to be a temptation to break the rules and light a cigarette, simply a safeguard in case somebody does it anyway.

27 April 2012

5 Surprising Facts about Black Boxes

Today, aircrash investigations centre around the black box – that is, the flight data recorder (FDR) and the cockpit voice recorder (CVR). I have always thought of them as rather straight forward: one collects flight data and the other records voices in the cockpit.

However, when I started to do some research about flight recorders, I was taken aback at how much I didn’t know. Explaining my own ignorance would take more than a single blog post so I limited myself to the top five things that surprised me.

1. The very first flight data recorder was invented by the Wright brothers. They created a device which recorded propeller rotations, distance travelled and time spent in the air.

Charles Lindbergh also had a flight data recorder which was in a plywood box and inked data, including altitude, onto a paper roll. A major breakthrough took place at the Marignane flight test centre in 1939. They created the “type HB” flight recorder that kept a record on photographic film. But not until World War II did we have an FDR which was expected to withstand high-speed impact and fire.

More information: Flight data recorder history – Wikipedia

2. There’s no clear history as to why the container of flight recorders (FDR and CVR) is called a black box. A black box obviously needs to be highly visible, so it can be found amongst wreckage and even underwater. The flight recorder container has a minimum height and width and it is painted bright orange and highlighted with reflective tape.

I found a number of theories explaining why we called them black boxes, none of which seem particularly compelling:

  • A journalist referred to the initial prototype as “a wonderful black box” as it was based on a wire recorder used for espionage.
  • Early recorders were painted black (there’s no evidence of this that I can find).
  • They can get charred in accidents and turn black.
  • During World War II, the RAF experimented with various electronic innovations for aircraft and often covered the prototypes in black metal boxes to prevent reflections. Thus any new electronics added to an aircraft was referred to as a black box and the name stuck.
  • The initial flight data recorders had to be opened in a dark room to prevent light from corrupting the record.

Convinced? Me neither. Regardless, the phrase “black box” has been used within the transport industry for various forms of recording devices, including planes, trains and automobiles, since the 1940s.

3. Australia was the first country to make cockpit voice recorders a requirement for commercial aircraft. I knew that the modern flight data recorder was effectively invented in Australia but not that the Australians the first to make flight recorders compulsory.

In 1960, a twin-engine Fokker Friendship F-27 flew into the ocean with 25 passengers and 4 crew on board. The investigation failed to find the cause and the inquiry recommended that all passenger airliners have flight recorders installed. Not long thereafter, the Brooklyn airline collision in December of 1960 was the first time that the flight recorders were critical in a crash investigation. Now I can’t imagine an investigation that doesn’t rely on the data gathered from the black boxes.

More information:
Trans Australia Airlines Flight 538 – Wikipedia
Photos of 1960 Brooklyn airline crash that sparked new era of ‘black boxes’ | Mail Online

4. Recorders were originally housed in the cockpit along with the instruments and the pilots. Only after several accidents where the Flight Data Recorder was not recoverable did they get moved to the rear of the aircraft, based on the presumption that following the initial impact, the rear of the aircraft would be moving at a slower speed. In addition, the units initially only had to withstand a 100gs impact which was increased to 1000gs.

The key components of modern solid-state flight recorders are called Crash-Surivable Memory Units (CSMUs).

They go through a whole sequence of surviveability testing including:

Crash Impact Test — It has been agreed that 3400gs for 6.5 ms would be required to meet most accident scenarios. This test is actually performed with a cannon. A Fairchild CVR has survived a crash that was estimated to be more than 6000 gs.

Static Crush — In this test, 5,000-pound pressure is applied against all six axis points.

Pierce Test — A pierce test employs a 500-lb. weight dropped from 10 feet. It has been modified to be performed with a hardened steel pin.

Fire Test — The devices are subjected to 1100 degrees Centigrade for 60 minutes, then undergo 10 hours at 260 degrees Centigrade.

Source:
L-3 Aviation Recorders

5. Personal black boxes already exist. Microsoft has developed technology called the SenseCam, conceived as a personal black box accident recorder.

It is a thin, light-weight camera with a wide-angle lens which takes photographs automatically as you go about your business. Cathal Gurrin has worn one around his neck every day for the past five years.

The SenseCam doesn’t have a viewfinder and there is no way to frame the photo. It has a fish-eye lens to capture as much of the wearer’s viewpoint as possible. It can be triggered by a timer or using internal sensors that watch for changes in light-intensity or light-colour, the wearer’s temperature, or even a change in direction/speed using a multiple-axis accelerometer. These changes can trigger a photograph to be taken.

The Vicon Revue is currently available as a commercial product for £299. It is being pitched as a memory aid for special events and to support people with memory impairments.

More information: Microsoft Research SenseCam

I don’t think I’ll be wearing a little life logger around my neck any day soon, though. It gives me the chills. Would you?

20 April 2012

Motion Induced Blindness

I received this from reader Albert Masetti as a demonstration on eye fixation.

Michael Bach, a Professor at the University of Freiburg has a full page of Optical Illusions and Visual Phenomena. The strength of this site is that he allows for controls for each of the illusions, so that you can check for yourself what is actually happening (as opposed to what you are seeing). Each illusion has a full explanation as to the effect and why it occurs. He’s kindly given permission for his experiments to be recreated, so you play with his Motion Induced Blindness example here:

You should see a rotating array of blue crosses and 3 yellow dots. Now fixate on the centre (watch the flashing red/green spot). Note that the yellow spots disappear once in a while: singly, in pairs or all three simultaneously, right?

In reality, the 3 yellow spots are continuously present, honest! This is captively called “motion induced blindness” or MIB.

A retired Marine aviator describes the phenomenon:

This is a great illustration of what we were taught about scanning outside the cockpit when I went through training.

We were told to scan the horizon for a short distance, stop momentarily, and repeat the process. I can remember being told why this was the most effective technique to locate other aircraft. It was emphasized repeatedly to not fix your gaze for more than a couple of seconds on any single object. The instructors, some of whom were veterans with years of experience, instructed us to continually “keep our eyes moving and our head on a swivel” because this was the best way to survive, not only in combat, but from peacetime hazards (like a midair collision) as well.

We basically had to take the advice on faith (until we could experience for ourselves) because the technology to demonstrate it didn’t exist at that time.

Michael Bach of the University of Freiburg, who created the original page, explains the effect:

Steady fixation favours disappearance, blinks or gaze shifts induce reappearance. All in all reminiscent of the Troxler effect, but stronger and more resistant to residual eye movements.

There is no consensus as to the explanation in vision literature yet. I personally think that motion is not necessary, any (temporal) change in the image will suffice. [Note added 2008-03-07: see now Wallis & Arnold, 2008.] A more recent paper from that group (2009) sugggests a link of MIB to “motion blur / motion streak” suppression. If so, MIB would be illusion subserving a useful purpose in everyday vision. This also holds for a different explanatory approach by New & Scholl (2008) who conclude that “rather than being a failure of visual processing, MIB may be a functional product of the visual system’s attempt to separate distal stimuli from artifacts of damage to the visual system itself.”

If you fixate steadily, all structures are imaged on their same retinal location. This leads to local adaptation on the retina (the Troxler effect, often incorrectly addressed as “fatigue”). By adding additional temporal modulation (here the rotation), effectively the background noise is increased. Thus the Troxler disappearence is more pronouned and/or happens faster.

In other words, it may be that the reason for this effect is to keep us from being distracted from motion blur affecting distant objects when we are moving quickly.