C55 alternate calculation

[HOURBUILDER]

there are 2 different airports that could be used as your alternate.

first airport has just one approach: a straight in VOR approach with (HAT 400/VIS 1)

second airport has two approaches each serving 2 different suitable runways:

first has (HAT 200 / VIS 1/2)
second (HAT 700 / VIS 1)

please calculate the alternate weather minimum using C55 and tell me which airport you would use as an alternate?

thanks

 

[FORE LEFT]

Just becasue the first airport has lower alternate minimums using the 400/1 or 200/1/2 rule. I would choose the second because the alternate mins are for dispatch only, and I would choose an ILS over a VOR. Of course proximity and need to get the airplane on the ground may require the first.

 

[V-1]

Is this a trick question?

Doesn't the use of C55 require two alternate airports? I don't have my reference material handy, but I'd suspect it doesn't matter which of the two you select, because two are required anyway.

 

[rickair7777]

The calculations vary between airlines, do you have specific airline in mind?

Typically it would go something like this:

Airport #1
Single App Model: Add 200' and 1/2SM, which gives you 600' and 1 1/2SM

Airport #2
Single App Model: Select the lowest App, and add 200' and 1/2SM, which gives you 400' and 1 SM

Let's also try the two-approach model:
1) Add 400' to both approaches:
1st App: 600'
2nd App: 1100

2) Then add 1 SM to both approaches
1st App: 1 1/2 SM
2nd. App: 2 SM

3) Now take the best (lowest) CIG and VIS of the two (it IS OK to take one from each approach). This gives you:
CIG: 600'
VIS: 1 1/2 SM

You have the choice of using either the 1 or 2 app model at airport #2, and the one app model looks better.

So in this case the best mins are 400/1 at airport #2 using the single approach method.

Note: As always, alternate mins apply ONLY for planning purposes, once airborne these mins are meaningless and the actual publishedmins on the approach plate apply.

 

[HOURBUILDER]

yes you are the man rick air.

like you said in this scenario it is better to use the single approach model at the airport that has 2 approaches.
and in that case u add 400 and 1 to the ILS which gives you 600 and 1 1/2.

if you use the other method u would have to add 200 and 1/2 to the higher approach which would end up beeing 700+200/1+1/2 = 900/1 1/2.

now i have another question, it is not a trick question i am just not sure:

what if you have to choose between those 2 airports
first airport 1 approach (400/1)
second airport 2 approaches one is (700/1) and the other is also (700/1)

u would get for the first airport alternate weather min of 800/2
and for the second airport you would get using the dual approach model 900 / 1 1/2

in that case which airport do u use since the first as a lower ceiling but the second has a lower vis?

 

[HOURBUILDER]

Airport #1
Single App Model: Add 200' and 1/2SM, which gives you 600' and 1 1/2SM


also rick on your explanation for airport 1 it is not 200 and 1/2 that u add but 400 and 1 so for the first airport it is 800 and 1 and not 600 and 1 1/2

 

[HOURBUILDER]

i mean 800 and 2

 

[rickair7777]

also rick on your explanation for airport 1 it is not 200 and 1/2 that u add but 400 and 1 so for the first airport it is 800 and 1 and not 600 and 1 1/2

Depends on who you work for, different companies have slightly different rules on this in their OPSPECs. I'll have to check mine to be sure...I might actually be using the method from my LAST airline not my current one. I can't keep that sh*it straight anymore.

 

[regionalcap]

The calculations vary between airlines, do you have specific airline in mind?

Typically it would go something like this:

Airport #1
Single App Model: Add 200' and 1/2SM, which gives you 600' and 1 1/2SM

Airport #2
Single App Model: Select the lowest App, and add 200' and 1/2SM, which gives you 400' and 1 SM

Let's also try the two-approach model:
1) Add 400' to both approaches:
1st App: 600'
2nd App: 1100

2) Then add 1 SM to both approaches
1st App: 1 1/2 SM
2nd. App: 2 SM

3) Now take the best (lowest) CIG and VIS of the two (it IS OK to take one from each approach). This gives you:
CIG: 600'
VIS: 1 1/2 SM

You have the choice of using either the 1 or 2 app model at airport #2, and the one app model looks better.

So in this case the best mins are 400/1 at airport #2 using the single approach method.

Note: As always, alternate mins apply ONLY for planning purposes, once airborne these mins are meaningless and the actual publishedmins on the approach plate apply.

You are all screwed up on this. Go back and hit the books. For a one-nav method, you add 400-1 to the approach. For a two nav method, you add 200 to the highest ceiling and 1/2 to the highest visibility.

 

[regionalcap]

yes you are the man rick air.

like you said in this scenario it is better to use the single approach model at the airport that has 2 approaches.
and in that case u add 400 and 1 to the ILS which gives you 600 and 1 1/2.

if you use the other method u would have to add 200 and 1/2 to the higher approach which would end up beeing 700+200/1+1/2 = 900/1 1/2.

now i have another question, it is not a trick question i am just not sure:

what if you have to choose between those 2 airports
first airport 1 approach (400/1)
second airport 2 approaches one is (700/1) and the other is also (700/1)

u would get for the first airport alternate weather min of 800/2
and for the second airport you would get using the dual approach model 900 / 1 1/2

in that case which airport do u use since the first as a lower ceiling but the second has a lower vis?

What is the weather forecast at the alternates? Pick the one with the best weather.

 

[BOHICAgain]

Dont know what you guys were taught but for an airport with one operational facility providing one staright in approach you add 400 and 1.

For an airport with more than one approach providing two seperate straight in approaches to 2 different sutable runways you have to add 200 and 1/2 to the HIGHEST OF THE TWO LOWEST. So if an airport has an ILS to runway lets say 18L and a VOR to 18R . The 200 and 1/2 mins applies to the vor.

The company I work for now states that you cannot choose which formula to apply. If an airport has only one app you must use 400/1 and if the airport has 2 or more u have to use 200 1/2. I know the way the regs were written says different but out POI wants it this way

 

[BOHICAgain]

u would get for the first airport alternate weather min of 800/2
and for the second airport you would get using the dual approach model 900 / 1 1/2

in that case which airport do u use since the first as a lower ceiling but the second has a lower vis?

Look at the approaches being used and the trend of the visibility for both airports. I prefer the 2 mile because visibility is what allows me to continue past the final approach fix. 1 1/2 is not that bad so I would probably prefer to be released to the further airport so I get more fuel and If i really need the alternate I would change it in flight weather permitting to the closer airport.

 

[bertengineer]

Dont know what you guys were taught but for an airport with one operational facility providing one staright in approach you add 400 and 1.

For an airport with more than one approach providing two seperate straight in approaches to 2 different sutable runways you have to add 200 and 1/2 to the HIGHEST OF THE TWO LOWEST. So if an airport has an ILS to runway lets say 18L and a VOR to 18R . The 200 and 1/2 mins applies to the vor.

The company I work for now states that you cannot choose which formula to apply. If an airport has only one app you must use 400/1 and if the airport has 2 or more u have to use 200 1/2. I know the way the regs were written says different but out POI wants it this way

If it was one runway that had an approach to both ends ie.. 18 and 36 and had the same frequency with two seperate identifiers...you can apply the 200 1/2 rule for that airport per C55.

 

[mdanno808]

If it was one runway that had an approach to both ends ie.. 18 and 36 and had the same frequency with two seperate identifiers...you can apply the 200 1/2 rule for that airport per C55.

In this case, both runways would have to be useable, so if the wind was 360/15, you're stuck with adding 400/1.

 

[LowlyPropCapt]

The company I work for now states that you cannot choose which formula to apply. If an airport has only one app you must use 400/1 and if the airport has 2 or more u have to use 200 1/2. I know the way the regs were written says different but out POI wants it this way

Isn't it strange how different companies and POIs read the opsecs differently? At PDT and at TSA when I was there, we could choose which method to apply. Whatever, I say...

Another interesting thing is winds. A lot of dispatchers swear up and down that you don't have to take forecast (or actual as applicable) winds into account when determining the type of alternate rule to apply. I say hooey to that... The runway has to be USABLE! Again, the opspecs give you just enough rope with which to hang yourself.

The bottom line is be conservative and don't let the dispatcher push you around.

 

[regionalcap]

The bottom line is be conservative and don't let the dispatcher push you around.

Absolutely agree

 

[405]

Isn't it strange how different companies and POIs read the opsecs differently? At PDT and at TSA when I was there, we could choose which method to apply. Whatever, I say...

Another interesting thing is winds. A lot of dispatchers swear up and down that you don't have to take forecast (or actual as applicable) winds into account when determining the type of alternate rule to apply. I say hooey to that... The runway has to be USABLE! Again, the opspecs give you just enough rope with which to hang yourself.

The bottom line is be conservative and don't let the dispatcher push you around.

Those dispatchers aren't figuring alternate mins correctly in my opinion then. Your dispatchers sure as hell better plan on an alternate based on winds. If you have a disqualifying tailwind/crosswind to a runway, then that runway is unusable and shouldn't even be in the equation regarding alternate minimums. Period. That's my opinion at least.

 

[Rielly09]

Thathat is a legal altnk You 405
As a dispatcher, you have to take winds into account with reguard to "suitablle" airport. I have had many time when i get crap for bringing out charts to check the runways and aproaches available to decide if that is a legal alt.

 

[LowlyPropCapt]

Thathat is a legal altnk You 405
As a dispatcher, you have to take winds into account with reguard to "suitablle" airport. I have had many time when i get crap for bringing out charts to check the runways and aproaches available to decide if that is a legal alt.

Yeah... Right. I am guessing by your horrible spelling and obviously flawed logic that you are joking. Well, you got a chuckle out of me. Four out of ten points are awarded. You should have gone for more over the top.

On the off chance you are a dispatcher and this post is actually real: Just get me the weather, make sure the performance appears on my release and put whatever alternates and fuel I tell you to put. Do this and we'll get along just fine. Oh yeah, how about arranging for a crewmeal for my next leg?

 

[405]

...put whatever alternates and fuel I tell you to put. Do this and we'll get along just fine.

I take it you don't have that much respect for dispatchers.