Alternate Distance
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Alternate Distance
Hi,
Assume you are going to fly from Istanbul to Sharjah.
Wich could maybe be your alternate airport? Dubai is to close isn't it?
Is it recommended that the alternate distance is over 60 NM but closer
than 250NM??
Thanks
Assume you are going to fly from Istanbul to Sharjah.
Wich could maybe be your alternate airport? Dubai is to close isn't it?
Is it recommended that the alternate distance is over 60 NM but closer
than 250NM??
Thanks
The alternate need only have the required weather (assuming the plane in question can land on it) that the governing authorities have stipulated in either the Ops Specs or the regulation.
There are times the the destination could be the alternate!! Example, weather requires an alternate, the destination is above alternate weather mins and has two separate runways and approaches. Maybe not wise, but legal
GF
There are times the the destination could be the alternate!! Example, weather requires an alternate, the destination is above alternate weather mins and has two separate runways and approaches. Maybe not wise, but legal
GF
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I've flown several times to Dubai with a major airline, and Sharjah was our alternate every time. Matter of fact, there's lots of places we go to where the alternate is within 20-40 nm from the destination. It all depends on the weather at the ETA.
In the same way, there's no limit to how far your alternate can be, as long as you carry enough fuel to go to it. However, carrying lots of fuel will make you burn more too due to the extra weight; so the closer the alternate is, the more economical it becomes in regards to fuel cost. That's why you'll often have the closest suitable airport as your alternate, weather permitting of course.
In the same way, there's no limit to how far your alternate can be, as long as you carry enough fuel to go to it. However, carrying lots of fuel will make you burn more too due to the extra weight; so the closer the alternate is, the more economical it becomes in regards to fuel cost. That's why you'll often have the closest suitable airport as your alternate, weather permitting of course.
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Alternates
If you fly YYZ to FLL you would use MIA for alternate. Presuming weather etc is good. Actual flying distance is less than 20 nm I think. Turn left vectors for MIA.
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I Agree with RWY IN SIGHT...
If there would be sandstorm and 45 kts crosswind (x-treme case but
surely not impossible) in SHJ then Dubai would get the same weather,
and if you have no idea were to divert then you probably put down the lady
on Abu Musa or Sirri Island
If there would be sandstorm and 45 kts crosswind (x-treme case but
surely not impossible) in SHJ then Dubai would get the same weather,
and if you have no idea were to divert then you probably put down the lady
on Abu Musa or Sirri Island
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Shouldnt't the alternate be far enough not to be influenced by the same weather system?
Note: EHAM may still be part of the same system (high pressure), but because the forecast is ok it's usable.
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Shouldnt't the alternate be far enough not to be influenced by the same weather system?
BUT, as told, it's part of the common sense consideration(s)
e.g. expected parking available, tech agreement, commercial agreement, pax management, wx environment compared to destn, etc.
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Choice of alternate needs to be related to the risk of requiring it. Lots of work has been done to develop risk based alternate selection processes.
The principles of risk based selection are:
1. Safety
2. Regulatory compliance
3. Commercial requirements
The risk evaluation uses a process flow chart methodology to assess weather factors; celing, visibility, wind, precipitation, runway surface condtions, severe weather events (CB, ZR) in conjunction with aircraft performance, runway length and approach aids.
If the risk of requiring the alternate is low or very low, use the No Alternate option or the closest legal alternate (you are not going there).
As the risk of requiring the alternate increases more care is required in risk evaluation and the third prinicple is required - commercial requirements. Commercial requirements evaluation can be challenging and is dependent on the aircraft type, the airline commercial agreements with handling agents, partner airlines, airport facilities, crew duty day and replacement ability.
Putting this together for an individual airline requires a little bit of work and analysis to determine the ranking of alternate airports with respect to handling capability, airport approach aids etc. for each destination.
The objective should be to balance the correct alternate choice against the distance to the alternate. A closer alternate is more fuel efficient, but may not be suitable from a weather or aircraft handling capability. However, care must be taken to remember that the focus on airport facilities needs to be tempered with the assessment of likelihood of going to the alternate. In practice in many parts of the world, for many flights, the risk of going to the alternate is low and the alternate airport merely satisfies a regulatory requirement.
Every flight we operate always has a risk of diversion, but we must temper our pilot paranoia over a diversion, against running the business. You cannot eliminate all diversions. Diversions are a cost of doing business, but we cannot pile on the fuel "just in case", believing we will avoid diversions. Yes I know diversions have associated costs, but in a reasonable size airline the fuel carriage costs can easily be 25-100 times higher than all the diversion costs.
The principles of risk based selection are:
1. Safety
2. Regulatory compliance
3. Commercial requirements
The risk evaluation uses a process flow chart methodology to assess weather factors; celing, visibility, wind, precipitation, runway surface condtions, severe weather events (CB, ZR) in conjunction with aircraft performance, runway length and approach aids.
If the risk of requiring the alternate is low or very low, use the No Alternate option or the closest legal alternate (you are not going there).
As the risk of requiring the alternate increases more care is required in risk evaluation and the third prinicple is required - commercial requirements. Commercial requirements evaluation can be challenging and is dependent on the aircraft type, the airline commercial agreements with handling agents, partner airlines, airport facilities, crew duty day and replacement ability.
Putting this together for an individual airline requires a little bit of work and analysis to determine the ranking of alternate airports with respect to handling capability, airport approach aids etc. for each destination.
The objective should be to balance the correct alternate choice against the distance to the alternate. A closer alternate is more fuel efficient, but may not be suitable from a weather or aircraft handling capability. However, care must be taken to remember that the focus on airport facilities needs to be tempered with the assessment of likelihood of going to the alternate. In practice in many parts of the world, for many flights, the risk of going to the alternate is low and the alternate airport merely satisfies a regulatory requirement.
Every flight we operate always has a risk of diversion, but we must temper our pilot paranoia over a diversion, against running the business. You cannot eliminate all diversions. Diversions are a cost of doing business, but we cannot pile on the fuel "just in case", believing we will avoid diversions. Yes I know diversions have associated costs, but in a reasonable size airline the fuel carriage costs can easily be 25-100 times higher than all the diversion costs.
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FJR would be another possible alternate; I believe their ILS is working now. It would be pretty unusual to want to go there and not DXB though.
Last edited by Semu; 20th Dec 2008 at 20:03.
