Capt PPRuNe
26th Aug 2001, 01:37
FRIDAY, 24 AUGUST 2001
When the wind blows
Commercial airline pilots complain of occasional severe turbulence onapproach to Athens' new international airport; for the moment, there is onlydiscomfort to report
BY ANDREW LEECH
A view of the new airport during construction looking southwest, the direction from which planes come in to land. Clashing northern and southern gusts caused by the surrounding hills have led to turbulent landing conditions
ALTHOUGH the new Athens International Airport (AIA) in Spata, eastern Attica, has been presented to the public as a modern, technological marvel, there are some disquieting questions about turbulence on landing that mar this picture.
The airport is subject to wind shear (sudden changes in wind direction) and crosswinds, particularly on the main approach from the south, what pilots call approach 03. Here, the surrounding terrain magnifies winds and barrels them over the flight path. Ask pilots who have flown into Spata whether they encountered turbulence - there will be more yeas than nays. Even light winds can be magnified to an uncomfortable level while strong ones can be terrifying to passengers.
The Athens News submitted a questionnaire to commercial airline pilots over the Professional Pilots' Rumour Network, an Internet site designed for private and professional pilots to exchange views and information. The answers, given on condition of anonymity, are cautious but revealing. "I noticed excessive yaw (wing dropping usually followed by abrupt pilot corrections), passengers using the sick bag and a general passenger nervousness. And these are big birds," says one pilot. Another says: "On two occasions I bet my licence we would do a go-around, but I lost."
A third believed that "the main problem is the southerly tailwinds on approach to 03 until around 4DME [four miles before the runway] when you finally 'tune' to the local northerly winds. Hence: wind shear alerts all the time!"
On approach 03, aircraft fly over Fleves island on a compass direction of 034 degrees, the plane lowers altitude and drops undercarriage. Speed slackens and pilots can see the old airport of Hellenikon on the left and the two AIA runways ahead. To the left is Mt Ymittos and to the right a range of peaks called Paneio and Olympos. This gives the impression when flying of going through a wide barn door with the nearest peaks acting like doorposts. As aircraft go between these ranges and drop below 2,000 feet the winds start buffeting the aircraft and pilots are constantly on alert to anticipate wind movement and direction.
The main winds are those coming from the north. However, the various mountain ranges distort them, so a wind initially coming from the north may do a U-turn and suddenly become southerly. After passing Fleves, aircraft encounter a tailwind that lifts the tail, causing them to lose altitude unless pilots compensate and increase engine power. It also (being in the rear) increases forward speed at a time when pilots want to reduce it for the landing approach. The pilot who warns of "constant wind shear alerts" refers to the critical point at which aircraft have passed through the "wide barn door". Before meeting the northern headwinds in their normal position there is a transition period of being pushed by a southerly and facing a northerly wind simultaneously. This creates turbulence and can produce wind shears.
The average wind strength in this area is around 20 knots (nearly 40km) so even a large plane feels it, while the pilots are dealing with a phenomenon that both lifts and depresses the plane at the same time (causes an up-down motion like a fun park thrill ride) and alters the characteristics of the landing approach.
Yet, pilots philosophically shrug it off. "We don't build airports," said one, "we just cope with them." "Yes, there is turbulence, but not as bad as Hong Kong," said another.
It is to AIA's credit that they installed a specialised wind machine to detect turbulence and warn pilots, but this can do nothing to minimise it or improve passenger comfort, and pilots only receive up-to-date information just before encountering turbulence.
Wind shear can, of course, be deadly at the wrong moment and in sufficient strength. If they occur near ground level, wind shears can drive an aircraft into the ground. That is what happened to Delta Flight 191 in 1985. As the L1011 approached Dallas Ft Worth airport, a sudden downburst caused it to crash, killing 133 people.
However, no pilot using AIA considers the wind shear here dangerous, unless close to the ground - just uncomfortable. The Civil Aviation Authority's air traffic control chief, Vassilis Eliou, agrees: "We know there is turbulence but it doesn't affect the safety of flights. It has never been reported as dangerous."
Fog alert
Ther e is another fear. A senior source at the Civil Aviation Authority, speaking under customary anonymity, says that AIA is likely to become severely fog-bound in the winter months and, while this happens at many European airports, AIA's equipment is far below the level of that used by a major airport such as Heathrow (which is at Level 3; AIA is at Level 1). He anticipates problems in winter, if AIA is hit by particularly bad conditions.
Old and new airports: The glide path of incoming aircraft is marked in red. When landing at Hellenikon, Mount Ymittos protected aircraft from northern gusts. Now planes face a complicated set of winds distorted by the terrain surrounding the Spata airport
Levels 1, 2 and 3 roughly refer to the generations of the equipment and how precise they are. This is the terminology used by the flying profession, airports and manufacturers of these systems. Level 1 on ILS (Instrument Landing System) guides aircraft down to 200 feet above the ground. If pilots cannot see the runway then they abort the landing and divert to another airport. It also covers 700 foot visibility ahead (RVR - runway visibility range). For a successful landing pilots need to see both ahead and below. Level 2 guides aircraft down to 100 feet above the ground with RVR of 1,200 feet, while Level 3 guides aircraft down to 50 feet (in some cases 7 feet) and gives RVR of 1,800 feet. So far the official recommendation is that AIA doesn't need a level higher than 1.
Alternative runways
The last disquieting point concerns the fact that if a plane cannot land at AIA it must divert to Thessaloniki or Crete: the nearest runways to handle large jets such as Boeing 747s and Airbus 340s. (One could theoretically include Mykonos, but if weather conditions were bad in Athens, they are likely to be worse in Mykonos, and transport to the mainland difficult).
Many major hubs, such as Heathrow and Schiphol, provide alternative landing sites nearby. Athens may be unique in Europe in being the only capital city with no nearby alternative airport.
The military airports of Tanagra and Elefsina could also prove viable alternatives in an emergency, such as fire, engine failure or fuel leak, when passengers' lives are in danger. But they are unlikely to give landing permission to commercial flights under merely windy circumstances. Aside from the security problems of civilians landing at an airbase, there would be the expense of bussing them with luggage to AIA's immigration and customs authorities. Furthermore, Tanagra's military ILS system is incompatible with civilian versions.
Still, Athens is blessed with one powerful redeeming factor: the existence of Hellenikon, the former airport, only 30km away and already equipped with two long runways. One could be kept in operation for emergencies. A second blessing is that the same mountains that cause turbulence at AIA protect Hellenikon, so an emergency at one could be a routine landing at the other. In all its years of operation, Hellenikon had remarkably trouble-free operation and was very rarely closed due to high winds or other natural conditions. It used to cope with 80kph meltemi winds blowing.
Since moving to Spata a furore has raged behind closed doors as to what to do with Hellenikon. While the government publicly maintains it would like to build a park, the mayors of the four local municipalities (Glyfada, Alimos, Ilioupoli and Kalamaki) are said to have privately earmarked much of the land for housing; with billions of drachmas accruing to those involved.
However, local flying organisations, such as Aeroservices, Aero Leschi Hellenikon, Airman and other private services and clubs, have offered a very viable alternative. Athens News talked to Dimitrios Daphnis and Petros Sakellariou.
Carefully worked out drafts and area plans set aside 20 percent of available space for Hellenikon's continued use as an airport (small planes and helicopters that make little or negligible noise), leaving 80 percent for future development, either government or private. This plan would also cover most maintenance costs of the only nearby runway that could handle an emergency landing of a large jet.
© ATHENS NEWS, 24/08/2001
[ 26 August 2001: Message edited by: Capt PPRuNe ]
When the wind blows
Commercial airline pilots complain of occasional severe turbulence onapproach to Athens' new international airport; for the moment, there is onlydiscomfort to report
BY ANDREW LEECH
A view of the new airport during construction looking southwest, the direction from which planes come in to land. Clashing northern and southern gusts caused by the surrounding hills have led to turbulent landing conditions
ALTHOUGH the new Athens International Airport (AIA) in Spata, eastern Attica, has been presented to the public as a modern, technological marvel, there are some disquieting questions about turbulence on landing that mar this picture.
The airport is subject to wind shear (sudden changes in wind direction) and crosswinds, particularly on the main approach from the south, what pilots call approach 03. Here, the surrounding terrain magnifies winds and barrels them over the flight path. Ask pilots who have flown into Spata whether they encountered turbulence - there will be more yeas than nays. Even light winds can be magnified to an uncomfortable level while strong ones can be terrifying to passengers.
The Athens News submitted a questionnaire to commercial airline pilots over the Professional Pilots' Rumour Network, an Internet site designed for private and professional pilots to exchange views and information. The answers, given on condition of anonymity, are cautious but revealing. "I noticed excessive yaw (wing dropping usually followed by abrupt pilot corrections), passengers using the sick bag and a general passenger nervousness. And these are big birds," says one pilot. Another says: "On two occasions I bet my licence we would do a go-around, but I lost."
A third believed that "the main problem is the southerly tailwinds on approach to 03 until around 4DME [four miles before the runway] when you finally 'tune' to the local northerly winds. Hence: wind shear alerts all the time!"
On approach 03, aircraft fly over Fleves island on a compass direction of 034 degrees, the plane lowers altitude and drops undercarriage. Speed slackens and pilots can see the old airport of Hellenikon on the left and the two AIA runways ahead. To the left is Mt Ymittos and to the right a range of peaks called Paneio and Olympos. This gives the impression when flying of going through a wide barn door with the nearest peaks acting like doorposts. As aircraft go between these ranges and drop below 2,000 feet the winds start buffeting the aircraft and pilots are constantly on alert to anticipate wind movement and direction.
The main winds are those coming from the north. However, the various mountain ranges distort them, so a wind initially coming from the north may do a U-turn and suddenly become southerly. After passing Fleves, aircraft encounter a tailwind that lifts the tail, causing them to lose altitude unless pilots compensate and increase engine power. It also (being in the rear) increases forward speed at a time when pilots want to reduce it for the landing approach. The pilot who warns of "constant wind shear alerts" refers to the critical point at which aircraft have passed through the "wide barn door". Before meeting the northern headwinds in their normal position there is a transition period of being pushed by a southerly and facing a northerly wind simultaneously. This creates turbulence and can produce wind shears.
The average wind strength in this area is around 20 knots (nearly 40km) so even a large plane feels it, while the pilots are dealing with a phenomenon that both lifts and depresses the plane at the same time (causes an up-down motion like a fun park thrill ride) and alters the characteristics of the landing approach.
Yet, pilots philosophically shrug it off. "We don't build airports," said one, "we just cope with them." "Yes, there is turbulence, but not as bad as Hong Kong," said another.
It is to AIA's credit that they installed a specialised wind machine to detect turbulence and warn pilots, but this can do nothing to minimise it or improve passenger comfort, and pilots only receive up-to-date information just before encountering turbulence.
Wind shear can, of course, be deadly at the wrong moment and in sufficient strength. If they occur near ground level, wind shears can drive an aircraft into the ground. That is what happened to Delta Flight 191 in 1985. As the L1011 approached Dallas Ft Worth airport, a sudden downburst caused it to crash, killing 133 people.
However, no pilot using AIA considers the wind shear here dangerous, unless close to the ground - just uncomfortable. The Civil Aviation Authority's air traffic control chief, Vassilis Eliou, agrees: "We know there is turbulence but it doesn't affect the safety of flights. It has never been reported as dangerous."
Fog alert
Ther e is another fear. A senior source at the Civil Aviation Authority, speaking under customary anonymity, says that AIA is likely to become severely fog-bound in the winter months and, while this happens at many European airports, AIA's equipment is far below the level of that used by a major airport such as Heathrow (which is at Level 3; AIA is at Level 1). He anticipates problems in winter, if AIA is hit by particularly bad conditions.
Old and new airports: The glide path of incoming aircraft is marked in red. When landing at Hellenikon, Mount Ymittos protected aircraft from northern gusts. Now planes face a complicated set of winds distorted by the terrain surrounding the Spata airport
Levels 1, 2 and 3 roughly refer to the generations of the equipment and how precise they are. This is the terminology used by the flying profession, airports and manufacturers of these systems. Level 1 on ILS (Instrument Landing System) guides aircraft down to 200 feet above the ground. If pilots cannot see the runway then they abort the landing and divert to another airport. It also covers 700 foot visibility ahead (RVR - runway visibility range). For a successful landing pilots need to see both ahead and below. Level 2 guides aircraft down to 100 feet above the ground with RVR of 1,200 feet, while Level 3 guides aircraft down to 50 feet (in some cases 7 feet) and gives RVR of 1,800 feet. So far the official recommendation is that AIA doesn't need a level higher than 1.
Alternative runways
The last disquieting point concerns the fact that if a plane cannot land at AIA it must divert to Thessaloniki or Crete: the nearest runways to handle large jets such as Boeing 747s and Airbus 340s. (One could theoretically include Mykonos, but if weather conditions were bad in Athens, they are likely to be worse in Mykonos, and transport to the mainland difficult).
Many major hubs, such as Heathrow and Schiphol, provide alternative landing sites nearby. Athens may be unique in Europe in being the only capital city with no nearby alternative airport.
The military airports of Tanagra and Elefsina could also prove viable alternatives in an emergency, such as fire, engine failure or fuel leak, when passengers' lives are in danger. But they are unlikely to give landing permission to commercial flights under merely windy circumstances. Aside from the security problems of civilians landing at an airbase, there would be the expense of bussing them with luggage to AIA's immigration and customs authorities. Furthermore, Tanagra's military ILS system is incompatible with civilian versions.
Still, Athens is blessed with one powerful redeeming factor: the existence of Hellenikon, the former airport, only 30km away and already equipped with two long runways. One could be kept in operation for emergencies. A second blessing is that the same mountains that cause turbulence at AIA protect Hellenikon, so an emergency at one could be a routine landing at the other. In all its years of operation, Hellenikon had remarkably trouble-free operation and was very rarely closed due to high winds or other natural conditions. It used to cope with 80kph meltemi winds blowing.
Since moving to Spata a furore has raged behind closed doors as to what to do with Hellenikon. While the government publicly maintains it would like to build a park, the mayors of the four local municipalities (Glyfada, Alimos, Ilioupoli and Kalamaki) are said to have privately earmarked much of the land for housing; with billions of drachmas accruing to those involved.
However, local flying organisations, such as Aeroservices, Aero Leschi Hellenikon, Airman and other private services and clubs, have offered a very viable alternative. Athens News talked to Dimitrios Daphnis and Petros Sakellariou.
Carefully worked out drafts and area plans set aside 20 percent of available space for Hellenikon's continued use as an airport (small planes and helicopters that make little or negligible noise), leaving 80 percent for future development, either government or private. This plan would also cover most maintenance costs of the only nearby runway that could handle an emergency landing of a large jet.
© ATHENS NEWS, 24/08/2001
[ 26 August 2001: Message edited by: Capt PPRuNe ]