What are Cockpit Checklists and how do they help Pilots?

Day of awakening: October 30, 1935

The most sophisticated aircraft in aviation history at the time, a strategic military bomber Boeing B-17 ''FLYING FORTRESS'' rolled off the runway, pitched up in a perfect lift and within seconds entered into a deadly stall from which it couldn't recover, crashing onto a nearby field. While the co-pilot and the other flight engineers were rescued, the pilot couldn't make it out alive.

How could this majestic marvel of engineering and technology, which had been in development for a long time, possibly fail? Investigations would later on reveal it was simply because the pilots had forgotten to release the flight control gust locks before taking off. The fact that something so trivial could be forgotten only pointed to the realisation that aircrafts systems had become much more complex and it was beyond human capacity to remember each and every intricate details for a safe flight. Following the crash of the B-17, Boeing strictly mandated the use of Cockpit checklists in its entire fleet and checklists have been an integral part of flight decks ever since.

Jim Landon – Boeing B-17

So, what are checklists and why exactly are they essential?

Let's get started

When it comes to aviation,'' safety'' is of paramount importance. A slight breach of focus and an incident can turn into a fatal accident. If you thought everything could be read from instruments on-board, then you couldn't be more wrong. There are certain things a pilot needs to have at the back of their head at all times, also known as ''memory-items''- refer to those corrective actions that need to be executed in ''time-critical" events such as engine flame-out, sudden loss of pressure and such. Checklists are manuals that guide the crew through mandated procedures in the event of a ''time-critical'' event. This would essentially lead to effective crew resource management and efficient decisions. Cockpits in the past were notorious for being stacked with piles of charts, logbooks and technical documents. Modern aircrafts have evolved to de-clutter the cockpit and provide a more electronic way of accessing things.

Checklist on MFD

“A Cockpit checklist is a list used by the crew to make sure the aircraft is in the proper configuration for a given phase of flight. These phases of flight include take-off, climb, cruise, descent, approach, and landing. ”

Several pilots of major carriers when interviewed stated on conditions of anonymity that they have their own checklist procedure which they perform from memory just prior to take-off to assure themselves that the plane is configured correctly. These memory techniques have some inherent hazards such as dependency on the availability of time, vulnerable to distractions such as air traffic control (ATC) communications, outside scan and most importantly they are memory based and not on a step-by-step challenge-and-response procedure.

Paper Checklist

A ground-breaking study

Asaf Degani, a researcher who published 1990 study Human Factors of Flight-Deck Checklists: The Normal Checklist  listed the following objectives for the need of a checklist:

Aid the pilot in recalling the process of configuring the plane.

Provide a standard foundation for verifying aircraft configuration that will defeat any reduction in the flight crew’s psychological and physical condition.

Provide convenient sequences for motor movements and eye fixations along the cockpit panels.

Provide a sequential framework to meet internal and external cockpit operational requirements.

Allow mutual supervision (cross checking) among crew members.

Enhance a team (crew) concept for configuring the plane by keeping all crew members ‘in the loop’.

Dictate the duties of each crew member in order to facilitate optimum crew coordination as well as logical distribution of cockpit workload.

Serve as a quality control tool by flight management and government regulators over the pilots in the process of configuring the plane for the flight.

When a checklist is run through completely, the pilot monitoring makes sure everyone in the cockpit is aware and this is called a ''loop''.

AOPA : Cockpit Flow

Classification of check-lists

Depending on predefined situations, checklists are classified as:

NORMAL CHECKLIST :-

Take-off, Descent and Landing are critical aspects of flight. Normal checklist begins with pre-flight checklist- This includes checks before starting the engines. In this stage, generally all mandatory pre-flight checks are ticked. The ''pilot-monitoring'' refers to the checklist and cross verifies with the ''pilot flying'' for all the steps mentioned in the checklist. In case a pilot has missed something, he/she can then perform the appropriate action. Similar steps are followed before initiating a descent and approach into the destination airport.

NON-NORMAL CHECKLIST :-

Also dubbed as '' read and do'' checklist-They usually relate to abnormal/emergency procedures where a cockpit flow pattern from memory( as is the case in normal checklist) is not desirable. This checklist gives the pilot the power to make his own decision based on his/her awareness of the situation and must be mutually assessed and agreed upon by both crew members before further action. Modern cockpits are so advanced that errors are auto-detected by the sensors themselves and the corresponding correct checklists are displayed to the pilots.

Checklist Applications for portable devices

DIFFERENTIATION BY TYPE OF DEVICE USED :-

Various types of checklist devices have evolved over the years. Among them are the scroll, mechanical, and vocal checklist. More modern ones involve computer-based text displayed on a CRT and electronic checklist devices that sense sub-system’s state. Quite understandably, it has been observed that veteran flight crew members still prefer paper checklist over any other form. On the other hand, modern day pilots make good use of everything that technology has got to offer.

Boeing B777 – Electronic Checklist

Summing up

There is temptation, on the part of experienced pilots, to memorize a checklist and avoid the burden of reading it from the card. A responsible aviator will always verify his actions in the cockpit as well as during pre-flight inspection and post-flight duties by going through the checklist provided the manufacturer.

Regardless, checklists are only a last minute help to guide in a critical situation. They cannot alone fly a plane and hence the importance of human performance cannot be stated enough. Flying has never been safer and we owe it all to the clever minds that designed the humble, yet so critical, checklists that we have today.

Air travel is touted to be one of the safest modes of travel out there. With the onslaught of the devastating Novel Coronavirus pandemic, it has left us in tenterhooks whether to go ahead with our travel plans or not, especially the long haul ones since they are considered high risk for virus transmissions. A popular myth amongst fliers is that one sick person on-board can transmit the Coronavirus to the rest, which is far from true. With precautions and advisories in place and assuming people adhere to them, air travel can be one of the, if not the most, safest mode of travel.

airbus

To understand the degree of transmission risk, let's look at how air circulates within the cabin.

Air circulation inside an Airliner

Aircrafts fly at altitudes that are unsustainable for human life. Compared to the ideal conditions we have at ground, conditions up there can wreak havoc on human biological cycles. Hence it becomes imperative that aircraft air systems be designed to maintain the cabin pressure levels suitable for humans while at the same time keep the air fresh and at an ambient temperature. Here's how it works.

asian journeys

The air outside the cabin is breathed into the engines which then flows into the compressor. After being compressed to a density safe enough for humans to breathe, this compressed air enters into what is called a ''mixing manifold''. The compressed air is hot and hence it needs to be cooled. This compressed air is then mixed with the re-circulating air from the cabin in the mixing chamber and passes through special filters known as ''HEPA'' filters (more on that later). This filtered air then passes throughout the cabin via connecting ducts where the ceiling meets the sideboard. Half of the air is dumped overboard ensuring a continuous flow of air within the cabin.

High efficacy particulate air filters (HEPA)

HEPA filters are high quality aircraft air filtration systems of medical grade, touted to remove an astonishing 99.99% of airborne microbes and dust particles in air. 

“HEPA filters are effective at trapping microscopic particles as small as bacteria and viruses” - IATA said in a paper, Cabin air quality – Risk of communicable diseases transmission, published in 2018

iata

According to experts though, air filtration systems and HEPA filters alone cannot completely negate the risk of transmission. These filters are designed to only filter particles that reach it. Thereby the risk of transmission from unfiltered particles still lingers and that’s exactly why Coronavirus appropriate activities like physical distancing and donning a mask still needs to be followed.

Conclusions from certain case studies

Airbus tried simulating a highly accurate flow of air in an A320 cabin using CFD to detect the transmission of cough particles with people seated next to each other Vs people staying 6 feet apart. The result concluded the risk of transmission as lower in the former than the latter

Research by the US Transcom propagated that suspended air particles were rapidly diluted by the high exchange rates of air in a typical aircraft cabin. Tests in B777 and B767 proved that particulate matter was removed 15 times faster than in a home ventilation system and 5-6 times faster than a typical hospital ventilation setting.

Researchers at the Harvard School of Public Health have found that following Novel Coronavirus appropriate behaviour coupled with the aircraft's ventilation systems resulted in a very negligible risk of transmission

qatar airways

Modelling the remaining risk

Manufacturers have developed a risk-management model which calculates the risk of Novel Coronavirus transmission and translocation by modelling the various steps and parameters in the curb-to-curb air travel journey. The objective of the model is to support government and regulatory bodies in making data-substantiated decisions when reopening air travel. This is timely and relevant as the first travel corridors are being discussed between low risk or “green” countries.

The evaluation quantifies the level of risk for each step and takes into account the various health and safety measures, such as wearing face protection and different testing and quarantine scenarios.  In practice, the model displays several protection and screening strategies that can be activated on a chosen route and simulates the impact on lowering the overall risk through applying those measures.

emirates

Disembarking the light way

In response to pre-emptive passenger offboarding, experts are introducing a solution to ensure an orderly and safe way to disembark, avoiding crowding of the aisles and keeping everyone onboard comfortable. The solution is a novel lighting design based on simple traffic guiding principles: the scenario uses different cabin illumination combinations to indicate the rows which are designated to disembark next. The lighting scenarios complement the verbal cues given by the cabin crew to facilitate an orderly and rush-free departure from the plane.

airbus

Initiatives from major carriers

Qatar Airways became one of the first global carriers to implement the use of UV(ultraviolet) cabin systems by Honeywell. Clinical trials have proved the efficiency of UV light in successfully inactivating a number of airborne microbes when applied in the right doses. Also, The Doha based airline along with Emirates have been seen running massive PR campaigns boasting of fully vaccinated crews.

cathay pacific b747

“We understand there will be some (aircrew) who cannot take a vaccine and we will look into accommodating them on a short-term basis where we can. However, we will review the future employment of those who are unable to become vaccinated and assess whether they can continue to be employed as aircrew with Cathay Pacific.” - a spokesperson for Cathay Pacific said last week.

“We are pleased to operate flights with fully vaccinated crew – a significant step in protecting our employees’ and customers’ health safety. We have been squarely focused on working very hard to ensure the safety of our staff and passengers since the pandemic broke out and this is another testament to our continued commitment.” - Ethiopian Airlines Group CEO Mr. Tewolde GebreMariam

qatar airways

The way forward

Despite all assurances, It will still take time before people overcome their fear completely. For this very same reason, awareness should be created regarding public safety on-board. With some positive signs of recovery, especially in countries with high rates of vaccination, a sustained global recovery will only be realized with an escalation of vaccination campaigns, the continued development of digital health passes, and coordinated and cohesive policy support from governments.

In what can be termed as a strategic boost to the "Atmanirbhar Bharat" initiative, an Indian aircraft leasing company, Vman Aviation has placed the first ever order with Airbus on Wednesday for the acquisition of a H125 helicopter in what would be its first ever dry lease transaction. Vman is an India based aircraft leasing company located in GIFT city, Gujarat. So, how is it relevant to the Atmanirbhar Bharat initiative and how could this be a stepping stone to future developments in Indian Aviation? Read on

Facts and Figures

India ranks third globally when it comes to domestic civil aviation and is poised to become the third largest air passenger market by 2024, overtaking the UK. Out of the 700+ aircrafts registered in India, about 81% are leased and they are leased from foreign companies. Now that is against a figure of 53% of the aircrafts worldwide that are leased. What that points out is the fact that despite a huge demand for aircrafts India has no home-based aircraft lessors in the country. Most of the aircrafts leased in India are either from Irish companies or firms based in the UAE and Hong Kong.

A majority of the airlines in India are relatively new to the market, barring a few, with most of them being LCCs with a relatively fragile financial build-up and the Covid pandemic has only added to their woes. The leased aircrafts take a lion's share of all the operator fleets in the country. Hence it only makes sense that the need of the hour is to give the necessary push for Indian aircraft leasing company that it so desperately deserves.

The Union Budget for the financial year 2021-22 came as a welcome move for the entire civil aviation industry in India. Key highlights of the budget were the introduction of tax incentives to custom duty reductions, from asset monetization and disinvestment to resource allocation to establish India as a major aviation manufacturing hub worldwide.

How do these reforms impact the leasing industry ?

Under the tax reformation policy, the Indian Government is determined to establish the IFSC (International Financial Services Centre), in Gujarat city as a major global aviation hotspot for aircraft leasing. They include:-

Tax holiday for capital gains income of aircraft leasing and financial company.Investment division of foreign banks installed in IFSC to be exempted from tax.Tax incentive for re-location of foreign funds in IFSC.Tax exemptions for aircraft leasing/royalty paid to the lessors.

As can be seen, all these reforms have been meticulously formulated to act as a major driver in the growth of aircraft leasing and financial ecosystem in IFSC, GIFT city, Gujarat. Besides pushing leasing activities further, they also offer better terms for domestic and foreign airlines alike.

What do the experts say ?

"Vman is focused on general aviation, aircraft and helicopters which include trainer aircraft. We are starting with helicopters and we will add general aviation aircraft in our portfolio gradually. We hope this will enable general aviation to also grow in line with commercial aviation to double digits in the near future.”- Vishok Mansingh, CEO of Vman said.

India, with a rich history of pilgrimages and the never ending demand for access to these spots, the company opted to choose the Airbus H125 helicopter as it was the perfect pick for Heli-pilgrimage, aerial medical and rescue missions both domestically and globally. According to the CEO of Vman, the transaction deal cost the company a staggering 5 million Euros and the assets are expected to be delivered by Sept-October of this year.

What, according to him, are the challenges to the leasing industry though? "Access to leased aircrafts at reasonable costs"- comes his prompt reply.

The Indian Aircraft Leasing Company also has plans of adding general aviation and trainer aircraft to their portfolio and are in talks with potential flying schools in India to lease their trainer aircraft. It is also hoped that with the recent government announcements in favour of the leasing industry, this niche would grow at par with the civil aviation of the country. And of course, this is just one of many to come.

“The aircraft purchase signing is a landmark event in the Indian aviation history. This agreement is the result of the efforts put in for the last four to five years to create a viable leasing and financing ecosystem in the country” -  said Civil aviation secretary Pradeep Singh Kharola.

Overview: Aircraft engine certification

Every time an aircraft rolls off the production line, its goes through a series of stringent tests before we see them take to the skies. A '' Type Certificate'' is issued which ensures the aircraft model is compliant with all applicable airworthiness requirements and safety standards and is eligible for mass production. The same applies to ''engines'' as well. 

General Electric, Rolls Royce and Pratt & Whitney are the top names when it comes to engine manufacturing and they've been powering aircrafts for decades. As we sit comfortably in our seats sipping on a glass of wine, we often take the reliability of these engines for granted, given the manufacturer's records and reputation. While that is true, it is to be understood that a lot of work is put into making that happen. Let's take a look.

rolls royce - indoor testing phase

The need for engine testing

Like anywhere else, testing is the last and the most indispensable part before engine certification. Engines have to go through a series of tests, both on-ground and in-flight before the airworthiness authorities give the final go-ahead. The main task of the testing team is to make sure the engine works in accordance with all the parameters set by the engineer. The engine will be tested in all possible scenarios mimicking conditions during taxiing, take-off ,descent, cruise, approach, landing and some other. (As we will soon see)

Water Ingestion

Engines ingest massive amounts of water during their operational life hence water ingestion tests are standard. At Boeing and Airbus, airplanes are made to taxi through special water channels known as "troughs". As the planes speed through these troughs, various engine parameters such as thrust, temperature, engine blade performance etc are evaluated and any deviation from the expected ideal performance is worked upon further.

airbus - water ingestion test

The engines have to weather the fiercest of rains and the hardest of storms. For this very reason, manufacturers spray gallons of water, for instance, The GeNx pumps 800 gallons of water per minute into the engines during test run. Now technically if the engine meets all the design and safety parameters the water is expected to ideally come out without harming the engine frame or its safe operation. Icy conditions can get a little tricky as the FAA mandates that for various different types of ice particles, and we're talking huge balls of ice and not small icicles, the engine will recover as soon as possible without much damage.

rolls royce

A bird for a bird

Remember the crash landing of US AIRWAYS on the Hudson river in 2009 by Captain Sully? It serves as a grim reminder to the fact that even our feathery friends can do a fair amount of damage to jet engines. Bird strikes are common and when they do happen, birds-especially the big ones can bend the blades at the front of the engine causing an inflight engine shutdown or stall. Hence manufacturers have devised a, what is called a ''chicken gun''-that shoots chicken carcasses into the engine, mimicking a bird strike in nature and the tests are evaluated. Ideal outcome of the test is for the blades to remain intact upon impact and post collision.

Pratt & Whitney

Blade-Off procedure

Touted to be one of the most violent tests of all. This simulates an event where an engine blade snaps off the revolving shaft- the shaft could be revolving at 3000 RPM, and turns into shrapnel. The shrapnel turns into flying debris and could potentially tear through the fuselage and the rest of the plane if it is not contained. Hence this procedure aims at containing the shrapnel within the engine chamber and diffusing the energy using the casing.

Inflight Testing

In addition to ground tests, jet engines are also subjected to evaluations while in flight and this puts the ultimate engine reliability to test. For this very purpose, manufacturers use ''testbeds''-which are basically modified aircrafts used for testing. Most of the B747s that are retired find use as testbeds.

rolls royce - b747 platform for engine test

“As a flying testbed, it will get fitted with the latest testing capabilities and, for the first time, will test engines which power both commercial and business aircraft. New systems will obtain better data faster than ever before, and technologies will get tested at higher altitudes and faster speeds” – Rolls Royce (2019)

Summing up

Once the plane manufacturers are ready with their models, they run those models through a series of their own tests to ensure all aspects of flight safety, aircraft and engine performance are met to the highest standards as defined by aviation regulations worldwide. In Airbus’s words,'' It is only a matter of going up and beyond what is required ''- Truly said.

For those of us who are not aviation enthusiasts, the idea that aircrafts sometimes dump fuel just after the take-off or right before they land might sound psychotic and deranged. But it turns out that the practice of “fuel dumping” or “fuel jettisoning” is a fairly well-established procedure used by planes primarily in certain emergency situations to lessen the aircraft’s weight. So why would pilots dump costly fuel onboard, which you as a passenger has just paid for? Did the pilots miscalculate the fuel required to go from A to B? Perhaps not.

Cockpit Panel

Why is such a procedure performed at all?

The most probable rationale is a necessity to attempt an emergency landing soon after take-off. This could be due to an mechanical fault, a bird strike or a medical emergency, and since maximum take-off weight(MTOW) is far greater than maximum landing weight(MLW), the pilot needs to dump fuel. For example, an Airbus A380 carries 250 tonnes of fuel when fully topped up. While the maximum take-off weight of the aircraft is 575 tonnes, the maximum landing weight is 394 tonnes only, whopping 181 tonnes less. Landing with a heavier aircraft than that figure risks buckling the undercarriage, with potentially catastrophic results.

Aeroflot Flight 1492 (5 May 2019) was a scheduled passenger flight from Moscow to Murmansk suffered electrical failure due to lightning strike on climbing out. Captain's injudicious decision to land back immediately without considering landing weight limitations resulted in bounced landing and hard touchdown, causing the landing gear to collapse, fuel to spill out of the wings, and a fire to erupt. The fire incinerated the rear of the aircraft, killing 41 of the 78 souls on board. On 2 October 2019, investigators filed criminal charges against the captain for not following guidelines in aircraft manuals for safe operation.

What to consider ? Overweight landing - Jettisoning - Holding pattern to burn off fuel

Due to steep increase in the cost of fuel, airlines are hesitant in deciding whether to land overweight, burn off fuel, or jettison fuel. Each choice has its own set of factors to consider. Holding to burn off fuel or jettisoning fuel prior to landing will result in increased fuel cost and time-related operational costs. Landing overweight requires an overweight landing inspection with its associated cost. Most operators provide their flight crews with guidelines to enable the pilot to make an intelligent decision to burn off fuel, jettison fuel, or land overweight considering all relevant factors of any given situation.

credits : Devinder Sangha

A pilot will choose to dump fuel only on very rare occasions. Unless there is a medical emergency on board, someone is dying and you don't really have time to fly around and burn fuel. So, that's when you would dump fuel so that you can lose weight quickly. In any which case, for an aircraft to land safely, the MLW must always be lesser than the MTOW.

Not elementary as opening a tap

Ideally, the minimum altitude for a fuel dump is around 6000 feet above ground level. Fuel is ejected at the rate of several tonnes per minute through valves on the trailing edge of the wings, close to the wingtips and away from the engines to avoid combustion. Even though fuel is vaporized, it is still suspended in the atmosphere. The odour can be pronounced, and the fuel will eventually reach the ground.

Because of the relatively small amount of fuel that is jettisoned, the infrequency of use, and the safety issues that may require a fuel jettison, such regulations are not likely to be promulgated. Other factors such as fuel jettison nozzle dispersion characteristics, airplane wake, and other atmospheric conditions can affect the amount of fuel that reaches the ground.  Generally speaking, designated areas are above water bodies or unpopulated regions above land.

NBC News

Delta Airlines Flight 89 is an example of fuel dumping that violated established regulations: on 14 January 2020, it dumped more than 10,000 gallons of fuel at a low altitude over a populated area in Los Angeles, causing injuries to 56 people including school children below.

How long is the process

Only long range aircraft such as the B777 or A380 have a fuel dump mechanism. Manufacturers have not been able to provide a specific rate since the dumped fuel is not pumped but delivered by gravity feed so as to be more independent of electrical systems, which might be unavailable in a fuel-dump scenario. As a rule of thumb for the Boeing 747, pilots quote dump rates ranging from a ton per minute, to two tons per minute, to a thumb formula of dump time = (dump weight / 2) + 5 in minutes.

B767 Panel

Many planes are not fitted with the fuel dump feature, as it happens. That’s the case across most narrow-body planes like the B737, A320 and most regional jets. That’s because they meet strict parameters laid out by aviation regulators showing they can still perform critical manoeuvres and hence, doesn't compromise on safety.

On 27th May 2021, Flight crew of an Air India flight (AI105) serviced by a Boeing B777-300ER operating from Delhi to Newark decided to return due to a bat in the cabin. Passengers and Flight attendants noticed the mammal around 20 minutes after take-off. However, landing a Boeing 777-300ER filled with fuel for a 15-hour flight is not simple as it seems. Before landing back safely, the crew had to fly numerous holding patterns for over two hours in the vicinity of Delhi Airport and dump fuel to reach the maximum landing weight permitted.

What Indian regulation says

Directorate General of Civil Aviation (DGCA) has a handful of regulations in place: the flight crew shall request Air Traffic Controller (ATC) for permission. The plane has to be at least 6,000 feet above the highest obstacle along the route. The route to be flown, which, if possible, should be clear of cities and towns, preferably over water and away from areas where thunderstorms have been reported or are expected.

The horizontal boundaries of the area within which other traffic requires appropriate vertical separation extend for 10 NM either side of the track flown by the aircraft which is dumping fuel, from 10 NM ahead, to 50 NM or 15 minutes along track behind it (including turns).

Aircrafts fly through extremes of temperatures and this subjects it to a variety of performance issues. One such phenomenon is the accumulation of ice on aircraft structures which is very common but can turn perilous quickly if not dealt with. Let's take a look at the how and why...

What is aircraft icing and why is it dangerous?

One of the greatest hazards of flying in cold weather is aircraft icing. Aircraft icing refers to coating or deposit of ice on any object of the aircraft, caused by freezing and impingement of liquid hydrometers. It can have a detrimental effect on the aircraft, and it can make it hard for the pilot to fly the plane.

Ice can collect on the surface of the plane and can change the shape of aerofoils and flight control surfaces and hamper the function of the wings, propellers, and control surface as well as canopies and windscreens, pitot tubes, static vents, air intakes, carburetors and radio antennas.

Effects of Icing

Aircraft icing increases weight and drag, decreases lift and can decrease thrust. Ice reduces engine power by blocking air intake. When ice builds up by freezing upon impact or freezing as runoff, it changes the aerodynamics of the surface by modifying the shape and the smoothness of the surface which increases drag and decreases wing lift or propeller thrust. Both a decrease in the lift on the wing due to an altered aerofoil shape and the increase in weight from the ice load will usually result in having to fly at a greater angle of attack to compensate for the lost lift to maintain altitude. This increases fuel consumption and further reduces speed, making a stall more likely to occur, causing the aircraft to lose altitude.

Ice also accumulates on helicopter rotor blades and propellers causing weight and aerodynamic imbalances that are amplified due to their rotation. The first place of an aircraft where ice usually forms first is the thin outside air temperature gauge. The ice generally takes over the wings at the end. Occasionally, a thin coating of ice may form on the aircraft’s windshield. This may occur on landing and take-off.

Archive

Flight instruments may not operate if ice builds up on the static pressure ports of the plane and the pilot tube. The rate of climb, airspeed, and altimeter might be affected. Gyroscope instruments inside the aircraft that are powered by a venture might get affected too when ice builds up on the throat of the venture.

Types of Aircraft De-icing and Anti-icing methods

Pneumatic de-icing boots: The pneumatic boot is usually made of layers of rubber with one or more air chambers between the layers. It is placed on the leading edge of an aircraft's wings and stabilizers. The rapid change in the shape of the boot is designed to break the adhesive force between the ice and the rubber, and allow the ice to be carried away by the air flowing past the wing.

Flight Engineer

Fluid De-icing: These external ground-based systems use a de-icing fluid—typically based on ethylene glycol or isopropyl alcohol to prevent ice forming and to break up accumulated ice on critical surfaces of an aircraft. Fluid is forced through holes in panels on the leading edges of the wings, horizontal stabilizers, fairings, struts, engine inlets, and from a slinger ring on the propeller and the windshield sprayer.

Wikimedia

Bleed Air: Bleed Air systems are used by most large aircraft with jet engines or turboprops. Hot air is "bled" off one or more engines' compressor sections into tubes routed through wings, tail surfaces, and engine inlets. A disadvantage of these systems is that supplying an adequate amount of bleed air can negatively affect the engine performance. Higher-than-normal power settings are often required during cruise or descent, particularly with one or more inoperative engines.

“The Boeing 787 Dreamliner uses electro-thermal ice protection. In this case the heating coils are embedded within the composite wing structure. The system uses half the energy of engine fed bleed-air systems, and reduces drag and noise.” – Boeing

B787 Thermo electric Anti-icing system

So what makes the difference between Anti-Icing and De-Icing?

Anti-icing equipment is turned on before entering icing conditions and is designed to prevent ice from forming in the first place. De-icing equipment is designed to remove ice after it begins to accumulate on the airframe.

Some notable air crashes due to ice accumulation

Air France 447: A scheduled passenger flight, an Airbus A330 from Brazil to France crashed into the Atlantic on 01 June 2009 killing everyone onboard. The aircraft crashed after temporary inconsistencies between the airspeed measurements—likely due to the aircraft's pitot tubes being obstructed by ice crystals—caused the autopilot to disconnect, after which the crew reacted incorrectly and ultimately caused the aircraft to enter an aerodynamic stall, from which it did not recover.

Aero Caribbean Flight 883: Another scheduled flight(ATR-72) from Haiti to Havana (2010), encountered severe icing conditions at 20,000 ft which were not handled properly, leading to the crash.