Thursday, May 28, 2009
Sunday, May 24, 2009
Monday, May 18, 2009
Crosswind Landings...how to do them
Significance
Aircraft in flight are subject to the direction of the winds in which the aircraft is operating. For example, an aircraft in flight that is pointed directly north along its longitudinal axis will, generally, fly in the that northerly direction. However, if there is a west wind in the air in which the aircraft is flying, then the actual trajectory of the aircraft will be slightly to the east of north. If the aircraft was landing on a northbound runway, it would need to compensate for this easterly component of velocity caused by the west crosswind.
In situations where a crosswind is present, the aircraft will adopt a yaw orientation with respect to the runway and will drift laterally as it approaches the runway. These pose significant safety issues when safe operation of the undercarriage requires the body and the velocity of the aircraft to be aligned with the runway at touch down. The landing gear on the B-52 included an unusual feature to counteract the problem: all landing gear bogies could be steered, allowing the aircraft to land with the wheels facing the direction of travel even if the nose was not pointed in the same direction.
To meet these conflicting requirements, three standard procedures are used for executing a safe landing in a cross wind situation. These landings are called the Crab, De-Crab and Sideslip techniques.
If the crosswind landing is not executed safely, the aircraft may experience wingstrike, where a wing hits the runway.
[edit] Techniques
The following guidelines are advised by Boeing for a crosswind landing. These guidelines assume steady wind (no gusting). These winds are measured at 33 foot (10 m) tower height for a runway 148 feet (45 m) in width. Basically, there are 3 landing techniques which may be used to correct for cross winds: De-Crab, Crab, and Sideslip.
[edit] De-Crab
The objective of this technique is to maintain wings level and the aircraft position near the runway centerline during approach. The nose points into the wind so that the aircraft approaches the runway slightly skewed with respect to the runway centerline (crabbing). This gives the impression of approaching the runway flying sideways, which can be disorienting for the pilot. Position is maintained by balancing the crosswind component, or more accurately the drag force arising from it, with engine thrust. Wings are maintained level throughout the approach. Just before the flare, opposite rudder (downwind rudder) is applied to eliminate the crab, with a simultaneous application of opposite aileron to maintain a wings-level attitude, so that at touch down, the body, velocity vector, and bank angle are all aligned with the runway, and the aircraft is positioned near the center.
[edit] Crab
The airplane can land using crab only (zero slideslip)up to the landing crosswind guideline speeds.
On dry runways, upon touchdown the airplane tracks towards the upwind edge of the runway while de-crabbing to align with the runway. Immediate upwind aileron is needed to ensure the wings remain level while rudder is needed to track centerline. The greater the amount of crab at touchdown, the larger the lateral deviation from the point of touchdown. For this reason, touchdown in a crab only condition is not recommended when landing on a dry runway.
On very slippery runways, landing the airplane using crab only reduces drift towards the downwind side a touchdown, and may reduce pilot workload since the airplane does not have to de-crabbed before touchdown. However, proper rudder and upwind aileron must be applied after touchdown to ensure directional control is maintained.
[edit] Sideslip
This sideslip crosswind technique is to maintain the aircraft's heading aligned with the runway centerline. The initial phase of the approach is flown using the Crab technique to correct for drift. The aircraft heading is adjusted using rudder and ailerons to align with the runway. This places the aircraft at a constant sideslip angle, which its natural stability will tend to correct. Sufficient rudder and aileron must be applied continuously to maintain the sideslip at this value. The dihedral action of the wings has a tendency to cause the aircraft to roll, so aileron must be applied to check the bank angle.
With a slight residual bank angle, a touchdown is typically accomplished with the upwind main wheels touching down just before the downwind wheels. Excessive control must be avoided because over-banking could cause the engine nacelle or outboard wing flap to contact the runway/ground.
In strong crosswind conditions, it is sometimes necessary to combine the crab technique with the sideslip technique.
Crosswind Landings...how to do them
Significance
Aircraft in flight are subject to the direction of the winds in which the aircraft is operating. For example, an aircraft in flight that is pointed directly north along its longitudinal axis will, generally, fly in the that northerly direction. However, if there is a west wind in the air in which the aircraft is flying, then the actual trajectory of the aircraft will be slightly to the east of north. If the aircraft was landing on a northbound runway, it would need to compensate for this easterly component of velocity caused by the west crosswind.
In situations where a crosswind is present, the aircraft will adopt a yaw orientation with respect to the runway and will drift laterally as it approaches the runway. These pose significant safety issues when safe operation of the undercarriage requires the body and the velocity of the aircraft to be aligned with the runway at touch down. The landing gear on the B-52 included an unusual feature to counteract the problem: all landing gear bogies could be steered, allowing the aircraft to land with the wheels facing the direction of travel even if the nose was not pointed in the same direction.
To meet these conflicting requirements, three standard procedures are used for executing a safe landing in a cross wind situation. These landings are called the Crab, De-Crab and Sideslip techniques.
If the crosswind landing is not executed safely, the aircraft may experience wingstrike, where a wing hits the runway.
[edit] Techniques
The following guidelines are advised by Boeing for a crosswind landing. These guidelines assume steady wind (no gusting). These winds are measured at 33 foot (10 m) tower height for a runway 148 feet (45 m) in width. Basically, there are 3 landing techniques which may be used to correct for cross winds: De-Crab, Crab, and Sideslip.
[edit] De-Crab
The objective of this technique is to maintain wings level and the aircraft position near the runway centerline during approach. The nose points into the wind so that the aircraft approaches the runway slightly skewed with respect to the runway centerline (crabbing). This gives the impression of approaching the runway flying sideways, which can be disorienting for the pilot. Position is maintained by balancing the crosswind component, or more accurately the drag force arising from it, with engine thrust. Wings are maintained level throughout the approach. Just before the flare, opposite rudder (downwind rudder) is applied to eliminate the crab, with a simultaneous application of opposite aileron to maintain a wings-level attitude, so that at touch down, the body, velocity vector, and bank angle are all aligned with the runway, and the aircraft is positioned near the center.
[edit] Crab
The airplane can land using crab only (zero slideslip)up to the landing crosswind guideline speeds.
On dry runways, upon touchdown the airplane tracks towards the upwind edge of the runway while de-crabbing to align with the runway. Immediate upwind aileron is needed to ensure the wings remain level while rudder is needed to track centerline. The greater the amount of crab at touchdown, the larger the lateral deviation from the point of touchdown. For this reason, touchdown in a crab only condition is not recommended when landing on a dry runway.
On very slippery runways, landing the airplane using crab only reduces drift towards the downwind side a touchdown, and may reduce pilot workload since the airplane does not have to de-crabbed before touchdown. However, proper rudder and upwind aileron must be applied after touchdown to ensure directional control is maintained.
[edit] Sideslip
This sideslip crosswind technique is to maintain the aircraft's heading aligned with the runway centerline. The initial phase of the approach is flown using the Crab technique to correct for drift. The aircraft heading is adjusted using rudder and ailerons to align with the runway. This places the aircraft at a constant sideslip angle, which its natural stability will tend to correct. Sufficient rudder and aileron must be applied continuously to maintain the sideslip at this value. The dihedral action of the wings has a tendency to cause the aircraft to roll, so aileron must be applied to check the bank angle.
With a slight residual bank angle, a touchdown is typically accomplished with the upwind main wheels touching down just before the downwind wheels. Excessive control must be avoided because over-banking could cause the engine nacelle or outboard wing flap to contact the runway/ground.
In strong crosswind conditions, it is sometimes necessary to combine the crab technique with the sideslip technique.
Sunday, May 17, 2009
First case of swine flu in India confirmed
New Delhi:
Its official now, India on Saturday confirmed first case of deadly H1N1 virus. A 23 year old passenger who arrived at Hyderabad from US has been confirmed to be carrying the virus.
While, the IT student whose samples confirmed positive for H1N1 virus has been put on Tami flu, his co-passengers who departed New York on May 11(Emirates Airline EK-202), transiting Dubai (Emirates airline EK-524) are being tracked.
“We have informed Dubai and New York health authorities through the World Health Organisation (WHO) about the case and informed them to track all those he might have passed on the infection to,” Naresh Dayal, health secretary told the Indian Express, confirming the case.
According to the health ministry officials, all the passengers who traveled in the connecting flight from Dubai to Hyderabad have also been identified and they are being contacted through Integrated Disease Surveillance Project “their health status would be monitored. These passengers are also being advised to remain under home quarantine for further period of seven days,” added the official in the ministry.
The passenger found to be positive for the virus was quarantined at the Hyderabad airport early morning on May 13 as he was found to be having fever. “He was then immediately shifted to the identified isolation facility and his samples were taken,” an official in the National Institute of Communicable Diseases (NICD) said.
The local contacts of the passenger have also been tracked. With India reporting first case, officials are however not alarmed, “We are rather happy that we got to know about it as it came in. The system is in place,” added Dayal.
You cant change that damn glide slope angle !!!!
Aviation’s silly symphonies
CAPT. A. RANGANATHAN AND ANANTH KRISHNAN
| Four years ago, Indian aviation was booming while China had just ended three decades of state monopoly. Today, China has left India far behind in both infrastructural and operational terms. Continuing the series on aviation safety by aviation expert |
The AAI, during the boom of the late 1990s and the first part of this decade, focused only on short-term profits, allowing airlines to proliferate unchecked and ignoring ground infrastructure. Today, India’s bleeding airlines are paying the price for growth plans that were both short-sighted and simply unrealistic.
Amid all the gloom afflicting air carriers worldwide, China is possibly the world’s only aviation market that investors are still bullish about.
An approach with a Normal Glide path angle of 2.75 and 3.25 will result in a stabilised approach and more controlled landing
An approach with a Glide path angle of 3.30 and 3.4 0 provided at the new Bangalore and Hyderabad airports will require a steep d
Flying High: Naverus RNP path follows the river between mountains for a landing in Linzhi, one of the most difficult approaches in the Himalayan region;
The “Silly Symphony” caricature of Aesop’s fable ‘Hare and the tortoise” is played out by the aviation in India and China. While one seeks and has taken all the advice to build a world class infrastructure, the other considers it infra-dig to seek or take any advice. What the former Chancellor of Germany, Konrad Adenauer said “We all live under the same sky, but we don’t all have the same horizon” is apt when you compare aviation in the two countries
Until 2003, the position of the aviation markets in Asian’s two biggest economies was hardly recognisable from what they are today. In 2004, Indian aviation was booming: 30 per cent year-on-year growth was projected and a largely unchecked proliferation of airlines made India Asia’s best aviation market for foreign investors; 500 airports were to be built by 2020! China, by contrast, ended a three-decade state monopoly only that year and, was a far less attractive proposition, as far as foreign investment was concerned.
Today, the contrast between the two countries is quite pronounced. In the last five years, while the Chinese Government has outlined an ambitious plan to build an impressive network of airports across the country — and the Chinese government, more often than not, executes its plans — India’s aviation authorities have dithered. Before Deng Xiaoping’s opening up of the Chinese economy in the late 1970s, air travel for Chinese was rare. The country only had 36 airports. Today, China has 152 civilian airports, and the number will rise to more than 190 by 2010 and cross 250 in 2020. By contrast, the Airport Authority of India’s plans to build second-tier airports have not materialised. Not only that, airport infrastructure even in India’s so-called world class airports is nothing to be proud of. Expansion projects in Kolkata and Chennai, talked about for years, remain grounded or planned in unviable mode; while those that did take off, in Bangalore and Hyderabad, have been plagued by haphazard planning. An intrepid traveller only need arrive at IGI or (try to) depart Chennai for conclusive proof of the country’s failing aviation infrastructure.
“Enter the Dragon” was a movie set in Hong Kong. The growth of this city’s aviation infrastructure is something that our aviation pundits would do well to emulate. Fifteen years back, the standing the Dragon enjoyed on aviation safety and security bordered on the danger zone. Today, they have gone leaps and bounds ahead of the system in India. The main reason — China thrives on pride and hard work while we, in India, are full of ego and inflated self esteem.
Challenging airport
Hong Kong had one of the most challenging airports located at Kai Tek. While the approach to Runway 31 was a straightforward Instrument Landing System, the landing into the opposite direction Runway 13 was an ingenious brainwave. The approach had high terrain and high-rise buildings. The only clear path was the waterway between hills and buildings. The direction was not aligned but at an angle of almost 70°! The British, who ruled Hong Kong for several years, installed an Instrument Landing System but modified the procedure to call it an IGS (Instrument Guidance System). This enabled pilots to fly a precision approach to an altitude, which was low enough to sight the runway and make a turning manoeuvre to complete a safe landing. Because of this mix of precision/visual combination approach, the airport was utilised to the maximum limit. The pilots required special clearance to operate in this challenging airport, which required a lot of skill in adverse weather conditions.
The exponential growth in aviation into Hong Kong compelled the Chinese authorities to build a completely new airport on reclaimed land on an adjacent island. Even before the airport was complete, the infrastructure to connect the airport with the other islands in the city was complete.
Lhasa airport in Tibet is located amidst high terrain.The Naverus path follows the river valley between high terrain;
Today, Hong Kong airport holds the top position among the best 10 airports in the world. This is what pride, hard work and a forward-looking mindset can achieve. Chek Lap Kok airport has two runways, which are just 12,400 feet long and they cater to all types of flights, whether extra-long haul or heaviest. The airport is one of the busiest in Asia and handles about 48 million passengers per year. Contrast this with the total of 42 million passengers for the whole of India! The dragon enjoys the quiet pride of its achievements.
China does not confine world class airports only to Hong Kong and Beijing. Kunming, in Yunnan province, is located at an altitude of 7200 feet. The access to this region is difficult. The airport personnel move around in cycles or cycle carriages to conserve fuel. Airports have been rebuilt to world standards Even in extremely difficult locations like Lhasa and Lin Zhi, in the middle of Himalayas, they have ensured year-long access. The Chinese authorities accepted that “to progress one needs to change and change for the better”. They embraced international standards with open arms.
The International Air Transport Association (IATA) forecasts Asia’s airlines to double their losses from $500 million in 2008 to a staggering $1.1 billion this in 2009 with “the two main growth markets, China and India, expected to deliver a major shift in performance.” China’s airlines, like our own, have indeed been severely impacted by the credit crunch and the oscillating prices of fuel. The country’s two biggest airlines, China Southern based in Guangzhou and China Eastern that operates out of Shanghai, are expected to shortly receive a $440 million capital injection from the government to help tide over the current crisis. Their performance will be strictly monitored unlike the easy doles handed out to Air India and private carriers.
Source of succour
Amid all the gloom afflicting air carriers worldwide, China is possibly the world’s only aviation market that investors are still bullish about. Last month, the first ever American aerospace trade mission toured China, scouring the region for investment in the midst of all the financial turmoil. China is increasingly being seen by the West as the only source of succour in aviation’s darkest period in recent memory. Since 2003, aerospace trade between U.S and China has grown 200 per cent, reaching $45.32 billion last year. Francis Chao, managing director and publisher of the China Civil Aviation Report and a senior consultant to the U.S. delegation, says the Chinese government’s focus on infrastructure has been crucial to this perception. For western firms, with their technical expertise, China presents opportunities they will likely not find in their own countries. “In China, the aviation market has been growing very fast,” Chao says. “It ranks second in the world for turnover, though there is still a big gap between China and the US. But it will continue to grow, as China needs a lot of regional airports and regional aircraft.”
Contrasting responses
China’s response to the current crisis — which markedly contrasts India’s — has only reinforced perceptions that the fortunes of the two countries’ aviation markets continue to move in opposite directions. As part of the $586 billion stimulus package China unveiled, the Civil Aviation Administration of China announced a slew of airport infrastructure projects worth $36.6 billion, including airport expansion projects at Shanghai — whose Pudong airport already dwarfs any of India’s best — Wuhan and Nanjing, and 20 other tier-two cities. The CAAC has also been smart in roping in foreign airlines in JVs to jointly develop these airports, following the U.S. model. The AAI, during the boom of the late 1990s and the first part of this decade, focused only on short-term profits, allowing airlines to proliferate unchecked and ignoring ground infrastructure. Today, India’s bleeding airlines are paying the price for growth plans that were both short-sighted and simply unrealistic.
When physicist and science fiction writer Isaac Asimov published Adding a Dimension, he used the expression “Pre-Fixing It Up”. This has become the benchmark of our aviation standards. From the head start that our aviation system had, we have been left behind by the Chinese dragon. The difference is visible when you compare a system that is proud and a system that is prejudiced. Instead of a 3-dimensional vision we thrive on pre-fixed notions. Multiplication of preconceived figures is the name of the game.
Kunming airport at an elevation of 7200 feet in Yunnan province of China. Airport staff move around in cycles to conserve fuel;
To borrow a phrase from the advertisement slogan used in the 2002 Cricket World Cup, the guardians of airports in India, can use “Nothing International about it” as their motto. On April Fool’s Day in 1995, IAAI (International Airports Authority of India ) dropped the ‘International’ prefix and became AAI. A few years later, they have got into a mindset that they need not comply with international standards or norms. The runway maintenance schedules of AAI are completely out of synch with ICAO norms. Their continued ignorance of international standards is going to result in a major accident in the near future.
Their fancy for ‘pre-fixing –it-up’ goes a step better when it comes to installing vital navigation equipment. To err is human but when an error is committed repeatedly, one must credit them with complete incompetence. They have proved that they are champions in “Bending it like Beckham”!
New Greenfield airports are constructed in Bangalore and Hyderabad. The runways are located in areas free of obstacles and the builders install PAPIs (Precision Approach Path Indicators) at a perfect 3° angle. PAPIs are mandatory equipment required by ICAO for airfields where airliner jets operate. These assist pilots to complete a precise landing in the touch down zone after they transition from an instrument approach. All the four runways, two in each city, had these installed at 3° angle.
Angle problem
The AAI installed the ILS (Instrument Landing System ) for all the four runways. And they showed why they are great fans of the footballer. They bent the glide slope angles to 3.30° and 3.40°, instead of synchronising them with the 3° PAPIs. With this masterstroke, they killed the two airports from being capable of operating flights in CAT 2 and CAT 3 ILS conditions in fog. The recent diversions from Bangalore and Hyderabad, and the resultant air traffic congestion at Mumbai could have been avoided if the ILS Glide Slope had been less than 3.25° . The airport owners should have insisted on the AAI redoing the glide slopes. Instead, they bend the PAPI angles up to synchronise with the ILS! This is progressive thinking! Airports which should have functioned ‘24 x 365’ hours in a year are restricted to operations ONLY when the visibility is more than 550 metres,
High Glide Slope angles at Hyderabad and Bangalore
The implications do not stop there. All aircrafts have a structural limit for their landing gear. The maximum rate of descent permitted is 600 feet per minute. A glide slope up to 3.25° will ensure a controlled flare and landing within this limit. Any higher angle will require a descent rate of 800 to 900FPM. A positive flare in the correct time is required. Any delay can result in a hard landing or a late touch down. These are a major threat while landing in heavy rain conditions. If the rain condition is accompanied by changing winds, especially tail winds, it becomes a dangerous recipe. On November 9, 2007, an Iberia Airlines Airbus A-340-600 overshot the runway while landing in rain. The runway at Quito, Ecuador, has ILS Glide slope angle similar to what AAI has provided in Bangalore and Hyderabad. The aircraft has been written off.
Civil Aviation in India needs a catalyst to catch up with China. Living on past glory built up by JRD Tata is not going to help. When the system is run by people whose knowledge of aviation is limited, it is difficult to progress. To quote the civil aviation minister on another context, we need to perform or we perish. The dragon and the tortoise will leave us far behind.
The author is an Airline Instructor Pilot on Boeing 737 with a flying experience of 20,000 hrs. He is also a Consultant for Wet Runway Operations Training and Accident Prevention.
Source- The Hindu, Magazine. Dated - January 25, 2009
