Are you asking if you can use two RNAV/GPS approaches for the 2 navaid rule ?
Don't forget the add-ons for CAT II/CAT III Mins...Oh my!OPPSPEC C055
a. The certificate holder is authorized to derive alternate airport weather minimums from Table 1
below, according to the limitations and provisions of this operations specification.
For airports with at least one operational navigational facility providing a straight-in
non-precision approach procedure, or Category I precision approach, or, when applicable, a circling
maneuver from an IAP. For airports with at least two operational navigational facilities, each
providing a straight-in approach procedure to different suitable runways.
Special limitations and provisions.
(1) The certificate holder must not use an alternate airport weather minimum other than any
applicable minimum derived from Table 1. The certificate holder must not use any GPS-based
Instrument Approach Procedures (IAP) unless the certificate holder is authorized to conduct
GPS-based IAP and meets the requirements in subparagraph b(8).
(2) In determining alternate airport weather minimums, the certificate holder must not use any
published IAP which specifies that alternate airport weather minimums are not authorized.
(3) When determining the usability of a runway, wind including gust must be forecast to be
within operating limits, including reduced visibility limits, and should be within the manufacturer's
maximum demonstrated crosswind.
(4) All conditional forecast elements below the lowest applicable operating minimums must be
taken into account. Additives are applied only to the height value (H) to determine the required
ceiling.
One Navaid Rule
Add 400 ft to MDA(H) or DA(H), as applicable.
Add 1 statute mile or 1600 m to the landing minimum.
Two Navaid Rule
Add 200 ft to higher DA(H) or MDA(H) of the two approaches used.
Add ½ sm or 800 m to the higher authorized landing minimum of the two approaches used.
Example
Flight 9999 from MSP-DTW using KGRR as alternate with an arrival time at GRR of 1830z on the 5th
KGRR (Grand Rapids, MI)
KGRR 051353Z 07005KT 10SM FEW020 SCT055 BKN220 19/14 A3008 RMK AO2 SLP185 T01940144
KGRR 051120Z 0512/0618 13005KT P6SM FEW250
FM051800 16006KT P6SM FEW050 SCT250
TEMPO 0518/0522 26016KT 2SM RA BKN005
FM060300 17006KT P6SM BKN250
FM061200 16005KT P6SM SCT050 BKN250
!GRR 08/003 (KGRR A3867/15) GRR SVC MICROBURST/WINDSHEAR DETECTION SYSTEM NOT AVBL 1508051300-1508052000
!GRR 07/029 (KGRR A3817/15) GRR TWY D BTN TWY M AND TWY B CLSD TO ACFT WINGSPAN MORE THAN 118FT 1507151336-1508211100
!GRR 06/049 (KGRR A3710/15) GRR RWY 26L VASI OUT OF SERVICE 1506221139-1509301200
!GRR 06/048 (KGRR A3709/15) GRR RWY 35 ALS OUT OF SERVICE 1506221136-1509301200
Looking at our approaches authorized for use as alternate we find the following approaches for Grand Rapids
ILS 8R, ILS 26L ILS35 and a whole host of non ILS approaches. ILS approaches generally will give the best mins so I'm gonna look at those first. I need at least 2 approaches, that do not use the same NAVAID as reference and are not to the same runway, reciprocal is ok. Since a Localizer is established for only 1 runway, I will have 3 navaids to choose from but will pick the best 2 I can find. (ie. lowest minimums)
- First I'm gonna check the winds. Since I have a 16 KT Tailwind on 08R which exceeds my limit of 10kts, I can not use it. Thus I am left with ILS 26L and ILS 35
- Now I am going to check my NOTAMS. I see that 26L has a VASI out of service and 35 has an ALS out of service.
- Now I am going to read my plates
ILS 26L
Visibility Minimum: 1/2 SM
Decision Height: 200 ft
VASI does not affect minimum
ILS 35
Visibility Minimum: 3/4 SM (not 1/2*)
Decision Height: 200 ft
*ALS Out of Service does affect visibility minimum and we have to move to the appropriate minimum box on the chart
1 NAVAID Rule
I am allowed to select the least restrictive (lowest) approach out of all my available options to derive my minimums off the 1 NAVAID rule. In this example it is ILS 26L.
ILS 26L
Visibility Minimum: 1/2 SM
Decision Height: 200 ft
Now that we have our approach, we add the additives to find the minimums
ILS 26L
Visibility Minimum: 1/2 SM + 1SM -> Visibility Alternate Minimum 1 1/2 SM
Decision Height: 200 ft + 400 ft -> Ceiling Minimum 600'
Thus using the 1 Navaid rule, the alternate minimums for GRR are 1 1/2 SM and 600'
2 NAVAID Rule
Using the 2 NAVAID rule, I am allowed to use 2 approaches to different runways utilizing 2 different navaids. This allows me lower additives to the approaches, but in exchange, I have to use the higher of the 2 derived numbers as my minimum
ILS 26L
Visibility Minimum: 1/2 SM + 1/2 SM -> 1 SM
Decision Height: 200 ft + 200 ft -> 400 ft
Alternate Minimum for ILS 26L = 1 SM and 400 ft
ILS 35
Visibility Minimum: 3/4 SM (not 1/2*) -> 1 1/4 SM
Decision Height: 200 ft + 200 ft -> 400 ft
Alternate Minimum for ILS 35 = 1 1/4 SM and 400 ft
To find the alternate minimums for the airport, we take the most restrictive (highest) of the two
ILS 26L: 1SM 400 ft
ILS 35: 1 1/4SM 400ft (Higher)
Alternate Minimums for KGRR using 2 Navaid Rule: 1 1/4 SM and 400 ft
That's the basics.
Couple of tricks, an ILS will usually provide you with better minimums than any other approach type.
The reciprocal of one runway (ie. 18 and 36) on the same piece of pavement counts as two separate runways (except in Canada) so if you have an ILS approach to each, you can use the 2 NAVAID rule if winds allow.
Be very careful of VOR and NDB approaches as they normally use the same NAVAID as the reference point for the approach. So you only have 1 NAVAID even though you have 2 approaches.
There are some cases where the 1 NAVAID rule will provide better minimums than the 2 NAVAID rule, so do not automatically assume that the 2 NAVAID rule is better.
Class Dismissed
Yeah but isn't CAT || / ||| as is with no adding ?Don't forget the add-ons for CAT II/CAT III Mins...Oh my!
Maybe my wording was off. In our ops specs (C55) there are specific minimum that you don't add so I got confused when he said add ons.
OPPSPEC C055
a. The certificate holder is authorized to derive alternate airport weather minimums from Table 1
below, according to the limitations and provisions of this operations specification.
For airports with at least one operational navigational facility providing a straight-in
non-precision approach procedure, or Category I precision approach, or, when applicable, a circling
maneuver from an IAP. For airports with at least two operational navigational facilities, each
providing a straight-in approach procedure to different suitable runways.
Special limitations and provisions.
(1) The certificate holder must not use an alternate airport weather minimum other than any
applicable minimum derived from Table 1. The certificate holder must not use any GPS-based
Instrument Approach Procedures (IAP) unless the certificate holder is authorized to conduct
GPS-based IAP and meets the requirements in subparagraph b(8).
(2) In determining alternate airport weather minimums, the certificate holder must not use any
published IAP which specifies that alternate airport weather minimums are not authorized.
(3) When determining the usability of a runway, wind including gust must be forecast to be
within operating limits, including reduced visibility limits, and should be within the manufacturer's
maximum demonstrated crosswind.
(4) All conditional forecast elements below the lowest applicable operating minimums must be
taken into account. Additives are applied only to the height value (H) to determine the required
ceiling.
One Navaid Rule
Add 400 ft to MDA(H) or DA(H), as applicable.
Add 1 statute mile or 1600 m to the landing minimum.
Two Navaid Rule
Add 200 ft to higher DA(H) or MDA(H) of the two approaches used.
Add ½ sm or 800 m to the higher authorized landing minimum of the two approaches used.
Example
Flight 9999 from MSP-DTW using KGRR as alternate with an arrival time at GRR of 1830z on the 5th
KGRR (Grand Rapids, MI)
KGRR 051353Z 07005KT 10SM FEW020 SCT055 BKN220 19/14 A3008 RMK AO2 SLP185 T01940144
KGRR 051120Z 0512/0618 13005KT P6SM FEW250
FM051800 16006KT P6SM FEW050 SCT250
TEMPO 0518/0522 26016KT 2SM RA BKN005
FM060300 17006KT P6SM BKN250
FM061200 16005KT P6SM SCT050 BKN250
!GRR 08/003 (KGRR A3867/15) GRR SVC MICROBURST/WINDSHEAR DETECTION SYSTEM NOT AVBL 1508051300-1508052000
!GRR 07/029 (KGRR A3817/15) GRR TWY D BTN TWY M AND TWY B CLSD TO ACFT WINGSPAN MORE THAN 118FT 1507151336-1508211100
!GRR 06/049 (KGRR A3710/15) GRR RWY 26L VASI OUT OF SERVICE 1506221139-1509301200
!GRR 06/048 (KGRR A3709/15) GRR RWY 35 ALS OUT OF SERVICE 1506221136-1509301200
Looking at our approaches authorized for use as alternate we find the following approaches for Grand Rapids
ILS 8R, ILS 26L ILS35 and a whole host of non ILS approaches. ILS approaches generally will give the best mins so I'm gonna look at those first. I need at least 2 approaches, that do not use the same NAVAID as reference and are not to the same runway, reciprocal is ok. Since a Localizer is established for only 1 runway, I will have 3 navaids to choose from but will pick the best 2 I can find. (ie. lowest minimums)
- First I'm gonna check the winds. Since I have a 16 KT Tailwind on 08R which exceeds my limit of 10kts, I can not use it. Thus I am left with ILS 26L and ILS 35
- Now I am going to check my NOTAMS. I see that 26L has a VASI out of service and 35 has an ALS out of service.
- Now I am going to read my plates
ILS 26L
Visibility Minimum: 1/2 SM
Decision Height: 200 ft
VASI does not affect minimum
ILS 35
Visibility Minimum: 3/4 SM (not 1/2*)
Decision Height: 200 ft
*ALS Out of Service does affect visibility minimum and we have to move to the appropriate minimum box on the chart
1 NAVAID Rule
I am allowed to select the least restrictive (lowest) approach out of all my available options to derive my minimums off the 1 NAVAID rule. In this example it is ILS 26L.
ILS 26L
Visibility Minimum: 1/2 SM
Decision Height: 200 ft
Now that we have our approach, we add the additives to find the minimums
ILS 26L
Visibility Minimum: 1/2 SM + 1SM -> Visibility Alternate Minimum 1 1/2 SM
Decision Height: 200 ft + 400 ft -> Ceiling Minimum 600'
Thus using the 1 Navaid rule, the alternate minimums for GRR are 1 1/2 SM and 600'
2 NAVAID Rule
Using the 2 NAVAID rule, I am allowed to use 2 approaches to different runways utilizing 2 different navaids. This allows me lower additives to the approaches, but in exchange, I have to use the higher of the 2 derived numbers as my minimum
ILS 26L
Visibility Minimum: 1/2 SM + 1/2 SM -> 1 SM
Decision Height: 200 ft + 200 ft -> 400 ft
Alternate Minimum for ILS 26L = 1 SM and 400 ft
ILS 35
Visibility Minimum: 3/4 SM (not 1/2*) -> 1 1/4 SM
Decision Height: 200 ft + 200 ft -> 400 ft
Alternate Minimum for ILS 35 = 1 1/4 SM and 400 ft
To find the alternate minimums for the airport, we take the most restrictive (highest) of the two
ILS 26L: 1SM 400 ft
ILS 35: 1 1/4SM 400ft (Higher)
Alternate Minimums for KGRR using 2 Navaid Rule: 1 1/4 SM and 400 ft
That's the basics.
Couple of tricks, an ILS will usually provide you with better minimums than any other approach type.
The reciprocal of one runway (ie. 18 and 36) on the same piece of pavement counts as two separate runways (except in Canada) so if you have an ILS approach to each, you can use the 2 NAVAID rule if winds allow.
Be very careful of VOR and NDB approaches as they normally use the same NAVAID as the reference point for the approach. So you only have 1 NAVAID even though you have 2 approaches.
There are some cases where the 1 NAVAID rule will provide better minimums than the 2 NAVAID rule, so do not automatically assume that the 2 NAVAID rule is better.
Class Dismissed
