What is Turbulence? Is it safe for planes to fly in turbulence? Are passengers safe in turbulence?

The Physiology of Turbulence

The sensations during turbulence, however you think about it, will remind many of frightening roller-coaster rides taken when they were younger; of being in fast moving elevators where the only sign of movement other than their sensations were the elevator numbers changing; and being helpless passengers in the back seat of fast moving, curve-taking cars.

All these represent situations of inescapability, loss of control, and high levels of uncomfortable sensations, principally as a result of experiencing g forces.

g forces?

Yes, in this case g stands for Gravity, which is a force we all experience as we stand on the Earth's surface. Of course, we don't actually feel this force but it's there nonetheless - it keeps us on the surface, and brings us down again when we jump.

But in the context of turbulence and flying, g force is also a measure of acceleration. This is a measure of how our speed changes over time.

If a car goes at 60 consistently, then its occupants will not experience the effects of acceleration because there are none! The green car below is travelling at the same speed across the page, so its occupants experience no acceleration. Good taxi drivers try to drive like this! The red and blue cars though speed up as they go across the page. Notice how the red car leads for a while, then the blue car accelerates faster and overtakes it. Its occupants would likely feel greater forces of acceleration, which for some might be thrilling, and for others frightening.

Deceleration is the opposite, and also represents a change of speed (or to be accurate, velocity) over time, except this time it is negative. In physics, the terms used are positive and negative acceleration, and is measured as a change of velocity over time.

In the car when you accelerate sharply, you are pushed back in the seat - when you decelerate sharply you tend to be thrown forward.

You don't have to go to school to learn these actions, it's a part of how objects, including people, respond to g forces. Sports cars designed to accelerate and brake rapidly usually have specially designed seats and harnesses to hold its occupants in place so they can remain in control of the car. (Which is why placing objects on the rear window shelf can turn them into missiles when you come to a sudden stop).

Once we reach a constant speed and stay there, we will no longer feel the effects of g forces, no matter how fast we travel. Which is why you sometimes need to pinch yourself looking out the airplane window at the slow moving ground under you to remind yourself the plane is travelling at nearly 600 mph! And also why very fast moving elevators feel worse at the beginning and end of the journey but are OK once they settle down to constant speed. The more rapid the acceleration (not constant velocity) the more you will feel the effects.

In other words, we seem to be built as good acceleration detectors (despite it not feeling good), but we're not very good velocity detectors. We actually need instruments in our cars to remind us of our speed, which is why police often hover near freeway exits to pick up speeding drivers before they make a speed adjustment to local traffic conditions. Indeed there is a field of study (ergonomics) which looks at how best to indicate speed in a car so as to help people keep to speed limits.

Now a little task for you! In turbulence, or on a rollercoaster, where do you most feel the uncomfortable sensations? Most people tell me "in the pit of my stomach", or solar plexus, and perhaps it would be reasonable to assume that's where our acceleration detectors are located.

But you would be wrong!

Our accelerometers (a device that measures g force or acceleration) are in fact located in our heads! Indeed, when you feel dizzy or faint, it is usually felt "in the head" more than anywhere else.

The peripheral device that first detects our changing motion in space over time (acceleration) is comprised of a two sets of three semi-circular canals which sit on top of our inner ears, one set for each ear. They are each connected to two sacs or vestibules, the Utricle and the Saccule, and each contains their own type of fluid.

This is what it looks like:

The canal and vestibule fluids move when your head turns, in response to its acceleration, and small hairs in the canals wave as the liquid moves through them. The hairs are part of a nerve-innervated membrane, and their movements cause nerve conduction down the vesitbular nerve to occur, and these are interpreted in the brain. This also triggers, in turn, signals to our eyes, so that when we walk and our head bobs up and down we keep our field of view constant. Which is why if you video while walking - by taking a point of view shot as if the camera were your eyes - it can make you feel ill watching it back. There is a loss of integration of signals between the optic and vestibular systems, known as the vestibulo-ocular reflex.

(Newer roller coaster rides where the vehicle only moves side to side or up and down on a platform in front of a projector screen take advantage of this system to fool us into believing we are in the real thing. And indeed, you can make yourself a little queasy by building your own rollercoaster on the internet! You'll need Macromedia's Flash, but have some fun at an Australian site, called MakeTracks, from Questacon. Don't blame me if you have a technicolour yawn - you've been warned!)

The semi-circular canals, the utricle and the saccule each have a role to perform when working together as an accelerometer system.

The semi-circular canals, comprised of three canals at right angles to each other, are sensitive to angular accelerations like head rotations. They seem to work in pairs, such that any positioning of the head will have two canals working to give a positive, and the third to give a negative value. In nervous system terminology, two are excitatory and the third one is inhibitory. What this boils down to is that we are exquisitively sensitive to head movements, both angle and speed.

In the above diagram you can see how each system on opposite sides of the head send contrasting messages, working in tandem, to the brain so we know where our head is in space. If they didn't we would get very dizzy all the time, which is what sometimes happens when we have an inner ear infection.

The other parts of the vestibular or balance system also measure g forces - up/down; forward/back; left/right. So all bases are covered.

All these organs are known as the peripheral vestibular system, which feeds information to the brain - the central nervous system or CNS - which makes sense of all the data and causes action, feeling, or thought to occur.

So while you may feel nausea in your tummy in high g force conditions, the organs responsible for the sensations are in your skull!

Let me finish off this introductory section by letting you know that your experience of discomfort during inflight turbulence is due to three forces at work: downwards acceleration of the plane leading to transient feelings of weightlessness; upwards acceleration of the plane leading to transient feelings of heaviness, and transverse or sideways acceleration of the plane, leading to feelings of disorientation.

All these physical sensations can often be experienced as discomfort, and if very strong, can cause nausea, dizziness, light-headedness and perspiration. Not too different from those sensations felt during various rollercoaster rides.


The Psychology of Turbulence

From the psychologist's viewpoint, these sensations are often associated with an innate fear of falling, which I have mentioned in another blog entry. (If the initial movement of the plane is upwards, experienced flyers know there will follow a downwards acceleration soon after).

If you think about it, falling is usually associated with injury. At some point in our evolution, human beings developed a sense of depth perception, such that they no longer needed to fall off a cliff to "know" that cliff falling often had unwanted side-effects - same goes for falling out of trees. So we could walk along a hill which might quickly fall away, like the cliffs near the ocean, and know not to walk any further.

Babies develop protective depth perception at a very early age, and it is a property of having two eyes set wide apart in our heads. Each eye gets a slightly different perspective of the world it sees, and the brain then puts together these two slightly different pictures to make our world 3-D, rather than flat as in a painting or photograph.

Babies use their innate depth perception to avoid falling over cliffs, as was shown in a series of ingenious experiments performed by Eleanor Gibson in the 1960s, known as the Visual Cliff experiments. Here mothers coaxed their babies over "cliffs" represented by the falling away of surfaces. In reality, glass was placed over the "cliff" so the babies were never in danger of actually falling. In a series of experiments, Gibson and her colleagues were able to determine that somewhere between 6-10 months babies could discriminate depth, and required coaxing by their mothers to overcome their fears and cross the cliff to be with them. Her experiments showed various animal offspring develop depth perception within days or weeks.

Being able to develop depth perception has profound effects on the survivability of a species. For human beings, knowing they are at a height where a fall might mean hitting the ground hard - and injuring or killing oneself - can be lifesaving. Unfortunately, learning that falling from a height can kill you usually means you don't get any second chances or the opportunity to pass on your knowledge to your offspring.

Thus falling has associated with it very uncomfortable sensations which teach us to avoid heights where falling might occur. We can learn to overcome these sensations when we "know" that we are in fact safe, which is how people who take rollercoaster rides are able to enjoy them, much like skydivers do. These people actually learn to anticipate with excitement the "rush" that comes with accelerations of their body through space. Same with fast sports car rides that push you into the seat when you "slam the pedal to the metal", as they saying goes.

And guess what? You can have anticipation of falling even before you do, just by approaching what you "know" is a cliff or drop! By "know" I mean to write that in fact you can be fooled into believing a cliff is there, just like the babies in Gibson's Visual Cliff experiments were fooled into seeing a cliff when there wasn't one. This is why sometimes you might need to back away from a railing or fence in a high rise building because you "know" that it wouldn't take much to step over that fence and fall. You may even feel a zing of adrenaline shoot through your spine as you approach the railing and have to pull back for fear you will feel a compulsion to leap off the building.

Some of the interesting work in Virtual Reality has been to try and create a virtual cliff in a head mounted display and measure how anxious people become when approaching it - this is one way of quantifying a measure in VR studies known as presence, the feeling that you are in the virtual world, not just watching it.

Here is a representation of a virtual cliff set up, actually referred to by the experimenters as a virtual pit, where subjects rehearse actions in the room to the left in a head mounted display then move to the room on the right. They are then instructed to stand on a ledge and look down... in reality the ledge is just a few inches high, but the view they see in the display they have been wearing (which has become their visual reality) looks like that depicted under the room to the right.

It looks like a sheer drop!

What is interesting is that subjects report a strong sense of being on the edge, looking down and their physical sensations as measured by physiological instruments show they are truly responding to a frightening scene.

This little excursion into VR is all about how we human beings have mechanisms we have inherited over generations to help us both identify risky situations (heights) and react to them (feeling ill, reflexively stepping back, gripping onto seats or branches to stop us from falling, etc...). This is built-in to us - it's what makes us human.

Now comes the time for me to write how not all people perceive and experience height, depth and acceleration, at least in an airplane, the same way. Some seem more susceptible, easily complaining of the ill effects of motion sickness and vertigo, while others seem almost immune to the same cues. (I'm personally quite susceptible to motion sickness, perhaps stemming from years as a child enduring frequent painful ear infections).

On the other hand, there are some groups who have inherited strong resistance to feeling wobbly at great heights. In the 1920s, when the Empire State Building on 34th Street in Manhattan was being built, the construction company employed Mohawk Indians who seem to have an uncanny ability to work high rise constructions in New York City. Indeed they have done so over six generations, and helped to dismantle the remains of the World Trade Centre Towers after September 11, 2001, buildings their fathers and uncles had helped built in the 1960s.

So if you are susceptible to motion sickness, turbulence in a plane represents an uncomfortable experience, usually paired with falling and associated danger. It does so at a deep, primitive level, without requiring any thought or planning, and likely residing in genes passed on over many generations.

In other words, for many people it is perfectly normal to perceive danger during flights where there is significant turbulence. Your gut tells you it is dangerous by producing sensations, mediated by your vestibular system, usually associated with falling, and by definition, injury.

And without thinking, you likely try to overcome the discomfort of falling by reflexively gripping the seat, or the person next to you, as if to maintain your balance. This set of reflexes, which by definition require no thought, has special consequences for stress. As I'll shortly explain, doing what comes naturally actually makes your experience of turbulence worse!


Aviation Meteorology and Turbulence

This is a special field of Meteorology devoted to Aviation. Knowing about the weather and how it affects flying is something pilots learn from day one of their training. Knowing about it is a core activity of good airmanship and is central to safe flying at whatever level of aviation, from those who are learning to fly, through to those who fly for a living at the highest professional levels. And of course certain speciality areas of aviation, such as gliding and hot air ballooning, rely on the weather to actually perform their activities.

In his book, Flying the Big Jets, Stanley Stewart, a captain with British Airways, has devoted a chapter to the subject. He writes, "Weather, with fuel a close second, is the most important factor of any flight; the former often deciding the quantity of the latter, and at pre-flight briefing weather is normally the first item checked."

(For those who have come here from a Google search, one of the best references you can go to is Peter Lester's site here and his book, Aviation Weather.)

For our purposes, we'll look at what you need to know about meteorology, and of course turbulence which is a part of that. So are thunderstorms which aircraft can be directed to avoid, or, if over an airport or nearby, will keep aircraft on the ground, or circling some distance away, which may serve to delay your flight.

All of us at some level have a working knowledge of weather since it affects us everyday. From planning what to wear, how fast to drive, when to take holidays, where to live and when to sell our house is all affected by the weather.

We take the weather into account without knowing much about it, perhaps tuning in to the TV or radio which always conclude their bulletins with a weather forecast.

Indeed, most of us are vitally interested in weather changes, knowing that the weather has certain patterns which can be planned for; fearful flyers especially often have a vital interest in the weather, making their own predictions as to what sort of flight they might expect on a given day, and carefully listening to the flight crew's announcements regarding the smoothness, or otherwise, of the flight.

As I have written elsewhere in this blog, the weather you see outside your home may not bear much relationship at all to the weather your flight will experience. Looking at television weather forecasts will often show very local variations in temperature, wind speed and direction, and precipitation to name a few. And that is just at sea level, where your journey will start (unless you are in Mexico City or some other locations high above sea level).

So let me cut to the chase. What follows is much of what I am prepared to discuss with my fear of flying clients, although the details will vary depending on relevance to their needs:


1. We live on a planet which is almost a perfect sphere, composed of water and land masses, which rotates on an axis every 24 hours while circling the Sun once every 365 and a quarter days. The axis is also "tilted" such that the Earth's hemispheres experience predictable, but opposite, seasons during the course of the year.

2. The Earth's surface is covered in a layer of gases - our atmosphere - which is thickest at the Earth's surface, and which progressively thins out as we increases in altitude. These gases are needed for life to survive, as well to protect life from the deadly ultraviolet rays of the Sun.

3. The Earth's surface is not smooth, having valleys and hills, which in the form of mountain ranges, can reach great heights.

4. At the Earth's poles are great frozen masses, which have an impact on the rest of the planet. They are least directly exposed to the Sun's heating rays.

5. Because the Earth rotates on its tilted axis, we experience periods of direct exposure to the Sun, and other periods where we are in its shadow. During the sunlight or daytime hours, the Earth's exposed surfaces heat up, and during the night hours they tend to cool. Moreover, water and land absorb and reflect the Sun's rays differentially.

6. When the oceans, which occupy 70% of the Earth's surface, warm by their direct exposure to the Sun, evaporation occurs, causing moisture to rise into the atmosphere. Certain areas have more moisture in them than others, depending on their proximity to the equator and the poles. The warmer the air the greater its capacity to hold moisture. These can be divided into zones, such as tropical, polar and arctic. When large masses of air of similar temperature and humidity (or moisture content) meet other masses of different characteristics, conflict can occur along a front. You may recall hearing the weather forecaster talking of cold or warm fronts. And these fronts move, as the Earth rotates and different zones heat up as they are exposed to the Sun's rays. Such fronts are well known to weather forecasters, and aviators pay close attention to the charts they produce which show the fronts on the day they are flying and the regions in which they will be flying.

Together with the Earth's rotation, zones of different atmospheric pressures exist, causing movement of the atmosphere from high to low pressure zones. This movement is also know as wind, and winds can reach great speeds. Like the ocean's currents which are caused by similar forces at work, there exist localised patterns of weather, dependent on local terrain such as nearby mountain ranges, oceans, lakes, and land surfaces.

There is much more to weather than this very brief description, but it's important to know that weather is a constant, in the sense that it changes due to quite predictable properties of the Earth.

So let's turn to wind, then to turbulence now...

Movement of air depends on heating of the surfaces during the day, the ability of the land to hold the heat at night, local terrain which can cause the air to tunnel between mountain ranges for instance or cause "eddies" as they roll over the mountain tops.

Wind movement is often thought about in terms of its direction and speed at the surface (which will determine the direction of runways as aircraft prefer taking off into the wind), as well as its movement at higher altitudes which may be quite different.

In other words, it is not possible to judge the smoothness or otherwise of a flight based on the local weather!

Where can flyers expect to fly in turbulence?

The answer to this is best described by looking how the aviation world discusses turbulence. It classifies turbulence by type and strength.

Peter Lester, a professor of meteorology, has written a book for pilots on Turbulence, and has described four sources of turbulence which can affect your flight.

1. Low level turbulence is what can be experienced in the first few moments of takeoff when the aircraft leaves the ground and experiences low level winds, similar to what can be felt on your drive to the airport. What we refer to as a "windy" day will be moving masses of air responding to local forces, and may not necessarily travel at constant speed, often gusting in fact. They may also travel in a direction not exactly down the centreline of the runway, so after takeoff the plane may "crab" along the centreline as the wind tries to push it to one side. The size of the aircraft's fuselage mean it can act like a giant sail, and the pilot may need to apply both rudder and aileron to keep the wings level as the plane climbs out.

Additionally, on very hot days with thermals rising from the ground (which gliders and birds use to circle and stay at altitiude), the air can feel "lumpy" as the plane bobbles along after takeoff. Think of it as being like a lake with small waves breaking to the shore, and you are swimming or paddling against them.

What this means is that it is quite likely you will perceive the plane's climbout after takeoff as either smooth, bumpy, or swaying, as the local air movements affect it.

My advice: Know that commercial aircraft have an abundance of power for takeoff and climb out. Before each flight, the crew have calculated the speed at which the aircraft will "unstick" and be capable of flight. The effects of crosswind gusts can be felt while on the takeoff run by a swaying or rocking of the aircraft as the wings begin to generate lift and the plane's fuselage acts as a sail. In strong winds, you can expect to see the wing's control surfaces come into play as a procedure to keep the plane on a steady heading and the wings level.

As the plane unsticks, breathe out steadily. Do not grip the seat arms even if this is reflexively what you usually do. You will not help your breathing and only intensify any discomfort. Remember that turbulence might be uncomfortable but it is not unsafe. Turbulence at takeoff and climb out usually only lasts a few minutes until the low level winds are left behind.

If you are climbing out through clouds you can also expect some bumps and dips due to the air thinning and thickening with moisture and changing the smooth flow of air over the wings. Again once you climb above the low level clouds in a few minutes, the ride will likely smooth out.

2. Turbulence due to other conditions may occur because of high speed winds hitting mountains and rolling up them to great heights, as well as around the edges of thunderstorm activity. Thunderstorms contains air and water moving up and down at rapid speed and are best avoided because they place stress on both passengers and the aircraft. Under all circumstances, pilots will navigate around large storm "cells" even if it takes them some distance off their planned course.

The motto for commercial aviation is to deliver customers to their destinations, 1. Safely, then 2. in Comfort, then 3, Economically in that order.

An airline that cannot act in a way that its passengers cannot expect the first to occur, isn't going to worry about the other other two! You'll know that airlines only ever compete on the capacities they can demonstrate in 2 and 3, never 1. No one competes on 1, although airlines like Qantas and Singapore notably are proud of their safety reputations. Here in Australia, many fearful flyers prefer to fly with Qantas because of its reputation for safety even though its domestic competitor, Virgin Blue, also has a superb safety record, albeit over a much shorter period of operation.

I will make another blog entry at some future point about how safety in airlines is a somewhat misunderstood concept. For myself, single large incidents are not as informative as an airline that may have lots of "fender-benders", which tells me its safety culture needs scrutiny.

3. Turbulence during cruise at high altitude can come about through a variety of factors, and can be quite frightening since it can occur unexpectedly, in fits and starts, and without signals as to when it might stop. Unlike the bumps and lifts due to weather visible on the radar (where rain masses show up as red), clear air turbulence relies more on pilots' abilities to extract information from their weather charts and meterological forecasts, the reports of other aircraft in the vicinity, and good old fashioned experience.

This kind of turbulence is usually the one associated with inflight injuries, where people have been out of their seats, when a large movement of their aircraft takes place - that's the one when the planeload of passengers goes, "Whoa!", some scream, some cry, some pray, and some put their hands above their heads as if they are on a rollercoaster ride.

This is also the sort of turbulence most responsible for a small number of cabin crew injuries since they more than most are often out of their seats during the cruise part of the flight, perhaps performing a meal service, or attending to passengers' needs.

Turbulence associated with clear air (CAT) is often quite forceful in nature. Pilots noting the curling cloud formations in the picture above would likely conclude CAT was in the vicinity. Quite sophisticated means of estimating the presence of CAT are now available to meterologists.

Some airlines are beginning to take advantage of these new methods and pilots will be able to "see" CAT using predictive computer-generated diagrams that look like this:

The red marks a zone of predicted high CAT activity, using what are called Deformation-Vertical Shear Index (DVSI) reports.

It can usually occur around the edges of fast moving rivers of air known as Jetstreams. Pilots are always briefed about these winds, because they can add or subtract time to a journey, therefore affecting fuel calculations as well as route planning. Knowing where and when the plane may encounter these winds will also help the fight crew help the cabin crew in their meal service planning. Within the Jetreams the air can be smooth if one is flying in the same direction (West to East usually) but entering or crossing them can get choppy, as in the rough patches of water at a fast moving stream's edge.

Here is a map of jetstream activity over the North America showing two zones of activity.


Other forms of turbulence during cruise may be more associated with crossing various zones flying north to south and vice versa. Winds can characteristically change direction, and various areas of the world have for centuries been affected by so-called Trade Winds like the Roaring 40s which sailing clippers relied on before the age of steam and oil fueled ships. in which case it is more like driving along an unsealed country road, and giving the suspension a good workout, with the occasional pothole thrown in.

On a plane, the wings help act as shock absorbers, which is why you can sometimes see the tips flexing. They can actually bend quite significantly, and are designed and built this way to take into account all possible forces of nature the plane will encounter during its life. If the wings weren't flexible, they would develop cracks where they are subjected to force over many flights, and that is not good. Same with the fuselage which expands and contracts due its going through pressurisation cycles, and heating and cooling from its contact with the atmosphere at high speeds. Concorde was legendary in lengthening several inches in the course of a flight due to metal expansion from the friction even flying in very thin air at 55,000 feet, way above where subsonic jets fly.

The takehome message here is that unless you have to be out of your seat, remain there with your seatbelt fastened comfortably around you. You should be able to slip a hand, preferably your own (but what you do on your flight is up to you) between the belt and your body. I don't like it when cabin crew say "low and tight" when describing how to fasten the belt during their safety drills, as tight might also restrict your breathing. The seatbelt is a restraint, to hold you in your seat should you experience significant acceleration. It's not there like a harness to hold you rock-steady in place. Flight and cabin crew wear harnesses during the takeoff and landing, as well as significant turbulence to maximise their well being during these flight phases. It's unnecessary for passengers to have this much restraint during normal flying, and would greatly add to the aircraft's weight, and thus your airline ticket's cost.

4. Turbulence during descent and landing

As your plane reaches what's called the top of descent, a location programmed into its flight computer, you may feel a deceleration as the engine throttles close. You'll perhaps hear it too as the reduction in engine thrust usually reduces noise as well depending on where you are seated.

At this point, the aircraft has turned into a glider, using gravity to make a controlled descent. Flying into lower level clouds may increase chop but again this is not dangerous but a normal part of flying.

Flying near where land and water meet on a hot day can see some thermal activity raising and lowering the aircraft, giving you alternating feelings of heaviness and weightlessness. Faster moving winds close to the ground can also move the aircraft side to side, as the flight crew attempt to keep the craft steady on its glidepath.

As we get closer to the airport you can expect to see and feel engine thrust being reapplied and constantly adjusted in order to land the aircraft at the desired area on the runway at the right speed. Headwinds coming toward the aircraft might see power applied and feelings of being pushed back in the chair, while tailwinds may see power backed off. If there have been rapid wind changes (direction and speed) close to the runway, pilots will often report this to the Tower, who may pass on the information to approaching aircraft which may then apply more power to deal with this.

All these sensations are normal, and of course each flight will be different from the next even flying into the same airport on the same aircraft type. Meanwhile the aircraft will also be slowing due to the employment of flaps and slats on the trailing and leading edges of the wings. These effectively change the wings' capacity to generate lift, allowing the aircraft to fly more slowly without stalling. Flying more slowly is preferred to landing fast. On top of the wings you may see large square panels open at various angles during descent. Known as speed brakes, the panels disturb the smooth follow of air over the top surface of the wings, causing less lift to be generated. These brakes are often employed when air traffic control have given the flight a rapid or high speed descent as part of traffic separation. You know when these spoilers have been deployed as there is more wind noise generated and the ride seems a little rougher. Pilots refer to this as flying the plane "dirty", and when after takeoff all flaps and undercarriage are no longer deployed, this is referred to as "cleaning up the aircraft" and setting it up for the cruise phase.

Eventually, the speed brakes will be closed for final approach, and will be employed automatically again when sensors in the main undercarriage are triggered on landing when the wheels touch down and their suspension is compressed as the plane's weight settles on them. Firm landings are often preferred especially in wet conditions to ensure good braking effect to help slow the aircraft.

Sudden changes of wind direction close to the touchdown point, known as wind shear, might see the flight crew reject their landing, and a "go around" procedure is employed. A steep climb is felt along with a surge of power. The full flaps are reduced to a lesser amount for climb out, the undercarriage retracts, and the plane is then flown on a predicted and set pattern (each runway at each airport has a set procedure) while the pilots reconfigure it for another approach.

Don't expect the crew to immediately come onto the PA (Public Address) system to inform you of what has happened. They will be busy with their reconfiguration efforts to prepare for another landing, combining discussion on the flight deck with communication with air traffic control (ATC). There may be some communication with their airline's ground control to inform them of any expected delay due to the go around. Be reminded that this is a planned manouevre each crew discusses at or just after the top of descent for each flight. It is also regularly practised in the flight simulators during regular checks.

Eventually the crew may offer you an explanation for the go around, and hopefully explain that it is an uncommon event, but one they handle as part of normal flying experiences. Don't be suspicious of delays in communicating with you as their crew's first priority is to fly the aircraft and communicate later. It's a little like driving and getting a blowout - if you were on the cellphone you are likely to discontinue your conversation while you bring the car under your control and move it safely off the road.

In all my years of flying I have experienced only a few go arounds, and they are nothing to get excited about. If I am flying United Airlines, I will listen to Channel 9 on the audio pogram and hear the pilots reporting their go around to ATC. Once flying into San Francisco I heard our pilots informed that debris had been spotted on our runway, and told my set companion we would be going around. This duly happened and I'm she thought I was either psychic or a fearful flyer expecting the worst.

Some airports by the way have earnt a reputation for more than their fare share of go arounds. Two that come immediately to mind are Wellington, New Zealand and Denver, Colorado, each located near mountains with quite strong winds which can suddenly gust, foiling well prepared descents.

6. What to do in Turbulence.

Above all - remember turbulence may be uncomfortable but is not unsafe. Planes are built to easily withstand turbulence, and flight crews pride themselves on smooth flights. Holding tightly onto your seat arms won't help, and will make things worse by driving tension through your body and disrupting breathing.

My advice is to sit there with your hands in your lap, palms upwards so as to minimise any reflex grabbing of seat arms or companion's thighs! If the turbulence begins to feel like the plane is being bounced about, then gently but rhythmically bounce in your seat to take control of your movements - think of singing a happy song like "Jingle Bells" under your breath.


7. Final thoughts about turbulence.

People often describe flights as hitting air pockets, as if the air has gone missing and the wings can no longer generate lift. As such they expect the plane to drop like a brick.
Neither is true. Air doesn't suddenly go missing, but it can thin and thicken and move due to the immediate weather. This will cause the plane to move about which you experience as acceleration or g force.

The sensations are like falling, so people believe the planes drop in turbulence or in "air pockets". The plane and its contents (you) may experience a downward acceleration but remember two things are happening:

1. While the acceleration you feel might have you thinking you are dropping thousands of feet, in reality any change of altitude in that brief moment is likely to be measured in tens of feet, or several hundred feet in rare extremes. Often the altitude change is not visible on the altimeter on the flight deck. Those accelerometers on your ears aren't very good at measuring distance.

Here's a graph of severe turbulence encountered in a flight over several minutes. The parts of interest are the rapid changes in vertical acceleration - and the distance travelled, in this case about 500 feet over about 2 seconds (at time 210 seconds). Notice how far the plane travelled in 25 seconds of the worst of the turbulence. Now you can see why it feels like the plane drops!

2. Even if the plane's altitude changes by 100 feet in say 3 seconds, a plane travelling 500 mph will have travelled forward 2200 feet, or just short of half a mile! Even in one second, the distance travelled is more than 700 feet. So it travels forward 7 times further than it "drops". In effect it doesn't drop like a brick but it feels as if it does, and it's scary! If you know that it's both safe and it's not in fact dropping, it makes it easier to keep calm during turbulence.

3. The media will often reports stories of planes falling out of the air, or dropping like bricks, using quite strong images to convey a feeling. They will often reports passengers' descriptions of "dropping thousands of feet" (as if they would know). It would be more accurate to report a passenger saying "it felt like we dropped a thousand feet, but how would I know?"

I expect that from news media, and ask my clients in preparing a journey to stop reading such stories. Thus, I have to write here that I am appalled to read my own Aussie government's Civil Aviation Safety Authority's website advice to travellers about turbulence. See what's wrong and unhelpful with this entry on its page:

During a flight from Singapore to Sydney with 236 passengers and 16 crew, the airplane encountered turbulence over central Australia. The plane hit an "air pocket" which caused it to drop 300 feet. Nine passengers including one pregnant woman and three crew members suffered various neck, back and hip injuries, with one of the passengers requiring surgery. Those who were injured were not wearing seat belts.

The site of course is designed to help passengers fly safely, but there is no need to use popular media terms like "air pocket" and reinforce notions of "dropping", which connotes planes out of control and heading for imminent disaster. Come on guys, the site is otherwise great, but let's tidy it up just a tad, huh?

Because this subject is so central to many people's fear of flying, I want you to get more information about it. I am a psychologist not a pilot. Some of you might wish to read a pilot's views on turbulence, so I am going to refer you to Captain Lim's webpage, devoted to the Boeing 777 which he flies. There he also provides some credible answers to common questions about turbulence. Captain Ron Neilsen's website also has some excellent pictorial coverage of turbulence I recommend.

The University of Idaho also has an excellent website which as well as being interactive, has a great entry on weather and turbulence.

And returning to the subject of Virtual Reality, the Journal of the American Medical Association (JAMA) published in October 2003, a good review of current thinking, in a piece authored by science journalist Paul D. Thacker.

Come back to this entry often, as I will be often adding more pictures and links.