It’s 90% done. Here is my chapter dedicated to weather. No, it is not geared to the well informed, “top-of-their- game-pilot” but more so for the travelling public.
Chapter 8 Weather Stuff
Can clouds foretell flight conditions? Clouds do foretell flight conditions. Billowy, puffy clouds signal a bumpy ride ahead, while clouds based a few thousand feet above the ground typically give way to smooth conditions when climbing above. Usually, layered clouds also lead to a steady ride. An experienced eye can recognize clouds that are associated with a weather phenomenon. Even fog, a cloud based at the ground, renders six atmospheric processes. The shape of the streaks that form from another aircraft’s exhaust at higher altitudes can tip off pilots to flight conditions. I’m always attuned to the telltale signs of clouds, but that could just be the meteorologist in me.
By knowing how they form reveals the process transpiring in the atmosphere. Day time heating will cause air to rise creating puffy cumulus cloud meaning bumps. It’s those clouds you learned to draw in elementary school. Sure, these puffy white billowy clouds have a cute appearance but they can pack a punch especially when they grow taller and fatter becoming teenage and adult equivalents.
Layered cloud usually infers smoothness. A mackerel sky, appearing like the scales of a fish, is high based cirrus cloud, called cirrocumulus. This implies possible bumps from a fast-moving jet stream. Clouds also cause ice on airplanes, reduce visibility near the ground, and clouds forming aft of our jet engines called contrails, will foreshadow advancing weather if they take a long time to disperse. Many think the nomenclature of clouds is extensive and difficult. Not so. By learning your clouds, you are indirectly learning flight conditions.
Clouds in my sky
The idiom, “Being on Cloud Nine,” is an oxymoron. This billowy, lofty, puffy, cotton-batten-like cloud exudes pleasantry and is labelled #9 on the cloud chart, called cumulonimbus. But it’s a wolf in sheep’s clothing and pilots know to avoid it all costs. Think thunderstorm.
There are low, middle and high clouds and clouds of vertical development. I am constantly querying the shape, intensity and the process as to why clouds are there. It helps me find you smooth rides. Clouds are either composed of liquid water droplets, supercooled water droplets, ice crystals or all the above. Those high thin wispy clouds called cirrus, a.k.a mare’s tails, is composed entirely of ice crystals. Flying in cloud below zero Celsius may cause ice to form on an aircraft. Water can exist in liquid form in clouds well below freezing, in fact all the way down to frigid - 40° C (-40° F, yes, they are the same at this value). At that point, meteorologists coin it homogeneous nucleation.
In 1802, Englishman Luke Howard, a pharmacist by trade, gave clouds the common names we still use today. He noted three basic shapes of clouds: heaps of separated cloud masses with flat bottoms and cauliflower tops, which he named cumulus (the Latin word for “little heap”); layers of clouds like blankets, much wider than they are thick, which he named stratus (Latin for “layer”); wispy curls, like a child’s hair, which he called cirrus (Latin for “curl”). To clouds that generate precipitation, he gave the name nimbus/nimbo (Latin for “rain”).
Cirrus (Ci) Cirrus clouds are high, thin, wavy, wispy, fibrous tufts of white cloud. These fibrous bands can take the shape of horse tails; thus, they are sometimes called mares’ tails. They indicate fair weather, but if they start to thicken, inclement weather is approaching. Cumulus clouds due to daytime heating, form and reform in about 10 minutes. Try watching it transpire on time lapse photography.
Why the bumps?
Nearly twenty-two years ago, my first article for enRoute ¾ my company’s inflight magazine ¾ explained the seven types of turbulence titled Why the Bumps? This is the most commonly asked question and concern from passengers. Technology has certainly helped to contend with the unpredictable nature of bumpy rides. A pilot’s iPad can now superimpose a specific routing on weather charts that depict areas of bumps. We can also interrogate other airplane reports from this site. These ‘heartbeats’ show the whereabouts of the airplane, its altitude and whether bumps occurred during the flight. Our flight plan also assigns a numerical value for possible bumps along every waypoint, while flight dispatch sends us inflight reports via datalink. Everyone is striving to deliver the smoothest ride possible.
AIRPLANE SMILEY Physicist Theodore von Kármán is credited with saying, “There are two great unexplained mysteries in our understanding of the universe. One is the nature of a unified generalized theory to explain both gravity and electromagnetism. The other is an understanding of the nature of turbulence. After I die, I expect God to clarify the general field theory to me. I have no such hope for turbulence.”
My flight plan denotes a number from zero to nine for each navigation point along the route. A zero or one means things should be smooth, but when numbers three, four and five appear the seat belt sign is likely to be illuminated. Many think there is a device that automatically turns on the seat belt sign when bumps occur, but it’s strictly subjective and done with the concurrence of the captain.
AIRPLANE SMILEY Finally, the internet has made its way into the flight deck. For a few years, the internet was only available in the cabin due to technical reasons. I jokingly averred I could go to a passenger in business class during the flight and ask him what the weather is doing up ahead. Now, I don’t have to.
Is there any way to detect and detour around severe turbulence?
Policy and common sense is to avoid or circumnavigate known areas of severe turbulence, especially thunderstorms. Most airliners also have wind-shear detection systems to detect shearing winds near the ground. It does not detect high level wind shear. No device detects turbulence due to jet streams, but weather maps depict and forecast all types of turbulence. Flight dispatchers will avoid such areas or plan flights at different altitudes. Sometimes this is all it takes to ensure a smooth ride.
AIRPLANE SMILEY Dear Mr. Morris. Whenever I fly, the second I sit down I reach for the EnRoute magazine and your article of the month. I am a very, very nervous flyer, often to the point of tears. I often want to drive to Vancouver and even risk the Coquihalla in the winter. My fear of flying has greatly impacted our travel plans much to my husband's dismay. And, yes, it is usually associated with turbulence. Therefore, I was very happy to see this article. I live in Kelowna, BC and most of the time I am leaving here it is on a prop airplane. It isn't the prop I mind so much, although I would prefer a jet, it is the fact that almost all the time coming in and out of Kelowna, there is turbulence. Not just a bump or two, often I fear we are going to fall from the sky it is so rough. And often, the weather appears just fine. So, I don't get it. Having said this, the last time I flew 1 1/2 weeks ago from Vancouver to Kelowna the captain made an announcement prior to take off to say that it would be rough going in to Kelowna but nothing to worry about. Just hearing his calm announcement and his reassurance that this was all quite normal, helped me tremendously. I can't tell you the difference it made in my short flight home. That is only the second time I have ever heard from the cockpit in many years. Usually there is nothing said at all. When I got off the flight, the captain was standing in the cockpit doorway and I told him exactly how much I appreciated what he had said. It took so little time and meant so much to me and I am sure others. Susan
Is turbulence dangerous? No and sometimes yes. Any airliner must be built to handle any amount of turbulence, but no sane person wants to challenge this extreme realm. Yes, you will see the wings flex up and down as they contend with the rough air. This is normal, although for most, it is disconcerting. The danger arises when passengers don’t have their seatbelts fasten as rough turbulence can suddenly appear catching many off guard. It can toss you about violently, and if items are not secure, act as projectiles. People try to get comfy by undoing their seatbelt or allow a child to sleep on the floor. They are the ones injured when mother nature starts throwing nasty punches. Over my entire career, I can count on one hand, okay maybe two, where things got scary rough. I admit, I am a wimp when it comes to rough air and for you as a passenger this is a good thing.
Many passengers get a false impression when the seatbelt sign is illuminated and yet the flight attendants are going about their business. Some pilots turn on the seat belt sign at the onset of the first ripple envisioning lawsuits if they don’t illuminate the sign but deciding when to put the sign on is purely subjective. For a long haul flight the seatbelt sign may cycle on and off ten or more times. This on again, off again trend can bestow a laissez-faire approach among passengers.
And don’t think pilots are up in the flight deck saying nonchalantly, “oh well.” We too don’t like rough air. Its annoyance wears on everyone. Our job is to get you to your destination safely and expeditiously. No one likes turbulence, including pilots!
AIRPLANE SMILEY Part of our mandatory briefing with the in-charge flight attendant includes reporting on expected ride conditions. One day, the in-charge flight attendant quickly intervened, saying, “I know, I know. . .it’s going to be smooth between the bumps.”
Doesn’t a weather radar detect turbulence? On-board weather radar detects precipitation, which, if significant, implies turbulence because the air is unstable and moving about to cause a bumpy ride. In the nose of every airliner is where the weather radar and antenna is fixed. The nose cone, called a radome (radar dome), can be hinged opened on the ground to inspect the weather radar. Weather radar honed from WWII technology, is a great detector of rain, however, other types of precipitation reflects less energy back so a pilot must challenge these “returns.” Generally, light precipitation is depicted (painted) as green, heavier rain is yellow with red as heavy to extremely heavy. Some radars paint magenta for the extreme category. Pilots want to avoid all returns. But red should be avoided at all costs and rest assured the seat belt sign will be illuminated. This is no place for any airplane and pilots know it. We want to avoid, avoid, avoid but sometimes pilots get into tight situations and things can get rough. One recent frequent flyer nearing the million-mile category, asked if air traffic controllers purposely vector pilots into bad weather because of constraints. They will try their best not to do so, but sometimes a pilot must weigh the consequences. This is not a good predicament and it’s not where anyone wants to be.
AIRPLANE SMILEY One of the best methods still to this day for avoiding showers, heavy rain and turbulent cloud is with a pair of eyeballs. You’ll find me scanning the sky and at night with the flight deck lighting turned down and acutely looking outside.
What’s a jet stream? (sky snakes)
We all probably have some vague notion of what a jet stream is, those streaky white trails that appear behind high-flying jetliners? Well, no, that’s a common misconception. Those are condensation trails formed by the exhaust of aircraft jet engines. Jet streams are a much more spectacular phenomenon — long, thin bands of extremely fast-moving air that form at high altitudes and corkscrew through the atmosphere around our planet.
In 400 BC, Aristotle wrote a treatise on weather entitled Meteorologica, in which he noted that higher clouds may move faster than lower clouds. Over 2000 years later, when manned balloons were first launched during the 18th century, those aboard noticed that winds tended to increase with height. But it wasn’t until World War II and the advent of high-altitude flight that jet streams were encountered and their presence confirmed.
On November 24, 1944, 111 U.S. Air Force B-29 bombers were sent from the Pacific island of Saipan to attack industrial sites near Tokyo, Japan, in the first high-altitude bombing mission of World War II. As the airplanes approached the island of Honshu at 33,000 feet (10,058 m), they were suddenly hit by winds of 140 knots (161 mph or 260 km/hr), which knocked them completely off course. Only 16 of the 111 pilots managed to hit their targets, while the rest were blown over the ocean and forced to return to base. Pilots on subsequent missions also reported encountering extremely powerful winds and unexpected turbulence when flying westward to Japan. What were these incredibly strong winds? One pilot likened them to a jet of air streaming out of a hose with enormous velocity; hence the name jet stream.
We now know that jet streams are produced because of the significant temperature changes where air masses collide. In North America, for instance, where there may be four distinctive air masses, up to three separate jet streams would exist. They can be hundreds of miles long, tens of miles wide and a few to several thousand feet thick. (I liken their dimensions to a Christmas ribbon when teaching my weather classes). They migrating southward in winter and decrease in altitude the further north they are found and flow at different heights depending on the season. Jet streams are strongest during the winter months because the frontal zones or temperature differences between air masses are more dramatic in winter. They mark the dividing line between seasonable and unseasonable temperatures. They also indicate in what direction and at what speed surface weather (highs, lows, fronts, etc.) is traveling.
To locate jet streams, weather balloons are sent up to penetrate the higher atmosphere, climbing to 100,000 feet (30,480 m). As well, airliners have equipment onboard to gauge upper atmospheric wind conditions, and satellites capture some of the telltale cloud patterns associated with jet streams. It’s a fast-moving current of air that circulates around the Earth in a corkscrew motion at altitudes of 25,000 to 45,000 feet. A jet stream’s speed and momentum are affected by the varying temperatures in the southern and northern latitudes as well as by the Earth’s rotation. Average high speeds are between 100 and 180 knots. The force of a jet stream often leads to quicker flight times by creating what pilots refer to as “push.” A flight from New York to Los Angeles can take five hours, but with the effect of a jet stream, the return trip can be reduced by 40 minutes.
Sometimes a pilot will want to get into this fast-moving air; at other times, he or she will want to avoid it. We try to capitalize on strong tailwinds and, if able, duck out of the stronger than normal headwinds. If any turbulence is detected, pilots always ask for ride reports from air traffic control and then climb or descend to find smoother air. On occasion, this air can also be rough and become so quickly, which is why regulations have you keep your seat belt fastened at all times.
AIRPLANE SMILEY Robert Buck, in his iconic pilot weather book, Weather Flying, 1998, described the elusiveness of high-altitude turbulence this way: “Meteorologists can locate the jet stream rather accurately, they cannot pinpoint exactly where the turbulence will be. They can tell you in general terms. I can assure you that sometimes it will be rough when they say it won’t and smooth when they say it will be rough.” To this very day, it remains a hard and fast observation.
Aurora Borealis – northern lights (dawn of the north)
Winter’s long nights and frequent clear skies in northern latitudes renders fantastic views of the dancing light show some 60 miles above. Charged particles released from the sun (solar wind) collide with the Earth’s magnetosphere. This causes earth’s oxygen to yield a pale green or pinkish display. Higher up, about where the space shuttle cruised (200 miles), nitrogen promulgates blue or purplish-red. Many of our flights take in this awesome display so keep your window shades open to catch Mother Nature’s free light show.
Facts: The northern lights dazzle about the earth’s magnetic poles, so northern Canada (where the magnetic pole is located) is privy to some of the best shows especially the Yukon, Nunavut and the Northwest Territories. The southern lights are known as Aurora Australis.
Santa Claus operates from the geographic North Pole, but the Aurora Borealis centers around the magnetic pole — some 500 (800 km) miles away.
On many northern flights, I’ve witnessed the many guises of the dancing northern lights — from docile patches of light, bursting streamers, arcs and undulating curtains, and spiking rays sometimes with ominous glows.
When Mother Nature sets up her stage full of lights we frequently ask flight attendants to visit the flight deck to take in the show.
Wind beneath our wings
Wind direction dictates the runway used for takeoffs and landings because flight into the wind (headwind) enhances performance. But frequently winds blow across the runway (crosswind) with each aircraft having inherent limits on wind speed and runway conditions. Don’t be alarmed if you see a pilot finesse a landing briefly touching on one main wheel because that’s how crosswind landings are performed. Winds generally increase with altitude, so much so, they can surpass hurricane strength due to jet streams. Winds can suddenly change in direction and/or speed called wind shear. But near the ground onboard devices warn pilots of this, plus many American airports have a system forewarning shearing winds. In Canada, this warning system does not exist.
Wind facts: Maximum tailwind and crosswind limits for an autoland is 10 knots and 15 knots, respectively.
Winds are reported and forecast in direction of true north, but Air Traffic Control state them in relation to magnetic north because runways are orientated in magnetic.
I’ve been in winds clocked at 220 knots (400 km/hr) at cruising level.
The minimum speed to constitute a jet stream in Canada is 60 knots. In the U.S.A and Britain, it’s 80 knots.
Maximum crosswind (90-degree angle) limit for the B787 I fly is 38 knots. That is gale force strength.
The device that measures wind speed and direction is an anemometer. Strictly speaking an anemometer measures wind speed, but colloquially it’s a device that determines both speed and direction.
The measurement of wind is observed at 10 meter (33 feet) heights at airports around the world.
Wind speed is measured in knots in the aviation world except China, Mongolia and Russia where meters per second is used.
Wind is referenced to where they are coming from. Not where they are going. A south wind means it is blowing from the south.
Every airliner has wind readout and groundspeed to see how fast we are moving across the ground due to winds.
Iconic singer Bob Dylan claimed, “You don't need a weatherman to know which way the wind blows.” But in aviation you do!
Upper level winds (crucial for flight planning) are derived from weather balloons from over 900 stations around the world launched twice a day.
Data from aircraft, called AMDAR (Aircraft Meteorological Data Relay), is used to drive the weather supercomputers to forecast wind at all flying levels around the world.
Technique for keeping the aircraft tracking straight during a crosswind landing, “turn into the wind and apply opposite rudder.”
I noticed a circular rainbow with the shadow of the airplane inside it. How does it occur?
A “glory” forms in moisture and the larger and more uniform the better. These droplets act like little prisms scattering out the primary colors and bending them back to you, the passenger. You also need the sun behind you, with the aircraft eclipsing a shadow in the center as a bonus. When an aircraft’s shadow is seen to dance inside, it’s called, “The glory of the pilot.” Glory may be a precursor to possible air frame icing. Pilots don’t like flying very close to cloud tops for two reasons. Described as “bouncing on the tops” implies a bumpy ride and potential airframe icing.
The Deice Man Cometh (Taking it off and keeping it off)
As you sit comfortably in your seat, take a moment to notice ground crew working outside in freezing temperatures. They appear to be washing the airplane, but they’re ridding the wings and sometimes the fuselage of ice and snow. This procedure is deicing and is necessary for departure, as airline safety standards prohibit takeoff when ice, frost or snow is adhering to the airplane. But why?
Many think it’s because it adds weight, but the main culprit is it disrupts air to smoothly flow over the wings and it increases drag. The captain is ultimately responsible, but the lead ramp attendant must also be in concurrence. Even flight attendants and passengers can voice concerns.
No place better illustrates deicing than the CDF (Central Deice Facility) at Toronto’s Lester B. Pearson airport – the world’s largest. This 65-acre “drive-through airplane wash” consists of six huge bays subdivided into three capable of handling hundreds of aircraft daily. Official deicing season is October 1st to April 30th. Because this is a “live” or “engines running” operation precise terminology and electronic signboards are used to keep things safe. Pilots contact the “Iceman” in the deicing control tower appropriately named the “Icehouse.” Once in position, two expensive ($1.4 million each) made in Denmark vehicles called the Vestergaard Elephant Betas (the facility has about 40 of them) springs into action. The deice procedure involves spraying an orange deice Type I fluid composed of hot water and glycol to rid the ice and snow. If precipitation is falling or imminent, it is followed up with a cold application of a bright neon green anti-icing Type IV fluid to stop precipitation from sticking. The “throughput” time for an Airbus 320 is an amazing 12 minutes. For a light snow event, it takes about 300 L of Type I at a cost of 1$ per liter and 250 L of Type IV at 2$ per liter plus a $350 visit fee. This is all part of doing business in winter.
Is weather getting worse? Is turbulence more intense? Are thunderstorms higher?
If you fall for the “CNN Effect” then you will be convinced turbulence is more frequent and more violent. I can’t give a definitive yes or no, but just maybe. Mother Nature must balance the books and that includes the heat budget. For jet streams to be stronger it would mean temperature differences are increasing i.e. the North pole is getting colder and further south is getting warmer. For thunderstorms to get bigger means the layer in which we live, the troposphere, is getting higher. I’m not so sure. But expect more articles to infiltrate the media. We’re going to learn more terms, hear more opinions and surveys as we did for the “polar vortex” and the “cyclone bomb.”
How in the heck do you land in next to zero visibility? Foggy Landings
Have you ever looked out of an airplane window as it descends, and you go lower and lower, and wonder when, and if, the ground will appear? Many of us have probably been on flights like this, but just how do pilots find the runway?
A Pilot’s Approach
Despite what seems to be a precarious situation, commercial, and some private, pilots routinely fly safely into clouds with the aid of instruments. A handful of different instrument approaches are currently available, but the most precise and preferred approach is the ILS (Instrument Landing System), which provides both vertical and horizontal guidance in low-cloud conditions, fog, rain, snow, haze, and other obscuring phenomena.
How does it work? A localizer signal at the far end of the runway guides the pilot or autopilot in a straight line toward the runway, while a glide-slope signal on the sides of the runway leads the aircraft down vertically. An easy way to visualize this precision approach is to picture a children’s slide at a park. The aircraft flies at altitude just as a child sits on top of the slide. The airplane is then eventually steered in the direction of the runway, whereby the flight deck instruments lock on to both the localizer and glide-slope signals. When the aircraft is locked onto both signals, it is as if the airplane is in the crosshairs of a rifle. On board, sophisticated autopilots guide the aircraft all the way to the ground, automatically compensating for changing winds and other variables. The precision approach guides the pilot down to his or her landing sight (the runway), just as the slide guides the child to the landing. A localizer provides left–right orientation with the runway, like the sidewalls of the slide. The angle of this approach is typically three degrees. It’s the angle you may have noticed airplanes maintain while following one another on approach to a busy runway. The glide-slope signal guides the aircraft down vertically, and the auto-thrust system adjusts engine-power settings to ensure proper speed, even bringing the engine to idle at touchdown.
Other important features of ILS
Several other components augment the ILS and provide additional safety features for low approaches. These include devices that transmit exact distances from the runway, high-intensity runway and approach lighting (the intensity ranges from a dim setting of one to power-zapping strength five), and radio-beacon markers that transmit important distances to the pilot. One such marker is called the FAF (Final Approach Fix, which is typically located 4 to 6 miles (6.4–9.7 km) from the airport. At this point the pilot should have the landing gear down, a clearance to land from the control tower, and final flap settings for landing. Sitting by itself is a RVR (Runway Visual Range) sensor along the edge of the runway. It measures distance seen through obscuring weather phenomena in units of feet, and it gives a very accurate idea of what a pilot can expect to see, or not see.
Not all ILSs are created equal
There are three different categories of ILS, differentiated by the DH (Decision Height) and prevailing visibility. DH is the indicated altitude at which a pilot must decide to either continue the approach to a landing or abort it and go around. A category I ILS (the least accurate) has a DH of 200 feet (61 m) above ground. Most large airports around the world have this type of ILS. DH is determined by a barometric altimeter, which the pilot must adjust to the most recent pressure reading at the airport. Every pilot knows just one-tenth of a change in pressure in inches of mercury translates into a discrepancy of 100 feet (30.5 m).
A category II ILS has a lower decision height, 100 feet, and it determines height with a device that bounces signals from the airplane to the ground and back, called a radar altimeter (or radio altimeter). It allows the airplane to descend with a higher safety margin. The last, but certainly not the least, is the category III approach.
Welcome to Autoland
Category III ILS (autoland) has two levels. The first level brings the aircraft to a mere 50 feet (15.2 m) above the runway, at which time the pilot must make a snap decision. The second fully automated level has no decision height, meaning pilots do not look outside and wait for the bump. It is a procedural necessity: pilots looking outside could cause disorientation. Complete faith is bestowed in the system, which admittedly takes some getting used to. A gamut of requirements must be met to allow such an approach. The ground facilities must have high-intensity runway lights, centerline lighting, various markings on the runway, additional RVR sensors, and backup airport emergency power to ensure the runways and taxiways are lit up and the ILS is functioning, even during power outages. On board the aircraft, sophisticated autopilots bring the aircraft to the ground, automatically correcting for winds all the way to the touchdown. Only major airports have such a system, with most only having the system on one runway. (Vancouver, Toronto and now Calgary and St. John’s, Newfoundland (the one that needs it the most) have the only category III runways in Canada. Pilots must be certified to do autolands, requiring checkouts in flight simulators every six to eight months. The airline company and aircraft must also be certified for autolands. As you can see, there are a lot of parameters that must be met, clearly separating the amateurs from the pros.
For airliners, an autothrust system adjusts engine-power settings to ensure proper speed is obtained. In fact, it will even bring the engines to idle at touchdown. An autobrake system supplies the correct amount of braking at touchdown to stop the aircraft. As well, there are many computers that monitor the aircraft systems to ensure everything is functioning at 100 percent. They even make synthesized altitude call-outs to the pilots.
Waiting for the bump
The absolute minimum visibility for a category III landing is less than the length of a football field, with next to nothing to see when approaching at speeds of 150 knots (173 mph or 278 km/h). Once air traffic controllers clear the aircraft for a category III approach, the pilots attentively monitor the automatic systems, overpowering the urge to look outside, and patiently wait for the bump. Even with the main landing gear firmly on the runway, the flight deck may still be mired in fog because of the landing angle. From ab initio training, pilots are taught to trust their instruments; still, autoland bestows a much higher level of faith in technology.
Because the system is so accurate, the automatic pilot must be disengaged after landing or else the aircraft will try to reposition itself back on the centerline of the runway. Finding the terminal building in such heavy fog can be a difficult task, but many airports have bright green lights embedded in the taxiways to guide the pilots to the gate or “follow me” vehicles.
The autoland system truly is a marvel of technology and exemplifies just how technically advanced aircraft and airports have become. Nothing can replace the skill of an experienced pilot, but when extremely poor visibility dictates a category III autoland, technology rules.
Contrails or chemtrails?
Man-made clouds may form behind an aircraft, produced by the moisture of combustion exhaust saturating the air and causing condensation. Two by-products of hydrocarbon combustion are carbon dioxide and water vapor. For each pound of jet fuel burned, about 1.4 pounds of water vapor is produced. Many believe that the contrails we see in the sky are pollution, but they are
mostly frozen water. The vapor condenses into tiny water droplets, which freeze if the temperature is low enough. These millions of tiny water droplets and/or ice crystals form contrails. The exhaust particles act as a trigger, causing the trapped vapor to rapidly condense. Exhaust contrails usually occur above 25,000 feet, and only if the temperature there is below −40° C (− 40° F).
Conspirators, akin to the flat earth society, are adamant these white ice crystal streaks are chemtrails (chemical trails) imposing harm. It is said, don’t believe everything you read on the internet and this is one of them.
Four main layers of the atmosphere exist. We live in the troposphere where most weather occurs but your flight may also take you into the second layer, the stratosphere. The boundary between the two layers is deemed the tropopause. Pilots abbreviate and reference it as “trop” but it rhymes with “rope.” This interface is known to where turbulence lurks. It acts like a lid to most weather more specifically thunderstorms and is where jet streams corkscrew around the globe. It’s coincidentally where jet engines are most efficient. Because of it, pilots always want to know the whereabouts of the tropopause. It raises in the summer, lowers to the north and raises in southern latitudes. It also changes day by day according to the weather systems. Statistically it hovers around 36,000 feet, but elevates to 55,000 toward the equator thus higher thunderstorms. A pilot’s flight plan includes the location of the tropopause and is specified to within feet at every waypoint along the way.
Humidity. Amount of water vapor contained in air
Most find it hard to fathom that moist air is less dense than dry air, thus the air on a hot humid summer day is less dense than a cold dry winter’s day. That’s because there are fewer air molecules in a given volume of warm air than in the same volume of cooler air. This thinner air plays into aircraft and jet engine performance because when thinner air flows over a wing it means less lift, and thinner air in a jet engine means less thrust.
In 1965, Canadian meteorologists developed the Humidex, to describe how hot and humid weather feels by combining the effects of temperature and humidity into one number equivalent temperature.
The humidity of cabin air in standard aircraft is derived from conditioned air ducted from the engines, has humidity levels equal to desert air (5%). The new B787 Dreamliner, however, provides a more humid cabin allowing a more restful flight with 15% humidity. Cabin air pressurization is provided by electrically driven compressors, eliminating need to cool heated air from the engine and the cabin’s humidity is programmable based on the number of passengers carried.
An aviator will learn fog has many guises. In fact, there are six mechanisms whereby fog will form. One of the foggiest airports on the planet is on Canada’s east coast, St. John’s, Newfoundland where visibility will drop to a half a mile or less nearly one third the year ¾ 120 days. Fog will form when: air moves up a hillside, as warm air moves over a cool surface, when cool air advects over warm water, in frigid temperatures, when it rains, and overnight under clear skies and light winds. Fog’s less restrictive counterpart is mist. Weather observations abbreviates it as BR (some refer it to “British Rain”) which stems from French meaning Brume. Here is my poetic attempt to explain the six types in pilot prose.
It prances in diverse guises
It marks its misty presence as it ascends a hill little by little
As a warm wind moves over chilly waters it will form an immense white blanket
It can stay for days and wilt a spirit
Or appear at dusk and ebb at dawn
It may accompany a gale obscuring a pilot’s line of sight to mere feet
It can ally with raindrops inducing low visibility
Or play havoc in bitterly cold Arctic air
It can be a sign of seasonal change as it lunges from warm water
But no matter its genesis... it will challenge any aviator…
- Captain D
Can it be too hot to fly?
You’ll be hearing more and more about this as we progress into global warming. Recently, many flights were cancelled in southwestern USA because of the heat. Much of the southwest is higher in altitude also contributing to thinner air. One saving grace is the air is drier. Dry air is denser than moist air. You’re probably asking, why is that since I can see moisture like fog, mist and haze so shouldn’t it be denser? Nope. Water (H2O) weighs less than nitrogen, the main constituent of air.
Thus, it can be too hot to fly, as air is less dense and when it gets extremely hot, aircraft takeoff calculations will forbid safe departures. Every airliner in the world must have a balanced field in case of a rejected take off on the runway so it can come to a safe complete stop. When higher speeds are required to produce enough lift to get airborne then this balancing act for takeoff speeds becomes a major player. One way is to reduce the weight meaning less passengers or leaving cargo behind.
AIRPLANE SMILEY Years ago, during the heat of India, the temperature hovered at 31° C (88° F) near midnight being too hot for a safe and legal take off. When it cooled to 30° C (86° F), we were good to go. It still made for an interesting take off with the aircraft laden with fuel required for a 15-hour flight and a full load of passengers.
You’ll find many airlines in the middle east operating most of their flights during the wee hours of the night as temperatures are somewhat cooler. Luckily for them, most airports sit at elevations near sea level. On that note, airports sitting in higher elevations can be problematic. Denver (Mile High City), Mexico City and Bogota (our highest airport elevation) offers challenges. Luckily for Denver they have some of the longest runways in North America. It’s also why Calgary, Alberta has the two longest runways in Canada because it sits at an altitude of over 3,600 feet above sea level where Vancouver on the other side of the “Rocks” sits at 13 feet above sea level.
One also must factor in ground operations. The heat can be dangerous to ground personnel especially in the belly of the airplane. Animals would perish in the heat so restrictions are implemented. As well, airliners themselves have temperature limitations as they must keep certain components cool such as the avionics. If the on-board air conditioning units or supplied ground air can’t keep up, then boarding will be denied.
AIRPLANE SMILEY Years ago, while sitting at the stand (they call gates stands) in London, England our air conditioning unit was not working. The captain refused to allow boarding until we had acceptable air conditioning, but none was available. One would think London of all places wouldn’t be an issue with suppressive heat. Luckily, I convinced the captain to allow boarding or else the flight would have been canceled.
Can it be too cold to fly?
Cold air means denser air and is welcomed to any aviator. Cold air produces more lift over the wings and more thrust from the engines and propellers. But to start an engine requires temperatures above -40° C (-40° F) so they would have to be preheated. The airplane itself is used to cold temperatures as it hovers at - 57°C (-71° F) at cruising altitude. Again, it is the ground personnel that are challenged during extreme cold. Machinery won’t start, the heaters are less effective, even getting potable water to the airplane can be an issue as well as cabin doors freezing shut.
AIRPLANE SMILEY While arriving in Edmonton, Alberta during the middle of winter in a extreme cold snap, the wheels to the jetway froze. The rampies took 20 minutes to thaw out the frozen wheels. Winter operations are a challenge. While trying to push back from the gate in Stockholm, Sweden the push back tug spun its wheels to no avail. Another heavier tug equipped with chains came to the rescue.
Is lightning bad and is it detrimental?
Many of us envision those B rated Hollywood movies where an airplane is in a turbulent ride flying in and out of dark ominous clouds, when suddenly, a lightning strike knocks part of the wing off. Lightning will enter the aircraft and exit with no damage (usually), however, it may leave little pinholes or burns during its transit. Statistics show an airliner gets hit every 5,000 hours or about once a year. The FAA estimates every airliner in the U.S will be struck once a year. Aluminum is an excellent conductor, but some airplanes made of composite may experience lightning strikes a little more (Did I tell you I fly the composite B787?). If we do get christened with an electric jolt, it will mean the aircraft must be looked over with a fine-tooth comb by maintenance.
AIRPLANE SMILEY On my first flight released to the line as captain on the B787, the first officer looks over at me and mentions the slightly higher probability of lightning strikes with the B787. Guess what transpired that same day on the return flight from Los Angles to Toronto? I had to write up a lightning strike event in the logbook when we landed. Having said that, I’ve been flying the B787 for nearly two years since that episode ¾lightning free. Did I just jinx the weather gods?
St. Elmo’s Fire
Now and again, pilots will witness a static build up on their windscreens looking like dendritic fire strokes. Truth be told this dancing marvel is harmless, however the static build up is usually a sign that nearby thunderstorms are lurking which are not so harmless. Volcanic ash will also cause St. Elmo’s fire. Passengers may see this phenomenon around propellers or near the intakes of the jet engines. Frequently, we invite flight attendants up to the flight deck to witness this vibrant light show.
How high can thunderstorms get?
Most thunderstorms range from 30,000 to 55,000 feet with some topping to 65,000 possibly 70,0000 feet. Maximum altitudes for airliners are at 39,000 to 43,000 feet meaning we can only fly over the smaller monsters. Most turboprops get as high as 25,000 feet. And that’s what a thunderstorm aka cumulonimbus is, a meteorological monster! Even when flying over these deathtraps we try to give as much berth as we can. Flirting with the top on a thunderstorm is a bad idea. Small business jets have the capability of getting as high as 55,000 feet, but they too exercise caution with flying near these nasty clouds. It’s equivalent to driving into a 10-foot deep pothole. They still make me quiver when I brush up near them. Why so close you ask? Well there are thousands of thunderstorms per day with 2,000 booming at any time around the globe so their presence is inevitable. I prefer winter season in North America over summer for that reason alone, because these bad ass clouds are less frequent.
AIRPLANE SMILEY I still get apprehensive when nearing these weather beasts, especially when I am at 30,000 feet and only half way up alongside these meteorological monsters. It’s like a small boat coming alongside a massive ocean going ship. Just the ripples alone could capsize the boat. It’s dark and ominous presence must always be respected.
AIRPLANE SMILEY One of the biggest fears for an airline captain is making the news because of an incident. Without a doubt, it enters the equation during significant turbulence and only escalates the angst. Social media is now the new “six o’clock news” and one doesn’t have to be reminded almost every passenger has a smart phone, iPad or some other recording device. And with onboard internet, one doesn’t have to be on the ground to hear what has transpired. Airlines realize this and now have devoted teams to deal with issues.